js_component_bindgen/

transpile_bindgen.rs

use crate::core;
use crate::esm_bindgen::EsmBindgen;
use crate::files::Files;
use crate::function_bindgen::{
    ErrHandling, FunctionBindgen, ResourceData, ResourceMap, ResourceTable,
};
use crate::intrinsics::{render_intrinsics, Intrinsic};
use crate::names::{is_js_reserved_word, maybe_quote_id, maybe_quote_member, LocalNames};
use crate::source;
use crate::{uwrite, uwriteln};
use base64::{engine::general_purpose, Engine as _};
use heck::*;
use std::cell::RefCell;
use std::collections::{BTreeMap, BTreeSet, HashMap};
use std::fmt::Write;
use std::mem;
use wasmtime_environ::component::{ExportIndex, NameMap, NameMapNoIntern, Transcode};
use wasmtime_environ::{
    component,
    component::{
        CanonicalOptions, Component, ComponentTranslation, ComponentTypes, CoreDef, CoreExport,
        Export, ExportItem, FixedEncoding, GlobalInitializer, InstantiateModule, InterfaceType,
        LoweredIndex, ResourceIndex, RuntimeComponentInstanceIndex, RuntimeImportIndex,
        RuntimeInstanceIndex, StaticModuleIndex, Trampoline, TrampolineIndex, TypeDef,
        TypeFuncIndex, TypeResourceTableIndex,
    },
    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, SizeAlign, Type, TypeDefKind, TypeId, WorldId,
    WorldItem, WorldKey,
};

#[derive(Default, Clone)]
pub struct TranspileOpts {
    pub name: String,
    /// Disables generation of `*.d.ts` files and instead only generates `*.js`
    /// source files.
    pub no_typescript: bool,
    /// Provide a custom JS instantiation API for the component instead
    /// of the direct importable native ESM output.
    pub instantiation: 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.
    pub no_nodejs_compat: bool,
    /// Set the cutoff byte size for base64 inlining core Wasm in instantiation mode
    /// (set to 0 to disable all base64 inlining)
    pub base64_cutoff: usize,
    /// Enables compatibility for JS environments without top-level await support
    /// via an async $init promise export to wait for instead.
    pub tla_compat: bool,
    /// Disable verification of component Wasm data structures when
    /// lifting as a production optimization
    pub valid_lifting_optimization: bool,
    /// Whether or not to emit `tracing` calls on function entry/exit.
    pub tracing: bool,
    /// Whether to generate namespaced exports like `foo as "local:package/foo"`.
    /// These exports can break typescript builds.
    pub no_namespaced_exports: bool,
    /// Whether to output core Wasm utilizing multi-memory or to polyfill
    /// this handling.
    pub multi_memory: bool,
    /// Whether to generate types for a guest module using module declarations.
    pub guest: bool,
}

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

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

#[derive(Default, Clone, Debug)]
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>,
}

#[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, Export)>) {
    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(),
    };
    bindgen
        .local_names
        .exclude_globals(Intrinsic::get_global_names());
    bindgen.core_module_cnt = modules.len();

    // bindings is the actual `instantiate` method itself, created by this
    // structure.

    let mut instantiator = Instantiator {
        src: Source::default(),
        sizes: SizeAlign::default(),
        gen: &mut bindgen,
        modules,
        instances: Default::default(),
        resolve,
        world: id,
        translation: component,
        component: &component.component,
        types,
        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(),
        exports_resource_types: Default::default(),
        resources_initialized: (0..component.component.num_resources)
            .map(|_| false)
            .collect(),
        resource_tables_initialized: (0..component.component.num_resource_tables)
            .map(|_| false)
            .collect(),
    };
    instantiator.sizes.fill(resolve);
    instantiator.initialize();
    instantiator.instantiate();

    let mut intrinsic_definitions = source::Source::default();

    instantiator.resource_definitions(&mut intrinsic_definitions);
    instantiator.instance_flags();

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

    instantiator
        .gen
        .finish_component(name, files, &opts, intrinsic_definitions);

    let exports = instantiator
        .gen
        .esm_bindgen
        .exports()
        .iter()
        .map(|(export_name, canon_export_name)| {
            let export = if canon_export_name.contains(':') {
                instantiator
                    .component
                    .exports
                    .get(canon_export_name, &NameMapNoIntern)
                    .unwrap()
            } else {
                instantiator
                    .component
                    .exports
                    .get(&canon_export_name.to_kebab_case(), &NameMapNoIntern)
                    .unwrap()
            };
            (
                export_name.to_string(),
                instantiator.component.export_items[*export].clone(),
            )
        })
        .collect();

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

impl<'a> JsBindgen<'a> {
    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();

        // 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.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)
                );
            }
        }

        let js_intrinsics = render_intrinsics(
            &mut self.all_intrinsics,
            self.opts.no_nodejs_compat,
            self.opts.instantiation.is_some(),
        );

        if let Some(instantiation) = &self.opts.instantiation {
            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,
            );
        }

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

        if self.opts.instantiation.is_some() {
            self.esm_bindgen.render_exports(
                &mut self.src.js,
                self.opts.instantiation.is_some(),
                &mut self.local_names,
                opts,
            );
            uwrite!(
                output,
                "\
                        let gen = (function* init () {{
                            {}\
                            {};
                        }})();
                        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.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* init () {{
                            {}\
                            {}\
                        }})();
                        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,
            );

            self.esm_bindgen.render_exports(
                &mut output,
                self.opts.instantiation.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.
struct Instantiator<'a, 'b> {
    src: Source,
    gen: &'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,
    translation: &'a ComponentTranslation,
    exports_resource_types: BTreeMap<TypeId, ResourceIndex>,
    imports_resource_types: BTreeMap<TypeId, ResourceIndex>,
    resources_initialized: PrimaryMap<ResourceIndex, bool>,
    resource_tables_initialized: PrimaryMap<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>,
    lowering_options:
        PrimaryMap<LoweredIndex, (&'a CanonicalOptions, TrampolineIndex, TypeFuncIndex)>,
}

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!(),
                    WorldItem::Function(_) => unreachable!(),
                    WorldItem::Type(ty) => {
                        assert!(!matches!(
                            self.resolve.types[*ty].kind,
                            TypeDefKind::Resource
                        ))
                    }
                }
                continue;
            };
            match item {
                WorldItem::Interface { id, stability: _ } => {
                    let TypeDef::ComponentInstance(instance) = import else {
                        unreachable!()
                    };
                    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)) => {
                                let ty = crate::dealias(self.resolve, *ty);
                                let resource_idx = self.types[*resource].ty;
                                self.imports_resource_types.insert(ty, resource_idx);
                            }
                            Some(TypeDef::Interface(_)) | None => {}
                            Some(_) => unreachable!(),
                        }
                    }
                }
                WorldItem::Function(_) => {}
                WorldItem::Type(ty) => match import {
                    TypeDef::Resource(resource) => {
                        let ty = crate::dealias(self.resolve, *ty);
                        let resource_idx = self.types[*resource].ty;
                        self.imports_resource_types.insert(ty, resource_idx);
                    }
                    TypeDef::Interface(_) => {}
                    _ => unreachable!(),
                },
            }
        }
        self.exports_resource_types = self.imports_resource_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, stability: _ } => {
                    let iface = &self.resolve.interfaces[*id];
                    let Export::Instance { exports, .. } = &export else {
                        unreachable!()
                    };
                    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_idx = self.types[resource].ty;
                                self.exports_resource_types.insert(ty, resource_idx);
                            }
                            Export::Type(_) => {}
                            _ => unreachable!(),
                        }
                    }
                }
                WorldItem::Function(_) => {}
                WorldItem::Type(_) => unreachable!(),
            }
        }
    }
    fn instantiate(&mut self) {
        for (i, trampoline) in self.translation.trampolines.iter() {
            let Trampoline::LowerImport {
                index,
                lower_ty,
                options,
            } = trampoline
            else {
                continue;
            };
            let i = self.lowering_options.push((options, i, *lower_ty));
            assert_eq!(i, *index);
        }

        if let Some(InstantiationMode::Async) = self.gen.opts.instantiation {
            // 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(() => {{}});");
            }
        }

        // 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
        let mut lower_import_initializers = Vec::new();
        for init in self.component.initializers.iter() {
            match init {
                GlobalInitializer::InstantiateModule(_) => {
                    for init in lower_import_initializers.drain(..) {
                        self.instantiation_global_initializer(init);
                    }
                }
                GlobalInitializer::LowerImport { .. } => {
                    lower_import_initializers.push(init);
                    continue;
                }
                _ => {}
            }
            self.instantiation_global_initializer(init);
        }
        for init in lower_import_initializers.drain(..) {
            self.instantiation_global_initializer(init);
        }

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

        self.exports(&self.component.exports);

        // 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() {
            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, definitions: &mut source::Source) {
        // 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.gen.local_names.try_get(resource) {
                self.ensure_local_resource_class(local_name.to_string());
            }
        }

        // Write out the defined resource table indices for the runtime
        if self
            .gen
            .all_intrinsics
            .contains(&Intrinsic::ResourceTransferBorrow)
            || self
                .gen
                .all_intrinsics
                .contains(&Intrinsic::ResourceTransferBorrowValidLifting)
        {
            let defined_resource_tables = Intrinsic::DefinedResourceTables.name();
            uwrite!(definitions, "const {defined_resource_tables} = [");
            for tidx in 0..self.component.num_resource_tables {
                let tid = TypeResourceTableIndex::from_u32(tidx as u32);
                let rid = self.types[tid].ty;
                if let Some(defined_index) = self.component.defined_resource_index(rid) {
                    if self.types[tid].instance
                        == self.component.defined_resource_instances[defined_index]
                    {
                        uwrite!(definitions, "true,");
                    }
                } else {
                    uwrite!(definitions, ",");
                };
            }
            uwrite!(definitions, "];\n");
        }
    }

    // instead of always outputting resource tables for all resources, only
    // define resource tables that are explicitly used
    fn ensure_resource_table(&mut self, id: TypeResourceTableIndex) {
        if self.resource_tables_initialized[id] {
            return;
        }

        let resource = self.types[id].ty;

        let (is_imported, maybe_dtor) =
            if let Some(resource_idx) = self.component.defined_resource_index(resource) {
                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.gen.intrinsic(Intrinsic::HandleTables);
        let rsc_table_flag = self.gen.intrinsic(Intrinsic::ResourceTableFlag);
        let rsc_table_remove = self.gen.intrinsic(Intrinsic::ResourceTableRemove);

        let rtid = id.as_u32();
        if is_imported {
            uwriteln!(
                self.src.js,
                "const handleTable{rtid} = [{rsc_table_flag}, 0];",
            );
            if !self.resources_initialized[resource] {
                let ridx = resource.as_u32();
                uwriteln!(
                    self.src.js,
                    "const captureTable{ridx} = new Map();
                    let captureCnt{ridx} = 0;"
                );
                self.resources_initialized[resource] = true;
            }
        } else {
            let finalization_registry_create =
                self.gen.intrinsic(Intrinsic::FinalizationRegistryCreate);
            uwriteln!(
                self.src.js,
                "const handleTable{rtid} = [{rsc_table_flag}, 0];
                const finalizationRegistry{rtid} = {finalization_registry_create}((handle) => {{
                    const {{ rep }} = {rsc_table_remove}(handleTable{rtid}, handle);{maybe_dtor}
                }});
                ",
            );
        }
        uwriteln!(self.src.js, "{handle_tables}[{rtid}] = handleTable{rtid};");
        self.resource_tables_initialized[id] = 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
                | wasmtime_environ::component::FLAG_MAY_ENTER);
        }
        self.src.js_init.prepend_str(&instance_flag_defs);
    }

    fn trampoline(&mut self, i: TrampolineIndex, trampoline: &'a Trampoline) {
        let i = i.as_u32();
        match trampoline {
            // these are hoisted before initialization
            Trampoline::LowerImport { .. } => {}

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

            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,
                            "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 => unimplemented!("utf16 to utf8 transcoder"),
                    Transcode::Utf8ToCompactUtf16 => {
                        unimplemented!("utf8 to compact utf16 transcoder")
                    }
                    Transcode::Utf8ToLatin1 => unimplemented!("utf8 to latin1 transcoder"),
                    Transcode::Utf8ToUtf16 => unimplemented!("utf8 to utf16 transcoder"),
                };
            }

            Trampoline::ResourceNew(resource) => {
                self.ensure_resource_table(*resource);
                let rid = resource.as_u32();
                let rsc_table_create_own = self.gen.intrinsic(Intrinsic::ResourceTableCreateOwn);
                uwriteln!(
                    self.src.js,
                    "const trampoline{i} = {rsc_table_create_own}.bind(null, handleTable{rid});"
                );
            }
            Trampoline::ResourceRep(resource) => {
                self.ensure_resource_table(*resource);
                let rid = resource.as_u32();
                let rsc_flag = self.gen.intrinsic(Intrinsic::ResourceTableFlag);
                uwriteln!(
                    self.src.js,
                    "function trampoline{i} (handle) {{
                        return handleTable{rid}[(handle << 1) + 1] & ~{rsc_flag};
                    }}"
                );
            }
            Trampoline::ResourceDrop(resource) => {
                self.ensure_resource_table(*resource);
                let tid = resource.as_u32();
                let resource_ty = &self.types[*resource];
                let rid = resource_ty.ty.as_u32();
                let dtor = if let Some(resource_idx) =
                    self.component.defined_resource_index(resource_ty.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 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.gen.intrinsic(Intrinsic::SymbolDispose);
                    let symbol_cabi_dispose = self.gen.intrinsic(Intrinsic::SymbolCabiDispose);

                    // previous imports walk should define all imported resources which are accessible
                    if let Some(imported_resource_local_name) =
                        self.gen.local_names.try_get(resource_ty.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
                        "throw new TypeError('unreachable resource trampoline')".into()
                    }
                };

                let rsc_table_remove = self.gen.intrinsic(Intrinsic::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.gen.intrinsic(Intrinsic::ResourceTransferOwn);
                uwriteln!(self.src.js, "const trampoline{i} = {resource_transfer};");
            }
            Trampoline::ResourceTransferBorrow => {
                let resource_transfer =
                    self.gen
                        .intrinsic(if self.gen.opts.valid_lifting_optimization {
                            Intrinsic::ResourceTransferBorrowValidLifting
                        } else {
                            Intrinsic::ResourceTransferBorrow
                        });
                uwriteln!(self.src.js, "const trampoline{i} = {resource_transfer};");
            }
            Trampoline::ResourceEnterCall => {
                let scope_id = self.gen.intrinsic(Intrinsic::ScopeId);
                uwrite!(
                    self.src.js,
                    "function trampoline{i}() {{
                        {scope_id}++;
                    }}
                    ",
                );
            }
            Trampoline::ResourceExitCall => {
                let scope_id = self.gen.intrinsic(Intrinsic::ScopeId);
                let resource_borrows = self.gen.intrinsic(Intrinsic::ResourceCallBorrows);
                let handle_tables = self.gen.intrinsic(Intrinsic::HandleTables);
                // To verify that borrows are dropped, it is enough to verify that the handle
                // either no longer exists (part of free list) or belongs to another scope, since
                // the enter call closed off the ability to create new handles in the parent scope
                uwrite!(
                    self.src.js,
                    "function trampoline{i}() {{
                        {scope_id}--;
                        for (const {{ rid, handle }} of {resource_borrows}) {{
                            if ({handle_tables}[rid][handle << 1] === {scope_id})
                                throw new TypeError('borrows not dropped for resource call');
                        }}
                        {resource_borrows} = [];
                    }}
                    ",
                );
            }
        }
    }

    fn instantiation_global_initializer(&mut self, init: &GlobalInitializer) {
        match init {
            GlobalInitializer::InstantiateModule(m) => match m {
                InstantiateModule::Static(idx, args) => self.instantiate_static_module(*idx, args),
                // 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(&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_init, "realloc{idx} = {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_init, "postReturn{idx} = {def};");
            }
            GlobalInitializer::Resource(_) => {}
        }
    }

    fn instantiate_static_module(&mut self, idx: StaticModuleIndex, args: &[CoreDef]) {
        // 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[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());
        }
        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(idx);
        let iu32 = i.as_u32();
        let instantiate = self.gen.intrinsic(Intrinsic::InstantiateCore);
        uwriteln!(self.src.js, "let exports{iu32};");

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

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

    fn create_resource_fn_map(
        &mut self,
        func: &Function,
        ty_func_idx: TypeFuncIndex,
        resource_map: &mut ResourceMap,
    ) {
        let params_ty = &self.types[self.types[ty_func_idx].params];
        for ((_, ty), iface_ty) in func.params.iter().zip(params_ty.types.iter()) {
            if let Type::Id(id) = ty {
                self.connect_resource_types(*id, iface_ty, resource_map);
            }
        }
        let results_ty = &self.types[self.types[ty_func_idx].results];
        for (ty, iface_ty) in func.results.iter_types().zip(results_ty.types.iter()) {
            if let Type::Id(id) = ty {
                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];

        let (import_index, path) = &self.component.imports[import];
        let (import_name, _) = &self.component.import_types[*import_index];
        let world_key = &self.imports[import_name];

        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, stability: _ } => {
                    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!(),
            };

        // nested interfaces only currently possible through mapping
        let (import_specifier, maybe_iface_member) = map_import(
            &self.gen.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::Static(_) => {
                        let stripped = import_name.strip_prefix("[static]").unwrap();
                        &stripped[0..stripped.find(".").unwrap()]
                    }
                    FunctionKind::Constructor(_) => {
                        import_name.strip_prefix("[constructor]").unwrap()
                    }
                    FunctionKind::Freestanding => import_name,
                }
            },
        );

        let mut resource_map = ResourceMap::new();
        self.create_resource_fn_map(func, func_ty, &mut resource_map);

        let (callee_name, call_type) = match func.kind {
            FunctionKind::Freestanding => (
                self.gen
                    .local_names
                    .get_or_create(
                        format!(
                            "import:{}-{}-{}",
                            import_specifier,
                            maybe_iface_member.as_deref().unwrap_or(""),
                            &func.name
                        ),
                        &func.name,
                    )
                    .0
                    .to_string(),
                CallType::Standard,
            ),
            FunctionKind::Method(_) => (
                func.item_name().to_lower_camel_case(),
                CallType::CalleeResourceDispatch,
            ),
            FunctionKind::Static(resource_id) => (
                format!(
                    "{}.{}",
                    Instantiator::resource_name(
                        self.resolve,
                        &mut self.gen.local_names,
                        resource_id,
                        &self.imports_resource_types
                    ),
                    func.item_name().to_lower_camel_case()
                ),
                CallType::Standard,
            ),
            FunctionKind::Constructor(resource_id) => (
                format!(
                    "new {}",
                    Instantiator::resource_name(
                        self.resolve,
                        &mut self.gen.local_names,
                        resource_id,
                        &self.imports_resource_types
                    )
                ),
                CallType::Standard,
            ),
        };

        let nparams = self
            .resolve
            .wasm_signature(AbiVariant::GuestImport, func)
            .params
            .len();
        match self.gen.opts.import_bindings {
            None | Some(BindingsMode::Js) | Some(BindingsMode::Hybrid) => {
                uwrite!(self.src.js, "\nfunction trampoline{}", trampoline.as_u32());
                self.bindgen(
                    nparams,
                    call_type,
                    if import_name.is_empty() {
                        None
                    } else {
                        Some(import_name)
                    },
                    &callee_name,
                    options,
                    func,
                    &resource_map,
                    AbiVariant::GuestImport,
                );
                uwriteln!(self.src.js, "");
            }
            Some(BindingsMode::Optimized) | Some(BindingsMode::DirectOptimized) => {
                uwriteln!(self.src.js, "let trampoline{};", trampoline.as_u32());
            }
        };
        if !matches!(self.gen.opts.import_bindings, None | Some(BindingsMode::Js)) {
            let memory = options
                .memory
                .map(|idx| format!(" memory: memory{},", idx.as_u32()))
                .unwrap_or("".into());
            let realloc = options
                .realloc
                .map(|idx| format!(" realloc: realloc{},", idx.as_u32()))
                .unwrap_or("".into());
            let post_return = options
                .post_return
                .map(|idx| format!(" postReturn: postReturn{},", idx.as_u32()))
                .unwrap_or("".into());
            let string_encoding = match options.string_encoding {
                component::StringEncoding::Utf8 => "",
                component::StringEncoding::Utf16 => " stringEncoding: 'utf16',",
                component::StringEncoding::CompactUtf16 => " stringEncoding: 'compact-utf16',",
            };
            let callee_name = match func.kind {
                FunctionKind::Static(_) | FunctionKind::Freestanding => callee_name.to_string(),
                FunctionKind::Method(resource_id) => format!(
                    "{}.prototype.{callee_name}",
                    Instantiator::resource_name(
                        self.resolve,
                        &mut self.gen.local_names,
                        resource_id,
                        &self.imports_resource_types
                    )
                ),
                FunctionKind::Constructor(_) => callee_name[4..].to_string(),
            };
            let resource_tables = {
                let mut resource_tables: Vec<TypeResourceTableIndex> = Vec::new();

                for (_, data) in resource_map {
                    let ResourceTable {
                        data: ResourceData::Host { tid, .. },
                        ..
                    } = &data
                    else {
                        unreachable!();
                    };
                    resource_tables.push(*tid);
                }

                if resource_tables.is_empty() {
                    "".to_string()
                } else {
                    format!(
                        " resourceTables: [{}],",
                        resource_tables
                            .iter()
                            .map(|x| format!("handleTable{}", x.as_u32()))
                            .collect::<Vec<String>>()
                            .join(", ")
                    )
                }
            };
            match self.gen.opts.import_bindings {
                Some(BindingsMode::Hybrid) => {
                    let symbol_cabi_lower = self.gen.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.gen.intrinsic(Intrinsic::SymbolCabiLower);
                    if !self.gen.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!(),
            };
        }
        let (import_name, binding_name) = match func.kind {
            FunctionKind::Freestanding => (func_name.to_lower_camel_case(), callee_name),
            FunctionKind::Method(tid)
            | FunctionKind::Static(tid)
            | FunctionKind::Constructor(tid) => {
                let ty = &self.resolve.types[tid];
                (
                    ty.name.as_ref().unwrap().to_upper_camel_case(),
                    Instantiator::resource_name(
                        self.resolve,
                        &mut self.gen.local_names,
                        tid,
                        &self.imports_resource_types,
                    )
                    .to_string(),
                )
            }
        };

        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,
        );
    }

    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.gen.intrinsic(Intrinsic::GlobalThisIdlProxy);
        }
        // add the function import to the ESM bindgen
        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 {
                self.gen.esm_bindgen.add_import_binding(
                    &[
                        import_specifier,
                        iface_member.to_lower_camel_case(),
                        import_binding.unwrap().to_string(),
                    ],
                    local_name,
                );
            } else {
                self.gen.esm_bindgen.add_import_binding(
                    &[import_specifier, import_binding.unwrap().to_string()],
                    local_name,
                );
            }
        } else if let Some(iface_member) = iface_member {
            self.gen
                .esm_bindgen
                .add_import_binding(&[import_specifier, iface_member.into()], local_name);
        } else if let Some(import_binding) = import_binding {
            self.gen
                .esm_bindgen
                .add_import_binding(&[import_specifier, import_binding], local_name);
        } else {
            self.gen
                .esm_bindgen
                .add_import_binding(&[import_specifier], local_name);
        }
    }

    fn connect_resources(
        &mut self,
        t: TypeId,
        tid: TypeResourceTableIndex,
        resource_map: &mut ResourceMap,
    ) {
        self.ensure_resource_table(tid);
        let mut dtor_str = None;

        let imported = self
            .component
            .defined_resource_index(self.types[tid].ty)
            .is_none();

        let resource_id = crate::dealias(self.resolve, t);
        let resource = self.types[tid].ty;

        if let Some(resource_idx) = self.component.defined_resource_index(resource) {
            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));
            }
        }

        let ty = &self.resolve.types[resource_id];
        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)| *item == WorldItem::Type(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(ref 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.gen.local_names.get_or_create(resource, &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.gen.opts.map, &import_name);

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

            local_name_str
        } else {
            let (local_name, _) = self.gen.local_names.get_or_create(resource, &resource_name);
            local_name.to_string()
        };

        let entry = ResourceTable {
            imported,
            data: ResourceData::Host {
                tid,
                rid: self.types[tid].ty,
                local_name,
                dtor_name: dtor_str,
            },
        };
        if let Some(existing) = resource_map.get(&resource_id) {
            assert_eq!(*existing, entry);
        }
        resource_map.insert(resource_id, entry);
    }

    fn connect_resource_types(
        &mut self,
        id: TypeId,
        iface_ty: &InterfaceType,
        resource_map: &mut ResourceMap,
    ) {
        match (&self.resolve.types[id].kind, iface_ty) {
            (TypeDefKind::Flags(_), InterfaceType::Flags(_))
            | (TypeDefKind::Enum(_), InterfaceType::Enum(_)) => {}
            (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);
                    }
                }
            }
            (
                TypeDefKind::Handle(Handle::Own(t1) | Handle::Borrow(t1)),
                InterfaceType::Own(t2) | InterfaceType::Borrow(t2),
            ) => {
                self.connect_resources(*t1, *t2, resource_map);
            }
            (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);
                    }
                }
            }
            (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);
                    }
                }
            }
            (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);
                }
            }
            (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);
                }
            }
            (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);
                }
            }
            (TypeDefKind::Type(ty), _) => {
                if let Type::Id(id) = ty {
                    self.connect_resource_types(*id, iface_ty, resource_map);
                }
            }
            (_, _) => unreachable!(),
        }
    }

    #[allow(clippy::too_many_arguments)]
    fn bindgen(
        &mut self,
        nparams: usize,
        call_type: CallType,
        module_name: Option<&str>,
        callee: &str,
        opts: &CanonicalOptions,
        func: &Function,
        resource_map: &ResourceMap,
        abi: AbiVariant,
    ) {
        let memory = opts.memory.map(|idx| format!("memory{}", idx.as_u32()));
        let realloc = opts.realloc.map(|idx| format!("realloc{}", idx.as_u32()));
        let post_return = opts
            .post_return
            .map(|idx| format!("postReturn{}", idx.as_u32()));

        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) {
                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, ") {{");

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

        if self.gen.opts.tracing {
            let event_fields = func
                .params
                .iter()
                .enumerate()
                .map(|(i, (name, _ty))| format!("{name}=${{arguments[{i}]}}"))
                .collect::<Vec<String>>();
            uwriteln!(
                self.src.js,
                "console.error(`{tracing_prefix} call {}`);",
                event_fields.join(", ")
            );
        }

        if self.gen.opts.tla_compat
            && matches!(abi, AbiVariant::GuestExport)
            && self.gen.opts.instantiation.is_none()
        {
            let throw_uninitialized = self.gen.intrinsic(Intrinsic::ThrowUninitialized);
            uwrite!(
                self.src.js,
                "\
                if (!_initialized) {throw_uninitialized}();
            "
            );
        }

        let mut f = FunctionBindgen {
            resource_map,
            cur_resource_borrows: false,
            intrinsics: &mut self.gen.all_intrinsics,
            valid_lifting_optimization: self.gen.opts.valid_lifting_optimization,
            sizes: &self.sizes,
            err: if func.results.throws(self.resolve).is_some() {
                match abi {
                    AbiVariant::GuestExport => ErrHandling::ThrowResultErr,
                    AbiVariant::GuestImport => ErrHandling::ResultCatchHandler,
                }
            } else {
                ErrHandling::None
            },
            block_storage: Vec::new(),
            blocks: Vec::new(),
            callee,
            callee_resource_dynamic: matches!(call_type, CallType::CalleeResourceDispatch),
            memory: memory.as_ref(),
            realloc: realloc.as_ref(),
            tmp: 0,
            params,
            post_return: post_return.as_ref(),
            tracing_prefix: if self.gen.opts.tracing {
                Some(&tracing_prefix)
            } else {
                None
            },
            encoding: match opts.string_encoding {
                component::StringEncoding::Utf8 => StringEncoding::UTF8,
                component::StringEncoding::Utf16 => StringEncoding::UTF16,
                component::StringEncoding::CompactUtf16 => StringEncoding::CompactUTF16,
            },
            src: source::Source::default(),
            resolve: self.resolve,
        };
        abi::call(
            self.resolve,
            abi,
            match abi {
                AbiVariant::GuestImport => LiftLower::LiftArgsLowerResults,
                AbiVariant::GuestExport => LiftLower::LowerArgsLiftResults,
            },
            func,
            &mut f,
        );
        self.src.js(&f.src);
        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(e),
            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())
            }
        }
    }

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

    fn exports(&mut self, exports: &NameMap<String, ExportIndex>) {
        for (export_name, export_idx) in exports.raw_iter() {
            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 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!(),
                    };
                    self.create_resource_fn_map(func, *func_ty, &mut resource_map);

                    let local_name = if let FunctionKind::Constructor(resource_id)
                    | FunctionKind::Method(resource_id)
                    | FunctionKind::Static(resource_id) = func.kind
                    {
                        Instantiator::resource_name(
                            self.resolve,
                            &mut self.gen.local_names,
                            resource_id,
                            &self.exports_resource_types,
                        )
                    } else {
                        self.gen.local_names.create_once(export_name)
                    }
                    .to_string();
                    self.export_bindgen(
                        &local_name,
                        def,
                        options,
                        func,
                        export_name,
                        &resource_map,
                    );
                    if let FunctionKind::Constructor(ty)
                    | FunctionKind::Method(ty)
                    | FunctionKind::Static(ty) = func.kind
                    {
                        let ty = &self.resolve.types[ty];
                        self.gen.esm_bindgen.add_export_binding(
                            None,
                            local_name,
                            ty.name.as_ref().unwrap().to_upper_camel_case(),
                        );
                    } else {
                        self.gen.esm_bindgen.add_export_binding(
                            None,
                            local_name,
                            export_name.to_lower_camel_case(),
                        );
                    }
                }
                Export::Instance { exports, .. } => {
                    let id = match item {
                        WorldItem::Interface { id, stability: _ } => *id,
                        WorldItem::Function(_) | WorldItem::Type(_) => unreachable!(),
                    };
                    for (func_name, export_idx) in exports.raw_iter() {
                        let export = &self.component.export_items[*export_idx];
                        let (def, options, func_ty) = match export {
                            Export::LiftedFunction { func, options, ty } => (func, options, ty),
                            Export::Type(_) => continue, // ignored
                            _ => unreachable!(),
                        };

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

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

                        let local_name = if let FunctionKind::Constructor(resource_id)
                        | FunctionKind::Method(resource_id)
                        | FunctionKind::Static(resource_id) = func.kind
                        {
                            Instantiator::resource_name(
                                self.resolve,
                                &mut self.gen.local_names,
                                resource_id,
                                &self.exports_resource_types,
                            )
                        } else {
                            self.gen.local_names.create_once(func_name)
                        }
                        .to_string();

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

                        if let FunctionKind::Constructor(ty)
                        | FunctionKind::Method(ty)
                        | FunctionKind::Static(ty) = func.kind
                        {
                            let ty = &self.resolve.types[ty];
                            let resource = ty.name.as_ref().unwrap();
                            self.gen.esm_bindgen.add_export_binding(
                                Some(export_name),
                                local_name,
                                resource.to_upper_camel_case(),
                            );
                        } else {
                            self.gen.esm_bindgen.add_export_binding(
                                Some(export_name),
                                local_name,
                                func_name.to_lower_camel_case(),
                            );
                        }
                    }
                }

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

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

    fn export_bindgen(
        &mut self,
        local_name: &str,
        def: &CoreDef,
        options: &CanonicalOptions,
        func: &Function,
        export_name: &String,
        resource_map: &ResourceMap,
    ) {
        match func.kind {
            FunctionKind::Freestanding => uwrite!(self.src.js, "\nfunction {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} = 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());
            }
        }
        let callee = self.core_def(def);
        self.bindgen(
            func.params.len(),
            match func.kind {
                FunctionKind::Method(_) => CallType::FirstArgIsThis,
                _ => CallType::Standard,
            },
            if export_name.is_empty() {
                None
            } else {
                Some(export_name)
            },
            &callee,
            options,
            func,
            resource_map,
            AbiVariant::GuestExport,
        );
        match func.kind {
            FunctionKind::Freestanding => self.src.js("\n"),
            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);
    }
}

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() {
        if let Some(mapping) = map.get(impt) {
            return if let Some(hash_idx) = mapping[1..].find('#') {
                (
                    mapping[0..hash_idx + 1].to_string(),
                    Some(mapping[hash_idx + 2..].into()),
                )
            } else {
                (mapping.into(), None)
            };
        }
        if let Some(mapping) = map.get(impt_sans_version) {
            return if let Some(hash_idx) = mapping[1..].find('#') {
                (
                    mapping[0..hash_idx + 1].to_string(),
                    Some(mapping[hash_idx + 2..].into()),
                )
            } else {
                (mapping.into(), None)
            };
        }
        for (key, mapping) in map {
            if let Some(wildcard_idx) = key.find('*') {
                let lhs = &key[0..wildcard_idx];
                let rhs = &key[wildcard_idx + 1..];
                if impt_sans_version.starts_with(lhs) && impt_sans_version.ends_with(rhs) {
                    let matched = &impt_sans_version[wildcard_idx
                        ..wildcard_idx + impt_sans_version.len() - lhs.len() - rhs.len()];
                    let mapping = mapping.replace('*', matched);
                    return if let Some(hash_idx) = mapping[1..].find('#') {
                        (
                            mapping[0..hash_idx + 1].to_string(),
                            Some(mapping[hash_idx + 2..].into()),
                        )
                    } else {
                        (mapping, None)
                    };
                }
                if impt.starts_with(lhs) && impt.ends_with(rhs) {
                    let matched =
                        &impt[wildcard_idx..wildcard_idx + impt.len() - lhs.len() - rhs.len()];
                    let mapping = mapping.replace('*', matched);
                    return if let Some(hash_idx) = mapping[1..].find('#') {
                        (
                            mapping[0..hash_idx + 1].to_string(),
                            Some(mapping[hash_idx + 2..].into()),
                        )
                    } else {
                        (mapping, None)
                    };
                }
            }
        }
    }
    (impt_sans_version.to_string(), None)
}

pub fn parse_world_key(name: &str) -> Option<(&str, &str, &str)> {
    let registry_idx = match name.find(':') {
        Some(idx) => idx,
        None => return None,
    };
    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!("{}.core{i_str}.wasm", name)
}