js_component_bindgen/

lib.rs

#![cfg_attr(docsrs, feature(doc_auto_cfg))]
use std::collections::HashSet;

use anyhow::{bail, ensure, Context, Result};
use ts_bindgen::ts_bindgen;
use wasmtime_environ::component::{
    CanonicalOptions, ComponentTypesBuilder, Export, StaticModuleIndex,
};
use wasmtime_environ::wasmparser::WasmFeatures;
use wasmtime_environ::{PrimaryMap, ScopeVec, Tunables};
use wit_bindgen_core::wit_parser::{Function, FunctionKind};
use wit_component::DecodedWasm;
use wit_parser::{Package, Resolve, Stability, Type, TypeDefKind, TypeId, WorldId};

mod core;
mod files;
mod transpile_bindgen;
mod ts_bindgen;

pub mod esm_bindgen;
pub mod function_bindgen;
pub mod intrinsics;
pub mod names;
pub mod source;

use transpile_bindgen::transpile_bindgen;
pub use transpile_bindgen::{AsyncMode, BindingsMode, InstantiationMode, TranspileOpts};

/// Calls [`write!`] with the passed arguments and unwraps the result.
///
/// Useful for writing to things with infallible `Write` implementations like
/// `Source` and `String`.
///
/// [`write!`]: std::write
#[macro_export]
macro_rules! uwrite {
    ($dst:expr, $($arg:tt)*) => {
        write!($dst, $($arg)*).unwrap()
    };
}

/// Calls [`writeln!`] with the passed arguments and unwraps the result.
///
/// Useful for writing to things with infallible `Write` implementations like
/// `Source` and `String`.
///
/// [`writeln!`]: std::writeln
#[macro_export]
macro_rules! uwriteln {
    ($dst:expr, $($arg:tt)*) => {
        writeln!($dst, $($arg)*).unwrap()
    };
}

pub struct Transpiled {
    pub files: Vec<(String, Vec<u8>)>,
    pub imports: Vec<String>,
    pub exports: Vec<(String, Export)>,
}

pub struct ComponentInfo {
    pub imports: Vec<String>,
    pub exports: Vec<(String, wasmtime_environ::component::Export)>,
}

pub fn generate_types(
    name: &str,
    resolve: Resolve,
    world_id: WorldId,
    opts: TranspileOpts,
) -> Result<Vec<(String, Vec<u8>)>> {
    let mut files = files::Files::default();

    ts_bindgen(name, &resolve, world_id, &opts, &mut files)
        .context("failed to generate Typescript bindings")?;

    let mut files_out: Vec<(String, Vec<u8>)> = Vec::new();
    for (name, source) in files.iter() {
        files_out.push((name.to_string(), source.to_vec()));
    }
    Ok(files_out)
}

/// Generate the JS transpilation bindgen for a given Wasm component binary
/// Outputs the file map and import and export metadata for the Transpilation
#[cfg(feature = "transpile-bindgen")]
pub fn transpile(component: &[u8], opts: TranspileOpts) -> Result<Transpiled> {
    use wasmtime_environ::component::{Component, Translator};

    let name = opts.name.clone();
    let mut files = files::Files::default();

    // Use the `wit-component` crate here to parse `binary` and discover
    // the type-level descriptions and `Resolve` corresponding to the
    // component binary. This will synthesize a `Resolve` which has a top-level
    // package which has a single document and `world` within it which describes
    // the state of the component. This is then further used afterwards for
    // bindings Transpilation as-if a `*.wit` file was input.
    let decoded = wit_component::decode(component)
        .context("failed to extract interface information from component")?;

    let (resolve, world_id) = match decoded {
        DecodedWasm::WitPackage(_, _) => bail!("unexpected wit package as input"),
        DecodedWasm::Component(resolve, world_id) => (resolve, world_id),
    };

    // Components are complicated, there's no real way around that. To
    // handle all the work of parsing a component and figuring out how to
    // instantiate core wasm modules and such all the work is offloaded to
    // Wasmtime itself. This crate generator is based on Wasmtime's
    // low-level `wasmtime-environ` crate which is technically not a public
    // dependency but the same author who worked on that in Wasmtime wrote
    // this as well so... "seems fine".
    //
    // Note that we're not pulling in the entire Wasmtime engine here,
    // moreso just the "spine" of validating a component. This enables using
    // Wasmtime's internal `Component` representation as a much easier to
    // process version of a component that has decompiled everything
    // internal to a component to a straight linear list of initializers
    // that need to be executed to instantiate a component.
    let scope = ScopeVec::new();
    let tunables = Tunables::default_u32();

    // The validator that will be used on the component must enable support for all
    // CM features we expect components to use.
    //
    // This does not require the correct execution of the related features post-transpilation,
    // but without the right features specified, components won't load at all.
    let mut validator = wasmtime_environ::wasmparser::Validator::new_with_features(
        WasmFeatures::WASM2
            | WasmFeatures::COMPONENT_MODEL
            | WasmFeatures::CM_ASYNC
            | WasmFeatures::CM_ASYNC_BUILTINS
            | WasmFeatures::CM_ERROR_CONTEXT
            | WasmFeatures::MEMORY64
            | WasmFeatures::MULTI_MEMORY,
    );

    let mut types = ComponentTypesBuilder::new(&validator);

    let (component, modules) = Translator::new(&tunables, &mut validator, &mut types, &scope)
        .translate(component)
        .context("failed to translate component")?;

    let modules: PrimaryMap<StaticModuleIndex, core::Translation<'_>> = modules
        .into_iter()
        .map(|(_i, module)| core::Translation::new(module, opts.multi_memory))
        .collect::<Result<_>>()?;

    let wasmtime_component = Component::default();
    let types = types.finish(&wasmtime_component);

    // Insert all core wasm modules into the generated `Files` which will
    // end up getting used in the `generate_instantiate` method.
    for (i, module) in modules.iter() {
        files.push(&core_file_name(&name, i.as_u32()), module.wasm());
    }

    if !opts.no_typescript {
        ts_bindgen(&name, &resolve, world_id, &opts, &mut files)
            .context("failed to generate Typescript bindings")?;
    }

    let (imports, exports) = transpile_bindgen(
        &name, &component, &modules, &types.0, &resolve, world_id, opts, &mut files,
    );

    let mut files_out: Vec<(String, Vec<u8>)> = Vec::new();
    for (name, source) in files.iter() {
        files_out.push((name.to_string(), source.to_vec()));
    }
    Ok(Transpiled {
        files: files_out,
        imports,
        exports,
    })
}

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")
}

pub fn dealias(resolve: &Resolve, mut id: TypeId) -> TypeId {
    loop {
        match &resolve.types[id].kind {
            TypeDefKind::Type(Type::Id(that_id)) => id = *that_id,
            _ => break id,
        }
    }
}

/// Check if an item (usually some form of [`WorldItem`]) should be allowed through the feature gate
/// of a given package.
fn feature_gate_allowed(
    resolve: &Resolve,
    package: &Package,
    stability: &Stability,
    item_name: &str,
) -> Result<bool> {
    Ok(match stability {
        Stability::Unknown => true,
        Stability::Stable { since, .. } => {
            let Some(package_version) = package.name.version.as_ref() else {
                // If the package version is missing (we're likely dealing with an unresolved package)
                // and we can't really check much.
                return Ok(true);
            };

            ensure!(
                package_version >= since,
                "feature gate on [{item_name}] refers to an unreleased (future) package version [{since}] (current package version is [{package_version}])"
            );

            // Stabilization (@since annotation) overrides features and deprecation
            true
        }
        Stability::Unstable {
            feature,
            deprecated: _,
        } => {
            // If a @unstable feature is present but the related feature was not enabled
            // or all features was not selected, exclude
            resolve.all_features || resolve.features.contains(feature)
        }
    })
}

/// Utility function for deducing whether a type can throw
pub fn get_thrown_type(
    resolve: &Resolve,
    return_type: Option<Type>,
) -> Option<(Option<&Type>, Option<&Type>)> {
    match return_type {
        None => None,
        Some(Type::Id(id)) => match &resolve.types[id].kind {
            TypeDefKind::Result(r) => Some((r.ok.as_ref(), r.err.as_ref())),
            _ => None,
        },
        _ => None,
    }
}

/// Check whether a given function is a async lifted by by a guest
///
/// Functions that are designated as guest async lifted represent use of
/// the WASI p3 async feature.
///
/// These functions must be called from transpiled javsacript much differently
/// than they would otherwise be, i.e. in accordance to the Component Model
/// async feature.
pub(crate) fn is_guest_async_lifted_fn(func: &Function, canon_opts: &CanonicalOptions) -> bool {
    if canon_opts.async_ {
        return true;
    }
    matches!(
        func.kind,
        FunctionKind::AsyncMethod(_)
            | FunctionKind::AsyncStatic(_)
            | FunctionKind::AsyncFreestanding
    )
}

/// Identifier for a function used
enum FunctionIdentifier<'a> {
    Fn(&'a Function),
    CanonFnName(&'a str),
}

/// Check whether a function has been marked or async binding generation
///
/// When dealing with imports, functions that are designated to require async porcelain
/// are usually asynchronous host functions -- they will have code generated
/// that enables use of techniques like JSPI for exposing asynchronous host/platform
/// imports to WebAssembly guests.
///
/// When dealing with an export, functions that require async porcelain simply provide
/// an interface in the transpiled codebase that produces a `Promise`, i.e. one that can
/// be called in an *already* asynchronous context (JS `async` function) or resolved with a`.then()`.
///
/// Exports do not indicate a use of JSPI, as JSPI is only for bridging asynchronous *host* behavior
/// to synchronous WebAssembly modules
///
/// This function is *not* for detecting WASI P3 asynchronous behavior -- see [`is_guest_async_lifted_fn`].
pub(crate) fn requires_async_porcelain(
    func: FunctionIdentifier<'_>,
    id: &str,
    async_funcs: &HashSet<String>,
) -> bool {
    let name = match func {
        FunctionIdentifier::Fn(func) => func.name.as_str(),
        FunctionIdentifier::CanonFnName(name) => name,
    };

    if async_funcs.contains(name) {
        return true;
    }

    let qualified_name = format!("{id}#{name}");
    if async_funcs.contains(&qualified_name) {
        return true;
    }

    if let Some(pos) = id.find('@') {
        let namespace = &id[..pos];
        let namespaced_name = format!("{namespace}#{name}");

        if async_funcs.contains(&namespaced_name) {
            return true;
        }
    }
    false
}