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Make JsAsyncGenerator fully type safe #5066

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b14ff35
Make `JsAsyncGenerator` fully type safe
jedel1043 Mar 14, 2026
2a2c77e
cargo clippy
jedel1043 Mar 14, 2026
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88 changes: 64 additions & 24 deletions core/engine/src/builtins/async_generator/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -26,7 +26,7 @@ use crate::{
vm::{CompletionRecord, GeneratorResumeKind},
};
use boa_gc::{Finalize, Trace};
use std::collections::VecDeque;
use std::{collections::VecDeque, slice};

use super::{BuiltInBuilder, IntrinsicObject};

Expand Down Expand Up @@ -143,6 +143,21 @@ impl AsyncGenerator {
});
let generator = if_abrupt_reject_promise!(result, promise_capability, context);

Self::inner_next(
&generator,
promise_capability,
args.get_or_undefined(0).clone(),
context,
)
.map(JsValue::from)
}

pub(crate) fn inner_next(
generator: &JsObject<AsyncGenerator>,
cap: PromiseCapability,
value: JsValue,
context: &mut Context,
) -> JsResult<JsObject> {
// 5. Let state be generator.[[AsyncGeneratorState]].
let state = generator.borrow().data().state;

Expand All @@ -152,32 +167,29 @@ impl AsyncGenerator {
let iterator_result = create_iter_result_object(JsValue::undefined(), true, context);

// b. Perform ! Call(promiseCapability.[[Resolve]], undefined, « iteratorResult »).
promise_capability.resolve().call(
&JsValue::undefined(),
&[iterator_result],
context,
)?;
cap.resolve()
.call(&JsValue::undefined(), &[iterator_result], context)?;

// c. Return promiseCapability.[[Promise]].
return Ok(promise_capability.promise().clone().into());
return Ok(cap.promise);
}

// 7. Let completion be NormalCompletion(value).
let completion = CompletionRecord::Normal(args.get_or_undefined(0).clone());
let completion = CompletionRecord::Normal(value);

// 8. Perform AsyncGeneratorEnqueue(generator, completion, promiseCapability).
Self::enqueue(&generator, completion.clone(), promise_capability.clone());
Self::enqueue(generator, completion.clone(), cap.clone());

// 9. If state is either suspendedStart or suspendedYield, then
if state == AsyncGeneratorState::SuspendedStart
|| state == AsyncGeneratorState::SuspendedYield
{
// a. Perform AsyncGeneratorResume(generator, completion).
Self::resume(&generator, completion, context)?;
Self::resume(generator, completion, context)?;
}

// 11. Return promiseCapability.[[Promise]].
Ok(promise_capability.promise().clone().into())
Ok(cap.promise)
}

/// `AsyncGenerator.prototype.return ( value )`
Expand Down Expand Up @@ -216,12 +228,26 @@ impl AsyncGenerator {
});
let generator = if_abrupt_reject_promise!(result, promise_capability, context);

Self::inner_return(
&generator,
promise_capability,
args.get_or_undefined(0).clone(),
context,
)
.map(JsValue::from)
}

pub(crate) fn inner_return(
generator: &JsObject<AsyncGenerator>,
cap: PromiseCapability,
return_value: JsValue,
context: &mut Context,
) -> JsResult<JsObject> {
// 5. Let completion be Completion Record { [[Type]]: return, [[Value]]: value, [[Target]]: empty }.
let return_value = args.get_or_undefined(0).clone();
let completion = CompletionRecord::Return(return_value.clone());

// 6. Perform AsyncGeneratorEnqueue(generator, completion, promiseCapability).
Self::enqueue(&generator, completion.clone(), promise_capability.clone());
Self::enqueue(generator, completion.clone(), cap.clone());

// 7. Let state be generator.[[AsyncGeneratorState]].
let state = generator.borrow().data().state;
Expand All @@ -232,18 +258,18 @@ impl AsyncGenerator {
generator.borrow_mut().data_mut().state = AsyncGeneratorState::DrainingQueue;

// b. Perform ! AsyncGeneratorAwaitReturn(generator).
Self::await_return(&generator, return_value, context)?;
Self::await_return(generator, return_value, context)?;
}
// 9. Else if state is suspended-yield, then
else if state == AsyncGeneratorState::SuspendedYield {
// a. Perform AsyncGeneratorResume(generator, completion).
Self::resume(&generator, completion, context)?;
Self::resume(generator, completion, context)?;
}
// 10. Else,
// a. Assert: state is either executing or draining-queue.

// 11. Return promiseCapability.[[Promise]].
Ok(promise_capability.promise().clone().into())
Ok(cap.promise)
}

/// `AsyncGenerator.prototype.throw ( exception )`
Expand Down Expand Up @@ -281,6 +307,21 @@ impl AsyncGenerator {
.into()
});
let generator = if_abrupt_reject_promise!(result, promise_capability, context);
Self::inner_throw(
&generator,
promise_capability,
args.get_or_undefined(0).clone(),
context,
)
.map(JsValue::from)
}

pub(crate) fn inner_throw(
generator: &JsObject<AsyncGenerator>,
cap: PromiseCapability,
error_value: JsValue,
context: &mut Context,
) -> JsResult<JsObject> {
let mut r#gen = generator.borrow_mut();

// 5. Let state be generator.[[AsyncGeneratorState]].
Expand All @@ -301,34 +342,33 @@ impl AsyncGenerator {
// 7. If state is completed, then
if state == AsyncGeneratorState::Completed {
// a. Perform ! Call(promiseCapability.[[Reject]], undefined, « exception »).
promise_capability.reject().call(
cap.reject().call(
&JsValue::undefined(),
&[args.get_or_undefined(0).clone()],
slice::from_ref(&error_value),
context,
)?;

// b. Return promiseCapability.[[Promise]].
return Ok(promise_capability.promise().clone().into());
return Ok(cap.promise);
}

// 8. Let completion be ThrowCompletion(exception).
let completion =
CompletionRecord::Throw(JsError::from_opaque(args.get_or_undefined(0).clone()));
let completion = CompletionRecord::Throw(JsError::from_opaque(error_value));

// 9. Perform AsyncGeneratorEnqueue(generator, completion, promiseCapability).
Self::enqueue(&generator, completion.clone(), promise_capability.clone());
Self::enqueue(generator, completion.clone(), cap.clone());

// 10. If state is suspended-yield, then
if state == AsyncGeneratorState::SuspendedYield {
// a. Perform AsyncGeneratorResume(generator, completion).
Self::resume(&generator, completion, context)?;
Self::resume(generator, completion, context)?;
}

// 11. Else,
// a. Assert: state is either executing or draining-queue.

// 12. Return promiseCapability.[[Promise]].
Ok(promise_capability.promise().clone().into())
Ok(cap.promise)
}

/// `AsyncGeneratorEnqueue ( generator, completion, promiseCapability )`
Expand Down
71 changes: 35 additions & 36 deletions core/engine/src/object/builtins/jsasyncgenerator.rs
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Original file line number Diff line number Diff line change
@@ -1,16 +1,20 @@
//! A Rust API wrapper for Boa's `AsyncGenerator` Builtin ECMAScript Object
use super::JsPromise;
use crate::{
Context, JsNativeError, JsResult, JsValue, builtins::async_generator::AsyncGenerator,
object::JsObject, value::TryFromJs,
Context, JsNativeError, JsResult, JsValue,
builtins::{async_generator::AsyncGenerator, promise::PromiseCapability},
js_error,
object::JsObject,
value::TryFromJs,
};
use boa_gc::{Finalize, Trace};
use std::ops::Deref;

/// `JsAsyncGenerator` provides a wrapper for Boa's implementation of the ECMAScript `AsyncGenerator` builtin object.
#[derive(Debug, Clone, Trace, Finalize)]
#[boa_gc(unsafe_no_drop)]
pub struct JsAsyncGenerator {
inner: JsObject,
inner: JsObject<AsyncGenerator>,
}

impl JsAsyncGenerator {
Expand All @@ -22,13 +26,10 @@ impl JsAsyncGenerator {
/// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/AsyncGenerator
#[inline]
pub fn from_object(object: JsObject) -> JsResult<Self> {
if object.is::<AsyncGenerator>() {
Ok(Self { inner: object })
} else {
Err(JsNativeError::typ()
.with_message("object is not an AsyncGenerator")
.into())
}
object
.downcast::<AsyncGenerator>()
.map(|inner| Self { inner })
.map_err(|_| js_error!(TypeError: "object is not an AsyncGenerator object"))
}

/// Calls `AsyncGenerator.prototype.next()`.
Expand All @@ -41,14 +42,14 @@ impl JsAsyncGenerator {
where
T: Into<JsValue>,
{
let value = AsyncGenerator::next(&self.inner.clone().into(), &[value.into()], context)?;
let obj = value
.as_object()
.ok_or_else(|| {
JsNativeError::typ().with_message("async generator did not return a Promise")
})?
.clone();
JsPromise::from_object(obj)
let (typed_promise, functions) = JsPromise::new_pending(context);
let capability = PromiseCapability {
functions,
promise: JsObject::clone(&typed_promise).clone().upcast(),
};
AsyncGenerator::inner_next(&self.inner, capability, value.into(), context)?;

Ok(typed_promise)
}

/// Calls `AsyncGenerator.prototype.return()`.
Expand All @@ -61,14 +62,13 @@ impl JsAsyncGenerator {
where
T: Into<JsValue>,
{
let value = AsyncGenerator::r#return(&self.inner.clone().into(), &[value.into()], context)?;
let obj = value
.as_object()
.ok_or_else(|| {
JsNativeError::typ().with_message("async generator did not return a Promise")
})?
.clone();
JsPromise::from_object(obj)
let (typed_promise, functions) = JsPromise::new_pending(context);
let capability = PromiseCapability {
functions,
promise: JsObject::clone(&typed_promise).upcast(),
};
AsyncGenerator::inner_return(&self.inner, capability, value.into(), context)?;
Ok(typed_promise)
}

/// Calls `AsyncGenerator.prototype.throw()`.
Expand All @@ -81,21 +81,20 @@ impl JsAsyncGenerator {
where
T: Into<JsValue>,
{
let value = AsyncGenerator::throw(&self.inner.clone().into(), &[value.into()], context)?;
let obj = value
.as_object()
.ok_or_else(|| {
JsNativeError::typ().with_message("async generator did not return a Promise")
})?
.clone();
JsPromise::from_object(obj)
let (typed_promise, functions) = JsPromise::new_pending(context);
let capability = PromiseCapability {
functions,
promise: JsObject::clone(&typed_promise).clone().upcast(),
};
AsyncGenerator::inner_throw(&self.inner, capability, value.into(), context)?;
Ok(typed_promise)
}
}

impl From<JsAsyncGenerator> for JsObject {
#[inline]
fn from(o: JsAsyncGenerator) -> Self {
o.inner.clone()
o.inner.upcast()
}
}

Expand All @@ -107,7 +106,7 @@ impl From<JsAsyncGenerator> for JsValue {
}

impl Deref for JsAsyncGenerator {
type Target = JsObject;
type Target = JsObject<AsyncGenerator>;

#[inline]
fn deref(&self) -> &Self::Target {
Expand Down
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