js_component_bindgen/

transpile_bindgen.rs

use std::cell::RefCell;
use std::collections::{BTreeMap, BTreeSet, HashMap, HashSet};
use std::fmt::Write;
use std::mem;
use std::ops::Index;

use base64::Engine as _;
use base64::engine::general_purpose;
use heck::{ToKebabCase, ToLowerCamelCase, ToUpperCamelCase};
use semver::Version;
use wasmtime_environ::component::{
    CanonicalOptions, CanonicalOptionsDataModel, Component, ComponentTranslation, ComponentTypes,
    CoreDef, CoreExport, Export, ExportItem, FixedEncoding, GlobalInitializer, InstantiateModule,
    InterfaceType, LinearMemoryOptions, LoweredIndex, ResourceIndex, RuntimeComponentInstanceIndex,
    RuntimeImportIndex, RuntimeInstanceIndex, StaticModuleIndex, Trampoline, TrampolineIndex,
    TypeDef, TypeFuncIndex, TypeFutureTableIndex, TypeResourceTableIndex, TypeStreamTableIndex,
};
use wasmtime_environ::component::{
    ExtractCallback, NameMapNoIntern, Transcode, TypeComponentLocalErrorContextTableIndex,
};
use wasmtime_environ::{EntityIndex, PrimaryMap};
use wit_bindgen_core::abi::{self, LiftLower};
use wit_component::StringEncoding;
use wit_parser::abi::AbiVariant;
use wit_parser::{
    Function, FunctionKind, Handle, Resolve, Result_, SizeAlign, Type, TypeDefKind, TypeId,
    WorldId, WorldItem, WorldKey,
};

use crate::esm_bindgen::EsmBindgen;
use crate::files::Files;
use crate::function_bindgen::{
    ErrHandling, FunctionBindgen, FunctionBindgenComponentState, PayloadTypeMetadata, ResourceData,
    ResourceExtraData, ResourceMap, ResourceTable,
};
use crate::intrinsics::component::ComponentIntrinsic;
use crate::intrinsics::js_helper::JsHelperIntrinsic;
use crate::intrinsics::lift::LiftIntrinsic;
use crate::intrinsics::lower::LowerIntrinsic;
use crate::intrinsics::p3::async_future::AsyncFutureIntrinsic;
use crate::intrinsics::p3::async_stream::AsyncStreamIntrinsic;
use crate::intrinsics::p3::async_task::AsyncTaskIntrinsic;
use crate::intrinsics::p3::error_context::ErrCtxIntrinsic;
use crate::intrinsics::p3::host::HostIntrinsic;
use crate::intrinsics::p3::waitable::WaitableIntrinsic;
use crate::intrinsics::resource::ResourceIntrinsic;
use crate::intrinsics::string::StringIntrinsic;
use crate::intrinsics::webidl::WebIdlIntrinsic;
use crate::intrinsics::{
    AsyncDeterminismProfile, Intrinsic, RenderIntrinsicsArgs, render_intrinsics,
};
use crate::names::{LocalNames, is_js_reserved_word, maybe_quote_id, maybe_quote_member};
use crate::{
    FunctionIdentifier, ManagesIntrinsics, core, get_thrown_type, is_async_fn,
    requires_async_porcelain, source, uwrite, uwriteln,
};

/// Size of flat parameters that can be sent, for example via the `task.return`
/// intrinsic, when returning from an async func
const MAX_FLAT_PARAMS: usize = 16;
/// Maximum direct flat results for sync canonical lowering.
const MAX_FLAT_RESULTS: usize = 1;

#[derive(Debug, Default, Clone, bon::Builder)]
pub struct TranspileOpts {
    pub name: String,
    /// Disables generation of `*.d.ts` files and instead only generates `*.js`
    /// source files.
    #[builder(default)]
    pub no_typescript: bool,
    /// Provide a custom JS instantiation API for the component instead
    /// of the direct importable native ESM output.
    pub instantiation_mode: Option<InstantiationMode>,
    /// Configure how import bindings are provided, as high-level JS bindings,
    /// or as hybrid optimized bindings.
    pub import_bindings: Option<BindingsMode>,
    /// Comma-separated list of "from-specifier=./to-specifier.js" mappings of
    /// component import specifiers to JS import specifiers.
    pub map: Option<HashMap<String, String>>,
    /// Disables compatibility in Node.js without a fetch global.
    #[builder(default)]
    pub nodejs_compat_disabled: bool,
    /// Set the cutoff byte size for base64 inlining core Wasm in instantiation mode
    /// (set to 0 to disable all base64 inlining)
    #[builder(default)]
    pub base64_cutoff: usize,
    /// Enables compatibility for JS environments without top-level await support
    /// via an async $init promise export to wait for instead.
    #[builder(default)]
    pub tla_compat: bool,
    /// Disable verification of component Wasm data structures when
    /// lifting as a production optimization
    #[builder(default)]
    pub valid_lifting_optimization: bool,
    /// Whether or not to emit `tracing` calls on function entry/exit.
    #[builder(default)]
    pub tracing: bool,
    /// Whether to generate namespaced exports like `foo as "local:package/foo"`.
    /// These exports can break typescript builds.
    #[builder(default)]
    pub no_namespaced_exports: bool,
    /// Whether to output core Wasm utilizing multi-memory or to polyfill
    /// this handling.
    #[builder(default)]
    pub multi_memory: bool,
    /// Whether to generate types for a guest module using module declarations.
    #[builder(default)]
    pub guest: bool,
    /// Configure whether to use `async` imports or exports with
    /// JavaScript Promise Integration (JSPI).
    pub async_mode: Option<AsyncMode>,
    /// Configure whether to generate code that includes strict type checks
    #[builder(default)]
    pub strict: bool,
    /// Whether the core module(s) to be wrapped were actually transpiled from Wasm to JS (asm.js) and thus need shimming for i64
    #[builder(default)]
    pub asmjs: bool,
}

#[derive(Default, Clone, Debug)]
#[non_exhaustive]
pub enum AsyncMode {
    #[default]
    Sync,
    JavaScriptPromiseIntegration {
        imports: Vec<String>,
        exports: Vec<String>,
    },
}

#[derive(Default, Clone, Debug)]
#[non_exhaustive]
pub enum InstantiationMode {
    #[default]
    Async,
    Sync,
}

/// Internal Bindgen calling convention
enum CallType {
    /// Standard calls - inner function is called directly with parameters
    Standard,
    /// Standard calls that are async (p3)
    AsyncStandard,
    /// Exported resource method calls - this is passed as the first argument
    FirstArgIsThis,
    /// Exported resource method calls that are async (p3)
    AsyncFirstArgIsThis,
    /// Imported resource method calls - callee is a member of the parameter
    CalleeResourceDispatch,
    /// Imported resource method calls that are async (p3)
    AsyncCalleeResourceDispatch,
}

#[derive(Default, Clone, Debug)]
#[non_exhaustive]
pub enum BindingsMode {
    Hybrid,
    #[default]
    Js,
    Optimized,
    DirectOptimized,
}

struct JsBindgen<'a> {
    local_names: LocalNames,

    esm_bindgen: EsmBindgen,

    /// The source code for the "main" file that's going to be created for the
    /// component we're generating bindings for. This is incrementally added to
    /// over time and primarily contains the main `instantiate` function as well
    /// as a type-description of the input/output interfaces.
    src: Source,

    /// Core module count
    core_module_cnt: usize,

    /// Various options for code generation.
    opts: &'a TranspileOpts,

    /// List of all intrinsics emitted to `src` so far.
    all_intrinsics: BTreeSet<Intrinsic>,

    /// List of all core Wasm exported functions (and if is async) referenced in
    /// `src` so far.
    ///
    /// The second boolean is true when async procelain is required *or* if the
    /// export itself is async.
    all_core_exported_funcs: Vec<(String, bool)>,
}

/// Arguments provided to `JSBindgen::bindgen`, normally called to perform bindgen on a given function
struct JsFunctionBindgenArgs<'a> {
    /// Number of params that the function expects
    nparams: usize,
    /// Internal convention for function calls (ex. whether the first argument is known to be 'this')
    call_type: CallType,
    /// Interface name (if inside an interface)
    iface_name: Option<&'a str>,
    /// Callee of the function
    callee: &'a str,
    /// Canon opts provided for the functions
    opts: &'a CanonicalOptions,
    /// Parsed function metadata
    func: &'a Function,
    resource_map: &'a ResourceMap,
    /// ABI variant of the function
    abi: AbiVariant,
    /// Whether the function in question is a host async function (i.e. JSPI)
    requires_async_porcelain: bool,
    /// Whether the function in question is a guest async function (i.e. WASI P3)
    is_async: bool,
    /// Whether the function in question is being generated for an import
    /// (false implies generation is happening for an export)
    for_import: bool,
}

impl<'a> ManagesIntrinsics for JsBindgen<'a> {
    fn add_intrinsic(&mut self, intrinsic: Intrinsic) {
        self.intrinsic(intrinsic);
    }
}

#[derive(PartialEq, Eq, Clone)]
#[non_exhaustive]
pub enum ExportKind {
    /// Maps to `wasmtime_environ::export::LiftedFunction`
    LiftedFunction,
    /// Maps to `wasmtime_environ::export::Instance`
    Instance,
}

#[allow(clippy::too_many_arguments)]
pub fn transpile_bindgen(
    name: &str,
    component: &ComponentTranslation,
    modules: &PrimaryMap<StaticModuleIndex, core::Translation<'_>>,
    types: &ComponentTypes,
    resolve: &Resolve,
    id: WorldId,
    opts: TranspileOpts,
    files: &mut Files,
) -> (Vec<String>, Vec<(String, ExportKind)>) {
    let (async_imports, async_exports) = match opts.async_mode.clone() {
        None | Some(AsyncMode::Sync) => (Default::default(), Default::default()),
        Some(AsyncMode::JavaScriptPromiseIntegration { imports, exports }) => {
            (imports.into_iter().collect(), exports.into_iter().collect())
        }
    };

    let mut bindgen = JsBindgen {
        local_names: LocalNames::default(),
        src: Source::default(),
        esm_bindgen: EsmBindgen::default(),
        core_module_cnt: 0,
        opts: &opts,
        all_intrinsics: BTreeSet::new(),
        all_core_exported_funcs: Vec::new(),
    };
    bindgen.local_names.exclude_globals(
        &Intrinsic::get_global_names()
            .into_iter()
            .collect::<Vec<_>>(),
    );
    bindgen.core_module_cnt = modules.len();

    // Generate mapping of stream tables to components that are related
    let mut stream_tables = BTreeMap::new();
    for idx in 0..component.component.num_stream_tables {
        let stream_table_idx = TypeStreamTableIndex::from_u32(idx as u32);
        let stream_table_ty = &types[stream_table_idx];
        stream_tables.insert(stream_table_idx, stream_table_ty.instance);
    }

    // Generate mapping of future tables to components that are related
    let mut future_tables = BTreeMap::new();
    for idx in 0..component.component.num_future_tables {
        let future_table_idx = TypeFutureTableIndex::from_u32(idx as u32);
        let future_table_ty = &types[future_table_idx];
        future_tables.insert(future_table_idx, future_table_ty.instance);
    }

    // Generate mapping of err_ctx tables to components that are related
    let mut err_ctx_tables = BTreeMap::new();
    for idx in 0..component.component.num_error_context_tables {
        let err_ctx_table_idx = TypeComponentLocalErrorContextTableIndex::from_u32(idx as u32);
        let err_ctx_table_ty = &types[err_ctx_table_idx];
        err_ctx_tables.insert(err_ctx_table_idx, err_ctx_table_ty.instance);
    }

    // Bindings are generated when the `instantiate` method is called on the
    // Instantiator structure created below
    let mut instantiator = Instantiator {
        src: Source::default(),
        sizes: SizeAlign::default(),
        bindgen: &mut bindgen,
        modules,
        instances: Default::default(),
        error_context_component_initialized: (0..component
            .component
            .num_runtime_component_instances)
            .map(|_| false)
            .collect(),
        error_context_component_table_initialized: (0..component
            .component
            .num_error_context_tables)
            .map(|_| false)
            .collect(),
        resolve,
        world: id,
        translation: component,
        component: &component.component,
        types,
        async_imports,
        async_exports,
        imports: Default::default(),
        exports: Default::default(),
        lowering_options: Default::default(),
        used_instance_flags: Default::default(),
        defined_resource_classes: Default::default(),
        imports_resource_types: Default::default(),
        imports_resource_index_types: Default::default(),
        exports_resource_types: Default::default(),
        exports_resource_index_types: Default::default(),
        resource_exports: Default::default(),
        resource_imports: Default::default(),
        resources_initialized: BTreeMap::new(),
        resource_tables_initialized: BTreeMap::new(),
        stream_tables,
        future_tables,
        err_ctx_tables,
        init_current_module: None,
    };
    instantiator.sizes.fill(resolve);
    instantiator.initialize();
    instantiator.instantiate();

    instantiator.resource_definitions();
    instantiator.instance_flags();

    instantiator.bindgen.src.js(&instantiator.src.js);
    instantiator.bindgen.src.js_init(&instantiator.src.js_init);

    instantiator
        .bindgen
        .finish_component(name, files, &opts, source::Source::default());

    let exports = instantiator
        .bindgen
        .esm_bindgen
        .exports()
        .iter()
        .map(|(export_name, canon_export_name)| {
            let expected_export_name =
                if canon_export_name.contains(':') || canon_export_name.starts_with("[async]") {
                    canon_export_name.to_string()
                } else {
                    canon_export_name.to_kebab_case()
                };
            let export = instantiator
                .component
                .exports
                .get(&expected_export_name, &NameMapNoIntern)
                .unwrap_or_else(|| panic!("failed to find component export [{expected_export_name}] (original '{canon_export_name}')"));

            let export_kind = match &instantiator.component.export_items[*export] {
                wasmtime_environ::component::Export::LiftedFunction { .. } => {
                    ExportKind::LiftedFunction
                }
                wasmtime_environ::component::Export::Instance { .. } => {
                    ExportKind::Instance
                }
                _ => panic!("unexpected export kind"),
            };


            (
                export_name.to_string(),
export_kind,
            )
        })
        .collect();

    (bindgen.esm_bindgen.import_specifiers(), exports)
}

impl JsBindgen<'_> {
    fn finish_component(
        &mut self,
        name: &str,
        files: &mut Files,
        opts: &TranspileOpts,
        intrinsic_definitions: source::Source,
    ) {
        let mut output = source::Source::default();
        let mut compilation_promises = source::Source::default();
        let mut core_exported_funcs = source::Source::default();

        for (core_export_fn, is_async) in self.all_core_exported_funcs.iter() {
            let local_name = self.local_names.get(core_export_fn);
            if *is_async {
                uwriteln!(
                    core_exported_funcs,
                    "{local_name} = WebAssembly.promising({core_export_fn});",
                );
            } else {
                uwriteln!(core_exported_funcs, "{local_name} = {core_export_fn};",);
            }
        }

        // adds a default implementation of `getCoreModule`
        if matches!(self.opts.instantiation_mode, Some(InstantiationMode::Async)) {
            uwriteln!(
                compilation_promises,
                "if (!getCoreModule) getCoreModule = (name) => {}(new URL(`./${{name}}`, import.meta.url));",
                self.intrinsic(Intrinsic::FetchCompile)
            );
        }

        // Setup the compilation data and compilation promises
        let mut removed = BTreeSet::new();
        for i in 0..self.core_module_cnt {
            let local_name = format!("module{i}");
            let mut name_idx = core_file_name(name, i as u32);
            if self.opts.instantiation_mode.is_some() {
                uwriteln!(
                    compilation_promises,
                    "const {local_name} = getCoreModule('{name_idx}');"
                );
            } else if files.get_size(&name_idx).unwrap() < self.opts.base64_cutoff {
                assert!(removed.insert(i));
                let data = files.remove(&name_idx).unwrap();
                uwriteln!(
                    compilation_promises,
                    "const {local_name} = {}('{}');",
                    self.intrinsic(Intrinsic::Base64Compile),
                    general_purpose::STANDARD_NO_PAD.encode(&data),
                );
            } else {
                // Maintain numerical file orderings when a previous file was
                // inlined
                if let Some(&replacement) = removed.iter().next() {
                    assert!(removed.remove(&replacement) && removed.insert(i));
                    let data = files.remove(&name_idx).unwrap();
                    name_idx = core_file_name(name, replacement as u32);
                    files.push(&name_idx, &data);
                }
                uwriteln!(
                    compilation_promises,
                    "const {local_name} = {}(new URL('./{name_idx}', import.meta.url));",
                    self.intrinsic(Intrinsic::FetchCompile)
                );
            }
        }

        // Render the telemery directive
        uwriteln!(output, r#""use components";"#);

        let render_args = RenderIntrinsicsArgs::builder()
            .intrinsics(&mut self.all_intrinsics)
            .instantiation_occurred(self.opts.instantiation_mode.is_some())
            .determinism_profile(AsyncDeterminismProfile::default())
            .transpile_opts(opts)
            .build();
        let js_intrinsics = render_intrinsics(render_args);

        if let Some(instantiation) = &self.opts.instantiation_mode {
            uwrite!(
                output,
                "\
                    export function instantiate(getCoreModule, imports, instantiateCore = {}) {{
                        {}
                        {}
                        {}
                ",
                match instantiation {
                    InstantiationMode::Async => "WebAssembly.instantiate",
                    InstantiationMode::Sync =>
                        "(module, importObject) => new WebAssembly.Instance(module, importObject)",
                },
                &js_intrinsics as &str,
                &intrinsic_definitions as &str,
                &compilation_promises as &str,
            );
        }

        // Render all imports
        let imports_object = if self.opts.instantiation_mode.is_some() {
            Some("imports")
        } else {
            None
        };
        self.esm_bindgen
            .render_imports(&mut output, imports_object, &mut self.local_names);

        // Create instantiation code
        if self.opts.instantiation_mode.is_some() {
            uwrite!(&mut self.src.js, "{}", &core_exported_funcs as &str);
            self.esm_bindgen.render_exports(
                &mut self.src.js,
                self.opts.instantiation_mode.is_some(),
                &mut self.local_names,
                opts,
            );
            uwrite!(
                output,
                "\
                        let gen = (function* _initGenerator () {{
                            {}\
                            {};
                        }})();
                        let promise, resolve, reject;
                        function runNext (value) {{
                            try {{
                                let done;
                                do {{
                                    ({{ value, done }} = gen.next(value));
                                }} while (!(value instanceof Promise) && !done);
                                if (done) {{
                                    if (resolve) return resolve(value);
                                    else return value;
                                }}
                                if (!promise) promise = new Promise((_resolve, _reject) => (resolve = _resolve, reject = _reject));
                                value.then(nextVal => done ? resolve() : runNext(nextVal), reject);
                            }}
                            catch (e) {{
                                if (reject) reject(e);
                                else throw e;
                            }}
                        }}
                        const maybeSyncReturn = runNext(null);
                        return promise || maybeSyncReturn;
                    }};
                ",
                &self.src.js_init as &str,
                &self.src.js as &str,
            );
        } else {
            let (maybe_init_export, maybe_init) =
                if self.opts.tla_compat && opts.instantiation_mode.is_none() {
                    uwriteln!(self.src.js_init, "_initialized = true;");
                    (
                        "\
                        let _initialized = false;
                        export ",
                        "",
                    )
                } else {
                    (
                        "",
                        "
                        await $init;
                    ",
                    )
                };

            uwrite!(
                output,
                "\
                    {}
                    {}
                    {}
                    {maybe_init_export}const $init = (() => {{
                        let gen = (function* _initGenerator () {{
                            {}\
                            {}\
                            {}\
                        }})();
                        let promise, resolve, reject;
                        function runNext (value) {{
                            try {{
                                let done;
                                do {{
                                    ({{ value, done }} = gen.next(value));
                                }} while (!(value instanceof Promise) && !done);
                                if (done) {{
                                    if (resolve) resolve(value);
                                    else return value;
                                }}
                                if (!promise) promise = new Promise((_resolve, _reject) => (resolve = _resolve, reject = _reject));
                                value.then(runNext, reject);
                            }}
                            catch (e) {{
                                if (reject) reject(e);
                                else throw e;
                            }}
                        }}
                        const maybeSyncReturn = runNext(null);
                        return promise || maybeSyncReturn;
                    }})();
                    {maybe_init}\
                ",
                &js_intrinsics as &str,
                &intrinsic_definitions as &str,
                &self.src.js as &str,
                &compilation_promises as &str,
                &self.src.js_init as &str,
                &core_exported_funcs as &str,
            );

            self.esm_bindgen.render_exports(
                &mut output,
                self.opts.instantiation_mode.is_some(),
                &mut self.local_names,
                opts,
            );
        }

        let mut bytes = output.as_bytes();
        // strip leading newline
        if bytes[0] == b'\n' {
            bytes = &bytes[1..];
        }
        files.push(&format!("{name}.js"), bytes);
    }

    fn intrinsic(&mut self, intrinsic: Intrinsic) -> String {
        self.all_intrinsics.insert(intrinsic);
        intrinsic.name().to_string()
    }
}

/// Helper structure used to generate the `instantiate` method of a component.
///
/// This is the main structure for parsing the output of Wasmtime.
pub(crate) struct Instantiator<'a, 'b> {
    src: Source,
    bindgen: &'a mut JsBindgen<'b>,
    modules: &'a PrimaryMap<StaticModuleIndex, core::Translation<'a>>,
    instances: PrimaryMap<RuntimeInstanceIndex, StaticModuleIndex>,
    types: &'a ComponentTypes,
    resolve: &'a Resolve,
    world: WorldId,
    sizes: SizeAlign,
    component: &'a Component,

    /// Map of error contexts tables for a given component & error context index pair
    /// that have been initialized
    error_context_component_initialized: PrimaryMap<RuntimeComponentInstanceIndex, bool>,
    error_context_component_table_initialized:
        PrimaryMap<TypeComponentLocalErrorContextTableIndex, bool>,

    /// Component-level translation information, including trampolines
    translation: &'a ComponentTranslation,

    /// Lookup of exported types to resource indices
    exports_resource_types: BTreeMap<TypeId, ResourceIndex>,
    /// Lookup of resource indices to exported types
    exports_resource_index_types: BTreeMap<ResourceIndex, TypeId>,

    /// Lookup of imported types to resource indices
    imports_resource_types: BTreeMap<TypeId, ResourceIndex>,
    /// Lookup of resource indices to imported types
    #[allow(unused)]
    imports_resource_index_types: BTreeMap<ResourceIndex, TypeId>,

    resources_initialized: BTreeMap<ResourceIndex, bool>,
    resource_tables_initialized: BTreeMap<TypeResourceTableIndex, bool>,

    exports: BTreeMap<String, WorldKey>,
    imports: BTreeMap<String, WorldKey>,
    /// Instance flags which references have been emitted externally at least once.
    used_instance_flags: RefCell<BTreeSet<RuntimeComponentInstanceIndex>>,
    defined_resource_classes: BTreeSet<String>,
    async_imports: HashSet<String>,
    async_exports: HashSet<String>,
    lowering_options:
        PrimaryMap<LoweredIndex, (&'a CanonicalOptions, TrampolineIndex, TypeFuncIndex)>,

    /// Mapping of stream table indices to component indices
    stream_tables: BTreeMap<TypeStreamTableIndex, RuntimeComponentInstanceIndex>,

    /// Mapping of future table indices to component indices
    future_tables: BTreeMap<TypeFutureTableIndex, RuntimeComponentInstanceIndex>,

    /// Mapping of err ctx indices to component indices
    err_ctx_tables:
        BTreeMap<TypeComponentLocalErrorContextTableIndex, RuntimeComponentInstanceIndex>,

    /// Map of exported resources built during export bindgen
    resource_exports: ResourceMap,
    /// Map of imported resources built during export bindgen
    resource_imports: ResourceMap,

    /// Component index of the module that is currentlty being initialized
    ///
    /// This is only populated after processing of `GlobalInitializer::InstantiateModule`
    /// blocks has started, and is likely to be stale if read too late (i.e. it will be set
    /// to the last module processed).
    init_current_module: Option<RuntimeComponentInstanceIndex>,
}

impl<'a> ManagesIntrinsics for Instantiator<'a, '_> {
    fn add_intrinsic(&mut self, intrinsic: Intrinsic) {
        self.bindgen.intrinsic(intrinsic);
    }
}

impl<'a> Instantiator<'a, '_> {
    fn initialize(&mut self) {
        // Populate reverse map from import and export names to world items
        for (key, _) in &self.resolve.worlds[self.world].imports {
            let name = &self.resolve.name_world_key(key);
            self.imports.insert(name.to_string(), key.clone());
        }
        for (key, _) in &self.resolve.worlds[self.world].exports {
            let name = &self.resolve.name_world_key(key);
            self.exports.insert(name.to_string(), key.clone());
        }

        // Populate reverse map from TypeId to ResourceIndex
        // Populate the resource type to resource index map
        for (key, item) in &self.resolve.worlds[self.world].imports {
            let name = &self.resolve.name_world_key(key);
            let Some((_, (_, import))) = self
                .component
                .import_types
                .iter()
                .find(|(_, (impt_name, _))| impt_name == name)
            else {
                match item {
                    WorldItem::Interface { .. } => {
                        unreachable!("unexpected interface in import types during initialization")
                    }
                    WorldItem::Function(_) => {
                        unreachable!("unexpected function in import types during initialization")
                    }
                    WorldItem::Type { id, .. } => {
                        assert!(!matches!(
                            self.resolve.types[*id].kind,
                            TypeDefKind::Resource
                        ))
                    }
                }
                continue;
            };
            match item {
                WorldItem::Interface { id, .. } => {
                    let TypeDef::ComponentInstance(instance) = import else {
                        unreachable!("unexpectedly non-component instance import in interface")
                    };
                    let import_ty = &self.types[*instance];
                    let iface = &self.resolve.interfaces[*id];
                    for (ty_name, ty) in &iface.types {
                        match &import_ty.exports.get(ty_name) {
                            Some(TypeDef::Resource(resource_table_idx)) => {
                                let ty = crate::dealias(self.resolve, *ty);
                                let resource_table_ty = &self.types[*resource_table_idx];
                                let concrete_ty = resource_table_ty.unwrap_concrete_ty();
                                self.imports_resource_types.insert(ty, concrete_ty);
                                self.imports_resource_index_types.insert(concrete_ty, ty);
                            }
                            Some(TypeDef::Interface(_)) | None => {}
                            Some(_) => unreachable!("unexpected type in interface"),
                        }
                    }
                }
                WorldItem::Function(_) => {}
                WorldItem::Type { id, .. } => match import {
                    TypeDef::Resource(resource) => {
                        let ty = crate::dealias(self.resolve, *id);
                        let resource_table_ty = &self.types[*resource];
                        let concrete_ty = resource_table_ty.unwrap_concrete_ty();
                        self.imports_resource_types.insert(ty, concrete_ty);
                        self.imports_resource_index_types.insert(concrete_ty, ty);
                    }
                    TypeDef::Interface(_) => {}
                    _ => unreachable!("unexpected type in import world item"),
                },
            }
        }
        self.exports_resource_types = self.imports_resource_types.clone();
        self.exports_resource_index_types = self.imports_resource_index_types.clone();

        for (key, item) in &self.resolve.worlds[self.world].exports {
            let name = &self.resolve.name_world_key(key);
            let (_, export_idx) = self
                .component
                .exports
                .raw_iter()
                .find(|(expt_name, _)| ***expt_name == **name)
                .unwrap();
            let export = &self.component.export_items[*export_idx];
            match item {
                WorldItem::Interface { id, .. } => {
                    let iface = &self.resolve.interfaces[*id];
                    let Export::Instance { exports, .. } = &export else {
                        unreachable!("unexpectedly non export instance item")
                    };
                    for (ty_name, ty) in &iface.types {
                        match self.component.export_items
                            [*exports.get(ty_name, &NameMapNoIntern).unwrap()]
                        {
                            Export::Type(TypeDef::Resource(resource)) => {
                                let ty = crate::dealias(self.resolve, *ty);
                                let resource_table_ty = &self.types[resource];
                                let concrete_ty = resource_table_ty.unwrap_concrete_ty();
                                self.exports_resource_types.insert(ty, concrete_ty);
                                self.exports_resource_index_types.insert(concrete_ty, ty);
                            }
                            Export::Type(_) => {}
                            _ => unreachable!(
                                "unexpected type in component export items on iface [{iface_name}]",
                                iface_name = iface.name.as_deref().unwrap_or("<unknown>"),
                            ),
                        }
                    }
                }
                WorldItem::Function(_) => {}
                WorldItem::Type { .. } => unreachable!("unexpected exported world item type"),
            }
        }
    }

    fn instantiate(&mut self) {
        // Handle all built in trampolines
        for (i, trampoline) in self.translation.trampolines.iter() {
            let Trampoline::LowerImport {
                index,
                lower_ty,
                options,
            } = trampoline
            else {
                continue;
            };

            let options = self
                .component
                .options
                .get(*options)
                .expect("failed to find canon options");

            let i = self.lowering_options.push((options, i, *lower_ty));
            assert_eq!(i, *index);
        }

        if let Some(InstantiationMode::Async) = self.bindgen.opts.instantiation_mode {
            // To avoid uncaught promise rejection errors, we attach an intermediate
            // Promise.all with a rejection handler, if there are multiple promises.
            if self.modules.len() > 1 {
                self.src.js_init.push_str("Promise.all([");
                for i in 0..self.modules.len() {
                    if i > 0 {
                        self.src.js_init.push_str(", ");
                    }
                    self.src.js_init.push_str(&format!("module{i}"));
                }
                uwriteln!(self.src.js_init, "]).catch(() => {{}});");
            }
        }

        // Set up global stream map, which is used by intrinsics like stream.transfer.
        // Register the intrinsic so the `const STREAM_TABLES = {};` declaration
        // is emitted before these per-table assignments — without that, the
        // generated module references an undeclared identifier and fails to
        // load (ReferenceError: STREAM_TABLES is not defined).
        if !self.stream_tables.is_empty() {
            let global_stream_table_map = self.bindgen.intrinsic(Intrinsic::AsyncStream(
                AsyncStreamIntrinsic::GlobalStreamTableMap,
            ));
            let rep_table_class = Intrinsic::RepTableClass.name();
            for (table_idx, component_idx) in self.stream_tables.iter() {
                self.src.js.push_str(&format!(
                    "{global_stream_table_map}[{}] = {{ componentIdx: {}, table: new {rep_table_class}() }};\n",
                    table_idx.as_u32(),
                    component_idx.as_u32(),
                ));
            }
        }

        // Set up global future map, which is used by intrinsics like future.transfer.
        // Same registration fix as above for FUTURE_TABLES.
        if !self.future_tables.is_empty() {
            let global_future_table_map = self.bindgen.intrinsic(Intrinsic::AsyncFuture(
                AsyncFutureIntrinsic::GlobalFutureTableMap,
            ));
            let rep_table_class = Intrinsic::RepTableClass.name();
            for (table_idx, component_idx) in self.future_tables.iter() {
                self.src.js.push_str(&format!(
                    "{global_future_table_map}[{}] = {{ componentIdx: {}, table: new {rep_table_class}() }};\n",
                    table_idx.as_u32(),
                    component_idx.as_u32(),
                ));
            }
        }

        // Set up global error context map, which is used by intrinsics like err_ctx.transfer.
        // Same registration fix as above for ERR_CTX_TABLES.
        if !self.err_ctx_tables.is_empty() {
            let global_err_ctx_table_map = self
                .bindgen
                .intrinsic(Intrinsic::ErrCtx(ErrCtxIntrinsic::GlobalErrCtxTableMap));
            let rep_table_class = Intrinsic::RepTableClass.name();
            for (table_idx, component_idx) in self.err_ctx_tables.iter() {
                self.src.js.push_str(&format!(
                    "{global_err_ctx_table_map}[{}] = {{ componentIdx: {}, table: new {rep_table_class}() }};\n",
                    table_idx.as_u32(),
                    component_idx.as_u32(),
                ));
            }
        }

        // Process global initializers
        //
        // The order of initialization is unfortunately quite fragile.
        //
        // We take care in processing module instantiations because we must ensure that
        // $wit-component.fixups must be instantiated directly after $wit-component.shim
        //
        let mut lower_import_initializers = Vec::new();

        // Process first n lower import initializers until the first instantiate module initializer
        for init in self.component.initializers.iter() {
            match init {
                GlobalInitializer::InstantiateModule(_m, _maybe_idx) => {
                    // Ensure lower import initializers are processed before the first module instantiation
                    for lower_import_init in lower_import_initializers.drain(..) {
                        self.instantiation_global_initializer(lower_import_init);
                    }
                }

                // We push lower import initializers down to right before instantiate, so that the
                // memory, realloc and postReturn functions are available to the import lowerings
                // for optimized bindgen
                GlobalInitializer::LowerImport { .. } => {
                    lower_import_initializers.push(init);
                    continue;
                }
                _ => {}
            }

            self.instantiation_global_initializer(init);
        }

        // Process lower import initializers that were discovered after the last module instantiation
        for init in lower_import_initializers.drain(..) {
            self.instantiation_global_initializer(init);
        }

        // Process imports and build mappings
        self.process_imports();

        // Process exports and build mappings
        self.process_exports();

        // Some trampolines that correspond to host-provided imports need to be defined before the
        // instantiation bits since they are referred to.
        for (i, trampoline) in self
            .translation
            .trampolines
            .iter()
            .filter(|(_, t)| Instantiator::is_early_trampoline(t))
        {
            self.trampoline(i, trampoline);
        }

        if self.bindgen.opts.instantiation_mode.is_some() {
            let js_init = mem::take(&mut self.src.js_init);
            self.src.js.push_str(&js_init);
        }

        // Trampolines here so we have static module indices, and resource maps populated
        // (both imports and exports may still be populting resource map)
        for (i, trampoline) in self
            .translation
            .trampolines
            .iter()
            .filter(|(_, t)| !Instantiator::is_early_trampoline(t))
        {
            self.trampoline(i, trampoline);
        }
    }

    fn ensure_local_resource_class(&mut self, local_name: String) {
        if !self.defined_resource_classes.contains(&local_name) {
            uwriteln!(
                self.src.js,
                "\nclass {local_name} {{
                constructor () {{
                    throw new Error('\"{local_name}\" resource does not define a constructor');
                }}
            }}"
            );
            self.defined_resource_classes.insert(local_name.to_string());
        }
    }

    fn resource_definitions(&mut self) {
        // It is theoretically possible for locally defined resources used in no functions
        // to still be exported
        for resource in 0..self.component.num_resources {
            let resource = ResourceIndex::from_u32(resource);
            let is_imported = self.component.defined_resource_index(resource).is_none();
            if is_imported {
                continue;
            }
            if let Some(local_name) = self.bindgen.local_names.try_get(resource) {
                self.ensure_local_resource_class(local_name.to_string());
            }
        }

        // TODO(feat): In the past, we could eagerly build a mapping of resources defined to the tables they correspond to
        // to make runtime checks of which table a resource must have been created into first (i.e. the component that implements
        // creation of a given resource) a particular resource faster.
        //
        // This logic was based on component.num_resources and was broken for composed components --
        // wasmtime-environ reported a smaller number of resources, and the check was geared towards a *single* component,
        // not tying a particular component to a particular table (it is possible for *sub components* to originate different
        // resources).
        //
        // In theory, it should be posible to build this knowledge statically rather than at resource creation,
        // so in the future we should attempt to rebulid that code, if possible.
        //
        // Note that at runtime wasmtime maintains this information and looks it up during a transfer operation, see:
        //   - https://github.com/bytecodealliance/wasmtime/blob/5f3b67ea055857020bd1ac1f2c3f7fa2e6c31ec0/crates/wasmtime/src/runtime/component/instance.rs#L424
        //   - https://github.com/bytecodealliance/wasmtime/blob/9c49989a2e71382fd8639288088472f150f2f534/crates/wasmtime/src/runtime/vm/component.rs#L847
    }

    /// Ensure a component-local `error-context` table has been created
    ///
    /// # Arguments
    ///
    /// * `component_idx` - component index
    /// * `err_ctx_tbl_idx` - The component-local error-context table index
    ///
    fn ensure_error_context_local_table(
        &mut self,
        component_idx: RuntimeComponentInstanceIndex,
        err_ctx_tbl_idx: TypeComponentLocalErrorContextTableIndex,
    ) {
        if self.error_context_component_initialized[component_idx]
            && self.error_context_component_table_initialized[err_ctx_tbl_idx]
        {
            return;
        }
        let err_ctx_local_tables = self
            .bindgen
            .intrinsic(Intrinsic::ErrCtx(ErrCtxIntrinsic::ComponentLocalTable));
        let rep_table_class = Intrinsic::RepTableClass.name();
        let c = component_idx.as_u32();
        if !self.error_context_component_initialized[component_idx] {
            uwriteln!(self.src.js, "{err_ctx_local_tables}.set({c}, new Map());");
            self.error_context_component_initialized[component_idx] = true;
        }
        if !self.error_context_component_table_initialized[err_ctx_tbl_idx] {
            let t = err_ctx_tbl_idx.as_u32();
            uwriteln!(
                self.src.js,
                "{err_ctx_local_tables}.get({c}).set({t}, new {rep_table_class}({{ target: `component [{c}] local error ctx table [{t}]` }}));"
            );
            self.error_context_component_table_initialized[err_ctx_tbl_idx] = true;
        }
    }

    /// Ensure that a resource table has been initialized
    ///
    /// For the relevant resource table, this function will generate initialization
    /// blocks, exactly once.
    ///
    /// This is not done for *all* resources, but instead for those that are explicitly used.
    fn ensure_resource_table(&mut self, resource_table_idx: TypeResourceTableIndex) {
        if self
            .resource_tables_initialized
            .contains_key(&resource_table_idx)
        {
            return;
        }

        let resource_table_ty = &self.types[resource_table_idx];
        let resource_idx = resource_table_ty.unwrap_concrete_ty();

        let (is_imported, maybe_dtor) =
            if let Some(resource_idx) = self.component.defined_resource_index(resource_idx) {
                let resource_def = self
                    .component
                    .initializers
                    .iter()
                    .find_map(|i| match i {
                        GlobalInitializer::Resource(r) if r.index == resource_idx => Some(r),
                        _ => None,
                    })
                    .unwrap();

                if let Some(dtor) = &resource_def.dtor {
                    (false, format!("\n{}(rep);", self.core_def(dtor)))
                } else {
                    (false, "".into())
                }
            } else {
                (true, "".into())
            };

        let handle_tables = self.bindgen.intrinsic(Intrinsic::HandleTables);
        let rsc_table_flag = self
            .bindgen
            .intrinsic(Intrinsic::Resource(ResourceIntrinsic::ResourceTableFlag));
        let rsc_table_remove = self
            .bindgen
            .intrinsic(Intrinsic::Resource(ResourceIntrinsic::ResourceTableRemove));

        // Create the relevant handle table
        let rtid = resource_table_idx.as_u32();
        if is_imported {
            // imported
            uwriteln!(
                self.src.js,
                r#"
                  const handleTable{rtid} = [{rsc_table_flag}, 0];
                  handleTable{rtid}._createdReps = new Set();
                "#,
            );
            if !self.resources_initialized.contains_key(&resource_idx) {
                let ridx = resource_idx.as_u32();
                uwriteln!(
                    self.src.js,
                    r#"
                      const captureTable{ridx} = new Map();
                      let captureCnt{ridx} = 0;
                    "#
                );
                self.resources_initialized.insert(resource_idx, true);
            }
        } else {
            // non imported
            let finalization_registry_create = self
                .bindgen
                .intrinsic(Intrinsic::FinalizationRegistryCreate);
            uwriteln!(
                self.src.js,
                r#"
                   const handleTable{rtid} = [{rsc_table_flag}, 0];
                   handleTable{rtid}._createdReps = new Set();
                   const finalizationRegistry{rtid} = {finalization_registry_create}((handle) => {{
                       const {{ rep }} = {rsc_table_remove}(handleTable{rtid}, handle);{maybe_dtor}
                   }});
                "#,
            );
        }

        // Add the handle table to the global list
        uwriteln!(self.src.js, "{handle_tables}[{rtid}] = handleTable{rtid};");
        self.resource_tables_initialized
            .insert(resource_table_idx, true);
    }

    fn instance_flags(&mut self) {
        // SAFETY: short-lived borrow, and the refcell isn't mutably borrowed in the loop's body.
        let mut instance_flag_defs = String::new();
        for used in self.used_instance_flags.borrow().iter() {
            let i = used.as_u32();
            uwriteln!(
                &mut instance_flag_defs,
                "const instanceFlags{i} = new WebAssembly.Global({{ value: \"i32\", mutable: true }}, {});",
                wasmtime_environ::component::FLAG_MAY_LEAVE
            );
        }
        self.src.js_init.prepend_str(&instance_flag_defs);
    }

    // Trampolines defined in is_early_trampoline() below that use:
    //   const trampoline{} = ...
    // require early initialization since their bindings aren't auto-hoisted
    // like JS functions are in the JS runtime.
    fn is_early_trampoline(trampoline: &Trampoline) -> bool {
        matches!(
            trampoline,
            Trampoline::AsyncStartCall { .. }
                | Trampoline::BackpressureDec { .. }
                | Trampoline::BackpressureInc { .. }
                | Trampoline::EnterSyncCall
                | Trampoline::ErrorContextDebugMessage { .. }
                | Trampoline::ErrorContextDrop { .. }
                | Trampoline::ErrorContextNew { .. }
                | Trampoline::ErrorContextTransfer
                | Trampoline::ExitSyncCall
                | Trampoline::FutureCancelRead { .. }
                | Trampoline::FutureCancelWrite { .. }
                | Trampoline::FutureDropReadable { .. }
                | Trampoline::FutureDropWritable { .. }
                | Trampoline::FutureNew { .. }
                | Trampoline::FutureRead { .. }
                | Trampoline::FutureWrite { .. }
                | Trampoline::LowerImport { .. }
                | Trampoline::PrepareCall { .. }
                | Trampoline::ResourceDrop { .. }
                | Trampoline::ResourceNew { .. }
                | Trampoline::ResourceRep { .. }
                | Trampoline::ResourceTransferBorrow
                | Trampoline::ResourceTransferOwn
                | Trampoline::StreamCancelRead { .. }
                | Trampoline::StreamCancelWrite { .. }
                | Trampoline::StreamDropReadable { .. }
                | Trampoline::StreamDropWritable { .. }
                | Trampoline::StreamNew { .. }
                | Trampoline::StreamRead { .. }
                | Trampoline::StreamTransfer
                | Trampoline::StreamWrite { .. }
                | Trampoline::SubtaskCancel { .. }
                | Trampoline::SubtaskDrop { .. }
                | Trampoline::SyncStartCall { .. }
                | Trampoline::TaskCancel { .. }
                | Trampoline::TaskReturn { .. }
                | Trampoline::ThreadYield { .. }
                | Trampoline::ThreadYieldToSuspended { .. }
                | Trampoline::WaitableJoin { .. }
                | Trampoline::WaitableSetDrop { .. }
                | Trampoline::WaitableSetNew { .. }
                | Trampoline::WaitableSetPoll { .. }
                | Trampoline::WaitableSetWait { .. }
        )
    }

    fn trampoline(&mut self, i: TrampolineIndex, trampoline: &'a Trampoline) {
        let i = i.as_u32();
        match trampoline {
            Trampoline::TaskCancel { instance } => {
                let task_cancel_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::AsyncTask(AsyncTaskIntrinsic::TaskCancel));
                uwriteln!(
                    self.src.js,
                    "const trampoline{i} = {task_cancel_fn}.bind(null, {instance_idx});\n",
                    instance_idx = instance.as_u32(),
                );
            }

            Trampoline::SubtaskCancel { instance, async_ } => {
                let task_cancel_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::AsyncTask(AsyncTaskIntrinsic::SubtaskCancel));
                uwriteln!(
                    self.src.js,
                    "const trampoline{i} = {task_cancel_fn}.bind(null, {instance_idx}, {async_});\n",
                    instance_idx = instance.as_u32(),
                );
            }

            Trampoline::SubtaskDrop { instance } => {
                let component_idx = instance.as_u32();
                let subtask_drop_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::AsyncTask(AsyncTaskIntrinsic::SubtaskDrop));
                uwriteln!(
                    self.src.js,
                    "const trampoline{i} = {subtask_drop_fn}.bind(
                         null,
                         {component_idx},
                     );"
                );
            }

            Trampoline::WaitableSetNew { instance } => {
                let waitable_set_new_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::Waitable(WaitableIntrinsic::WaitableSetNew));
                uwriteln!(
                    self.src.js,
                    "const trampoline{i} = {waitable_set_new_fn}.bind(null, {});\n",
                    instance.as_u32(),
                );
            }

            Trampoline::WaitableSetWait { instance, options } => {
                let options = self
                    .component
                    .options
                    .get(*options)
                    .expect("failed to find options");
                assert_eq!(
                    instance.as_u32(),
                    options.instance.as_u32(),
                    "options index instance must match trampoline"
                );

                let CanonicalOptions {
                    instance,
                    async_,
                    data_model:
                        CanonicalOptionsDataModel::LinearMemory(LinearMemoryOptions { memory, .. }),
                    ..
                } = options
                else {
                    panic!("unexpected/missing memory data model during waitable-set.wait");
                };

                let instance_idx = instance.as_u32();
                let memory_idx = memory
                    .expect("missing memory idx for waitable-set.wait")
                    .as_u32();
                let waitable_set_wait_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::Waitable(WaitableIntrinsic::WaitableSetWait));

                uwriteln!(
                    self.src.js,
                    r#"
                    const trampoline{i} = new WebAssembly.Suspending({waitable_set_wait_fn}.bind(null, {{
                        componentIdx: {instance_idx},
                        isAsync: {async_},
                        memoryIdx: {memory_idx},
                        getMemoryFn: () => memory{memory_idx},
                    }}));
                    "#,
                );
            }

            Trampoline::WaitableSetPoll { options, .. } => {
                let CanonicalOptions {
                    instance,
                    async_,
                    data_model:
                        CanonicalOptionsDataModel::LinearMemory(LinearMemoryOptions { memory, .. }),
                    cancellable,
                    ..
                } = self
                    .component
                    .options
                    .get(*options)
                    .expect("failed to find options")
                else {
                    panic!("unexpected memory data model during waitable-set.poll");
                };

                let instance_idx = instance.as_u32();
                let memory_idx = memory
                    .expect("missing memory idx for waitable-set.poll")
                    .as_u32();
                let waitable_set_poll_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::Waitable(WaitableIntrinsic::WaitableSetPoll));

                uwriteln!(
                    self.src.js,
                    r#"
                    const trampoline{i} = {waitable_set_poll_fn}.bind(
                        null,
                        {{
                            componentIdx: {instance_idx},
                            isAsync: {async_},
                            isCancellable: {cancellable},
                            memoryIdx: {memory_idx},
                            getMemoryFn: () => memory{memory_idx},
                        }}
                    );
                    "#,
                );
            }

            Trampoline::WaitableSetDrop { instance } => {
                let waitable_set_drop_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::Waitable(WaitableIntrinsic::WaitableSetDrop));
                uwriteln!(
                    self.src.js,
                    "const trampoline{i} = {waitable_set_drop_fn}.bind(null, {instance_idx});\n",
                    instance_idx = instance.as_u32(),
                );
            }

            Trampoline::WaitableJoin { instance } => {
                let waitable_join_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::Waitable(WaitableIntrinsic::WaitableJoin));
                uwriteln!(
                    self.src.js,
                    "const trampoline{i} = {waitable_join_fn}.bind(null, {instance_idx});\n",
                    instance_idx = instance.as_u32(),
                );
            }

            Trampoline::StreamNew { ty, instance } => {
                let stream_new_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::AsyncStream(AsyncStreamIntrinsic::StreamNew));
                let instance_idx = instance.as_u32();
                let stream_table_idx = ty.as_u32();

                // Get to the payload type for the given stream table idx
                let table_ty = &self.types[*ty];
                let stream_ty_idx = table_ty.ty;
                let stream_ty = &self.types[stream_ty_idx];

                // TODO(???): do we have no way to go from interface type to in-component type idx?
                // TODO(???): does this work under type aliases?? we need the type def?
                // TODO(???): can the stream type be treated as a unique indicator of the payload type? maybe not?
                // need a way to go from iface type + stream type -> payload type idx?
                let payload_ty_name_js = stream_ty
                    .payload
                    .map(|iface_ty| format!("'{iface_ty:?}'"))
                    .unwrap_or_else(|| "null".into());

                // Gather type metadata
                let (
                    align_32_js,
                    size_32_js,
                    flat_count_js,
                    lift_fn_js,
                    lower_fn_js,
                    is_none_js,
                    is_numeric_type_js,
                    is_borrow_js,
                    is_async_value_js,
                    typed_array_js,
                ) = match stream_ty.payload {
                    // If there is no payload for the stream, we know the values
                    None => (
                        "0".into(),
                        "0".into(),
                        "0".into(),
                        "null".into(),
                        "null".into(),
                        "true",
                        "false".into(),
                        "false".into(),
                        "false".into(),
                        "undefined",
                    ),
                    // If there is a payload, generate relevant lift/lower and other metadata
                    Some(ty) => (
                        self.types.canonical_abi(&ty).align32.to_string(),
                        self.types.canonical_abi(&ty).size32.to_string(),
                        self.types
                            .canonical_abi(&ty)
                            .flat_count
                            .map(|v| v.to_string())
                            .unwrap_or_else(|| "null".into()),
                        gen_flat_lift_fn_js_expr(self, &ty, &None),
                        gen_flat_lower_fn_js_expr(self, &ty, &None),
                        "false",
                        format!(
                            "{}",
                            matches!(
                                ty,
                                InterfaceType::U8
                                    | InterfaceType::U16
                                    | InterfaceType::U32
                                    | InterfaceType::U64
                                    | InterfaceType::S8
                                    | InterfaceType::S16
                                    | InterfaceType::S32
                                    | InterfaceType::S64
                                    | InterfaceType::Float32
                                    | InterfaceType::Float64
                            )
                        ),
                        format!("{}", matches!(ty, InterfaceType::Borrow(_))),
                        format!(
                            "{}",
                            matches!(ty, InterfaceType::Stream(_) | InterfaceType::Future(_))
                        ),
                        js_typed_array_ctor(&ty).unwrap_or("undefined"),
                    ),
                };

                uwriteln!(
                    self.src.js,
                    "const trampoline{i} = {stream_new_fn}.bind(null, {{
                        streamTableIdx: {stream_table_idx},
                        callerComponentIdx: {instance_idx},
                        elemMeta: {{
                            liftFn: {lift_fn_js},
                            lowerFn: {lower_fn_js},
                            payloadTypeName: {payload_ty_name_js},
                            isNone: {is_none_js},
                            isNumeric: {is_numeric_type_js},
                            isBorrowed: {is_borrow_js},
                            isAsyncValue: {is_async_value_js},
                            typedArray: {typed_array_js},
                            flatCount: {flat_count_js},
                            align32: {align_32_js},
                            size32: {size_32_js},
                        }},
                    }});\n",
                );
            }

            Trampoline::StreamRead {
                instance,
                ty,
                options,
            } => {
                let options = self
                    .component
                    .options
                    .get(*options)
                    .expect("failed to find options");
                assert_eq!(
                    instance.as_u32(),
                    options.instance.as_u32(),
                    "options index instance must match trampoline"
                );

                let CanonicalOptions {
                    instance,
                    string_encoding,
                    async_,
                    data_model:
                        CanonicalOptionsDataModel::LinearMemory(LinearMemoryOptions { memory, realloc }),
                    ..
                } = options
                else {
                    unreachable!("missing/invalid data model for options during stream.read")
                };
                let memory_idx = memory.expect("missing memory idx for stream.read").as_u32();
                let (realloc_idx, get_realloc_fn_js) = match realloc {
                    Some(v) => {
                        let v = v.as_u32().to_string();
                        (v.to_string(), format!("() => realloc{v}"))
                    }
                    None => ("undefined".into(), "undefined".into()),
                };

                let component_instance_id = instance.as_u32();
                let string_encoding = string_encoding_js_literal(string_encoding);
                let stream_table_idx = ty.as_u32();
                let stream_read_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::AsyncStream(AsyncStreamIntrinsic::StreamRead));

                // PrepareCall for an async call is sometimes missing memories,
                // so we augment and save here, knowing that any stream.write/read operation
                // that uses a memory is indicative of that component's memory
                //
                let register_global_memory_for_component_fn =
                    Intrinsic::RegisterGlobalMemoryForComponent.name();
                uwriteln!(
                    self.src.js_init,
                    r#"{register_global_memory_for_component_fn}({{
                         componentIdx: {component_instance_id},
                         memoryIdx: {memory_idx},
                         memory: memory{memory_idx},
                     }});"#
                );

                uwriteln!(
                    self.src.js,
                    r#"const trampoline{i} = new WebAssembly.Suspending({stream_read_fn}.bind(
                         null,
                         {{
                             componentIdx: {component_instance_id},
                             memoryIdx: {memory_idx},
                             getMemoryFn: () => memory{memory_idx},
                             reallocIdx: {realloc_idx},
                             getReallocFn: {get_realloc_fn_js},
                             stringEncoding: {string_encoding},
                             isAsync: {async_},
                             streamTableIdx: {stream_table_idx},
                         }}
                     ));
                    "#,
                );
            }

            Trampoline::StreamWrite {
                instance,
                ty,
                options,
            } => {
                let options = self
                    .component
                    .options
                    .get(*options)
                    .expect("failed to find options");
                assert_eq!(
                    instance.as_u32(),
                    options.instance.as_u32(),
                    "options index instance must match trampoline"
                );

                let CanonicalOptions {
                    instance,
                    string_encoding,
                    async_,
                    data_model:
                        CanonicalOptionsDataModel::LinearMemory(LinearMemoryOptions { memory, realloc }),
                    ..
                } = options
                else {
                    unreachable!("unexpected memory data model during stream.write");
                };
                let component_instance_id = instance.as_u32();
                let memory_idx = memory
                    .expect("missing memory idx for stream.write")
                    .as_u32();
                let (realloc_idx, get_realloc_fn_js) = match realloc {
                    Some(v) => {
                        let v = v.as_u32().to_string();
                        (v.to_string(), format!("() => realloc{v}"))
                    }
                    None => ("undefined".into(), "undefined".into()),
                };

                let string_encoding = string_encoding_js_literal(string_encoding);
                let stream_table_idx = ty.as_u32();
                let stream_write_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::AsyncStream(AsyncStreamIntrinsic::StreamWrite));

                // PrepareCall for an async call is sometimes missing memories,
                // so we augment and save here, knowing that any stream.write/read operation
                // that uses a memory is indicative of that component's memory
                let register_global_memory_for_component_fn =
                    Intrinsic::RegisterGlobalMemoryForComponent.name();
                uwriteln!(
                    self.src.js_init,
                    r#"{register_global_memory_for_component_fn}({{
                         componentIdx: {component_instance_id},
                         memoryIdx: {memory_idx},
                         memory: memory{memory_idx},
                     }});"#
                );

                uwriteln!(
                    self.src.js,
                    r#"
                     const trampoline{i} = new WebAssembly.Suspending({stream_write_fn}.bind(
                         null,
                         {{
                             componentIdx: {component_instance_id},
                             memoryIdx: {memory_idx},
                             getMemoryFn: () => memory{memory_idx},
                             reallocIdx: {realloc_idx},
                             getReallocFn: {get_realloc_fn_js},
                             stringEncoding: {string_encoding},
                             isAsync: {async_},
                             streamTableIdx: {stream_table_idx},
                         }}
                     ));
                    "#,
                );
            }

            Trampoline::StreamCancelRead {
                instance,
                ty,
                async_,
            }
            | Trampoline::StreamCancelWrite {
                instance,
                ty,
                async_,
            } => {
                let stream_cancel_fn = match trampoline {
                    Trampoline::StreamCancelRead { .. } => self.bindgen.intrinsic(
                        Intrinsic::AsyncStream(AsyncStreamIntrinsic::StreamCancelRead),
                    ),
                    Trampoline::StreamCancelWrite { .. } => self.bindgen.intrinsic(
                        Intrinsic::AsyncStream(AsyncStreamIntrinsic::StreamCancelWrite),
                    ),
                    _ => unreachable!("unexpected trampoline"),
                };

                let stream_table_idx = ty.as_u32();
                let component_idx = instance.as_u32();
                uwriteln!(
                    self.src.js,
                    r#"
                      const trampoline{i} = new WebAssembly.Suspending({stream_cancel_fn}.bind(null, {{
                          streamTableIdx: {stream_table_idx},
                          isAsync: {async_},
                          componentIdx: {component_idx},
                      }}));
                    "#,
                );
            }

            Trampoline::StreamDropReadable { ty, instance }
            | Trampoline::StreamDropWritable { ty, instance } => {
                let intrinsic_fn = match trampoline {
                    Trampoline::StreamDropReadable { .. } => self.bindgen.intrinsic(
                        Intrinsic::AsyncStream(AsyncStreamIntrinsic::StreamDropReadable),
                    ),
                    Trampoline::StreamDropWritable { .. } => self.bindgen.intrinsic(
                        Intrinsic::AsyncStream(AsyncStreamIntrinsic::StreamDropWritable),
                    ),
                    _ => unreachable!("unexpected trampoline"),
                };
                let stream_idx = ty.as_u32();
                let instance_idx = instance.as_u32();
                uwriteln!(
                    self.src.js,
                    "const trampoline{i} = {intrinsic_fn}.bind(null, {{
                        streamTableIdx: {stream_idx},
                        componentIdx: {instance_idx},
                    }});\n",
                );
            }

            Trampoline::StreamTransfer => {
                let stream_transfer_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::AsyncStream(AsyncStreamIntrinsic::StreamTransfer));
                uwriteln!(self.src.js, "const trampoline{i} = {stream_transfer_fn};\n",);
            }

            Trampoline::FutureNew { instance, ty } => {
                let future_new_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::AsyncFuture(AsyncFutureIntrinsic::FutureNew));
                let future_table_idx = ty.as_u32();
                let component_idx = instance.as_u32();

                // Build element metadata
                let future_table_ty = &self.types[*ty];
                let future_ty = &self.types[future_table_ty.ty];
                let (
                    payload_size32,
                    payload_align32,
                    payload_flat_count_js,
                    payload_lift_fn_js,
                    payload_lower_fn_js,
                    is_borrowed,
                    is_none_type,
                    is_numeric_type,
                    is_async_value,
                ) = match future_ty.payload {
                    None => (
                        0,
                        0,
                        "0".into(),
                        "() => {{ throw new Error('empty future payload'); }}".into(),
                        "() => {{ throw new Error('empty future payload'); }}".into(),
                        false,
                        true,
                        false,
                        false,
                    ),
                    Some(payload_ty) => {
                        let cabi = self.types.canonical_abi(&payload_ty);
                        (
                            cabi.size32,
                            cabi.align32,
                            cabi.flat_count
                                .map(|v| format!("{v}"))
                                .unwrap_or_else(|| "null".into()),
                            gen_flat_lift_fn_js_expr(self, &payload_ty, &None),
                            gen_flat_lower_fn_js_expr(self, &payload_ty, &None),
                            matches!(payload_ty, InterfaceType::Borrow(_)),
                            false,
                            matches!(
                                payload_ty,
                                InterfaceType::U8
                                    | InterfaceType::U16
                                    | InterfaceType::U32
                                    | InterfaceType::U64
                                    | InterfaceType::S8
                                    | InterfaceType::S16
                                    | InterfaceType::S32
                                    | InterfaceType::S64
                                    | InterfaceType::Float32
                                    | InterfaceType::Float64
                            ),
                            matches!(
                                payload_ty,
                                InterfaceType::Stream(_) | InterfaceType::Future(_)
                            ),
                        )
                    }
                };
                let payload_ty_name_js = future_ty
                    .payload
                    .map(|iface_ty| format!("'{iface_ty:?}'"))
                    .unwrap_or_else(|| "null".into());

                uwriteln!(
                    self.src.js,
                    r#"
                      const trampoline{i} = {future_new_fn}.bind(null, {{
                          componentIdx: {component_idx},
                          futureTableIdx: {future_table_idx},
                          elemMeta: {{
                              liftFn: {payload_lift_fn_js},
                              lowerFn: {payload_lower_fn_js},
                              payloadTypeName: {payload_ty_name_js},
                              isNone: {is_none_type},
                              isNumeric: {is_numeric_type},
                              isBorrowed: {is_borrowed},
                              isAsyncValue: {is_async_value},
                              flatCount: {payload_flat_count_js},
                              align32: {payload_align32},
                              size32: {payload_size32},
                          }},
                      }});
                    "#,
                );
            }

            Trampoline::FutureWrite {
                instance,
                ty,
                options,
            }
            | Trampoline::FutureRead {
                instance,
                ty,
                options,
            } => {
                let intrinsic_fn = match trampoline {
                    Trampoline::FutureRead { .. } => self
                        .bindgen
                        .intrinsic(Intrinsic::AsyncFuture(AsyncFutureIntrinsic::FutureRead)),
                    Trampoline::FutureWrite { .. } => self
                        .bindgen
                        .intrinsic(Intrinsic::AsyncFuture(AsyncFutureIntrinsic::FutureWrite)),
                    _ => unreachable!("invalid trampoline"),
                };

                let options = self
                    .component
                    .options
                    .get(*options)
                    .expect("failed to find options");
                let CanonicalOptions {
                    async_,
                    string_encoding,
                    callback,
                    post_return,
                    data_model:
                        CanonicalOptionsDataModel::LinearMemory(LinearMemoryOptions { memory, realloc }),
                    ..
                } = options
                else {
                    unreachable!("unexpected memory data model during future intrinsic");
                };

                assert_eq!(
                    *instance, options.instance,
                    "component instances should match"
                );
                assert!(
                    callback.is_none(),
                    "callback should not be present for future intrinsic"
                );
                assert!(
                    post_return.is_none(),
                    "post_return should not be present for future intrinsic"
                );

                let future_table_idx = ty.as_u32();
                let component_idx = instance.as_u32();
                let memory_idx = memory
                    .expect("missing memory idx for future intrinsic")
                    .as_u32();
                let (realloc_idx, get_realloc_fn_js) = match realloc {
                    Some(idx) => (
                        idx.as_u32().to_string(),
                        format!("() => realloc{}", idx.as_u32()),
                    ),
                    None => ("undefined".into(), "undefined".to_string()),
                };
                let string_encoding = string_encoding_js_literal(string_encoding);

                uwriteln!(
                    self.src.js,
                    r#"
                      const trampoline{i} = new WebAssembly.Suspending({intrinsic_fn}.bind(
                          null,
                          {{
                              componentIdx: {component_idx},
                              memoryIdx: {memory_idx},
                              getMemoryFn: () => memory{memory_idx},
                              reallocIdx: {realloc_idx},
                              getReallocFn: {get_realloc_fn_js},
                              stringEncoding: {string_encoding},
                              futureTableIdx: {future_table_idx},
                              isAsync: {async_},
                          }},
                      ));
                    "#,
                );
            }

            Trampoline::FutureCancelRead {
                instance,
                ty,
                async_,
            }
            | Trampoline::FutureCancelWrite {
                instance,
                ty,
                async_,
            } => {
                let future_cancel_op_fn = match trampoline {
                    Trampoline::FutureCancelRead { .. } => self.bindgen.intrinsic(
                        Intrinsic::AsyncFuture(AsyncFutureIntrinsic::FutureCancelRead),
                    ),
                    Trampoline::FutureCancelWrite { .. } => self.bindgen.intrinsic(
                        Intrinsic::AsyncFuture(AsyncFutureIntrinsic::FutureCancelWrite),
                    ),
                    _ => unreachable!(),
                };

                let component_idx = instance.as_u32();
                let future_table_idx = ty.as_u32();

                uwriteln!(
                    self.src.js,
                    r#"
                      const trampoline{i} = new WebAssembly.Suspending({future_cancel_op_fn}.bind(
                          null,
                          {{
                              futureTableIdx: {future_table_idx},
                              componentIdx: {component_idx},
                              isAsync: {async_},
                          }},
                      ));
                    "#,
                );
            }

            Trampoline::FutureDropReadable { instance, ty }
            | Trampoline::FutureDropWritable { instance, ty } => {
                let future_drop_op_fn = match trampoline {
                    Trampoline::FutureDropReadable { .. } => self.bindgen.intrinsic(
                        Intrinsic::AsyncFuture(AsyncFutureIntrinsic::FutureDropReadable),
                    ),
                    Trampoline::FutureDropWritable { .. } => self.bindgen.intrinsic(
                        Intrinsic::AsyncFuture(AsyncFutureIntrinsic::FutureDropWritable),
                    ),
                    _ => unreachable!(),
                };

                let component_idx = instance.as_u32();
                let future_table_idx = ty.as_u32();

                uwriteln!(
                    self.src.js,
                    r#"
                      const trampoline{i} = new WebAssembly.Suspending({future_drop_op_fn}.bind(
                          null,
                          {{
                              futureTableIdx: {future_table_idx},
                              componentIdx: {component_idx},
                          }},
                      ));
                "#
                );
            }

            Trampoline::FutureTransfer => {
                let future_drop_writable_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::AsyncFuture(AsyncFutureIntrinsic::FutureTransfer));
                uwriteln!(
                    self.src.js,
                    "const trampoline{i} = {future_drop_writable_fn};"
                );
            }

            Trampoline::ErrorContextNew { ty, options, .. } => {
                let CanonicalOptions {
                    instance,
                    string_encoding,
                    data_model:
                        CanonicalOptionsDataModel::LinearMemory(LinearMemoryOptions { memory, .. }),
                    ..
                } = self
                    .component
                    .options
                    .get(*options)
                    .expect("failed to find options")
                else {
                    panic!("unexpected memory data model during error-context.new");
                };

                self.ensure_error_context_local_table(*instance, *ty);

                let local_err_tbl_idx = ty.as_u32();
                let component_idx = instance.as_u32();

                let memory_idx = memory
                    .expect("missing realloc fn idx for error-context.debug-message")
                    .as_u32();

                // Generate a string decoding function to match this trampoline that does appropriate encoding
                let decoder = match string_encoding {
                    wasmtime_environ::component::StringEncoding::Utf8 => self
                        .bindgen
                        .intrinsic(Intrinsic::String(StringIntrinsic::GlobalTextDecoderUtf8)),
                    wasmtime_environ::component::StringEncoding::Utf16 => self
                        .bindgen
                        .intrinsic(Intrinsic::String(StringIntrinsic::Utf16Decoder)),
                    enc => panic!(
                        "unsupported string encoding [{enc:?}] for error-context.debug-message"
                    ),
                };
                uwriteln!(
                    self.src.js,
                    "function trampoline{i}InputStr(ptr, len) {{
                         return {decoder}.decode(new DataView(memory{memory_idx}.buffer, ptr, len));
                    }}"
                );

                let err_ctx_new_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::ErrCtx(ErrCtxIntrinsic::ErrorContextNew));
                // Store the options associated with this new error context for later use in the global array
                uwriteln!(
                    self.src.js,
                    "const trampoline{i} = {err_ctx_new_fn}.bind(
                         null,
                         {{
                             componentIdx: {component_idx},
                             localTableIdx: {local_err_tbl_idx},
                             readStrFn: trampoline{i}InputStr,
                         }}
                     );
                    "
                );
            }

            Trampoline::ErrorContextDebugMessage {
                instance, options, ..
            } => {
                let CanonicalOptions {
                    async_,
                    callback,
                    post_return,
                    string_encoding,
                    data_model:
                        CanonicalOptionsDataModel::LinearMemory(LinearMemoryOptions { memory, realloc }),
                    ..
                } = self
                    .component
                    .options
                    .get(*options)
                    .expect("failed to find options")
                else {
                    panic!("unexpected memory data model during error-context.debug-message");
                };

                let debug_message_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::ErrCtx(ErrCtxIntrinsic::ErrorContextDebugMessage));

                let realloc_fn_idx = realloc
                    .expect("missing realloc fn idx for error-context.debug-message")
                    .as_u32();
                let memory_idx = memory
                    .expect("missing realloc fn idx for error-context.debug-message")
                    .as_u32();

                // Generate a string encoding function to match this trampoline that does appropriate encoding
                match string_encoding {
                    wasmtime_environ::component::StringEncoding::Utf8 => {
                        let encode_fn = self
                            .bindgen
                            .intrinsic(Intrinsic::String(StringIntrinsic::Utf8Encode));
                        uwriteln!(
                            self.src.js,
                            "function trampoline{i}OutputStr(s, outputPtr) {{
                                 const memory = memory{memory_idx};
                                 const reallocFn = realloc{realloc_fn_idx};
                                 let {{ ptr, len }} = {encode_fn}(s, reallocFn, memory);
                                 new DataView(memory.buffer).setUint32(outputPtr, ptr, true)
                                 new DataView(memory.buffer).setUint32(outputPtr + 4, len, true)
                             }}"
                        );
                    }
                    wasmtime_environ::component::StringEncoding::Utf16 => {
                        let encode_fn = self
                            .bindgen
                            .intrinsic(Intrinsic::String(StringIntrinsic::Utf16Encode));
                        uwriteln!(
                            self.src.js,
                            "function trampoline{i}OutputStr(s, outputPtr) {{
                                 const memory = memory{memory_idx};
                                 const reallocFn = realloc{realloc_fn_idx};
                                 let ptr = {encode_fn}(s, reallocFn, memory);
                                 let len = s.length;
                                 new DataView(memory.buffer).setUint32(outputPtr, ptr, true)
                                 new DataView(memory.buffer).setUint32(outputPtr + 4, len, true)
                             }}"
                        );
                    }
                    enc => panic!(
                        "unsupported string encoding [{enc:?}] for error-context.debug-message"
                    ),
                };

                let options_obj = format!(
                    "{{callback:{callback}, postReturn: {post_return}, async: {async_}}}",
                    callback = callback
                        .map(|v| v.as_u32().to_string())
                        .unwrap_or_else(|| "null".into()),
                    post_return = post_return
                        .map(|v| v.as_u32().to_string())
                        .unwrap_or_else(|| "null".into()),
                );

                let component_idx = instance.as_u32();
                uwriteln!(
                    self.src.js,
                    "const trampoline{i} = {debug_message_fn}.bind(
                         null,
                         {{
                             componentIdx: {component_idx},
                             options: {options_obj},
                             writeStrFn: trampoline{i}OutputStr,
                         }}
                     );"
                );
            }

            Trampoline::ErrorContextDrop { instance, ty } => {
                let drop_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::ErrCtx(ErrCtxIntrinsic::ErrorContextDrop));
                let local_err_tbl_idx = ty.as_u32();
                let component_idx = instance.as_u32();
                uwriteln!(
                    self.src.js,
                    r#"
                      const trampoline{i} = {drop_fn}.bind(
                          null,
                          {{ componentIdx: {component_idx}, localTableIdx: {local_err_tbl_idx} }},
                      );
                    "#
                );
            }

            Trampoline::ErrorContextTransfer => {
                let transfer_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::ErrCtx(ErrCtxIntrinsic::ErrorContextTransfer));
                uwriteln!(self.src.js, "const trampoline{i} = {transfer_fn};");
            }

            // This sets up a subtask (sets parent, etc) for guest -> guest calls
            Trampoline::PrepareCall { memory } => {
                let prepare_call_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::Host(HostIntrinsic::PrepareCall));
                let (memory_idx_js, memory_fn_js) = memory
                    .map(|v| {
                        (
                            v.as_u32().to_string(),
                            format!("() => memory{}", v.as_u32()),
                        )
                    })
                    .unwrap_or_else(|| ("null".into(), "() => null".into()));
                uwriteln!(
                    self.src.js,
                    "const trampoline{i} = {prepare_call_fn}.bind(null, {memory_idx_js}, {memory_fn_js});",
                )
            }

            Trampoline::SyncStartCall { callback } => {
                let sync_start_call_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::Host(HostIntrinsic::SyncStartCall));
                uwriteln!(
                    self.src.js,
                    "const trampoline{i} = {sync_start_call_fn}.bind(null, {});",
                    callback
                        .map(|v| v.as_u32().to_string())
                        .unwrap_or_else(|| "null".into()),
                );
            }

            // This actually starts a Task (whose parent is a subtask generated during PrepareCall)
            // for a from-component async import call
            Trampoline::AsyncStartCall {
                callback,
                post_return,
            } => {
                let async_start_call_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::Host(HostIntrinsic::AsyncStartCall));
                let (callback_idx, callback_fn) = callback
                    .map(|v| (v.as_u32().to_string(), format!("callback_{}", v.as_u32())))
                    .unwrap_or_else(|| ("null".into(), "null".into()));
                let (post_return_idx, post_return_fn) = post_return
                    .map(|v| (v.as_u32().to_string(), format!("postReturn{}", v.as_u32())))
                    .unwrap_or_else(|| ("null".into(), "null".into()));

                uwriteln!(
                    self.src.js,
                    "const trampoline{i} = {async_start_call_fn}.bind(
                         null,
                         {{
                             postReturnIdx: {post_return_idx},
                             getPostReturnFn: () => {post_return_fn},
                             callbackIdx: {callback_idx},
                             getCallbackFn: () => {callback_fn},
                         }},
                     );",
                );
            }

            Trampoline::LowerImport {
                index: _,
                lower_ty,
                options,
            } => {
                let canon_opts = self
                    .component
                    .options
                    .get(*options)
                    .expect("failed to find options");

                // TODO(fix): remove Global lowers, should enable using just exports[x] to export[y] call
                // TODO(fix): promising for the run (*as well as exports*)
                // TODO(fix): delete all asyncImports/exports
                // TODO(opt): opt-in sync import

                let component_idx = canon_opts.instance.as_u32();
                let is_async = canon_opts.async_;

                let cancellable = canon_opts.cancellable;

                let func_ty = self.types.index(*lower_ty);

                // Build list of lift functions for the params of the lowered import
                let param_types = &self.types.index(func_ty.params).types;
                let param_lift_fns_js =
                    gen_flat_lift_fn_list_js_expr(self, param_types.iter().as_slice(), &None);

                // Build list of lower functions for the results of the lowered import
                let result_types = &self.types.index(func_ty.results).types;
                let result_lower_fns_js =
                    gen_flat_lower_fn_list_js_expr(self, result_types.iter().as_slice(), &None);
                let result_flat_count = result_types.iter().try_fold(0usize, |count, ty| {
                    self.types
                        .canonical_abi(ty)
                        .flat_count
                        .map(|flat_count| count + usize::from(flat_count))
                });

                let get_callback_fn_js = canon_opts
                    .callback
                    .map(|idx| format!("() => callback_{}", idx.as_u32()))
                    .unwrap_or_else(|| "() => null".into());
                let get_post_return_fn_js = canon_opts
                    .post_return
                    .map(|idx| format!("() => postReturn{}", idx.as_u32()))
                    .unwrap_or_else(|| "() => null".into());

                // Build the memory and realloc js expressions, retrieving the memory index and getter functions
                let (memory_exprs, realloc_expr_js) =
                    if let CanonicalOptionsDataModel::LinearMemory(LinearMemoryOptions {
                        memory,
                        realloc,
                    }) = canon_opts.data_model
                    {
                        (
                            memory.map(|idx| {
                                (
                                    idx.as_u32().to_string(),
                                    format!("() => memory{}", idx.as_u32()),
                                )
                            }),
                            realloc.map(|idx| format!("() => realloc{}", idx.as_u32())),
                        )
                    } else {
                        (None, None)
                    };
                let (memory_idx_js, memory_expr_js) =
                    memory_exprs.unwrap_or_else(|| ("null".into(), "() => null".into()));
                let realloc_expr_js = realloc_expr_js.unwrap_or_else(|| "undefined".into());
                let string_encoding_js = string_encoding_js_literal(&canon_opts.string_encoding);

                // Build the lower import call that will wrap the actual trampoline
                let func_ty_async = func_ty.async_;
                let max_direct_results = if is_async || func_ty_async {
                    0
                } else {
                    MAX_FLAT_RESULTS
                };
                let has_result_pointer = result_flat_count
                    .map(|count| count > max_direct_results)
                    .unwrap_or(true);
                let call = format!(
                    r#"{lower_import_intrinsic}.bind(
                        null,
                        {{
                            trampolineIdx: {i},
                            componentIdx: {component_idx},
                            isAsync: {is_async},
                            isManualAsync: _trampoline{i}.manuallyAsync,
                            paramLiftFns: {param_lift_fns_js},
                            resultLowerFns: {result_lower_fns_js},
                            hasResultPointer: {has_result_pointer},
                            funcTypeIsAsync: {func_ty_async},
                            getCallbackFn: {get_callback_fn_js},
                            getPostReturnFn: {get_post_return_fn_js},
                            isCancellable: {cancellable},
                            memoryIdx: {memory_idx_js},
                            stringEncoding: {string_encoding_js},
                            getMemoryFn: {memory_expr_js},
                            getReallocFn: {realloc_expr_js},
                            importFn: _trampoline{i},
                        }},
                    )"#,
                    lower_import_intrinsic = if is_async || func_ty_async {
                        self.bindgen
                            .intrinsic(Intrinsic::AsyncTask(AsyncTaskIntrinsic::LowerImport))
                    } else {
                        self.bindgen.intrinsic(Intrinsic::AsyncTask(
                            AsyncTaskIntrinsic::LowerImportBackwardsCompat,
                        ))
                    }
                );

                // NOTE: For Trampoline::LowerImport, the trampoline index is actually already defined,
                // but we *redefine* it to call the lower import function first.
                if is_async || func_ty_async {
                    uwriteln!(
                        self.src.js,
                        "let trampoline{i} = new WebAssembly.Suspending({call});"
                    );
                } else {
                    // TODO(breaking): once manually specifying async imports is removed,
                    // we can avoid the second check below.
                    uwriteln!(
                        self.src.js,
                        "let trampoline{i} = _trampoline{i}.manuallyAsync ? new WebAssembly.Suspending({call}) : {call};"
                    );
                }
            }

            Trampoline::Transcoder {
                op,
                from,
                from64,
                to,
                to64,
            } => {
                if *from64 || *to64 {
                    unimplemented!("memory 64 transcoder");
                }
                let from = from.as_u32();
                let to = to.as_u32();
                match op {
                    Transcode::Copy(FixedEncoding::Utf8) => {
                        uwriteln!(
                            self.src.js,
                            r#"
                              function trampoline{i} (from_ptr, len, to_ptr) {{
                                  new Uint8Array(memory{to}.buffer, to_ptr, len).set(new Uint8Array(memory{from}.buffer, from_ptr, len));
                              }}
                            "#
                        );
                    }
                    Transcode::Copy(FixedEncoding::Utf16) => unimplemented!("utf16 copier"),
                    Transcode::Copy(FixedEncoding::Latin1) => unimplemented!("latin1 copier"),
                    Transcode::Latin1ToUtf16 => unimplemented!("latin to utf16 transcoder"),
                    Transcode::Latin1ToUtf8 => unimplemented!("latin to utf8 transcoder"),
                    Transcode::Utf16ToCompactProbablyUtf16 => {
                        unimplemented!("utf16 to compact wtf16 transcoder")
                    }
                    Transcode::Utf16ToCompactUtf16 => {
                        unimplemented!("utf16 to compact utf16 transcoder")
                    }
                    Transcode::Utf16ToLatin1 => unimplemented!("utf16 to latin1 transcoder"),
                    Transcode::Utf16ToUtf8 => {
                        uwriteln!(
                            self.src.js,
                            r#"
                              function trampoline{i} (src, src_len, dst, dst_len) {{
                                  const encoder = new TextEncoder();
                                  const {{ read, written }} = encoder.encodeInto(String.fromCharCode.apply(null, new Uint16Array(memory{from}.buffer, src, src_len)), new Uint8Array(memory{to}.buffer, dst, dst_len));
                                  return [read, written];
                              }}
                            "#,
                        );
                    }
                    Transcode::Utf8ToCompactUtf16 => {
                        unimplemented!("utf8 to compact utf16 transcoder")
                    }
                    Transcode::Utf8ToLatin1 => unimplemented!("utf8 to latin1 transcoder"),
                    Transcode::Utf8ToUtf16 => {
                        uwriteln!(
                            self.src.js,
                            r#"
                              function trampoline{i} (from_ptr, len, to_ptr) {{
                                  const decoder = new TextDecoder();
                                  const content = decoder.decode(new Uint8Array(memory{from}.buffer, from_ptr, len));
                                  const strlen = content.length
                                  const view = new Uint16Array(memory{to}.buffer, to_ptr, strlen * 2)
                                  for (var i = 0; i < strlen; i++) {{
                                      view[i] = content.charCodeAt(i);
                                  }}
                                  return strlen;
                              }}
                            "#,
                        );
                    }
                };
            }

            Trampoline::ResourceNew {
                ty: resource_ty_idx,
                ..
            } => {
                self.ensure_resource_table(*resource_ty_idx);
                let rid = resource_ty_idx.as_u32();
                let rsc_table_create_own = self.bindgen.intrinsic(Intrinsic::Resource(
                    ResourceIntrinsic::ResourceTableCreateOwn,
                ));
                uwriteln!(
                    self.src.js,
                    "const trampoline{i} = {rsc_table_create_own}.bind(null, handleTable{rid});"
                );
            }

            Trampoline::ResourceRep {
                ty: resource_ty_idx,
                ..
            } => {
                self.ensure_resource_table(*resource_ty_idx);
                let rid = resource_ty_idx.as_u32();
                let rsc_flag = self
                    .bindgen
                    .intrinsic(Intrinsic::Resource(ResourceIntrinsic::ResourceTableFlag));
                uwriteln!(
                    self.src.js,
                    "function trampoline{i} (handle) {{
                        return handleTable{rid}[(handle << 1) + 1] & ~{rsc_flag};
                    }}"
                );
            }

            Trampoline::ResourceDrop {
                ty: resource_table_ty_idx,
                ..
            } => {
                self.ensure_resource_table(*resource_table_ty_idx);
                let tid = resource_table_ty_idx.as_u32();
                let resource_table_ty = &self.types[*resource_table_ty_idx];
                let resource_ty = resource_table_ty.unwrap_concrete_ty();
                let rid = resource_ty.as_u32();

                // Build the code fragment that encapsulates calling the destructor
                let dtor = if let Some(resource_idx) =
                    self.component.defined_resource_index(resource_ty)
                {
                    let resource_def = self
                        .component
                        .initializers
                        .iter()
                        .find_map(|i| match i {
                            GlobalInitializer::Resource(r) if r.index == resource_idx => Some(r),
                            _ => None,
                        })
                        .unwrap();

                    // If a destructor index is defined for the resource, call it
                    if let Some(dtor) = &resource_def.dtor {
                        format!(
                            "
                            {}(handleEntry.rep);",
                            self.core_def(dtor)
                        )
                    } else {
                        "".into()
                    }
                } else {
                    // Imported resource is one without a defined resource index.
                    // If it is a captured instance (class instance was created externally so had to
                    // be assigned a rep), and there is a Symbol.dispose handler, call it explicitly
                    // for imported resources when the resource is dropped.
                    // Otherwise if it is an instance without a captured class definition, then
                    // call the low-level bindgen destructor.
                    let symbol_dispose = self.bindgen.intrinsic(Intrinsic::SymbolDispose);
                    let symbol_cabi_dispose = self.bindgen.intrinsic(Intrinsic::SymbolCabiDispose);

                    // previous imports walk should define all imported resources which are accessible
                    if let Some(imported_resource_local_name) =
                        self.bindgen.local_names.try_get(resource_ty)
                    {
                        format!(
                                            "
                            const rsc = captureTable{rid}.get(handleEntry.rep);
                            if (rsc) {{
                                if (rsc[{symbol_dispose}]) rsc[{symbol_dispose}]();
                                captureTable{rid}.delete(handleEntry.rep);
                            }} else if ({imported_resource_local_name}[{symbol_cabi_dispose}]) {{
                                {imported_resource_local_name}[{symbol_cabi_dispose}](handleEntry.rep);
                            }}"
                                        )
                    } else {
                        // If not, then capture / disposal paths are never called
                        format!(
                            "throw new TypeError('unreachable trampoline for resource [{:?}]')",
                            resource_ty
                        )
                    }
                };

                let rsc_table_remove = self
                    .bindgen
                    .intrinsic(Intrinsic::Resource(ResourceIntrinsic::ResourceTableRemove));
                uwrite!(
                    self.src.js,
                    "function trampoline{i}(handle) {{
                        const handleEntry = {rsc_table_remove}(handleTable{tid}, handle);
                        if (handleEntry.own) {{
                            {dtor}
                        }}
                    }}
                    ",
                );
            }

            Trampoline::ResourceTransferOwn => {
                let resource_transfer = self
                    .bindgen
                    .intrinsic(Intrinsic::Resource(ResourceIntrinsic::ResourceTransferOwn));
                uwriteln!(self.src.js, "const trampoline{i} = {resource_transfer};");
            }

            Trampoline::ResourceTransferBorrow => {
                let resource_transfer =
                    self.bindgen
                        .intrinsic(if self.bindgen.opts.valid_lifting_optimization {
                            Intrinsic::Resource(
                                ResourceIntrinsic::ResourceTransferBorrowValidLifting,
                            )
                        } else {
                            Intrinsic::Resource(ResourceIntrinsic::ResourceTransferBorrow)
                        });
                uwriteln!(self.src.js, "const trampoline{i} = {resource_transfer};");
            }

            Trampoline::TaskReturn {
                results, options, ..
            } => {
                let canon_opts = self
                    .component
                    .options
                    .get(*options)
                    .expect("failed to find options");
                let CanonicalOptions {
                    instance,
                    async_,
                    data_model:
                        CanonicalOptionsDataModel::LinearMemory(LinearMemoryOptions { memory, realloc }),
                    callback,
                    post_return,
                    string_encoding,
                    ..
                } = canon_opts
                else {
                    unreachable!("unexpected memory data model during task.return");
                };

                // Validate canonopts
                if realloc.is_some() && memory.is_none() {
                    panic!("memory must be present if realloc is");
                }
                if *async_ && post_return.is_some() {
                    panic!("async and post return must not be specified together");
                }
                if *async_ && callback.is_none() {
                    panic!("callback must be specified for async");
                }
                if let Some(cb_idx) = callback {
                    let cb_fn = &self.types[TypeFuncIndex::from_u32(cb_idx.as_u32())];
                    match self.types[cb_fn.params].types[..] {
                        [InterfaceType::S32, InterfaceType::S32, InterfaceType::S32] => {}
                        _ => panic!("unexpected params for async callback fn"),
                    }
                    match self.types[cb_fn.results].types[..] {
                        [InterfaceType::S32] => {}
                        _ => panic!("unexpected results for async callback fn"),
                    }
                }

                let result_types = &self.types[*results].types;

                // Calculate the number of parameters required to represent the results,
                // and whether they'll be stored in memory
                let result_flat_param_total: usize = result_types
                    .iter()
                    .map(|t| {
                        self.types
                            .canonical_abi(t)
                            .flat_count
                            .map(usize::from)
                            .unwrap_or(0)
                    })
                    .sum();
                let use_direct_params = result_flat_param_total < MAX_FLAT_PARAMS;

                // Build up a list of all the lifting functions that will be needed for the types
                // that are actually being passed through task.return
                let mut lift_fns: Vec<String> = Vec::with_capacity(result_types.len());
                for result_ty in result_types {
                    lift_fns.push(gen_flat_lift_fn_js_expr(self, result_ty, &None));
                }
                let lift_fns_js = format!("[{}]", lift_fns.join(","));

                // Build up a list of all the lowering functions that will be needed for the types
                // that are actually being passed through task.return
                //
                // This is usually only necessary if this task is part of a guest->guest async call
                // (i.e. via prepare & async start call)
                let mut lower_fns: Vec<String> = Vec::with_capacity(result_types.len());
                for result_ty in result_types {
                    lower_fns.push(gen_flat_lower_fn_js_expr(self, result_ty, &None));
                }
                let lower_fns_js = format!("[{}]", lower_fns.join(","));

                let get_memory_fn_js = memory
                    .map(|idx| format!("() => memory{}", idx.as_u32()))
                    .unwrap_or_else(|| "() => null".into());
                let memory_idx_js = memory
                    .map(|idx| idx.as_u32().to_string())
                    .unwrap_or_else(|| "null".into());
                let component_idx = instance.as_u32();
                let task_return_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::AsyncTask(AsyncTaskIntrinsic::TaskReturn));
                let callback_fn_idx = callback
                    .map(|v| v.as_u32().to_string())
                    .unwrap_or_else(|| "null".into());
                let string_encoding_js = string_encoding_js_literal(string_encoding);

                uwriteln!(
                    self.src.js,
                    "const trampoline{i} = {task_return_fn}.bind(
                         null,
                         {{
                             componentIdx: {component_idx},
                             useDirectParams: {use_direct_params},
                             getMemoryFn: {get_memory_fn_js},
                             memoryIdx: {memory_idx_js},
                             callbackFnIdx: {callback_fn_idx},
                             liftFns: {lift_fns_js},
                             lowerFns: {lower_fns_js},
                             stringEncoding: {string_encoding_js},
                         }},
                     );",
                );
            }

            Trampoline::BackpressureInc { instance } => {
                let backpressure_inc_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::Component(ComponentIntrinsic::BackpressureInc));
                uwriteln!(
                    self.src.js,
                    "const trampoline{i} = {backpressure_inc_fn}.bind(null, {instance});\n",
                    instance = instance.as_u32(),
                );
            }

            Trampoline::BackpressureDec { instance } => {
                let backpressure_dec_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::Component(ComponentIntrinsic::BackpressureDec));
                uwriteln!(
                    self.src.js,
                    "const trampoline{i} = {backpressure_dec_fn}.bind(null, {instance});\n",
                    instance = instance.as_u32(),
                );
            }

            Trampoline::ThreadYield {
                cancellable,
                instance,
            } => {
                let yield_fn = self
                    .bindgen
                    .intrinsic(Intrinsic::AsyncTask(AsyncTaskIntrinsic::Yield));
                let component_instance_idx = instance.as_u32();
                uwriteln!(
                    self.src.js,
                    r#"
                      const trampoline{i} = new WebAssembly.Suspending({yield_fn}.bind(null, {{
                          isCancellable: {cancellable},
                          componentIdx: {component_instance_idx},
                      }}));
                    "#,
                );
            }
            Trampoline::ThreadIndex => todo!("Trampoline::ThreadIndex"),
            Trampoline::ThreadNewIndirect { .. } => todo!("Trampoline::ThreadNewIndirect"),
            Trampoline::ThreadSuspend { .. } => todo!("Trampoline::ThreadSuspend"),
            Trampoline::ThreadSuspendTo { .. } => todo!("Trampoline::ThreadSuspendTo"),
            Trampoline::ThreadUnsuspend { .. } => todo!("Trampoline::ThreadUnsuspend"),
            Trampoline::ThreadYieldToSuspended { .. } => {
                todo!("Trampoline::ThreadYieldToSuspended")
            }
            Trampoline::ThreadSuspendToSuspended { .. } => {
                todo!("Trampoline::ThreadYieldToSuspended")
            }

            Trampoline::Trap => {
                uwriteln!(
                    self.src.js,
                    "function trampoline{i}(rep) {{ throw new TypeError('Trap'); }}"
                );
            }

            Trampoline::EnterSyncCall => {
                let enter_symmetric_sync_guest_call_fn = self.bindgen.intrinsic(
                    Intrinsic::AsyncTask(AsyncTaskIntrinsic::EnterSymmetricSyncGuestCall),
                );
                uwriteln!(
                    self.src.js,
                    r#"
                      const trampoline{i} = {enter_symmetric_sync_guest_call_fn};
                    "#,
                );
            }

            Trampoline::ExitSyncCall => {
                let exit_symmetric_sync_guest_call_fn = self.bindgen.intrinsic(
                    Intrinsic::AsyncTask(AsyncTaskIntrinsic::ExitSymmetricSyncGuestCall),
                );
                uwriteln!(
                    self.src.js,
                    "const trampoline{i} = {exit_symmetric_sync_guest_call_fn};\n",
                );
            }
        }
    }

    fn instantiation_global_initializer(&mut self, init: &GlobalInitializer) {
        match init {
            // Extracting callbacks is a part of the async support for hosts -- it ensures that
            // a given core export can be turned into a callback function that will be used
            // later.
            //
            // Generally what we have to do here is to create a callback that can be called upon re-entrance
            // into the component after a related suspension.
            GlobalInitializer::ExtractCallback(ExtractCallback { index, def }) => {
                let callback_idx = index.as_u32();
                let core_def = self.core_def(def);

                uwriteln!(self.src.js, "let callback_{callback_idx};",);

                // If the function returns an async value like a stream or future,
                // the callback that is executed in the the event loop (`AsyncTaskIntrinsic::DriverLoop`)
                // may attempt to wait due to calling necessarily async host imports like {stream, future}.{write, read}.
                //
                // Here, we mark the task with an indicator that denotes whether the callback should be run this way.
                //
                // TODO: can we be more selective here rather than wrapping every callback in WebAssembly.promising?
                // every callback *could* do stream.write, but many may not.
                uwriteln!(
                    self.src.js_init,
                    r#"
                      callback_{callback_idx} = WebAssembly.promising({core_def});
                      callback_{callback_idx}.fnName = "{core_def}";
                    "#
                );
            }

            GlobalInitializer::InstantiateModule(m, instance) => {
                // NOTE: we keep track of the current component instance index for the module being instantiatied
                // because some  because context.set/context.get are no longer trampolines,
                // and we do not have access to the correct component index that each operation belongs to at build time
                self.init_current_module = *instance;

                match m {
                    InstantiateModule::Static(idx, args) => {
                        self.instantiate_static_module(*idx, args, *instance);
                    }
                    // This is only needed when instantiating an imported core wasm
                    // module which while easy to implement here is not possible to
                    // test at this time so it's left unimplemented.
                    InstantiateModule::Import(..) => unimplemented!(),
                }
            }

            GlobalInitializer::LowerImport { index, import } => {
                self.lower_import(*index, *import);
            }

            GlobalInitializer::ExtractMemory(m) => {
                let def = self.core_export_var_name(&m.export);
                let idx = m.index.as_u32();
                uwriteln!(self.src.js, "let memory{idx};");
                uwriteln!(self.src.js_init, "memory{idx} = {def};");
            }

            GlobalInitializer::ExtractRealloc(r) => {
                let def = self.core_def(&r.def);
                let idx = r.index.as_u32();
                uwriteln!(self.src.js, "let realloc{idx};");
                uwriteln!(self.src.js, "let realloc{idx}Async;");
                uwriteln!(self.src.js_init, "realloc{idx} = {def};",);
                // NOTE: sometimes we may be fed a realloc that isn't a webassembly function at all
                // but has instead been converted to JS (see 'flavorful' test in test/runtime.js')
                uwriteln!(
                    self.src.js_init,
                    r#"
                      try {{
                          realloc{idx}Async = WebAssembly.promising({def});
                      }} catch(err) {{
                          realloc{idx}Async = {def};
                      }}
                    "#
                );
            }

            GlobalInitializer::ExtractPostReturn(p) => {
                let def = self.core_def(&p.def);
                let idx = p.index.as_u32();
                uwriteln!(self.src.js, "let postReturn{idx};");
                uwriteln!(self.src.js, "let postReturn{idx}Async;");
                uwriteln!(self.src.js_init, "postReturn{idx} = {def};");
                // NOTE: sometimes we may be fed a post return fn that isn't a webassembly function
                // at all but has instead been converted to JS (see 'flavorful' test in test/runtime.js)
                uwriteln!(
                    self.src.js_init,
                    r#"
                      try {{
                          postReturn{idx}Async = WebAssembly.promising({def});
                      }} catch(err) {{
                          postReturn{idx}Async = {def};
                      }}
                    "#
                );
            }

            GlobalInitializer::Resource(_) => {}

            GlobalInitializer::ExtractTable(_) => {}
        }
    }

    fn instantiate_static_module(
        &mut self,
        module_idx: StaticModuleIndex,
        args: &[CoreDef],
        instance: Option<RuntimeComponentInstanceIndex>,
    ) {
        // Build a JS "import object" which represents `args`. The `args` is a
        // flat representation which needs to be zip'd with the list of names to
        // correspond to the JS wasm embedding API. This is one of the major
        // differences between Wasmtime's and JS's embedding API.
        let mut import_obj = BTreeMap::new();
        for (module, name, arg) in self.modules[module_idx].imports(args) {
            let def = self.augmented_import_def(&arg);
            let dst = import_obj.entry(module).or_insert(BTreeMap::new());
            let prev = dst.insert(name, def);
            assert!(
                prev.is_none(),
                "unsupported duplicate import of `{module}::{name}`"
            );
            assert!(prev.is_none());
        }

        if self.bindgen.opts.asmjs {
            let component_instance_idx = instance
                .expect("missing runtime component index during static module instantiation")
                .as_u32();

            self.add_intrinsic(Intrinsic::AsyncTask(AsyncTaskIntrinsic::GetCurrentTask));
            self.add_intrinsic(Intrinsic::GetGlobalCurrentTaskMetaFn);
            let current_task_get_fn =
                Intrinsic::AsyncTask(AsyncTaskIntrinsic::GetCurrentTask).name();
            let get_global_current_task_meta_fn = Intrinsic::GetGlobalCurrentTaskMetaFn.name();

            let dst = import_obj.entry("env").or_insert(BTreeMap::new());
            let prev = dst.insert(
                "setTempRet0",
                format!(
                    "(x) => {{
                const {{ taskID }} = {get_global_current_task_meta_fn}({component_instance_idx});

                const taskMeta = {current_task_get_fn}({component_instance_idx}, taskID);
                if (!taskMeta) {{ throw new Error('invalid/missing async task meta'); }}

                const task = taskMeta.task;
                if (!task) {{ throw new Error('invalid/missing async task'); }}

                task.tmpRetI64HighBits = x|0;
            }}"
                ),
            );
            assert!(
                prev.is_none(),
                "unsupported duplicate import of `env::setTempRet0`"
            );
            assert!(prev.is_none());
        }

        // Build list of imports
        let mut imports = String::new();
        if !import_obj.is_empty() {
            imports.push_str(", {\n");
            for (module, names) in import_obj {
                imports.push_str(&maybe_quote_id(module));
                imports.push_str(": {\n");
                for (name, val) in names {
                    imports.push_str(&maybe_quote_id(name));
                    uwriteln!(imports, ": {val},");
                }
                imports.push_str("},\n");
            }
            imports.push('}');
        }

        let i = self.instances.push(module_idx);
        let iu32 = i.as_u32();
        let instantiate = self.bindgen.intrinsic(Intrinsic::InstantiateCore);
        uwriteln!(self.src.js, "let exports{iu32};");

        match self.bindgen.opts.instantiation_mode {
            Some(InstantiationMode::Async) | None => {
                uwriteln!(
                    self.src.js_init,
                    "({{ exports: exports{iu32} }} = yield {instantiate}(yield module{}{imports}));",
                    module_idx.as_u32(),
                )
            }

            Some(InstantiationMode::Sync) => {
                uwriteln!(
                    self.src.js_init,
                    "({{ exports: exports{iu32} }} = {instantiate}(module{}{imports}));",
                    module_idx.as_u32(),
                );
            }
        }
    }

    /// Map all types in parameters and results to local resource types
    ///
    /// # Arguments
    ///
    /// * `func` - The function in question
    /// * `ty_func_idx` - Type index of the function
    /// * `resource_map` - resource map of locally resolved types
    fn create_resource_fn_map(
        &mut self,
        func: &Function,
        ty_func_idx: TypeFuncIndex,
        resource_map: &mut ResourceMap,
    ) {
        // Connect resources used in parameters
        let params_ty = &self.types[self.types[ty_func_idx].params];
        for (p, iface_ty) in func.params.iter().zip(params_ty.types.iter()) {
            if let Type::Id(id) = p.ty {
                self.connect_resource_types(id, iface_ty, resource_map);
            }
        }
        // Connect resources used in results
        let results_ty = &self.types[self.types[ty_func_idx].results];
        if let (Some(Type::Id(id)), Some(iface_ty)) = (func.result, results_ty.types.first()) {
            self.connect_resource_types(id, iface_ty, resource_map);
        }
    }

    fn resource_name(
        resolve: &Resolve,
        local_names: &'a mut LocalNames,
        resource: TypeId,
        resource_map: &BTreeMap<TypeId, ResourceIndex>,
    ) -> &'a str {
        let resource = crate::dealias(resolve, resource);
        local_names
            .get_or_create(
                resource_map[&resource],
                &resolve.types[resource]
                    .name
                    .as_ref()
                    .unwrap()
                    .to_upper_camel_case(),
            )
            .0
    }

    fn lower_import(&mut self, index: LoweredIndex, import: RuntimeImportIndex) {
        let (options, trampoline, func_ty) = self.lowering_options[index];

        // Get the world key for the CM import
        let (import_index, path) = &self.component.imports[import];
        let (import_name, _) = &self.component.import_types[*import_index];
        let world_key = &self.imports[import_name];

        // Determine the name of the function
        let (func, func_name, iface_name) =
            match &self.resolve.worlds[self.world].imports[world_key] {
                WorldItem::Function(func) => {
                    assert_eq!(path.len(), 0);
                    (func, import_name, None)
                }
                WorldItem::Interface { id, .. } => {
                    assert_eq!(path.len(), 1);
                    let iface = &self.resolve.interfaces[*id];
                    let func = &iface.functions[&path[0]];
                    (
                        func,
                        &path[0],
                        Some(iface.name.as_deref().unwrap_or_else(|| import_name)),
                    )
                }
                WorldItem::Type { .. } => unreachable!("unexpected imported world item type"),
            };

        let is_async = is_async_fn(func, options);

        if options.async_ {
            assert!(
                options.post_return.is_none(),
                "async function {func_name} (import {import_name}) can't have post return",
            );
        }

        // Host lifted async import (i.e. JSPI)
        let requires_async_porcelain = requires_async_porcelain(
            FunctionIdentifier::Fn(func),
            import_name,
            &self.async_imports,
        );

        // Nested interfaces only currently possible through mapping
        let (import_specifier, maybe_iface_member) = map_import(
            &self.bindgen.opts.map,
            if iface_name.is_some() {
                import_name
            } else {
                match func.kind {
                    FunctionKind::Method(_) => {
                        let stripped = import_name.strip_prefix("[method]").unwrap();
                        &stripped[0..stripped.find(".").unwrap()]
                    }
                    FunctionKind::AsyncMethod(_) => {
                        let stripped = import_name.strip_prefix("[async method]").unwrap();
                        &stripped[0..stripped.find(".").unwrap()]
                    }
                    FunctionKind::Static(_) => {
                        let stripped = import_name.strip_prefix("[static]").unwrap();
                        &stripped[0..stripped.find(".").unwrap()]
                    }
                    FunctionKind::AsyncStatic(_) => {
                        let stripped = import_name.strip_prefix("[async static]").unwrap();
                        &stripped[0..stripped.find(".").unwrap()]
                    }
                    FunctionKind::Constructor(_) => {
                        import_name.strip_prefix("[constructor]").unwrap()
                    }
                    FunctionKind::Freestanding | FunctionKind::AsyncFreestanding => import_name,
                }
            },
        );

        // Create mappings for resources
        let mut import_resource_map = ResourceMap::new();

        self.create_resource_fn_map(func, func_ty, &mut import_resource_map);

        let (callee_name, call_type) = match func.kind {
            FunctionKind::Freestanding => (
                self.bindgen
                    .local_names
                    .get_or_create(
                        format!(
                            "import:{import}-{maybe_iface_member}-{func_name}",
                            import = import_specifier,
                            maybe_iface_member = maybe_iface_member.as_deref().unwrap_or(""),
                            func_name = &func.name
                        ),
                        &func.name,
                    )
                    .0
                    .to_string(),
                CallType::Standard,
            ),

            FunctionKind::AsyncFreestanding => (
                self.bindgen
                    .local_names
                    .get_or_create(
                        format!(
                            "import:async-{import}-{maybe_iface_member}-{func_name}",
                            import = import_specifier,
                            maybe_iface_member = maybe_iface_member.as_deref().unwrap_or(""),
                            func_name = &func.name
                        ),
                        &func.name,
                    )
                    .0
                    .to_string(),
                CallType::AsyncStandard,
            ),

            FunctionKind::Method(_) => (
                func.item_name().to_lower_camel_case(),
                CallType::CalleeResourceDispatch,
            ),

            FunctionKind::AsyncMethod(_) => (
                func.item_name().to_lower_camel_case(),
                CallType::AsyncCalleeResourceDispatch,
            ),

            FunctionKind::Static(resource_id) => (
                format!(
                    "{}.{}",
                    Instantiator::resource_name(
                        self.resolve,
                        &mut self.bindgen.local_names,
                        resource_id,
                        &self.imports_resource_types
                    ),
                    func.item_name().to_lower_camel_case()
                ),
                CallType::Standard,
            ),

            FunctionKind::AsyncStatic(resource_id) => (
                format!(
                    "{}.{}",
                    Instantiator::resource_name(
                        self.resolve,
                        &mut self.bindgen.local_names,
                        resource_id,
                        &self.imports_resource_types
                    ),
                    func.item_name().to_lower_camel_case()
                ),
                CallType::AsyncStandard,
            ),

            FunctionKind::Constructor(resource_id) => (
                format!(
                    "new {}",
                    Instantiator::resource_name(
                        self.resolve,
                        &mut self.bindgen.local_names,
                        resource_id,
                        &self.imports_resource_types
                    )
                ),
                CallType::Standard,
            ),
        };

        let abi = if is_async {
            AbiVariant::GuestImportAsync
        } else {
            AbiVariant::GuestImport
        };

        let nparams = self.resolve.wasm_signature(abi, func).params.len();

        // Generate the JS trampoline function for a bound import
        let trampoline_idx = trampoline.as_u32();
        match self.bindgen.opts.import_bindings {
            None | Some(BindingsMode::Js) | Some(BindingsMode::Hybrid) => {
                // TODO(breaking): remove as we do not not need to manually specify async imports anymore in P3 w/ native coloring
                if is_async | requires_async_porcelain {
                    // NOTE: for async imports that will go through Trampoline::LowerImport,
                    // we prefix the raw import with '_' as it will later be used in the
                    // definition of trampoline{i} which will actually be fed into
                    // unbundled modules
                    uwrite!(
                        self.src.js,
                        "\nconst _trampoline{trampoline_idx} = async function"
                    );
                } else {
                    uwrite!(
                        self.src.js,
                        "\nconst _trampoline{trampoline_idx} = function"
                    );
                }

                let iface_name = if import_name.is_empty() {
                    None
                } else {
                    Some(import_name.to_string())
                };

                // Write out the function (brace + body + brace)
                self.bindgen(JsFunctionBindgenArgs {
                    nparams,
                    call_type,
                    iface_name: iface_name.as_deref(),
                    callee: &callee_name,
                    opts: options,
                    func,
                    resource_map: &import_resource_map,
                    abi,
                    requires_async_porcelain,
                    is_async,
                    for_import: true,
                });
                uwriteln!(self.src.js, "");

                uwriteln!(
                    self.src.js,
                    "_trampoline{trampoline_idx}.fnName = '{}#{callee_name}';",
                    iface_name.unwrap_or_default(),
                );

                // TODO(breaking): remove once support for manually specified async imports is removed
                if requires_async_porcelain {
                    uwriteln!(
                        self.src.js,
                        "_trampoline{trampoline_idx}.manuallyAsync = true;"
                    );
                }
            }

            Some(BindingsMode::Optimized) | Some(BindingsMode::DirectOptimized) => {
                uwriteln!(self.src.js, "let trampoline{trampoline_idx};");
            }
        };

        // Build import bindings & trampolines for the import
        //
        // This is only necessary if an import binding mode is specified and not JS (the default),
        // (e.g. Optimized, Direct, Hybrid).
        if !matches!(
            self.bindgen.opts.import_bindings,
            None | Some(BindingsMode::Js)
        ) {
            let (memory, realloc) =
                if let CanonicalOptionsDataModel::LinearMemory(LinearMemoryOptions {
                    memory,
                    realloc,
                }) = options.data_model
                {
                    (
                        memory.map(|idx| format!(" memory: memory{},", idx.as_u32())),
                        realloc.map(|idx| format!(" realloc: realloc{},", idx.as_u32())),
                    )
                } else {
                    (None, None)
                };
            let memory = memory.unwrap_or_default();
            let realloc = realloc.unwrap_or_default();

            let post_return = options
                .post_return
                .map(|idx| format!(" postReturn: postReturn{},", idx.as_u32()))
                .unwrap_or("".into());
            let string_encoding = match options.string_encoding {
                wasmtime_environ::component::StringEncoding::Utf8 => "",
                wasmtime_environ::component::StringEncoding::Utf16 => " stringEncoding: 'utf16',",
                wasmtime_environ::component::StringEncoding::CompactUtf16 => {
                    " stringEncoding: 'compact-utf16',"
                }
            };

            let callee_name = match func.kind {
                FunctionKind::Constructor(_) => callee_name[4..].to_string(),

                FunctionKind::Static(_)
                | FunctionKind::AsyncStatic(_)
                | FunctionKind::Freestanding
                | FunctionKind::AsyncFreestanding => callee_name.to_string(),

                FunctionKind::Method(resource_id) | FunctionKind::AsyncMethod(resource_id) => {
                    format!(
                        "{}.prototype.{callee_name}",
                        Instantiator::resource_name(
                            self.resolve,
                            &mut self.bindgen.local_names,
                            resource_id,
                            &self.imports_resource_types
                        )
                    )
                }
            };

            // Save information about imported resources for later
            self.resource_imports.extend(import_resource_map.clone());

            let resource_tables = {
                let mut resource_table_ids: Vec<TypeResourceTableIndex> = Vec::new();

                for (_, data) in import_resource_map {
                    let ResourceTable {
                        data: ResourceData::Host { tid, .. },
                        ..
                    } = &data
                    else {
                        unreachable!("unexpected non-host resource table");
                    };
                    resource_table_ids.push(*tid);
                }

                if resource_table_ids.is_empty() {
                    "".to_string()
                } else {
                    format!(
                        " resourceTables: [{}],",
                        resource_table_ids
                            .iter()
                            .map(|x| format!("handleTable{}", x.as_u32()))
                            .collect::<Vec<String>>()
                            .join(", ")
                    )
                }
            };

            // Build trampolines for the import
            match self.bindgen.opts.import_bindings {
                Some(BindingsMode::Hybrid) => {
                    let symbol_cabi_lower = self.bindgen.intrinsic(Intrinsic::SymbolCabiLower);
                    uwriteln!(self.src.js_init, "if ({callee_name}[{symbol_cabi_lower}]) {{
                        trampoline{} = {callee_name}[{symbol_cabi_lower}]({{{memory}{realloc}{post_return}{string_encoding}{resource_tables}}});
                    }}", trampoline.as_u32());
                }
                Some(BindingsMode::Optimized) => {
                    let symbol_cabi_lower = self.bindgen.intrinsic(Intrinsic::SymbolCabiLower);
                    if !self.bindgen.opts.valid_lifting_optimization {
                        uwriteln!(self.src.js_init, "if (!{callee_name}[{symbol_cabi_lower}]) {{
                            throw new TypeError('import for \"{import_name}\" does not define a Symbol.for(\"cabiLower\") optimized binding');
                        }}");
                    }
                    uwriteln!(
                        self.src.js_init,
                        "trampoline{} = {callee_name}[{symbol_cabi_lower}]({{{memory}{realloc}{post_return}{string_encoding}{resource_tables}}});",
                        trampoline.as_u32()
                    );
                }
                Some(BindingsMode::DirectOptimized) => {
                    uwriteln!(
                        self.src.js_init,
                        "trampoline{} = {callee_name}({{{memory}{realloc}{post_return}{string_encoding}}});",
                        trampoline.as_u32()
                    );
                }
                None | Some(BindingsMode::Js) => unreachable!("invalid bindings mode"),
            };
        }

        // Figure out the function name and callee (e.g. class for a given resource) to use
        let (import_name, binding_name) = match func.kind {
            FunctionKind::Freestanding | FunctionKind::AsyncFreestanding => {
                (func_name.to_lower_camel_case(), callee_name)
            }

            FunctionKind::Method(tid)
            | FunctionKind::AsyncMethod(tid)
            | FunctionKind::Static(tid)
            | FunctionKind::AsyncStatic(tid)
            | FunctionKind::Constructor(tid) => {
                let ty = &self.resolve.types[tid];
                let class_name = ty.name.as_ref().unwrap().to_upper_camel_case();
                let resource_name = Instantiator::resource_name(
                    self.resolve,
                    &mut self.bindgen.local_names,
                    tid,
                    &self.imports_resource_types,
                )
                .to_string();
                (class_name, resource_name)
            }
        };

        self.ensure_import(
            import_specifier,
            iface_name,
            maybe_iface_member.as_deref(),
            if iface_name.is_some() {
                Some(import_name.to_string())
            } else {
                None
            },
            binding_name,
        );
    }

    /// Process an import if it has not already been processed
    ///
    /// # Arguments
    ///
    /// * `import_specifier` - The specifier of the import as used in JS (ex. `"@bytecodealliance/preview2-shim/random"`)
    /// * `iface_name` - The name of the WIT interface related to this binding, if present (ex. `"random"`)
    /// * `iface_member` - The name of the interface member, if present (ex. `"random"`)
    /// * `import_binding` - The name of binding, if present (ex. `"getRandomBytes"`)
    /// * `local_name` - Local name of the import (ex. `"getRandomBytes"`)
    ///
    fn ensure_import(
        &mut self,
        import_specifier: String,
        iface_name: Option<&str>,
        iface_member: Option<&str>,
        import_binding: Option<String>,
        local_name: String,
    ) {
        if import_specifier.starts_with("webidl:") {
            self.bindgen
                .intrinsic(Intrinsic::WebIdl(WebIdlIntrinsic::GlobalThisIdlProxy));
        }

        // Build the import path depending on the kind of interface
        let mut import_path = Vec::with_capacity(2);
        import_path.push(import_specifier);
        if let Some(_iface_name) = iface_name {
            // Mapping can be used to construct virtual nested namespaces
            // which is used eg to support WASI interface groupings
            if let Some(iface_member) = iface_member {
                import_path.push(iface_member.to_lower_camel_case());
            }
            import_path.push(import_binding.clone().unwrap());
        } else if let Some(iface_member) = iface_member {
            import_path.push(iface_member.into());
        } else if let Some(import_binding) = &import_binding {
            import_path.push(import_binding.into());
        }

        // Add the import binding that represents this import
        self.bindgen
            .esm_bindgen
            .add_import_binding(&import_path, local_name);
    }

    /// Connect resources that have no types
    ///
    /// Commonly this is used for resources that have a type on on the import side
    /// but no relevant type on the receiving side, for which local types must be generated locally:
    /// - `error-context`
    /// - `future<_>`
    /// - `stream<_>`
    ///
    fn connect_p3_resources(
        &mut self,
        id: &TypeId,
        maybe_elem_ty: &Option<Type>,
        iface_ty: &InterfaceType,
        resource_map: &mut ResourceMap,
    ) {
        let remote_resource = match iface_ty {
            InterfaceType::Future(table_idx) => {
                let future_table_ty = &self.types[*table_idx];
                let future_ty = &self.types[future_table_ty.ty];

                // Determine the level of future nesting
                let mut future_nesting_level = 0;
                let mut payload_ty = future_ty.payload;
                while let Some(InterfaceType::Future(inner_ty)) = payload_ty {
                    future_nesting_level += 1;
                    payload_ty = self.types[self.types[inner_ty].ty].payload;
                }

                ResourceTable {
                    imported: true,
                    data: ResourceData::Guest {
                        resource_name: "Future".into(),
                        prefix: Some(format!("${}", table_idx.as_u32())),
                        extra: Some(ResourceExtraData::Future {
                            table_idx: *table_idx,
                            nesting_level: future_nesting_level,
                            elem_ty: maybe_elem_ty.map(|ty| {
                                let table_ty = &self.types[*table_idx];
                                let future_ty_idx = table_ty.ty;
                                let future_ty = &self.types[future_ty_idx];
                                let iface_ty = future_ty.payload.expect(
                                    "missing future payload despite elem type being present",
                                );
                                let abi = self.types.canonical_abi(&iface_ty);
                                PayloadTypeMetadata {
                                    ty,
                                    iface_ty,

                                    // TODO: we need to use the currently-being-built resource map here,
                                    // because it may contain *just inserted* information (could be either imports or exports)
                                    // that should be used
                                    //
                                    // We need to *augment* the normal built in
                                    // `instantiator.resource_{exports,imports}` with things that we're resolving now.
                                    lift_js_expr: gen_flat_lift_fn_js_expr(
                                        self,
                                        &iface_ty,
                                        &Some(resource_map),
                                    ),
                                    lower_js_expr: gen_flat_lower_fn_js_expr(
                                        self,
                                        &iface_ty,
                                        &Some(resource_map),
                                    ),
                                    size32: abi.size32,
                                    align32: abi.align32,
                                    flat_count: abi.flat_count,
                                }
                            }),
                        }),
                    },
                }
            }
            InterfaceType::Stream(table_idx) => ResourceTable {
                imported: true,
                data: ResourceData::Guest {
                    resource_name: "Stream".into(),
                    prefix: Some(format!("${}", table_idx.as_u32())),
                    extra: Some(ResourceExtraData::Stream {
                        table_idx: *table_idx,
                        elem_ty: maybe_elem_ty.map(|ty| {
                            let table_ty = &self.types[*table_idx];
                            let stream_ty_idx = table_ty.ty;
                            let stream_ty = &self.types[stream_ty_idx];
                            let iface_ty = stream_ty
                                .payload
                                .expect("missing payload despite elem type being present");
                            let abi = self.types.canonical_abi(&iface_ty);
                            PayloadTypeMetadata {
                                ty,
                                iface_ty,
                                lift_js_expr: gen_flat_lift_fn_js_expr(
                                    self,
                                    &iface_ty,
                                    &Some(resource_map),
                                ),
                                lower_js_expr: gen_flat_lower_fn_js_expr(
                                    self,
                                    &iface_ty,
                                    &Some(resource_map),
                                ),
                                size32: abi.size32,
                                align32: abi.align32,
                                flat_count: abi.flat_count,
                            }
                        }),
                    }),
                },
            },
            InterfaceType::ErrorContext(table_idx) => ResourceTable {
                imported: true,
                data: ResourceData::Guest {
                    resource_name: "ErrorContext".into(),
                    prefix: Some(format!("${}", table_idx.as_u32())),
                    extra: Some(ResourceExtraData::ErrorContext {
                        table_idx: *table_idx,
                    }),
                },
            },
            _ => unreachable!("unexpected interface type [{iface_ty:?}] with no type"),
        };

        resource_map.insert(*id, remote_resource);
    }

    /// Connect two types as host resources
    ///
    /// # Arguments
    ///
    /// * `t` - the TypeId
    /// * `tid` - Index into the type resource table of the interface (foreign side)
    /// * `resource_map` - Resource map that holds resource pairings
    ///
    fn connect_host_resource(
        &mut self,
        t: TypeId,
        resource_table_ty_idx: TypeResourceTableIndex,
        resource_map: &mut ResourceMap,
    ) {
        self.ensure_resource_table(resource_table_ty_idx);

        // Figure out whether the resource index we're dealing with is for an imported type
        let resource_table_ty = &self.types[resource_table_ty_idx];
        let resource_idx = resource_table_ty.unwrap_concrete_ty();
        let imported = self
            .component
            .defined_resource_index(resource_idx)
            .is_none();

        // Retrieve the resource id for the type definition
        let resource_id = crate::dealias(self.resolve, t);
        let ty = &self.resolve.types[resource_id];

        // If the resource is defined by this component (i.e. exported/used internally, *not* imported),
        // then determine the destructor that should be run based on the relevant resource
        let mut dtor_str = None;
        if let Some(resource_idx) = self.component.defined_resource_index(resource_idx) {
            assert!(!imported);
            let resource_def = self
                .component
                .initializers
                .iter()
                .find_map(|i| match i {
                    GlobalInitializer::Resource(r) if r.index == resource_idx => Some(r),
                    _ => None,
                })
                .unwrap();

            if let Some(dtor) = &resource_def.dtor {
                dtor_str = Some(self.core_def(dtor));
            }
        }

        // Look up the local import name
        let resource_name = ty.name.as_ref().unwrap().to_upper_camel_case();

        let local_name = if imported {
            let (world_key, iface_name) = match ty.owner {
                wit_parser::TypeOwner::World(world) => (
                    self.resolve.worlds[world]
                        .imports
                        .iter()
                        .find(|&(_, item)| matches!(*item, WorldItem::Type { id, .. } if id == t))
                        .unwrap()
                        .0
                        .clone(),
                    None,
                ),
                wit_parser::TypeOwner::Interface(iface) => {
                    match &self.resolve.interfaces[iface].name {
                        Some(name) => (WorldKey::Interface(iface), Some(name.as_str())),
                        None => {
                            let key = self.resolve.worlds[self.world]
                                .imports
                                .iter()
                                .find(|&(_, item)| match item {
                                    WorldItem::Interface { id, .. } => *id == iface,
                                    _ => false,
                                })
                                .unwrap()
                                .0;
                            (
                                key.clone(),
                                match key {
                                    WorldKey::Name(name) => Some(name.as_str()),
                                    WorldKey::Interface(_) => None,
                                },
                            )
                        }
                    }
                }
                wit_parser::TypeOwner::None => unimplemented!(),
            };

            let import_name = self.resolve.name_world_key(&world_key);
            let (local_name, _) = self
                .bindgen
                .local_names
                .get_or_create(resource_idx, &resource_name);

            let local_name_str = local_name.to_string();

            // Nested interfaces only currently possible through mapping
            let (import_specifier, maybe_iface_member) =
                map_import(&self.bindgen.opts.map, &import_name);

            // Ensure that the import exists
            self.ensure_import(
                import_specifier,
                iface_name,
                maybe_iface_member.as_deref(),
                iface_name.map(|_| resource_name),
                local_name_str.to_string(),
            );
            local_name_str
        } else {
            let (local_name, _) = self
                .bindgen
                .local_names
                .get_or_create(resource_idx, &resource_name);
            local_name.to_string()
        };

        // Add a resource table to track the host resource
        let entry = ResourceTable {
            imported,
            data: ResourceData::Host {
                tid: resource_table_ty_idx,
                rid: resource_idx,
                local_name,
                dtor_name: dtor_str,
            },
        };

        // If the the resource already exists, then  ensure that it is exactly the same as the
        // value we're attempting to insert
        if let Some(existing) = resource_map.get(&resource_id) {
            assert_eq!(*existing, entry);
            return;
        }

        // Insert the resource into the map,
        resource_map.insert(resource_id, entry);
    }

    /// Connect resources that are defined at the type levels in `wit-parser`
    /// to their types as defined in `wasmtime-environ`
    ///
    /// The types that are connected here are stored in the `resource_map` for
    /// use later.
    ///
    /// # Arguments
    ///
    /// * `id` - The ID of the type if present (can be missing when dealing with `error-context`s, `future<_>`, etc)
    /// * `iface_ty` - The relevant interface type
    /// * `resource_map` - Resource map that we will update with pairings
    ///
    fn connect_resource_types(
        &mut self,
        id: TypeId,
        iface_ty: &InterfaceType,
        resource_map: &mut ResourceMap,
    ) {
        let kind = &self.resolve.types[id].kind;
        match (kind, iface_ty) {
            // For flags and enums we can do nothing -- they're simple values (string/number)
            (TypeDefKind::Flags(_), InterfaceType::Flags(_))
            | (TypeDefKind::Enum(_), InterfaceType::Enum(_)) => {}

            // Connect records to records
            (TypeDefKind::Record(t1), InterfaceType::Record(t2)) => {
                let t2 = &self.types[*t2];
                for (f1, f2) in t1.fields.iter().zip(t2.fields.iter()) {
                    if let Type::Id(id) = f1.ty {
                        self.connect_resource_types(id, &f2.ty, resource_map);
                    }
                }
            }

            // Handle connecting owned/borrowed handles to owned/borrowed handles
            (
                TypeDefKind::Handle(Handle::Own(t1) | Handle::Borrow(t1)),
                InterfaceType::Own(t2) | InterfaceType::Borrow(t2),
            ) => {
                self.connect_host_resource(*t1, *t2, resource_map);
            }

            // Connect tuples to interface tuples
            (TypeDefKind::Tuple(t1), InterfaceType::Tuple(t2)) => {
                let t2 = &self.types[*t2];
                for (f1, f2) in t1.types.iter().zip(t2.types.iter()) {
                    if let Type::Id(id) = f1 {
                        self.connect_resource_types(*id, f2, resource_map);
                    }
                }
            }

            // Connect inner types of variants to their interface types
            (TypeDefKind::Variant(t1), InterfaceType::Variant(t2)) => {
                let t2 = &self.types[*t2];
                for (f1, f2) in t1.cases.iter().zip(t2.cases.iter()) {
                    if let Some(Type::Id(id)) = &f1.ty {
                        self.connect_resource_types(*id, f2.1.as_ref().unwrap(), resource_map);
                    }
                }
            }

            // Connect option<t> to option<t>
            (TypeDefKind::Option(t1), InterfaceType::Option(t2)) => {
                let t2 = &self.types[*t2];
                if let Type::Id(id) = t1 {
                    self.connect_resource_types(*id, &t2.ty, resource_map);
                }
            }

            // Connect result<t> to result<t>
            (TypeDefKind::Result(t1), InterfaceType::Result(t2)) => {
                let t2 = &self.types[*t2];
                if let Some(Type::Id(id)) = &t1.ok {
                    self.connect_resource_types(*id, &t2.ok.unwrap(), resource_map);
                }
                if let Some(Type::Id(id)) = &t1.err {
                    self.connect_resource_types(*id, &t2.err.unwrap(), resource_map);
                }
            }

            // Connect list<t> to list types
            (TypeDefKind::List(t1), InterfaceType::List(t2)) => {
                let t2 = &self.types[*t2];
                if let Type::Id(id) = t1 {
                    self.connect_resource_types(*id, &t2.element, resource_map);
                }
            }

            // Connect list<t, size> to list types
            (TypeDefKind::FixedLengthList(t1, _len), InterfaceType::FixedLengthList(t2)) => {
                let t2 = &self.types[*t2];
                if let Type::Id(id) = t1 {
                    self.connect_resource_types(*id, &t2.element, resource_map);
                }
            }

            // Connect named types
            (TypeDefKind::Type(ty), _) => {
                if let Type::Id(id) = ty {
                    self.connect_resource_types(*id, iface_ty, resource_map);
                }
            }

            // Connect futures & stream types
            (TypeDefKind::Future(maybe_elem_ty), container_iface_ty)
            | (TypeDefKind::Stream(maybe_elem_ty), container_iface_ty) => {
                match maybe_elem_ty {
                    // The case of an empty future is the propagation of a `null`-like value, usually a simple signal
                    // which we'll connect with the *normally invalid* type value 0 as an indicator
                    None => {
                        self.connect_p3_resources(&id, maybe_elem_ty, iface_ty, resource_map);
                    }
                    // For custom types we must recur to properly connect the inner type
                    Some(elem_ty @ Type::Id(elem_ty_id)) => {
                        // As the internal type could be a resource, and connecting p3 resources
                        // may generate lifting/lowering fns, we must connect the payload of the
                        // future/stream first, if necessary
                        //
                        let maybe_elem_iface_ty = match container_iface_ty {
                            InterfaceType::Future(future_table_ty_idx) => {
                                let future_table_ty = &self.types[*future_table_ty_idx];
                                let future = &self.types[future_table_ty.ty];
                                future.payload
                            }
                            InterfaceType::Stream(stream_table_ty_idx) => {
                                let stream_table_ty = &self.types[*stream_table_ty_idx];
                                let stream = &self.types[stream_table_ty.ty];
                                stream.payload
                            }
                            _ => unreachable!("unexpected iface type"),
                        };
                        if let Some(elem_iface_ty) = maybe_elem_iface_ty {
                            // TODO(refactor): the last arg of `connect_resource_types()` (`extra_resource_map`) is
                            // necessary because we are not building the imports/exports array directly.
                            //
                            // It's a hack that *should* be removable if we do more explicit and intentional
                            // building of import/export resource mappings (i.e. not building a partial map that we
                            // later `.extend()` onto the instantiator's maps, depending on whether we were working on
                            // imports or exports).
                            self.connect_resource_types(*elem_ty_id, &elem_iface_ty, resource_map);
                        }

                        self.connect_p3_resources(&id, &Some(*elem_ty), iface_ty, resource_map);
                    }
                    // For basic types that are connected (non inner types) we can do a generic connect
                    Some(_) => {
                        self.connect_p3_resources(&id, maybe_elem_ty, iface_ty, resource_map);
                    }
                }
            }

            // Connect the types in an ok/error variant of a Result to the future that they're being sent in
            (
                TypeDefKind::Result(Result_ { ok, err }),
                tk2 @ (InterfaceType::Future(_) | InterfaceType::Stream(_)),
            ) => {
                if let Some(Type::Id(ok_t)) = ok {
                    self.connect_resource_types(*ok_t, tk2, resource_map)
                }
                if let Some(Type::Id(err_t)) = err {
                    self.connect_resource_types(*err_t, tk2, resource_map)
                }
            }

            // Connect the types in an option to the future that they're being sent in
            (
                TypeDefKind::Option(ty),
                tk2 @ (InterfaceType::Future(_) | InterfaceType::Stream(_)),
            ) => {
                if let Type::Id(some_t) = ty {
                    self.connect_resource_types(*some_t, tk2, resource_map)
                }
            }

            // Connect resources to the future/stream that they're being sent in
            (
                TypeDefKind::Handle(Handle::Own(t1) | Handle::Borrow(t1)),
                tk2 @ (InterfaceType::Future(_) | InterfaceType::Stream(_)),
            ) => self.connect_resource_types(*t1, tk2, resource_map),

            (TypeDefKind::Resource, InterfaceType::Future(_) | InterfaceType::Stream(_)) => {}

            // Connect the inner types of variants to the future they're being sent in
            (
                TypeDefKind::Variant(variant),
                tk2 @ (InterfaceType::Future(_) | InterfaceType::Stream(_)),
            ) => {
                for f1 in variant.cases.iter() {
                    if let Some(Type::Id(id)) = &f1.ty {
                        self.connect_resource_types(*id, tk2, resource_map);
                    }
                }
            }

            // Connect the inner types of variants to the future they're being sent in
            (
                TypeDefKind::Record(record),
                tk2 @ (InterfaceType::Future(_) | InterfaceType::Stream(_)),
            ) => {
                for f1 in record.fields.iter() {
                    if let Type::Id(id) = f1.ty {
                        self.connect_resource_types(id, tk2, resource_map);
                    }
                }
            }

            // Simliar to the non-stream/future case, we don't have to do anything for
            // flags and plain enums as they are read directly
            (
                TypeDefKind::Enum(_) | TypeDefKind::Flags(_),
                InterfaceType::Future(_) | InterfaceType::Stream(_),
            ) => {}

            (TypeDefKind::Resource, tk2) => {
                unreachable!(
                    "resource types do not need to be connected (in this case, to [{tk2:?}])"
                )
            }

            (TypeDefKind::Unknown, tk2) => {
                unreachable!("unknown types cannot be connected (in this case to [{tk2:?}])")
            }

            (tk1, tk2) => unreachable!("invalid typedef kind combination [{tk1:?}] [{tk2:?}]",),
        }
    }

    fn bindgen(&mut self, args: JsFunctionBindgenArgs) {
        let JsFunctionBindgenArgs {
            nparams,
            call_type,
            iface_name,
            callee,
            opts,
            func,
            resource_map,
            abi,
            requires_async_porcelain,
            is_async,
            for_import,
        } = args;

        let (memory, realloc) =
            if let CanonicalOptionsDataModel::LinearMemory(LinearMemoryOptions {
                memory,
                realloc,
            }) = opts.data_model
            {
                (
                    memory.map(|idx| format!("memory{}", idx.as_u32())),
                    realloc.map(|idx| {
                        format!(
                            "realloc{}{}",
                            idx.as_u32(),
                            if is_async {
                                "Async"
                            } else {
                                Default::default()
                            }
                        )
                    }),
                )
            } else {
                (None, None)
            };

        let post_return = opts.post_return.map(|idx| {
            format!(
                "postReturn{}{}",
                idx.as_u32(),
                if is_async {
                    "Async"
                } else {
                    Default::default()
                }
            )
        });

        let tracing_prefix = format!(
            "[iface=\"{}\", function=\"{}\"]",
            iface_name.unwrap_or("<no iface>"),
            func.name
        );

        // Write the function argument list
        //
        // At this point, only the function preamble (e.g. 'function nameOfFunc()') has been written
        self.src.js("(");
        let mut params = Vec::new();
        let mut first = true;
        for i in 0..nparams {
            if i == 0
                && matches!(
                    call_type,
                    CallType::FirstArgIsThis | CallType::AsyncFirstArgIsThis
                )
            {
                params.push("this".into());
                continue;
            }
            if !first {
                self.src.js(", ");
            } else {
                first = false;
            }
            let param = format!("arg{i}");
            self.src.js(&param);
            params.push(param);
        }
        uwriteln!(self.src.js, ") {{");

        // If tracing is enabled, output a function entry tracing message
        if self.bindgen.opts.tracing {
            let event_fields = func
                .params
                .iter()
                .enumerate()
                .map(|(i, p)| format!("{}=${{arguments[{i}]}}", p.name))
                .collect::<Vec<String>>();
            uwriteln!(
                self.src.js,
                "console.error(`{tracing_prefix} call {}`);",
                event_fields.join(", ")
            );
        }

        // If TLA compat was enabled, ensure that it was initialized
        if self.bindgen.opts.tla_compat
            && matches!(abi, AbiVariant::GuestExport)
            && self.bindgen.opts.instantiation_mode.is_none()
        {
            let throw_uninitialized = self.bindgen.intrinsic(Intrinsic::ThrowUninitialized);
            uwrite!(
                self.src.js,
                "\
                if (!_initialized) {throw_uninitialized}();
            "
            );
        }

        // Generate function body
        let mut f = FunctionBindgen {
            resource_map,
            clear_resource_borrows: false,
            intrinsics: &mut self.bindgen.all_intrinsics,
            valid_lifting_optimization: self.bindgen.opts.valid_lifting_optimization,
            sizes: &self.sizes,
            err: if get_thrown_type(self.resolve, func.result).is_some() {
                match abi {
                    AbiVariant::GuestExport
                    | AbiVariant::GuestExportAsync
                    | AbiVariant::GuestExportAsyncStackful => ErrHandling::ThrowResultErr,
                    AbiVariant::GuestImport | AbiVariant::GuestImportAsync => {
                        ErrHandling::ResultCatchHandler
                    }
                }
            } else {
                ErrHandling::None
            },
            block_storage: Vec::new(),
            blocks: Vec::new(),
            callee,
            callee_resource_dynamic: matches!(
                call_type,
                CallType::CalleeResourceDispatch | CallType::AsyncCalleeResourceDispatch
            ),
            memory: memory.as_ref(),
            realloc: realloc.as_ref(),
            tmp: 0,
            params,
            post_return: post_return.as_ref(),
            tracing_prefix: &tracing_prefix,
            tracing_enabled: self.bindgen.opts.tracing,
            encoding: match opts.string_encoding {
                wasmtime_environ::component::StringEncoding::Utf8 => StringEncoding::UTF8,
                wasmtime_environ::component::StringEncoding::Utf16 => StringEncoding::UTF16,
                wasmtime_environ::component::StringEncoding::CompactUtf16 => {
                    StringEncoding::CompactUTF16
                }
            },
            src: source::Source::default(),
            resolve: self.resolve,
            requires_async_porcelain,
            is_async,
            iface_name,
            asmjs: self.bindgen.opts.asmjs,
            component_state: Some(FunctionBindgenComponentState {
                component_idx: opts.instance,
                realloc_fn_idx: if let CanonicalOptionsDataModel::LinearMemory(
                    LinearMemoryOptions { realloc, .. },
                ) = opts.data_model
                {
                    realloc
                } else {
                    None
                },
                memory_idx: opts.memory(),
                callback_fn_idx: opts.callback,
            }),
            for_import: Some(for_import),
        };

        // Emit (and visit, via the `FunctionBindgen` object) an abstract sequence of
        // instructions which represents the function being generated.
        abi::call(
            self.resolve,
            abi,
            match abi {
                AbiVariant::GuestImport | AbiVariant::GuestImportAsync => {
                    LiftLower::LiftArgsLowerResults
                }
                AbiVariant::GuestExport
                | AbiVariant::GuestExportAsync
                | AbiVariant::GuestExportAsyncStackful => LiftLower::LowerArgsLiftResults,
            },
            func,
            &mut f,
            is_async,
        );

        // Once visiting has completed, write the contents the `FunctionBindgen` generated to output
        self.src.js(&f.src);

        // Close function body
        self.src.js("}");
    }

    fn augmented_import_def(&self, def: &core::AugmentedImport<'_>) -> String {
        match def {
            core::AugmentedImport::CoreDef(def) => self.core_def(def),
            core::AugmentedImport::Memory { mem, op } => {
                let mem = self.core_def(mem);
                match op {
                    core::AugmentedOp::I32Load => {
                        format!(
                            "(ptr, off) => new DataView({mem}.buffer).getInt32(ptr + off, true)"
                        )
                    }
                    core::AugmentedOp::I32Load8U => {
                        format!(
                            "(ptr, off) => new DataView({mem}.buffer).getUint8(ptr + off, true)"
                        )
                    }
                    core::AugmentedOp::I32Load8S => {
                        format!("(ptr, off) => new DataView({mem}.buffer).getInt8(ptr + off, true)")
                    }
                    core::AugmentedOp::I32Load16U => {
                        format!(
                            "(ptr, off) => new DataView({mem}.buffer).getUint16(ptr + off, true)"
                        )
                    }
                    core::AugmentedOp::I32Load16S => {
                        format!(
                            "(ptr, off) => new DataView({mem}.buffer).getInt16(ptr + off, true)"
                        )
                    }
                    core::AugmentedOp::I64Load => {
                        format!(
                            "(ptr, off) => new DataView({mem}.buffer).getBigInt64(ptr + off, true)"
                        )
                    }
                    core::AugmentedOp::F32Load => {
                        format!(
                            "(ptr, off) => new DataView({mem}.buffer).getFloat32(ptr + off, true)"
                        )
                    }
                    core::AugmentedOp::F64Load => {
                        format!(
                            "(ptr, off) => new DataView({mem}.buffer).getFloat64(ptr + off, true)"
                        )
                    }
                    core::AugmentedOp::I32Store8 => {
                        format!(
                            "(ptr, val, offset) => {{
                                new DataView({mem}.buffer).setInt8(ptr + offset, val, true);
                            }}"
                        )
                    }
                    core::AugmentedOp::I32Store16 => {
                        format!(
                            "(ptr, val, offset) => {{
                                new DataView({mem}.buffer).setInt16(ptr + offset, val, true);
                            }}"
                        )
                    }
                    core::AugmentedOp::I32Store => {
                        format!(
                            "(ptr, val, offset) => {{
                                new DataView({mem}.buffer).setInt32(ptr + offset, val, true);
                            }}"
                        )
                    }
                    core::AugmentedOp::I64Store => {
                        format!(
                            "(ptr, val, offset) => {{
                                new DataView({mem}.buffer).setBigInt64(ptr + offset, val, true);
                            }}"
                        )
                    }
                    core::AugmentedOp::F32Store => {
                        format!(
                            "(ptr, val, offset) => {{
                                new DataView({mem}.buffer).setFloat32(ptr + offset, val, true);
                            }}"
                        )
                    }
                    core::AugmentedOp::F64Store => {
                        format!(
                            "(ptr, val, offset) => {{
                                new DataView({mem}.buffer).setFloat64(ptr + offset, val, true);
                            }}"
                        )
                    }
                    core::AugmentedOp::MemorySize => {
                        format!("ptr => {mem}.buffer.byteLength / 65536")
                    }
                }
            }
        }
    }

    fn core_def(&self, def: &CoreDef) -> String {
        match def {
            CoreDef::Export(e) => self.core_export_var_name(e),
            CoreDef::TaskMayBlock => AsyncTaskIntrinsic::CurrentTaskMayBlock.name().into(),
            CoreDef::Trampoline(i) => format!("trampoline{}", i.as_u32()),
            CoreDef::InstanceFlags(i) => {
                // SAFETY: short-lived borrow-mut.
                self.used_instance_flags.borrow_mut().insert(*i);
                format!("instanceFlags{}", i.as_u32())
            }
            CoreDef::UnsafeIntrinsic(ui) => match ui {
                wasmtime_environ::component::UnsafeIntrinsic::ContextGetI32_0 => {
                    let context_get_fn =
                        Intrinsic::AsyncTask(AsyncTaskIntrinsic::ContextGet).name();
                    format!(
                        "{context_get_fn}.bind(null, {{ componentIdx: {}, slot: 0 }})",
                        self.init_current_module
                            .expect("missing current module")
                            .as_u32(),
                    )
                }
                wasmtime_environ::component::UnsafeIntrinsic::ContextSetI32_0 => {
                    let context_set_fn =
                        Intrinsic::AsyncTask(AsyncTaskIntrinsic::ContextSet).name();
                    format!(
                        "{context_set_fn}.bind(null, {{ componentIdx: {}, slot: 0 }})",
                        self.init_current_module
                            .expect("missing current module")
                            .as_u32(),
                    )
                }
                wasmtime_environ::component::UnsafeIntrinsic::ContextGetI32_1 => {
                    let context_get_fn =
                        Intrinsic::AsyncTask(AsyncTaskIntrinsic::ContextGet).name();
                    format!(
                        "{context_get_fn}.bind(null, {{ componentIdx: {}, slot: 1 }})",
                        self.init_current_module
                            .expect("missing current module")
                            .as_u32(),
                    )
                }
                wasmtime_environ::component::UnsafeIntrinsic::ContextSetI32_1 => {
                    let context_set_fn =
                        Intrinsic::AsyncTask(AsyncTaskIntrinsic::ContextSet).name();
                    format!(
                        "{context_set_fn}.bind(null, {{ componentIdx: {}, slot: 1 }})",
                        self.init_current_module
                            .expect("missing current module")
                            .as_u32(),
                    )
                }

                // All other intriniscs can be set generically
                ui => {
                    let idx = ui.index();
                    format!("unsafeIntrinsic{idx}")
                }
            },
        }
    }

    fn core_export_var_name<T>(&self, export: &CoreExport<T>) -> String
    where
        T: Into<EntityIndex> + Copy,
    {
        let name = match &export.item {
            ExportItem::Index(idx) => {
                let module_idx = self
                    .instances
                    .get(export.instance)
                    .expect("unexpectedly missing export instance");
                let module = &self
                    .modules
                    .get(*module_idx)
                    .expect("unexpectedly missing module by idx");
                let idx = (*idx).into();
                module
                    .exports()
                    .iter()
                    .find_map(|(name, i)| if *i == idx { Some(name) } else { None })
                    .unwrap()
                    .to_string()
            }
            ExportItem::Name(s) => s.to_string(),
        };
        let i = export.instance.as_u32() as usize;
        let quoted = maybe_quote_member(&name);
        format!("exports{i}{quoted}")
    }

    /// Process the component imports and build mappings
    fn process_imports(&mut self) {
        let mut import_resource_map = ResourceMap::new();
        for (_import_name, (import_idx, _import_path)) in self.component.imports.iter() {
            let (import_name, import_type_def) = &self.component.import_types[*import_idx];
            let import_world_key = &self
                .imports
                .get(import_name)
                .expect("missing import mapping");
            let import_world_item = &self
                .resolve
                .worlds
                .get(self.world)
                .expect("missing world")
                .imports
                .get(*import_world_key)
                .expect("missing import in world for import");

            // Generate type information for types used in functions
            match import_world_item {
                WorldItem::Interface { id: iface_id, .. } => {
                    let iface = &self.resolve.interfaces[*iface_id];

                    // Process functions imported by the iface, which will use (as arg or param)
                    // relevant resources
                    for (fn_name, iface_fn) in iface.functions.iter() {
                        match import_type_def {
                            TypeDef::ComponentInstance(instance_ty) => {
                                if let Some(TypeDef::ComponentFunc(type_func_index)) =
                                    &self.types[*instance_ty].exports.get(fn_name)
                                {
                                    self.create_resource_fn_map(
                                        iface_fn,
                                        *type_func_index,
                                        &mut import_resource_map,
                                    );
                                }
                            }
                            TypeDef::ComponentFunc(type_func_idx) => {
                                self.create_resource_fn_map(
                                    iface_fn,
                                    *type_func_idx,
                                    &mut import_resource_map,
                                );
                            }
                            _ => {}
                        }
                    }
                }

                // Process imported functions directly to build resource maps
                WorldItem::Function(func) => {
                    // TODO: get func type index
                    let TypeDef::ComponentFunc(func_ty_idx) = import_type_def else {
                        unreachable!("invalid fn export");
                    };
                    self.create_resource_fn_map(func, *func_ty_idx, &mut import_resource_map);
                }
                // Simply informational at this point
                WorldItem::Type { .. } => {}
            }
        }

        self.resource_imports.extend(import_resource_map);
    }

    /// Process component exports and build mappings
    fn process_exports(&mut self) {
        // Since imports may be referred to by exports, we include all imports in the exports array
        self.resource_exports.extend(self.resource_imports.clone());

        // Process individual component exports
        for (export_name, export_idx) in self.component.exports.raw_iter() {
            let export_name = export_name.as_ref().to_string();
            let export = &self.component.export_items[*export_idx];
            let world_key = &self.exports[&export_name];
            let item = &self.resolve.worlds[self.world].exports[world_key];
            let mut export_resource_map = ResourceMap::new();

            match export {
                Export::LiftedFunction {
                    func: def,
                    options,
                    ty: func_ty,
                } => {
                    let func = match item {
                        WorldItem::Function(f) => f,
                        WorldItem::Interface { .. } | WorldItem::Type { .. } => {
                            unreachable!("unexpectedly non-function lifted function export")
                        }
                    };

                    self.create_resource_fn_map(func, *func_ty, &mut export_resource_map);

                    let local_name = String::from(match func.kind {
                        // For resources, we must take the type name (adding `.prototype.<fn name>` later)
                        FunctionKind::Constructor(resource_id)
                        | FunctionKind::Method(resource_id)
                        | FunctionKind::AsyncMethod(resource_id)
                        | FunctionKind::Static(resource_id)
                        | FunctionKind::AsyncStatic(resource_id) => Instantiator::resource_name(
                            self.resolve,
                            &mut self.bindgen.local_names,
                            resource_id,
                            &self.exports_resource_types,
                        ),
                        // Fore free standing functions we can use the exoprt name directly as a local name
                        FunctionKind::Freestanding | FunctionKind::AsyncFreestanding => {
                            self.bindgen.local_names.create_once(&export_name)
                        }
                    });

                    let options = self
                        .component
                        .options
                        .get(*options)
                        .expect("failed to find options");

                    self.export_bindgen(
                        &local_name,
                        def,
                        options,
                        func,
                        func_ty,
                        &export_name,
                        &export_resource_map,
                    );

                    let js_binding_name = match func.kind {
                        // For resources, we must take the type name (adding `.prototype.<fn name>` later)
                        FunctionKind::Constructor(ty)
                        | FunctionKind::Method(ty)
                        | FunctionKind::AsyncMethod(ty)
                        | FunctionKind::Static(ty)
                        | FunctionKind::AsyncStatic(ty) => self.resolve.types[ty]
                            .name
                            .as_ref()
                            .unwrap()
                            .to_upper_camel_case(),
                        // For free standing functions we can use the export name directly
                        FunctionKind::Freestanding | FunctionKind::AsyncFreestanding => {
                            export_name.to_lower_camel_case()
                        }
                    };

                    // Add the export binding
                    self.bindgen.esm_bindgen.add_export_binding(
                        None,
                        local_name,
                        js_binding_name,
                        func,
                    );
                }

                Export::Instance { exports, .. } => {
                    let iface_id = match item {
                        WorldItem::Interface { id, .. } => *id,
                        WorldItem::Function(_) | WorldItem::Type { .. } => {
                            unreachable!("unexpectedly non-interface export instance")
                        }
                    };

                    // Process exported instances
                    for (func_name, export_idx) in exports.raw_iter() {
                        let func_name = func_name.as_ref().to_string();
                        let export = &self.component.export_items[*export_idx];

                        // Gather function information for all lifted functions in the isntance export
                        let (def, options, func_ty) = match export {
                            Export::LiftedFunction { func, options, ty } => (func, options, ty),
                            Export::Type(_) => continue, // ignored
                            _ => unreachable!("unexpected non-lifted function export"),
                        };

                        let func = &self.resolve.interfaces[iface_id].functions[&func_name];

                        self.create_resource_fn_map(func, *func_ty, &mut export_resource_map);

                        let local_name = String::from(match func.kind {
                            // For resources, we must use the name of the type
                            FunctionKind::Constructor(resource_id)
                            | FunctionKind::Method(resource_id)
                            | FunctionKind::AsyncMethod(resource_id)
                            | FunctionKind::Static(resource_id)
                            | FunctionKind::AsyncStatic(resource_id) => {
                                Instantiator::resource_name(
                                    self.resolve,
                                    &mut self.bindgen.local_names,
                                    resource_id,
                                    &self.exports_resource_types,
                                )
                            }
                            // For free standing functions we can use the bare func name
                            FunctionKind::Freestanding | FunctionKind::AsyncFreestanding => {
                                self.bindgen.local_names.create_once(&func_name)
                            }
                        });

                        let options = self
                            .component
                            .options
                            .get(*options)
                            .expect("failed to find options");

                        self.export_bindgen(
                            &local_name,
                            def,
                            options,
                            func,
                            func_ty,
                            &export_name,
                            &export_resource_map,
                        );

                        // Determine the export func name (this can also be a class name)
                        let export_binding_name = match func.kind {
                            // For resources, we must use the type name (later adding `.prototype.<actual fn>`)
                            FunctionKind::Constructor(ty)
                            | FunctionKind::Method(ty)
                            | FunctionKind::AsyncMethod(ty)
                            | FunctionKind::Static(ty)
                            | FunctionKind::AsyncStatic(ty) => self.resolve.types[ty]
                                .name
                                .as_ref()
                                .unwrap()
                                .to_upper_camel_case(),
                            // Free standing functions we can use the function name directly
                            FunctionKind::Freestanding | FunctionKind::AsyncFreestanding => {
                                func_name.to_lower_camel_case()
                            }
                        };

                        // Add the export binding
                        self.bindgen.esm_bindgen.add_export_binding(
                            Some(&export_name),
                            local_name,
                            export_binding_name,
                            func,
                        );
                    }
                }

                // ignore type exports for now
                Export::Type(_) => {}

                // This can't be tested at this time so leave it unimplemented
                Export::ModuleStatic { .. } | Export::ModuleImport { .. } => unimplemented!(),
            }

            // Save information about exported resources for later
            self.resource_exports.extend(export_resource_map);
        }

        self.bindgen.esm_bindgen.populate_export_aliases();
    }

    #[allow(clippy::too_many_arguments)]
    fn export_bindgen(
        &mut self,
        local_name: &str,
        def: &CoreDef,
        options: &CanonicalOptions,
        func: &Function,
        _func_ty_idx: &TypeFuncIndex,
        export_name: &String,
        export_resource_map: &ResourceMap,
    ) {
        // Determine whether the function should be generated as async
        let requires_async_porcelain = requires_async_porcelain(
            FunctionIdentifier::Fn(func),
            export_name,
            &self.async_exports,
        );
        // If the function is *also* async lifted, it
        if options.async_ {
            assert!(
                options.post_return.is_none(),
                "async function {local_name} (export {export_name}) can't have post return"
            );
        }

        let is_async = is_async_fn(func, options);

        let maybe_async = if requires_async_porcelain || is_async {
            "async "
        } else {
            ""
        };

        // Start building early variable declarations
        let core_export_fn = self.core_def(def);
        let callee = match self
            .bindgen
            .local_names
            .get_or_create(&core_export_fn, &core_export_fn)
        {
            (local_name, true) => local_name.to_string(),
            (local_name, false) => {
                let local_name = local_name.to_string();
                uwriteln!(self.src.js, "let {local_name};");
                self.bindgen
                    .all_core_exported_funcs
                    // TODO(breaking): remove requires_async_porcelain  once support
                    // for manual async import specification is removed, as p3 has
                    // built-in function async coloring
                    .push((core_export_fn.clone(), is_async | requires_async_porcelain));
                local_name
            }
        };

        let iface_name = if export_name.is_empty() {
            None
        } else {
            Some(export_name)
        };

        // Write function preamble (everything up to the `(` in `function (...`)
        match func.kind {
            FunctionKind::Freestanding => {
                uwrite!(self.src.js, "\n{maybe_async}function {local_name}")
            }
            FunctionKind::Method(_) => {
                self.ensure_local_resource_class(local_name.to_string());
                let method_name = func.item_name().to_lower_camel_case();

                uwrite!(
                    self.src.js,
                    "\n{local_name}.prototype.{method_name} = {maybe_async}function {}",
                    if !is_js_reserved_word(&method_name) {
                        method_name.to_string()
                    } else {
                        format!("${method_name}")
                    }
                );
            }
            FunctionKind::Static(_) => {
                self.ensure_local_resource_class(local_name.to_string());
                let method_name = func.item_name().to_lower_camel_case();
                uwrite!(
                    self.src.js,
                    "\n{local_name}.{method_name} = function {}",
                    if !is_js_reserved_word(&method_name) {
                        method_name.to_string()
                    } else {
                        format!("${method_name}")
                    }
                );
            }
            FunctionKind::Constructor(_) => {
                if self.defined_resource_classes.contains(local_name) {
                    panic!(
                        "Internal error: Resource constructor must be defined before other methods and statics"
                    );
                }
                uwrite!(
                    self.src.js,
                    "
                    class {local_name} {{
                        constructor"
                );
                self.defined_resource_classes.insert(local_name.to_string());
            }
            FunctionKind::AsyncFreestanding => {
                uwrite!(self.src.js, "\nasync function {local_name}")
            }
            FunctionKind::AsyncMethod(_) => {
                self.ensure_local_resource_class(local_name.to_string());
                let method_name = func.item_name().to_lower_camel_case();
                let fn_name = if !is_js_reserved_word(&method_name) {
                    method_name.to_string()
                } else {
                    format!("${method_name}")
                };
                uwrite!(
                    self.src.js,
                    "\n{local_name}.prototype.{method_name} = async function {fn_name}",
                );
            }
            FunctionKind::AsyncStatic(_) => {
                self.ensure_local_resource_class(local_name.to_string());
                let method_name = func.item_name().to_lower_camel_case();
                let fn_name = if !is_js_reserved_word(&method_name) {
                    method_name.to_string()
                } else {
                    format!("${method_name}")
                };
                uwrite!(
                    self.src.js,
                    "\n{local_name}.{method_name} = async function {fn_name}",
                );
            }
        };

        // Perform bindgen
        self.bindgen(JsFunctionBindgenArgs {
            nparams: func.params.len(),
            call_type: match func.kind {
                FunctionKind::Method(_) => CallType::FirstArgIsThis,
                FunctionKind::AsyncMethod(_) => CallType::AsyncFirstArgIsThis,
                FunctionKind::Freestanding
                | FunctionKind::Static(_)
                | FunctionKind::Constructor(_) => CallType::Standard,
                FunctionKind::AsyncFreestanding | FunctionKind::AsyncStatic(_) => {
                    CallType::AsyncStandard
                }
            },
            iface_name: iface_name.map(|v| v.as_str()),
            callee: &callee,
            opts: options,
            func,
            resource_map: export_resource_map,
            abi: AbiVariant::GuestExport,
            requires_async_porcelain,
            is_async,
            for_import: false,
        });

        // End the function
        match func.kind {
            FunctionKind::AsyncFreestanding | FunctionKind::Freestanding => self.src.js("\n"),
            FunctionKind::AsyncMethod(_)
            | FunctionKind::AsyncStatic(_)
            | FunctionKind::Method(_)
            | FunctionKind::Static(_) => self.src.js(";\n"),
            FunctionKind::Constructor(_) => self.src.js("\n}\n"),
        }
    }
}

#[derive(Default)]
pub struct Source {
    pub js: source::Source,
    pub js_init: source::Source,
}

impl Source {
    pub fn js(&mut self, s: &str) {
        self.js.push_str(s);
    }
    pub fn js_init(&mut self, s: &str) {
        self.js_init.push_str(s);
    }
}

/// Compute the semver "compatibility track" for a version string.
/// Mirrors wasmtime's `alternate_lookup_key()` logic.
///
/// Returns the compat key and parsed `Version` on success.
///
/// Examples (showing just the key):
///   "1.2.3"  → Some(("1", ..))     — major > 0, compat within major
///   "0.2.10" → Some(("0.2", ..))   — minor > 0, compat within 0.minor
///   "0.0.1"  → None                — no semver compat
///   "1.0.0-rc.1" → None            — pre-release, no compat
fn semver_compat_key(version_str: &str) -> Option<(String, Version)> {
    let version = Version::parse(version_str).ok()?;
    if !version.pre.is_empty() {
        None
    } else if version.major != 0 {
        Some((format!("{}", version.major), version))
    } else if version.minor != 0 {
        Some((format!("0.{}", version.minor), version))
    } else {
        None
    }
}

fn parse_mapping(mapping: &str) -> (String, Option<String>) {
    if mapping.len() > 1
        && let Some(hash_idx) = mapping[1..].find('#')
    {
        return (
            mapping[0..hash_idx + 1].to_string(),
            Some(mapping[hash_idx + 2..].into()),
        );
    }
    (mapping.into(), None)
}

fn resolve_wildcard_mapping(key: &str, mapping: &str, impt: &str) -> Option<String> {
    let idx = key.find('*')?;
    let lhs = &key[..idx];
    let rhs = &key[idx + 1..];

    if !impt.starts_with(lhs) || !impt.ends_with(rhs) {
        return None;
    }

    let matched_len = impt.len() - lhs.len() - rhs.len();
    let matched = &impt[lhs.len()..lhs.len() + matched_len];
    Some(mapping.replace('*', matched))
}

fn map_import(map: &Option<HashMap<String, String>>, impt: &str) -> (String, Option<String>) {
    let impt_sans_version = match impt.find('@') {
        Some(version_idx) => &impt[0..version_idx],
        None => impt,
    };
    if let Some(map) = map.as_ref() {
        // 1. Exact match (including version)
        if let Some(mapping) = map.get(impt) {
            return parse_mapping(mapping);
        }

        // 2. Exact match without version
        if let Some(mapping) = map.get(impt_sans_version) {
            return parse_mapping(mapping);
        }

        // Prefer versioned wildcards over unversioned fallbacks.
        for (key, mapping) in map {
            if !key.contains('@') {
                continue;
            }
            if let Some(mapping) = resolve_wildcard_mapping(key, mapping, impt) {
                return parse_mapping(&mapping);
            }
        }

        // Then apply unversioned wildcards to the version-stripped import.
        for (key, mapping) in map {
            if key.contains('@') {
                continue;
            }
            if let Some(mapping) = resolve_wildcard_mapping(key, mapping, impt_sans_version) {
                return parse_mapping(&mapping);
            }
        }

        // If the import has a parseable version and earlier steps didn't match,
        // try matching against map entries with compatible versions.
        if let Some(at) = impt.find('@') {
            let impt_ver_str = &impt[at + 1..];
            if let Some((impt_compat, _)) = semver_compat_key(impt_ver_str) {
                let mut best_match: Option<(String, Version)> = None;

                for (key, mapping) in map {
                    let key_at = match key.find('@') {
                        Some(at) => at,
                        None => continue,
                    };
                    let key_base = &key[..key_at];
                    let key_ver_str = &key[key_at + 1..];

                    let (key_compat, key_ver) = match semver_compat_key(key_ver_str) {
                        Some(k) => k,
                        None => continue,
                    };
                    if impt_compat != key_compat {
                        continue;
                    }

                    let resolved = if let Some(mapping) =
                        resolve_wildcard_mapping(key_base, mapping, impt_sans_version)
                    {
                        Some(mapping)
                    } else if key_base == impt_sans_version {
                        Some(mapping.clone())
                    } else {
                        None
                    };

                    if let Some(resolved_mapping) = resolved {
                        match &best_match {
                            Some((_, prev_ver)) if key_ver <= *prev_ver => {}
                            _ => {
                                best_match = Some((resolved_mapping, key_ver));
                            }
                        }
                    }
                }

                if let Some((mapping, _)) = best_match {
                    return parse_mapping(&mapping);
                }
            }
        }
    }
    (impt_sans_version.to_string(), None)
}

pub fn parse_world_key(name: &str) -> Option<(&str, &str, &str)> {
    let registry_idx = name.find(':')?;
    let ns = &name[0..registry_idx];
    match name.rfind('/') {
        Some(sep_idx) => {
            let end = if let Some(version_idx) = name.rfind('@') {
                version_idx
            } else {
                name.len()
            };
            Some((
                ns,
                &name[registry_idx + 1..sep_idx],
                &name[sep_idx + 1..end],
            ))
        }
        // interface is a namespace, function is a default export
        None => Some((ns, &name[registry_idx + 1..], "")),
    }
}

fn core_file_name(name: &str, idx: u32) -> String {
    let i_str = if idx == 0 {
        String::from("")
    } else {
        (idx + 1).to_string()
    };
    format!("{name}.core{i_str}.wasm")
}

/// Encode a [`StringEncoding`] as a string that can be used in Javascript
fn string_encoding_js_literal(val: &wasmtime_environ::component::StringEncoding) -> &'static str {
    match val {
        wasmtime_environ::component::StringEncoding::Utf8 => "'utf8'",
        wasmtime_environ::component::StringEncoding::Utf16 => "'utf16'",
        wasmtime_environ::component::StringEncoding::CompactUtf16 => "'compact-utf16'",
    }
}

/// Generate the javascript that corresponds to a list of lifting functions for a given list of types
///
/// # Arguments
///
/// * `instantiator`
/// * `types` - Types for which to generate lift functions
/// * `extra_resource_map` - Extra resource mapping that do not exist on the `instantiatior` that should be used ad-hoc
///
pub fn gen_flat_lift_fn_list_js_expr(
    instantiator: &mut Instantiator,
    types: &[InterfaceType],
    extra_resource_map: &Option<&mut ResourceMap>,
) -> String {
    let mut lift_fns: Vec<String> = Vec::with_capacity(types.len());
    for ty in types.iter() {
        lift_fns.push(gen_flat_lift_fn_js_expr(
            instantiator,
            ty,
            extra_resource_map,
        ));
    }
    format!("[{}]", lift_fns.join(","))
}

fn flat_count_js_expr(flat_count: &Option<u8>) -> String {
    flat_count
        .map(|count| count.to_string())
        .unwrap_or_else(|| "null".into())
}

/// Generate the javascript lifting function for a given type
///
/// This function will a function object that can be executed with the right
/// context in order to perform the lift. For example, running this for bool
/// will produce the following:
///
/// ```
/// _liftFlatBool
/// ```
///
/// This is becasue all it takes to lift a flat boolean is to run the _liftFlatBool function intrinsic.
///
/// The intrinsic it guaranteed to be in scope once execution time because it wlil be used in the relevant branch.
///
/// # Arguments
///
/// * `instantiator`
/// * `ty` - The type for which to generate a lift function
/// * `extra_resource_map` - Extra resource mapping that do not exist on the `instantiatior` that should be used ad-hoc
///
pub fn gen_flat_lift_fn_js_expr(
    instantiator: &mut Instantiator,
    ty: &InterfaceType,
    extra_resource_map: &Option<&mut ResourceMap>,
) -> String {
    let component_types = instantiator.types;

    match ty {
        InterfaceType::Bool => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatBool));
            Intrinsic::Lift(LiftIntrinsic::LiftFlatBool).name().into()
        }

        InterfaceType::S8 => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatS8));
            Intrinsic::Lift(LiftIntrinsic::LiftFlatS8).name().into()
        }

        InterfaceType::U8 => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatU8));
            Intrinsic::Lift(LiftIntrinsic::LiftFlatU8).name().into()
        }

        InterfaceType::S16 => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatS16));
            Intrinsic::Lift(LiftIntrinsic::LiftFlatS16).name().into()
        }

        InterfaceType::U16 => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatU16));
            Intrinsic::Lift(LiftIntrinsic::LiftFlatU16).name().into()
        }

        InterfaceType::S32 => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatS32));
            Intrinsic::Lift(LiftIntrinsic::LiftFlatS32).name().into()
        }

        InterfaceType::U32 => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatU32));
            Intrinsic::Lift(LiftIntrinsic::LiftFlatU32).name().into()
        }

        InterfaceType::S64 => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatS64));
            Intrinsic::Lift(LiftIntrinsic::LiftFlatS64).name().into()
        }

        InterfaceType::U64 => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatU64));
            Intrinsic::Lift(LiftIntrinsic::LiftFlatU64).name().into()
        }

        InterfaceType::Float32 => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatFloat32));
            Intrinsic::Lift(LiftIntrinsic::LiftFlatFloat32)
                .name()
                .into()
        }

        InterfaceType::Float64 => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatFloat64));
            Intrinsic::Lift(LiftIntrinsic::LiftFlatFloat64)
                .name()
                .into()
        }

        InterfaceType::Char => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatChar));
            Intrinsic::Lift(LiftIntrinsic::LiftFlatChar).name().into()
        }

        InterfaceType::String => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatStringAny));
            Intrinsic::Lift(LiftIntrinsic::LiftFlatStringAny)
                .name()
                .into()
        }

        InterfaceType::Record(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatRecord));
            let lift_fn = Intrinsic::Lift(LiftIntrinsic::LiftFlatRecord).name();
            let record_ty = &component_types[*ty_idx];
            let size32 = record_ty.abi.size32;
            let align32 = record_ty.abi.align32;
            let mut keys_and_lifts_expr = String::from("[");
            // For each field we build a list of [name, liftFn, 32bit alignment]
            // so that the record lifting function (which is a higher level function)
            // can properly generate a function that lifts the fields.
            for f in &record_ty.fields {
                let field_abi = component_types.canonical_abi(&f.ty);
                let field_size32 = field_abi.size32;
                let field_align32 = field_abi.align32;
                keys_and_lifts_expr.push_str(&format!(
                    "['{}', {}, {}, {}],",
                    f.name.to_lower_camel_case(),
                    gen_flat_lift_fn_js_expr(instantiator, &f.ty, extra_resource_map),
                    field_size32,
                    field_align32,
                ));
            }
            keys_and_lifts_expr.push(']');
            format!(
                "{lift_fn}({{ fieldMetas: {keys_and_lifts_expr}, size32: {size32}, align32: {align32} }})"
            )
        }

        InterfaceType::Variant(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatVariant));
            let lift_fn = Intrinsic::Lift(LiftIntrinsic::LiftFlatVariant).name();
            let variant_ty = &component_types[*ty_idx];
            let variant_flat_count = flat_count_js_expr(&variant_ty.abi.flat_count);
            let variant_size32 = variant_ty.abi.size32;
            let variant_align32 = variant_ty.abi.align32;
            let variant_payload_offset32 = variant_ty.info.payload_offset32;

            let mut lift_metas_expr = String::from("[");
            for (name, maybe_ty) in &variant_ty.cases {
                let (lift_fn_js, case_size32, case_align32, case_flat_count) = match maybe_ty {
                    Some(ty) => {
                        let cabi_info = component_types.canonical_abi(ty);
                        (
                            gen_flat_lift_fn_js_expr(instantiator, ty, extra_resource_map),
                            cabi_info.size32.to_string(),
                            cabi_info.align32.to_string(),
                            cabi_info
                                .flat_count(MAX_FLAT_PARAMS)
                                .map(|v| v.to_string())
                                .unwrap_or_else(|| "null".into()),
                        )
                    }
                    None => ("null".into(), "0".into(), "0".into(), "0".into()),
                };

                lift_metas_expr.push_str(&format!(
                    "['{name}', {lift_fn_js}, {case_size32}, {case_align32}, {case_flat_count}],",
                ));
            }
            lift_metas_expr.push(']');

            format!(
                "{lift_fn}({{
                     caseMetas: {lift_metas_expr},
                     variantSize32: {variant_size32},
                     variantAlign32: {variant_align32},
                     variantPayloadOffset32: {variant_payload_offset32},
                     variantFlatCount: {variant_flat_count},
                 }} )"
            )
        }

        InterfaceType::List(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatList));
            let f = Intrinsic::Lift(LiftIntrinsic::LiftFlatList).name();
            let list_ty = &component_types[*ty_idx];
            let lift_fn_expr =
                gen_flat_lift_fn_js_expr(instantiator, &list_ty.element, extra_resource_map);
            let elem_cabi = component_types.canonical_abi(&list_ty.element);
            let elem_align32 = elem_cabi.align32;
            let elem_size32 = elem_cabi.size32;
            let typed_array = js_typed_array_ctor(&list_ty.element).unwrap_or("undefined");
            format!(
                "{f}({{
                     elemLiftFn: {lift_fn_expr},
                     elemAlign32: {elem_align32},
                     elemSize32: {elem_size32},
                     typedArray: {typed_array},
                  }})"
            )
        }

        InterfaceType::FixedLengthList(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatList));
            let f = Intrinsic::Lift(LiftIntrinsic::LiftFlatList).name();
            let list_ty = &component_types[*ty_idx];
            let list_size32 = list_ty.abi.size32;
            let list_align32 = list_ty.abi.align32;
            let lift_fn_expr =
                gen_flat_lift_fn_js_expr(instantiator, &list_ty.element, extra_resource_map);
            let list_len = list_ty.size;
            let elem_cabi = component_types.canonical_abi(&list_ty.element);
            let elem_align32 = elem_cabi.align32;
            let elem_size32 = elem_cabi.size32;
            format!(
                "{f}({{
                     elemLiftFn: {lift_fn_expr},
                     elemAlign32: {elem_align32},
                     elemSize32: {elem_size32},
                     listSize32: {list_size32},
                     listAlign32: {list_align32},
                     knownLen: {list_len},
                 }})"
            )
        }

        InterfaceType::Tuple(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatTuple));
            let tuple_ty = &component_types[*ty_idx];
            let f = Intrinsic::Lift(LiftIntrinsic::LiftFlatTuple).name();
            let size_u32 = tuple_ty.abi.size32;
            let align_u32 = tuple_ty.abi.align32;

            let mut elem_lifts_expr = String::from("[");
            for ty in &tuple_ty.types {
                let lift_fn_js = gen_flat_lift_fn_js_expr(instantiator, ty, extra_resource_map);
                let elem_abi = component_types.canonical_abi(ty);
                let elem_size32 = elem_abi.size32;
                let elem_align32 = elem_abi.align32;
                elem_lifts_expr
                    .push_str(&format!("[{lift_fn_js}, {elem_size32}, {elem_align32}],"));
            }
            elem_lifts_expr.push(']');

            format!(
                "{f}({{ elemLiftFns: {elem_lifts_expr}, size32: {size_u32}, align32: {align_u32} }})"
            )
        }

        InterfaceType::Flags(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatFlags));
            let f = Intrinsic::Lift(LiftIntrinsic::LiftFlatFlags).name();
            let flags_ty = &component_types[*ty_idx];
            let size_u32 = flags_ty.abi.size32;
            let align_u32 = flags_ty.abi.align32;
            let names_expr = format!(
                "[{}]",
                flags_ty
                    .names
                    .iter()
                    .map(|s| format!("'{}'", s.to_lower_camel_case()))
                    .collect::<Vec<_>>()
                    .join(",")
            );
            let num_flags = flags_ty.names.len();
            let elem_size = if num_flags <= 8 {
                1
            } else if num_flags <= 16 {
                2
            } else {
                4
            };

            format!(
                "{f}({{ names: {names_expr}, size32: {size_u32}, align32: {align_u32}, intSizeBytes: {elem_size} }})"
            )
        }

        InterfaceType::Enum(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatEnum));
            let f = Intrinsic::Lift(LiftIntrinsic::LiftFlatEnum).name();
            let enum_ty = &component_types[*ty_idx];
            let enum_size32 = enum_ty.abi.size32;
            let enum_align32 = enum_ty.abi.align32;
            let enum_payload_offset32 = enum_ty.info.payload_offset32;
            let enum_flat_count = flat_count_js_expr(&enum_ty.abi.flat_count);

            let mut elem_lifts_expr = String::from("[");
            for name in &enum_ty.names {
                elem_lifts_expr.push_str(&format!(
                    "['{name}', null, {enum_size32}, {enum_align32}, {enum_payload_offset32}],"
                ));
            }
            elem_lifts_expr.push(']');

            format!(
                r#"
                  {f}({{
                      caseMetas: {elem_lifts_expr},
                      variantSize32: {enum_size32},
                      variantAlign32: {enum_align32},
                      variantPayloadOffset32: {enum_payload_offset32},
                      variantFlatCount: {enum_flat_count},
                  }})
               "#
            )
        }

        InterfaceType::Option(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatOption));
            let f = Intrinsic::Lift(LiftIntrinsic::LiftFlatOption).name();
            let option_ty = &component_types[*ty_idx];
            let option_payload_offset32 = option_ty.info.payload_offset32;
            let option_align32 = option_ty.abi.align32;
            let option_size32 = option_ty.abi.size32;
            let option_flat_count = flat_count_js_expr(&option_ty.abi.flat_count);

            let some_ty_abi = component_types.canonical_abi(&option_ty.ty);
            let some_ty_flat_count = flat_count_js_expr(&some_ty_abi.flat_count);
            let some_ty_size32 = some_ty_abi.size32;
            let some_ty_align32 = some_ty_abi.align32;
            let some_ty_lift_fn_js =
                gen_flat_lift_fn_js_expr(instantiator, &option_ty.ty, extra_resource_map);

            format!(
                r#"
                {f}({{
                    caseMetas: [
                        ['none', null, 0, 0, 0 ],
                        ['some', {some_ty_lift_fn_js}, {some_ty_size32}, {some_ty_align32}, {some_ty_flat_count} ],
                    ],
                    variantSize32: {option_size32},
                    variantAlign32: {option_align32},
                    variantPayloadOffset32: {option_payload_offset32},
                    variantFlatCount: {option_flat_count},
                }})
                "#
            )
        }

        InterfaceType::Result(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatResult));
            let lift_fn = Intrinsic::Lift(LiftIntrinsic::LiftFlatResult).name();
            let result_ty = &component_types[*ty_idx];
            let result_size32 = result_ty.abi.size32;
            let result_align32 = result_ty.abi.align32;
            let result_payload_offset32 = result_ty.info.payload_offset32;
            let result_flat_count = flat_count_js_expr(&result_ty.abi.flat_count);

            let mut cases_and_lifts_expr = String::from("[");
            if let Some(ok_ty) = result_ty.ok {
                let ok_ty_abi = component_types.canonical_abi(&ok_ty);
                let ok_ty_size32 = ok_ty_abi.size32;
                let ok_ty_align32 = ok_ty_abi.align32;
                let ok_flat_count = flat_count_js_expr(&ok_ty_abi.flat_count);
                let ok_ty_lift_fn =
                    gen_flat_lift_fn_js_expr(instantiator, &ok_ty, extra_resource_map);
                cases_and_lifts_expr.push_str(&format!(
                    "['ok', {ok_ty_lift_fn}, {ok_ty_size32}, {ok_ty_align32}, {ok_flat_count}],",
                ))
            } else {
                cases_and_lifts_expr.push_str("['ok', null, 0, 0, 0],");
            }

            if let Some(err_ty) = &result_ty.err {
                let err_ty_abi = component_types.canonical_abi(err_ty);
                let err_ty_size32 = err_ty_abi.size32;
                let err_ty_align32 = err_ty_abi.align32;
                let err_ty_flat_count = flat_count_js_expr(&err_ty_abi.flat_count);
                let err_ty_lift_fn =
                    gen_flat_lift_fn_js_expr(instantiator, err_ty, extra_resource_map);
                cases_and_lifts_expr.push_str(&format!(
                    "['err', {err_ty_lift_fn}, {err_ty_size32}, {err_ty_align32}, {err_ty_flat_count}],",
                ))
            } else {
                cases_and_lifts_expr.push_str("['err', null, 0, 0, 0],");
            }
            cases_and_lifts_expr.push(']');

            format!(
                r#"
                  {lift_fn}({{
                      caseMetas: {cases_and_lifts_expr},
                      variantSize32: {result_size32},
                      variantAlign32: {result_align32},
                      variantPayloadOffset32: {result_payload_offset32},
                      variantFlatCount: {result_flat_count},
                  }})
                "#
            )
        }

        InterfaceType::Own(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatOwn));
            instantiator.add_intrinsic(Intrinsic::JsHelper(JsHelperIntrinsic::EmptyFunc));
            instantiator.add_intrinsic(Intrinsic::SymbolResourceHandle);
            instantiator.add_intrinsic(Intrinsic::SymbolResourceRep);
            instantiator.add_intrinsic(Intrinsic::SymbolDispose);
            instantiator.add_intrinsic(Intrinsic::Resource(ResourceIntrinsic::ResourceTableRemove));
            instantiator.add_intrinsic(Intrinsic::Resource(ResourceIntrinsic::ResourceTableFlag));
            let f = Intrinsic::Lift(LiftIntrinsic::LiftFlatOwn).name();
            let table_ty = &component_types[*ty_idx];
            let component_idx = table_ty.unwrap_concrete_instance().as_u32();
            let resource_idx = table_ty.unwrap_concrete_ty();

            // Attempt to find information about the owned resource
            match instantiator.exports_resource_index_types.get(&resource_idx) {
                // Type information not found for this resource index
                None => format!(
                    r#"{f}({{
                       componentIdx: {component_idx},
                       className: null,
                       createResourceFn: () => {{ throw new Error('invalid/missing resource type data'); }},
                    }})
                "#,
                ),

                // If we have a resource type def, find more information about it to generate
                // the resource creation function
                Some(resource_typedef) => {
                    // Look in both the resource exports and the provided extra resource map for the resource
                    let (resource_class_name, create_resource_fn_js) = match (
                        instantiator.resource_exports.get(resource_typedef),
                        extra_resource_map
                            .as_ref()
                            .and_then(|v| v.get(resource_typedef)),
                    ) {
                        // Resource type information wasn't found
                        (None, None) => (
                            "null".into(),
                            "() => {{ throw new Error('missing resource information'); }}".into(),
                        ),

                        // Resource type was found in either resource_exports or extra provided resource map
                        (Some(ResourceTable { imported, data }), _)
                        | (_, Some(ResourceTable { imported, data })) => match data {
                            ResourceData::Guest { .. } => {
                                unimplemented!(
                                    "owned resources created by guests should must have host-side data"
                                )
                            }
                            ResourceData::Host {
                                tid,
                                rid,
                                local_name,
                                dtor_name,
                            } => {
                                let empty_func = JsHelperIntrinsic::EmptyFunc.name();
                                let symbol_resource_handle = Intrinsic::SymbolResourceHandle.name();
                                let symbol_dispose = Intrinsic::SymbolDispose.name();
                                let rsc_table_remove =
                                    ResourceIntrinsic::ResourceTableRemove.name();
                                let tid = tid.as_u32();
                                let rsc_flag = ResourceIntrinsic::ResourceTableFlag.name();

                                // Mirrors `Instruction::HandleLift` in `function_bindgen.rs`:
                                let create_resource_fn_js = if *imported {
                                    let symbol_resource_rep = Intrinsic::SymbolResourceRep.name();
                                    let rid = rid.as_u32();
                                    format!(
                                        r#"
                                      (handle) => {{
                                          const rep = handleTable{tid}[(handle << 1) + 1] & ~{rsc_flag};
                                          let resourceObj = captureTable{rid}.get(rep);
                                          if (!resourceObj) {{
                                              resourceObj = Object.create({local_name}.prototype);
                                              Object.defineProperty(resourceObj, {symbol_resource_handle}, {{ writable: true, value: handle }});
                                              Object.defineProperty(resourceObj, {symbol_resource_rep}, {{ writable: true, value: rep }});
                                          }} else {{
                                              captureTable{rid}.delete(rep);
                                          }}
                                          {rsc_table_remove}(handleTable{tid}, handle);
                                          return resourceObj;
                                      }}
                                     "#
                                    )
                                } else {
                                    let dtor_setup_js = dtor_name
                                    .as_ref()
                                    .map(|dtor|
                                         format!(
                                             r#"
                                               Object.defineProperty(
                                                   resourceObj,
                                                   {symbol_dispose},
                                                   {{
                                                       writable: true,
                                                       value: function() {{
                                                           finalizationRegistry{tid}.unregister(resourceObj);
                                                           {rsc_table_remove}(handleTable{tid}, handle);
                                                           resourceObj[{symbol_dispose}] = {empty_func};
                                                           resourceObj[{symbol_resource_handle}] = undefined;
                                                           {dtor}(handleTable{tid}[(handle << 1) + 1] & ~{rsc_flag});
                                                       }}
                                                  }}
                                              );
                                        "#
                                         )
                                    ).unwrap_or_default();

                                    format!(
                                        r#"
                                      (handle) => {{
                                          const resourceObj = Object.create({local_name}.prototype);
                                          Object.defineProperty(resourceObj, {symbol_resource_handle}, {{
                                              writable: true,
                                              value: handle,
                                          }});
                                          finalizationRegistry{tid}.register(resourceObj, handle, resourceObj);
                                          {dtor_setup_js}
                                          return resourceObj;
                                      }}
                                     "#
                                    )
                                };

                                (local_name.to_string(), create_resource_fn_js)
                            }
                        },
                    };

                    format!(
                        r#"{f}({{
                       componentIdx: {component_idx},
                       className: {resource_class_name},
                       createResourceFn: {create_resource_fn_js},
                    }})
                "#,
                    )
                }
            }
        }

        InterfaceType::Borrow(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatBorrow));
            let table_idx = ty_idx.as_u32();
            let f = Intrinsic::Lift(LiftIntrinsic::LiftFlatBorrow).name();
            format!("{f}.bind(null, {table_idx})")
        }

        InterfaceType::Future(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatFuture));
            let f = Intrinsic::Lift(LiftIntrinsic::LiftFlatFuture).name();
            let table_idx = ty_idx.as_u32();
            let table_ty = &component_types[*ty_idx];
            let component_idx = table_ty.instance.as_u32();
            format!("{f}({{ futureTableIdx: {table_idx}, componentIdx: {component_idx} }})")
        }

        InterfaceType::Stream(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatStream));
            let f = Intrinsic::Lift(LiftIntrinsic::LiftFlatStream).name();
            let table_idx = ty_idx.as_u32();
            let table_ty = &component_types[*ty_idx];
            let component_idx = table_ty.instance.as_u32();
            format!("{f}({{ streamTableIdx: {table_idx}, componentIdx: {component_idx} }})")
        }

        InterfaceType::ErrorContext(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lift(LiftIntrinsic::LiftFlatErrorContext));
            let table_idx = ty_idx.as_u32();
            let f = Intrinsic::Lift(LiftIntrinsic::LiftFlatErrorContext).name();
            format!("{f}.bind(null, {table_idx})")
        }

        InterfaceType::Map(_) => unimplemented!("map support"),
    }
}

fn js_typed_array_ctor(ty: &InterfaceType) -> Option<&'static str> {
    match ty {
        InterfaceType::U8 => Some("Uint8Array"),
        InterfaceType::S8 => Some("Int8Array"),
        InterfaceType::U16 => Some("Uint16Array"),
        InterfaceType::S16 => Some("Int16Array"),
        InterfaceType::U32 => Some("Uint32Array"),
        InterfaceType::S32 => Some("Int32Array"),
        InterfaceType::U64 => Some("BigUint64Array"),
        InterfaceType::S64 => Some("BigInt64Array"),
        InterfaceType::Float32 => Some("Float32Array"),
        InterfaceType::Float64 => Some("Float64Array"),
        _ => None,
    }
}

/// Generate the javascript that corresponds to a list of lowering functions for a given list of types
///
/// # Arguments
///
/// * `instantiator`
/// * `types` - Types for which to generate lift functions
/// * `extra_resource_map` - Extra resource mapping that do not exist on the `instantiatior` that should be used ad-hoc
///
pub fn gen_flat_lower_fn_list_js_expr(
    instantiator: &mut Instantiator,
    types: &[InterfaceType],
    extra_import_map: &Option<&mut ResourceMap>,
) -> String {
    let mut lower_fns: Vec<String> = Vec::with_capacity(types.len());
    for ty in types.iter() {
        lower_fns.push(gen_flat_lower_fn_js_expr(
            instantiator,
            ty,
            extra_import_map,
        ));
    }
    format!("[{}]", lower_fns.join(","))
}

/// Generate the javascript lowering function for a given type
///
/// This function will a function object that can be executed with the right
/// context in order to perform the lower. For example, running this for bool
/// will produce the following:
///
/// ```
/// _lowerFlatBool
/// ```
///
/// This is becasue all it takes to lower a flat boolean is to run the _lowerFlatBool function intrinsic.
///
/// The intrinsic it guaranteed to be in scope once execution time because it wlil be used in the relevant branch.
///
/// # Arguments
///
/// * `instantiator`
/// * `ty` - type for which to generate a lower function
/// * `extra_resource_map` - Extra resource mapping that do not exist on the `instantiatior` that should be used ad-hoc
///
pub fn gen_flat_lower_fn_js_expr(
    instantiator: &mut Instantiator,
    ty: &InterfaceType,
    extra_resource_map: &Option<&mut ResourceMap>,
) -> String {
    let component_types = instantiator.types;
    match ty {
        InterfaceType::Bool => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatBool));
            Intrinsic::Lower(LowerIntrinsic::LowerFlatBool)
                .name()
                .into()
        }

        InterfaceType::S8 => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatS8));
            Intrinsic::Lower(LowerIntrinsic::LowerFlatS8).name().into()
        }

        InterfaceType::U8 => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatU8));
            Intrinsic::Lower(LowerIntrinsic::LowerFlatU8).name().into()
        }

        InterfaceType::S16 => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatS16));
            Intrinsic::Lower(LowerIntrinsic::LowerFlatS16).name().into()
        }

        InterfaceType::U16 => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatU16));
            Intrinsic::Lower(LowerIntrinsic::LowerFlatU16).name().into()
        }

        InterfaceType::S32 => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatS32));
            Intrinsic::Lower(LowerIntrinsic::LowerFlatS32).name().into()
        }

        InterfaceType::U32 => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatU32));
            Intrinsic::Lower(LowerIntrinsic::LowerFlatU32).name().into()
        }

        InterfaceType::S64 => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatS64));
            Intrinsic::Lower(LowerIntrinsic::LowerFlatS64).name().into()
        }

        InterfaceType::U64 => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatU64));
            Intrinsic::Lower(LowerIntrinsic::LowerFlatU64).name().into()
        }

        InterfaceType::Float32 => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatFloat32));
            Intrinsic::Lower(LowerIntrinsic::LowerFlatFloat32)
                .name()
                .into()
        }

        InterfaceType::Float64 => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatFloat64));
            Intrinsic::Lower(LowerIntrinsic::LowerFlatFloat64)
                .name()
                .into()
        }

        InterfaceType::Char => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatChar));
            Intrinsic::Lower(LowerIntrinsic::LowerFlatChar)
                .name()
                .into()
        }

        InterfaceType::String => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatStringAny));
            Intrinsic::Lower(LowerIntrinsic::LowerFlatStringAny)
                .name()
                .into()
        }

        InterfaceType::Record(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatRecord));
            let lower_fn = Intrinsic::Lower(LowerIntrinsic::LowerFlatRecord).name();
            let record_ty = &component_types[*ty_idx];
            let size32 = record_ty.abi.size32;
            let align32 = record_ty.abi.align32;
            let mut keys_and_lowers_expr = String::from("[");
            for f in &record_ty.fields {
                // For each field we build a list of [name, lowerFn, 32bit alignment]
                // so that the record lowering function (which is a higher level function)
                // can properly generate a function that lowers the fields.
                let field_abi = component_types.canonical_abi(&f.ty);
                let field_size32 = field_abi.size32;
                let field_align32 = field_abi.align32;
                keys_and_lowers_expr.push_str(&format!(
                    "['{}', {}, {}, {} ],",
                    f.name.to_lower_camel_case(),
                    gen_flat_lower_fn_js_expr(instantiator, &f.ty, &None),
                    field_size32,
                    field_align32,
                ));
            }
            keys_and_lowers_expr.push(']');
            format!(
                "{lower_fn}({{ fieldMetas: {keys_and_lowers_expr}, size32: {size32}, align32: {align32} }})"
            )
        }

        InterfaceType::Variant(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatVariant));
            let lower_fn = Intrinsic::Lower(LowerIntrinsic::LowerFlatVariant).name();
            let variant_ty = &component_types[*ty_idx];
            let variant_flat_count = flat_count_js_expr(&variant_ty.abi.flat_count);
            let size32 = variant_ty.abi.size32;
            let align32 = variant_ty.abi.align32;
            let payload_offset32 = variant_ty.info.payload_offset32;

            let mut lower_metas_expr = String::from("[");
            for (name, maybe_ty) in variant_ty.cases.iter() {
                let (case_size32, case_align32, case_flat_count) = if let Some(iface_ty) = maybe_ty
                {
                    let cabi_info = component_types.canonical_abi(iface_ty);
                    (
                        cabi_info.size32.to_string(),
                        cabi_info.align32.to_string(),
                        cabi_info
                            .flat_count(MAX_FLAT_PARAMS)
                            .map(|v| v.to_string())
                            .unwrap_or_else(|| "null".into()),
                    )
                } else {
                    ("0".into(), "0".into(), "0".into())
                };

                lower_metas_expr.push_str(&format!(
                    "[ '{name}', {}, {case_size32}, {case_align32}, {case_flat_count} ],",
                    maybe_ty
                        .map(|ty| gen_flat_lower_fn_js_expr(instantiator, &ty, &None))
                        .unwrap_or_else(|| "null".into()),
                ));
            }
            lower_metas_expr.push(']');

            format!(
                "{lower_fn}({{
                     caseMetas: {lower_metas_expr},
                     variantSize32: {size32},
                     variantAlign32: {align32},
                     variantPayloadOffset32: {payload_offset32},
                     variantFlatCount: {variant_flat_count},
                 }} )"
            )
        }

        InterfaceType::List(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatList));
            let f = Intrinsic::Lower(LowerIntrinsic::LowerFlatList).name();
            let list_ty = &component_types[*ty_idx];
            let elem_ty_lower_expr =
                gen_flat_lower_fn_js_expr(instantiator, &list_ty.element, extra_resource_map);
            let elem_cabi = component_types.canonical_abi(&list_ty.element);
            let elem_align32 = elem_cabi.align32;
            let elem_size32 = elem_cabi.size32;

            format!(
                "{f}({{
                elemLowerFn: {elem_ty_lower_expr},
                elemSize32: {elem_size32},
                elemAlign32: {elem_align32},
            }})"
            )
        }

        InterfaceType::FixedLengthList(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatList));
            let f = Intrinsic::Lower(LowerIntrinsic::LowerFlatList).name();
            let list_ty = &component_types[*ty_idx];
            let elem_ty_lower_expr =
                gen_flat_lower_fn_js_expr(instantiator, &list_ty.element, extra_resource_map);
            let list_len = list_ty.size;
            let list_align32 = list_ty.abi.size32;
            let list_size32 = list_ty.abi.size32;
            let elem_cabi = component_types.canonical_abi(&list_ty.element);
            let elem_align32 = elem_cabi.align32;
            let elem_size32 = elem_cabi.size32;

            format!(
                r#"{f}({{
                       elemLowerFn: {elem_ty_lower_expr},
                       elemAlign32: {elem_align32},
                       elemSize32: {elem_size32},
                       align32: {list_align32},
                       size32: {list_size32},
                       knownLen: {list_len},
                   }})"#
            )
        }

        InterfaceType::Tuple(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatTuple));
            let f = Intrinsic::Lower(LowerIntrinsic::LowerFlatTuple).name();
            let tuple_ty = &component_types[*ty_idx];
            let size_u32 = tuple_ty.abi.size32;
            let align_u32 = tuple_ty.abi.align32;

            let mut elem_lowers_expr = String::from("[");
            for ty in &tuple_ty.types {
                let lower_fn_js = gen_flat_lower_fn_js_expr(instantiator, ty, extra_resource_map);
                let elem_abi = component_types.canonical_abi(ty);
                let elem_size32 = elem_abi.size32;
                let elem_align32 = elem_abi.align32;
                elem_lowers_expr
                    .push_str(&format!("[{lower_fn_js}, {elem_size32}, {elem_align32}],"));
            }
            elem_lowers_expr.push(']');

            format!(
                "{f}({{ elemLowerMetas: {elem_lowers_expr}, size32: {size_u32}, align32: {align_u32} }})"
            )
        }

        InterfaceType::Flags(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatFlags));
            let f = Intrinsic::Lower(LowerIntrinsic::LowerFlatFlags).name();
            let flags_ty = &component_types[*ty_idx];
            let size32 = flags_ty.abi.size32;
            let align32 = flags_ty.abi.align32;
            let names_list_js = format!(
                "[{}]",
                flags_ty
                    .names
                    .iter()
                    .map(|s| format!("'{}'", s.to_lower_camel_case()))
                    .collect::<Vec<_>>()
                    .join(",")
            );
            let num_flags = flags_ty.names.len();
            let elem_size = if num_flags <= 8 {
                1
            } else if num_flags <= 16 {
                2
            } else {
                4
            };

            format!(
                "{f}({{ names: {names_list_js}, size32: {size32}, align32: {align32}, intSizeBytes: {elem_size} }})"
            )
        }

        InterfaceType::Enum(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatEnum));
            let f = Intrinsic::Lower(LowerIntrinsic::LowerFlatEnum).name();
            let enum_ty = &component_types[*ty_idx];
            let enum_size32 = enum_ty.abi.size32;
            let enum_align32 = enum_ty.abi.align32;
            let enum_flat_count = flat_count_js_expr(&enum_ty.abi.flat_count);
            let enum_payload_offset32 = enum_ty.info.payload_offset32;

            let mut elem_lowers_expr = String::from("[");
            for name in &enum_ty.names {
                elem_lowers_expr.push_str(&format!(
                    "['{name}', null, {enum_size32}, {enum_align32}, {enum_payload_offset32}],"
                ));
            }
            elem_lowers_expr.push(']');

            format!(
                r#"
                  {f}({{
                       caseMetas: {elem_lowers_expr},
                       variantSize32: {enum_size32},
                       variantAlign32: {enum_align32},
                       variantPayloadOffset32: {enum_payload_offset32},
                       variantFlatCount: {enum_flat_count},
                  }})
                "#
            )
        }

        InterfaceType::Option(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatOption));
            let f = Intrinsic::Lower(LowerIntrinsic::LowerFlatOption).name();
            let option_ty = &component_types[*ty_idx];
            let option_size32 = option_ty.abi.size32;
            let option_align32 = option_ty.abi.align32;
            let option_payload_offset32 = option_ty.info.payload_offset32;
            let option_flat_count = flat_count_js_expr(&option_ty.abi.flat_count);

            let some_ty_abi = component_types.canonical_abi(&option_ty.ty);
            let some_ty_flat_count = flat_count_js_expr(&some_ty_abi.flat_count);
            let some_ty_size32 = some_ty_abi.size32;
            let some_ty_align32 = some_ty_abi.align32;
            let some_ty_lower_fn_js =
                gen_flat_lower_fn_js_expr(instantiator, &option_ty.ty, extra_resource_map);

            format!(
                r#"
                  {f}({{
                       caseMetas: [
                           [ 'none', null, 0, 0, 0 ],
                           [ 'some', {some_ty_lower_fn_js}, {some_ty_size32}, {some_ty_align32}, {some_ty_flat_count}],
                       ],
                       variantSize32: {option_size32},
                       variantAlign32: {option_align32},
                       variantPayloadOffset32: {option_payload_offset32},
                       variantFlatCount: {option_flat_count},
                   }})
                "#
            )
        }

        InterfaceType::Result(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatResult));
            let lower_fn = Intrinsic::Lower(LowerIntrinsic::LowerFlatResult).name();
            let result_ty = &component_types[*ty_idx];
            let result_size32 = result_ty.abi.size32;
            let result_align32 = result_ty.abi.align32;
            let result_payload_offset32 = result_ty.info.payload_offset32;
            let result_flat_count = flat_count_js_expr(&result_ty.abi.flat_count);

            let ok_lower_fn_js = result_ty
                .ok
                .map(|ty| gen_flat_lower_fn_js_expr(instantiator, &ty, extra_resource_map))
                .unwrap_or_else(|| "null".into());
            let err_lower_fn_js = result_ty
                .err
                .map(|ty| gen_flat_lower_fn_js_expr(instantiator, &ty, extra_resource_map))
                .unwrap_or_else(|| "null".into());

            format!(
                r#"
                   {lower_fn}({{
                       caseMetas: [
                           [ 'ok', {ok_lower_fn_js}, {result_size32}, {result_align32}, {result_payload_offset32} ],
                           [ 'err', {err_lower_fn_js}, {result_size32}, {result_align32}, {result_payload_offset32} ],
                       ],
                       variantSize32: {result_size32},
                       variantAlign32: {result_align32},
                       variantPayloadOffset32: {result_payload_offset32},
                       variantFlatCount: {result_flat_count},
                   }})
                "#
            )
        }

        InterfaceType::Own(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatOwn));
            let f = Intrinsic::Lower(LowerIntrinsic::LowerFlatOwn).name();
            let resource_table_ty = &component_types[*ty_idx];
            let component_idx = resource_table_ty.unwrap_concrete_instance().as_u32();
            let resource_idx = resource_table_ty.unwrap_concrete_ty();

            // Retrieve resource information for the given resource, looking
            // in both the extra resource map and the instantiator's dedicated resource-to-imports/
            // exports maps.
            let (_, ResourceTable { imported, data }) = match (
                instantiator.imports_resource_index_types.get(&resource_idx),
                instantiator.exports_resource_index_types.get(&resource_idx),
            ) {
                (Some(import_ty_id), _) => {
                    let ty = crate::dealias(instantiator.resolve, *import_ty_id);
                    let maybe_resource_table =
                        instantiator.resource_imports.get(&ty).or(extra_resource_map
                            .as_ref()
                            .and_then(|m| m.get(import_ty_id)));
                    (
                        ty,
                        maybe_resource_table.expect("missing imported resource table information"),
                    )
                }
                (_, Some(export_ty_id)) => {
                    let ty = crate::dealias(instantiator.resolve, *export_ty_id);
                    let maybe_resource_table =
                        instantiator.resource_exports.get(&ty).or(extra_resource_map
                            .as_ref()
                            .and_then(|m| m.get(export_ty_id)));
                    (
                        ty,
                        maybe_resource_table.expect("missing exported resource table information"),
                    )
                }

                // If resource was not found in the index type map at all, we're missing resource metadata.
                (None, None) => {
                    return format!(
                        "{f}({{
                             componentIdx: {component_idx},
                             lowerFn: () => {{ throw new Error('missing/invalid resource metadata'); }}
                         }})"
                    );
                }
            };

            // Build the function to create the resource, depending on how it was provided
            let lower_fn_js = match data {
                // If the resource was provided by the host, build the function to create it.
                ResourceData::Host {
                    tid,
                    rid,
                    local_name,
                    ..
                } => {
                    let tid = tid.as_u32();
                    let rid = rid.as_u32();
                    let symbol_resource_rep =
                        instantiator.bindgen.intrinsic(Intrinsic::SymbolResourceRep);
                    let symbol_resource_handle = instantiator
                        .bindgen
                        .intrinsic(Intrinsic::SymbolResourceHandle);
                    let symbol_dispose = instantiator.bindgen.intrinsic(Intrinsic::SymbolDispose);

                    if *imported {
                        // If imported (and from the host), we must ensure that the incoming object is of the right
                        // instance, then add it to the capture table w/ the right resource ID,
                        let create_own_fn = instantiator.bindgen.intrinsic(Intrinsic::Resource(
                            ResourceIntrinsic::ResourceTableCreateOwn,
                        ));
                        format!(
                            r#"
                              function lowerImportedOwnedHost_{local_name}(obj) {{
                                  if (!(obj instanceof {local_name})) {{
                                      throw new TypeError('Resource error: Not a valid \"{local_name}\" resource.');
                                  }}
                                  let handle = obj[{symbol_resource_handle}];
                                  if (!handle) {{
                                    const rep = obj[{symbol_resource_rep}] || ++captureCnt{rid};
                                    captureTable{rid}.set(rep, obj);
                                    handle = {create_own_fn}(handleTable{tid}, rep);
                                  }}
                                  return handle;
                              }}
                            "#
                        )
                    } else {
                        // If the resource was not imported (and came from the host), it comes from the component receiving it,
                        // and the object should already have a handle associated inside of it (the component must have created it).
                        //
                        // We disconnect the external connections for dispose and remove the external
                        // facing resource handle that was added when lifted out.
                        let empty_func = instantiator
                            .bindgen
                            .intrinsic(Intrinsic::JsHelper(JsHelperIntrinsic::EmptyFunc));
                        format!(
                            r#"
                               function lowerExportedOwnedHost_{local_name}(obj) {{
                                   let handle = obj[{symbol_resource_handle}];
                                   if (!handle) {{
                                       throw new TypeError('Resource error: Not a valid \"{local_name}\" resource.');
                                   }}
                                   finalizationRegistry{tid}.unregister(obj);
                                   obj[{symbol_dispose}] = {empty_func};
                                   obj[{symbol_resource_handle}] = undefined;
                                   return handle;
                               }}
                        "#
                        )
                    }
                }

                // If the resource was provided by the guest, build the function to create it.
                ResourceData::Guest {
                    resource_name,
                    prefix,
                    extra,
                } => {
                    assert!(
                        extra.is_none(),
                        "plain resource handles do not carry extra data"
                    );

                    let upper_camel = resource_name.to_upper_camel_case();
                    let lower_camel = resource_name.to_lower_camel_case();
                    let prefix = prefix.as_deref().unwrap_or("");

                    if *imported {
                        // If we get a resource that is provided by the host, then
                        // it should already have an external-facing resource handle on it.
                        let symbol_resource_handle = instantiator
                            .bindgen
                            .intrinsic(Intrinsic::SymbolResourceHandle);
                        format!(
                            r#"
                              function lowerImportedOwnedGuest_{upper_camel}(obj) {{
                                  const handle = obj[{symbol_resource_handle}];
                                  finalizationRegistry_import${prefix}{lower_camel}.unregister(obj);
                                  return handle;
                              }}
                            "#
                        )
                    } else {
                        // If we get a resource that was exported by the guest and is being lowered in,
                        // we can check that the object is of the right kidn of instance, and
                        // create rep for it if one does not already exist.
                        let symbol_resource_handle = instantiator
                            .bindgen
                            .intrinsic(Intrinsic::SymbolResourceHandle);
                        format!(
                            r#"
                              function lowerExportedOwnedGuest_{upper_camel}(obj) {{
                                  if (!(obj instanceof {upper_camel})) {{
                                    throw new TypeError('Resource error: Not a valid \"{upper_camel}\" resource.');
                                  }}
                                  let handle = obj[{symbol_resource_handle}];
                                  if (handle === undefined) {{
                                      const localRep = repCnt++;
                                      repTable.set(localRep, {{ rep: obj, own: true }});
                                      handle = $resource_{prefix}new${lower_camel}(localRep);
                                      obj[{symbol_resource_handle}] = handle;
                                      finalizationRegistry_export${prefix}{lower_camel}.register(obj, handle, obj);
                                  }}
                                  return handle;
                              }}
                            "#
                        )
                    }
                }
            };

            format!(
                "{f}({{
                     componentIdx: {component_idx},
                     lowerFn: {lower_fn_js},
                 }})"
            )
        }

        InterfaceType::Borrow(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatBorrow));
            let table_idx = ty_idx.as_u32();
            let f = Intrinsic::Lower(LowerIntrinsic::LowerFlatBorrow).name();
            format!("{f}.bind(null, {table_idx})")
        }

        InterfaceType::Future(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatFuture));
            let f = Intrinsic::Lower(LowerIntrinsic::LowerFlatFuture).name();
            let table_idx = ty_idx.as_u32();
            let table_ty = &component_types[*ty_idx];
            let component_idx = table_ty.instance.as_u32();
            let future_ty_idx = table_ty.ty;
            let future_ty = &component_types[future_ty_idx];
            let payload = future_ty.payload;
            let payload_ty_name_js = future_ty
                .payload
                .map(|iface_ty| format!("'{iface_ty:?}'"))
                .unwrap_or_else(|| "null".into());

            // Gather element metadata
            let (
                payload_size32,
                payload_align32,
                payload_flat_count_js,
                payload_lift_fn_js,
                payload_lower_fn_js,
                is_borrowed,
                is_none_type,
                is_numeric_type,
                is_async_value,
            ) = match payload {
                None => (
                    0,
                    0,
                    "0".into(),
                    "() => {{ throw new Error('empty future payload'); }}".into(),
                    "() => {{ throw new Error('empty future payload'); }}".into(),
                    false,
                    true,
                    false,
                    false,
                ),
                Some(payload_ty) => {
                    let cabi = instantiator.types.canonical_abi(&payload_ty);
                    (
                        cabi.size32,
                        cabi.align32,
                        cabi.flat_count
                            .map(|v| format!("{v}"))
                            .unwrap_or_else(|| "null".into()),
                        gen_flat_lift_fn_js_expr(instantiator, &payload_ty, extra_resource_map),
                        gen_flat_lower_fn_js_expr(instantiator, &payload_ty, extra_resource_map),
                        matches!(payload_ty, InterfaceType::Borrow(_)),
                        false,
                        matches!(
                            payload_ty,
                            InterfaceType::U8
                                | InterfaceType::U16
                                | InterfaceType::U32
                                | InterfaceType::U64
                                | InterfaceType::S8
                                | InterfaceType::S16
                                | InterfaceType::S32
                                | InterfaceType::S64
                                | InterfaceType::Float32
                                | InterfaceType::Float64
                        ),
                        matches!(
                            payload_ty,
                            InterfaceType::Stream(_) | InterfaceType::Future(_)
                        ),
                    )
                }
            };

            // Determine the level of future nesting
            let mut future_nesting_level = 0;
            let mut payload_ty = future_ty.payload;
            while let Some(InterfaceType::Future(inner_ty)) = payload_ty {
                future_nesting_level += 1;
                payload_ty = component_types[component_types[inner_ty].ty].payload;
            }

            format!(
                r#"{f}.bind(null, {{
                       futureTableIdx: {table_idx},
                       futureNestingLevel: {future_nesting_level},
                       componentIdx: {component_idx},
                       elemMeta: {{
                           liftFn: {payload_lift_fn_js},
                           lowerFn: {payload_lower_fn_js},
                           payloadTypeName: {payload_ty_name_js},
                           isNone: {is_none_type},
                           isNumeric: {is_numeric_type},
                           isBorrowed: {is_borrowed},
                           isAsyncValue: {is_async_value},
                           flatCount: {payload_flat_count_js},
                           align32: {payload_align32},
                           size32: {payload_size32},
                       }},
                   }})
                "#
            )
        }

        InterfaceType::Stream(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatStream));
            let table_idx = ty_idx.as_u32();
            let f = Intrinsic::Lower(LowerIntrinsic::LowerFlatStream).name();
            let table_ty = &component_types[*ty_idx];
            let component_idx = table_ty.instance.as_u32();
            let stream_ty_idx = table_ty.ty;
            let stream_ty = &component_types[stream_ty_idx];
            let payload = stream_ty.payload;
            let payload_ty_name_js = stream_ty
                .payload
                .map(|iface_ty| format!("'{iface_ty:?}'"))
                .unwrap_or_else(|| "null".into());

            // TODO(fix): payload u8 should be special cased here

            let (
                payload_size32,
                payload_align32,
                payload_flat_count_js,
                payload_lift_fn_js,
                payload_lower_fn_js,
                is_borrowed,
                is_none_type,
                is_numeric_type,
                is_async_value,
                typed_array_js,
            ) = match payload {
                None => (
                    0,
                    0,
                    "0".into(),
                    "() => {{ throw new Error('empty stream payload'); }}".into(),
                    "() => {{ throw new Error('empty stream payload'); }}".into(),
                    false,
                    true,
                    false,
                    false,
                    "undefined",
                ),
                Some(payload_ty) => {
                    let cabi = instantiator.types.canonical_abi(&payload_ty);
                    (
                        cabi.size32,
                        cabi.align32,
                        cabi.flat_count
                            .map(|v| format!("{v}"))
                            .unwrap_or_else(|| "null".into()),
                        gen_flat_lift_fn_js_expr(instantiator, &payload_ty, extra_resource_map),
                        gen_flat_lower_fn_js_expr(instantiator, &payload_ty, extra_resource_map),
                        matches!(payload_ty, InterfaceType::Borrow(_)),
                        false,
                        matches!(
                            payload_ty,
                            InterfaceType::U8
                                | InterfaceType::U16
                                | InterfaceType::U32
                                | InterfaceType::U64
                                | InterfaceType::S8
                                | InterfaceType::S16
                                | InterfaceType::S32
                                | InterfaceType::S64
                                | InterfaceType::Float32
                                | InterfaceType::Float64
                        ),
                        matches!(
                            payload_ty,
                            InterfaceType::Stream(_) | InterfaceType::Future(_)
                        ),
                        js_typed_array_ctor(&payload_ty).unwrap_or("undefined"),
                    )
                }
            };

            format!(
                r#"{f}({{
                       streamTableIdx: {table_idx},
                       componentIdx: {component_idx},
                       elemMeta: {{
                           liftFn: {payload_lift_fn_js},
                           lowerFn: {payload_lower_fn_js},
                           payloadTypeName: {payload_ty_name_js},
                           isNone: {is_none_type},
                           isNumeric: {is_numeric_type},
                           isBorrowed: {is_borrowed},
                           isAsyncValue: {is_async_value},
                           typedArray: {typed_array_js},
                           flatCount: {payload_flat_count_js},
                           align32: {payload_align32},
                           size32: {payload_size32},
                       }},
                   }})
                "#
            )
        }

        InterfaceType::ErrorContext(ty_idx) => {
            instantiator.add_intrinsic(Intrinsic::Lower(LowerIntrinsic::LowerFlatErrorContext));
            let table_idx = ty_idx.as_u32();
            let lower_flat_err_ctx_fn =
                Intrinsic::Lower(LowerIntrinsic::LowerFlatErrorContext).name();
            format!("{lower_flat_err_ctx_fn}.bind(null, {table_idx})")
        }

        InterfaceType::Map(_) => unimplemented!("map support"),
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    /// Helper to extract just the compat key string for cleaner test assertions.
    fn compat_key(version_str: &str) -> Option<String> {
        semver_compat_key(version_str).map(|(key, _)| key)
    }

    #[test]
    fn test_semver_compat_key() {
        assert_eq!(compat_key("1.0.0"), Some("1".into()));
        assert_eq!(compat_key("1.2.3"), Some("1".into()));
        assert_eq!(compat_key("2.0.0"), Some("2".into()));
        assert_eq!(compat_key("0.2.0"), Some("0.2".into()));
        assert_eq!(compat_key("0.2.10"), Some("0.2".into()));
        assert_eq!(compat_key("0.1.0"), Some("0.1".into()));
        assert_eq!(compat_key("0.0.1"), None);
        assert_eq!(compat_key("1.0.0-rc.1"), None);
        assert_eq!(compat_key("0.2.0-pre"), None);
        assert_eq!(compat_key("not-a-version"), None);
    }

    #[test]
    fn test_semver_compat_key_returns_parsed_version() {
        let (key, ver) = semver_compat_key("1.2.3").unwrap();
        assert_eq!(key, "1");
        assert_eq!(ver, Version::new(1, 2, 3));
    }

    #[test]
    fn test_map_import_exact_match() {
        let mut map = HashMap::new();
        map.insert("wasi:http/types@0.2.0".into(), "./http.js#types".into());
        let map = Some(map);
        assert_eq!(
            map_import(&map, "wasi:http/types@0.2.0"),
            ("./http.js".into(), Some("types".into()))
        );
    }

    #[test]
    fn test_map_import_sans_version_match() {
        let mut map = HashMap::new();
        map.insert("wasi:http/types".into(), "./http.js".into());
        let map = Some(map);
        assert_eq!(
            map_import(&map, "wasi:http/types@0.2.10"),
            ("./http.js".into(), None)
        );
    }

    #[test]
    fn test_map_import_wildcard_sans_version() {
        // Unversioned wildcard key matches via version-stripped path (pre-existing logic)
        let mut map = HashMap::new();
        map.insert("wasi:http/*".into(), "./http.js#*".into());
        let map = Some(map);
        assert_eq!(
            map_import(&map, "wasi:http/types@0.2.10"),
            ("./http.js".into(), Some("types".into()))
        );
    }

    #[test]
    fn test_map_import_semver_exact_key() {
        // Map has @0.2.0, import is @0.2.10 — should match via semver
        let mut map = HashMap::new();
        map.insert("wasi:http/types@0.2.0".into(), "./http.js".into());
        let map = Some(map);
        assert_eq!(
            map_import(&map, "wasi:http/types@0.2.10"),
            ("./http.js".into(), None)
        );
    }

    #[test]
    fn test_map_import_semver_wildcard_key() {
        // Map has wasi:http/*@0.2.0, import is @0.2.10 — should match via semver
        let mut map = HashMap::new();
        map.insert("wasi:http/*@0.2.1".into(), "./http.js#*".into());
        let map = Some(map);
        assert_eq!(
            map_import(&map, "wasi:http/types@0.2.10"),
            ("./http.js".into(), Some("types".into()))
        );
    }

    #[test]
    fn test_map_import_semver_lower_import_version() {
        // Import version (0.2.1) is lower than map entry (0.2.10) — same compat track
        let mut map = HashMap::new();
        map.insert("wasi:http/types@0.2.10".into(), "./http.js".into());
        let map = Some(map);
        assert_eq!(
            map_import(&map, "wasi:http/types@0.2.1"),
            ("./http.js".into(), None)
        );
    }

    #[test]
    fn test_map_import_semver_no_cross_minor() {
        // 0.2.x should NOT match 0.3.x
        let mut map = HashMap::new();
        map.insert("wasi:http/types@0.3.0".into(), "./http.js".into());
        let map = Some(map);
        assert_eq!(
            map_import(&map, "wasi:http/types@0.2.10"),
            ("wasi:http/types".into(), None)
        );
    }

    #[test]
    fn test_map_import_semver_prefers_highest() {
        // Multiple compatible versions — should prefer highest
        let mut map = HashMap::new();
        map.insert("wasi:http/types@0.2.1".into(), "./http-old.js".into());
        map.insert("wasi:http/types@0.2.5".into(), "./http-new.js".into());
        let map = Some(map);
        assert_eq!(
            map_import(&map, "wasi:http/types@0.2.10"),
            ("./http-new.js".into(), None)
        );
    }

    #[test]
    fn test_map_import_no_match_prerelease() {
        let mut map = HashMap::new();
        map.insert("wasi:http/types@0.2.0-rc.1".into(), "./http.js".into());
        let map = Some(map);
        assert_eq!(
            map_import(&map, "wasi:http/types@0.2.0"),
            ("wasi:http/types".into(), None)
        );
    }

    #[test]
    fn test_map_import_prerelease_versioned_wildcard_wins_over_unversioned_wildcard() {
        // p3 imports (pre-release version) must route to the
        // version-pinned wildcard, not the unversioned p2 fallback.
        let mut map = HashMap::new();
        map.insert(
            "wasi:cli/*".into(),
            "@bytecodealliance/preview2-shim/cli#*".into(),
        );
        map.insert(
            "wasi:cli/*@0.3.0".into(),
            "@bytecodealliance/preview3-shim/cli#*".into(),
        );
        let map = Some(map);
        assert_eq!(
            map_import(&map, "wasi:cli/stdout@0.3.0"),
            (
                "@bytecodealliance/preview3-shim/cli".into(),
                Some("stdout".into())
            )
        );
        // Same map, p2 import should still resolve to preview2-shim.
        assert_eq!(
            map_import(&map, "wasi:cli/stdout@0.2.6"),
            (
                "@bytecodealliance/preview2-shim/cli".into(),
                Some("stdout".into())
            )
        );
        // Unversioned import should also flow to p2.
        assert_eq!(
            map_import(&map, "wasi:cli/stdout"),
            (
                "@bytecodealliance/preview2-shim/cli".into(),
                Some("stdout".into())
            )
        );
    }

    #[test]
    fn test_map_import_no_match_zero_zero() {
        let mut map = HashMap::new();
        map.insert("wasi:http/types@0.0.1".into(), "./http.js".into());
        let map = Some(map);
        assert_eq!(
            map_import(&map, "wasi:http/types@0.0.2"),
            ("wasi:http/types".into(), None)
        );
    }

    #[test]
    fn test_map_import_semver_major_version() {
        // Major version compat: 1.0.0 and 1.2.3 share compat key "1"
        let mut map = HashMap::new();
        map.insert("wasi:http/types@1.0.0".into(), "./http.js".into());
        let map = Some(map);
        assert_eq!(
            map_import(&map, "wasi:http/types@1.2.3"),
            ("./http.js".into(), None)
        );
    }

    #[test]
    fn test_map_import_semver_no_cross_major() {
        // 1.x.y should NOT match 2.x.y
        let mut map = HashMap::new();
        map.insert("wasi:http/types@1.0.0".into(), "./http.js".into());
        let map = Some(map);
        assert_eq!(
            map_import(&map, "wasi:http/types@2.0.0"),
            ("wasi:http/types".into(), None)
        );
    }

    #[test]
    fn test_map_import_no_map() {
        // No map provided — returns import sans version
        assert_eq!(
            map_import(&None, "wasi:http/types@0.2.0"),
            ("wasi:http/types".into(), None)
        );
    }

    #[test]
    fn test_map_import_no_map_unversioned() {
        // No map, no version — returns import as-is
        assert_eq!(
            map_import(&None, "wasi:http/types"),
            ("wasi:http/types".into(), None)
        );
    }

    #[test]
    fn test_parse_mapping_with_hash() {
        assert_eq!(
            parse_mapping("./http.js#types"),
            ("./http.js".into(), Some("types".into()))
        );
    }

    #[test]
    fn test_parse_mapping_without_hash() {
        assert_eq!(parse_mapping("./http.js"), ("./http.js".into(), None));
    }

    #[test]
    fn test_parse_mapping_leading_hash() {
        // Leading '#' should not be treated as a separator
        assert_eq!(parse_mapping("#foo"), ("#foo".into(), None));
    }

    #[test]
    fn test_parse_mapping_empty() {
        assert_eq!(parse_mapping(""), ("".into(), None));
    }
}