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//! Boa's implementation of ECMAScript's global `AsyncGenerator` object.
//!
//! More information:
//! - [ECMAScript reference][spec]
//!
//! [spec]: https://tc39.es/ecma262/#sec-asyncgenerator-objects
use crate::{
builtins::{
generator::GeneratorContext, iterable::create_iter_result_object,
promise::if_abrupt_reject_promise, promise::PromiseCapability, Promise,
},
context::intrinsics::Intrinsics,
error::JsNativeError,
js_string,
native_function::NativeFunction,
object::{FunctionObjectBuilder, JsObject, CONSTRUCTOR},
property::Attribute,
realm::Realm,
string::common::StaticJsStrings,
symbol::JsSymbol,
value::JsValue,
vm::{CompletionRecord, GeneratorResumeKind},
Context, JsArgs, JsData, JsError, JsResult, JsString,
};
use boa_gc::{Finalize, Trace};
use boa_profiler::Profiler;
use std::collections::VecDeque;
use super::{BuiltInBuilder, IntrinsicObject};
/// Indicates the state of an async generator.
#[derive(Debug, Clone, Copy, PartialEq)]
pub(crate) enum AsyncGeneratorState {
SuspendedStart,
SuspendedYield,
Executing,
AwaitingReturn,
Completed,
}
/// `AsyncGeneratorRequest Records`
///
/// More information:
/// - [ECMAScript reference][spec]
///
/// [spec]: https://tc39.es/ecma262/#sec-asyncgeneratorrequest-records
#[derive(Debug, Clone, Finalize, Trace)]
pub(crate) struct AsyncGeneratorRequest {
/// The `[[Completion]]` slot.
pub(crate) completion: CompletionRecord,
/// The `[[Capability]]` slot.
capability: PromiseCapability,
}
/// The internal representation of an `AsyncGenerator` object.
#[derive(Debug, Clone, Finalize, Trace, JsData)]
pub struct AsyncGenerator {
/// The `[[AsyncGeneratorState]]` internal slot.
#[unsafe_ignore_trace]
pub(crate) state: AsyncGeneratorState,
/// The `[[AsyncGeneratorContext]]` internal slot.
pub(crate) context: Option<GeneratorContext>,
/// The `[[AsyncGeneratorQueue]]` internal slot.
pub(crate) queue: VecDeque<AsyncGeneratorRequest>,
}
impl IntrinsicObject for AsyncGenerator {
fn init(realm: &Realm) {
let _timer = Profiler::global().start_event(std::any::type_name::<Self>(), "init");
BuiltInBuilder::with_intrinsic::<Self>(realm)
.prototype(
realm
.intrinsics()
.objects()
.iterator_prototypes()
.async_iterator(),
)
.static_method(Self::next, js_string!("next"), 1)
.static_method(Self::r#return, js_string!("return"), 1)
.static_method(Self::throw, js_string!("throw"), 1)
.static_property(
JsSymbol::to_string_tag(),
Self::NAME,
Attribute::CONFIGURABLE,
)
.static_property(
CONSTRUCTOR,
realm
.intrinsics()
.constructors()
.async_generator_function()
.prototype(),
Attribute::CONFIGURABLE,
)
.build();
}
fn get(intrinsics: &Intrinsics) -> JsObject {
intrinsics.objects().async_generator()
}
}
impl AsyncGenerator {
const NAME: JsString = StaticJsStrings::ASYNC_GENERATOR;
/// `AsyncGenerator.prototype.next ( value )`
///
/// More information:
/// - [ECMAScript reference][spec]
///
/// [spec]: https://tc39.es/ecma262/#sec-asyncgenerator-prototype-next
pub(crate) fn next(
this: &JsValue,
args: &[JsValue],
context: &mut Context,
) -> JsResult<JsValue> {
// 1. Let generator be the this value.
let generator = this;
// 2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
let promise_capability = PromiseCapability::new(
&context.intrinsics().constructors().promise().constructor(),
context,
)
.expect("cannot fail with promise constructor");
// 3. Let result be Completion(AsyncGeneratorValidate(generator, empty)).
// 4. IfAbruptRejectPromise(result, promiseCapability).
let result: JsResult<_> = generator.as_object().ok_or_else(|| {
JsNativeError::typ()
.with_message("generator resumed on non generator object")
.into()
});
let generator_object = if_abrupt_reject_promise!(result, promise_capability, context);
let result: JsResult<_> = generator_object.downcast_mut::<Self>().ok_or_else(|| {
JsNativeError::typ()
.with_message("generator resumed on non generator object")
.into()
});
let mut generator = if_abrupt_reject_promise!(result, promise_capability, context);
// 5. Let state be generator.[[AsyncGeneratorState]].
let state = generator.state;
// 6. If state is completed, then
if state == AsyncGeneratorState::Completed {
drop(generator);
// a. Let iteratorResult be CreateIterResultObject(undefined, true).
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)
.expect("cannot fail per spec");
// c. Return promiseCapability.[[Promise]].
return Ok(promise_capability.promise().clone().into());
}
// 7. Let completion be NormalCompletion(value).
let completion = CompletionRecord::Normal(args.get_or_undefined(0).clone());
// 8. Perform AsyncGeneratorEnqueue(generator, completion, promiseCapability).
generator.enqueue(completion.clone(), promise_capability.clone());
// 9. If state is either suspendedStart or suspendedYield, then
if state == AsyncGeneratorState::SuspendedStart
|| state == AsyncGeneratorState::SuspendedYield
{
// a. Perform AsyncGeneratorResume(generator, completion).
let generator_context = generator
.context
.take()
.expect("generator context cannot be empty here");
drop(generator);
Self::resume(
generator_object,
state,
generator_context,
completion,
context,
);
}
// 11. Return promiseCapability.[[Promise]].
Ok(promise_capability.promise().clone().into())
}
/// `AsyncGenerator.prototype.return ( value )`
///
/// More information:
/// - [ECMAScript reference][spec]
///
/// [spec]: https://tc39.es/ecma262/#sec-asyncgenerator-prototype-return
pub(crate) fn r#return(
this: &JsValue,
args: &[JsValue],
context: &mut Context,
) -> JsResult<JsValue> {
// 1. Let generator be the this value.
let generator = this;
// 2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
let promise_capability = PromiseCapability::new(
&context.intrinsics().constructors().promise().constructor(),
context,
)
.expect("cannot fail with promise constructor");
// 3. Let result be Completion(AsyncGeneratorValidate(generator, empty)).
// 4. IfAbruptRejectPromise(result, promiseCapability).
let result: JsResult<_> = generator.as_object().ok_or_else(|| {
JsNativeError::typ()
.with_message("generator resumed on non generator object")
.into()
});
let generator_object = if_abrupt_reject_promise!(result, promise_capability, context);
let result: JsResult<_> = generator_object.downcast_mut::<Self>().ok_or_else(|| {
JsNativeError::typ()
.with_message("generator resumed on non generator object")
.into()
});
let mut generator = if_abrupt_reject_promise!(result, promise_capability, context);
// 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).
generator.enqueue(completion.clone(), promise_capability.clone());
// 7. Let state be generator.[[AsyncGeneratorState]].
let state = generator.state;
// 8. If state is either suspendedStart or completed, then
if state == AsyncGeneratorState::SuspendedStart || state == AsyncGeneratorState::Completed {
// a. Set generator.[[AsyncGeneratorState]] to awaiting-return.
generator.state = AsyncGeneratorState::AwaitingReturn;
// b. Perform ! AsyncGeneratorAwaitReturn(generator).
drop(generator);
Self::await_return(generator_object.clone(), return_value, context);
}
// 9. Else if state is suspendedYield, then
else if state == AsyncGeneratorState::SuspendedYield {
// a. Perform AsyncGeneratorResume(generator, completion).
let generator_context = generator
.context
.take()
.expect("generator context cannot be empty here");
drop(generator);
Self::resume(
generator_object,
state,
generator_context,
completion,
context,
);
}
// 11. Return promiseCapability.[[Promise]].
Ok(promise_capability.promise().clone().into())
}
/// `AsyncGenerator.prototype.throw ( exception )`
///
/// More information:
/// - [ECMAScript reference][spec]
///
/// [spec]: https://tc39.es/ecma262/#sec-asyncgenerator-prototype-throw
pub(crate) fn throw(
this: &JsValue,
args: &[JsValue],
context: &mut Context,
) -> JsResult<JsValue> {
// 1. Let generator be the this value.
let generator = this;
// 2. Let promiseCapability be ! NewPromiseCapability(%Promise%).
let promise_capability = PromiseCapability::new(
&context.intrinsics().constructors().promise().constructor(),
context,
)
.expect("cannot fail with promise constructor");
// 3. Let result be Completion(AsyncGeneratorValidate(generator, empty)).
// 4. IfAbruptRejectPromise(result, promiseCapability).
let result: JsResult<_> = generator.as_object().ok_or_else(|| {
JsNativeError::typ()
.with_message("generator resumed on non generator object")
.into()
});
let generator_object = if_abrupt_reject_promise!(result, promise_capability, context);
let result: JsResult<_> = generator_object.downcast_mut::<Self>().ok_or_else(|| {
JsNativeError::typ()
.with_message("generator resumed on non generator object")
.into()
});
let mut generator = if_abrupt_reject_promise!(result, promise_capability, context);
// 5. Let state be generator.[[AsyncGeneratorState]].
let mut state = generator.state;
// 6. If state is suspendedStart, then
if state == AsyncGeneratorState::SuspendedStart {
// a. Set generator.[[AsyncGeneratorState]] to completed.
generator.state = AsyncGeneratorState::Completed;
generator.context = None;
// b. Set state to completed.
state = AsyncGeneratorState::Completed;
}
// 7. If state is completed, then
if state == AsyncGeneratorState::Completed {
drop(generator);
// a. Perform ! Call(promiseCapability.[[Reject]], undefined, « exception »).
promise_capability
.reject()
.call(
&JsValue::undefined(),
&[args.get_or_undefined(0).clone()],
context,
)
.expect("cannot fail per spec");
// b. Return promiseCapability.[[Promise]].
return Ok(promise_capability.promise().clone().into());
}
// 8. Let completion be ThrowCompletion(exception).
let completion =
CompletionRecord::Throw(JsError::from_opaque(args.get_or_undefined(0).clone()));
// 9. Perform AsyncGeneratorEnqueue(generator, completion, promiseCapability).
generator.enqueue(completion.clone(), promise_capability.clone());
// 10. If state is suspendedYield, then
if state == AsyncGeneratorState::SuspendedYield {
let generator_context = generator
.context
.take()
.expect("generator context cannot be empty here");
drop(generator);
// a. Perform AsyncGeneratorResume(generator, completion).
Self::resume(
generator_object,
state,
generator_context,
completion,
context,
);
}
// 12. Return promiseCapability.[[Promise]].
Ok(promise_capability.promise().clone().into())
}
/// `AsyncGeneratorEnqueue ( generator, completion, promiseCapability )`
///
/// More information:
/// - [ECMAScript reference][spec]
///
/// [spec]: https://tc39.es/ecma262/#sec-asyncgeneratorenqueue
pub(crate) fn enqueue(
&mut self,
completion: CompletionRecord,
promise_capability: PromiseCapability,
) {
// 1. Let request be AsyncGeneratorRequest { [[Completion]]: completion, [[Capability]]: promiseCapability }.
let request = AsyncGeneratorRequest {
completion,
capability: promise_capability,
};
// 2. Append request to the end of generator.[[AsyncGeneratorQueue]].
self.queue.push_back(request);
}
/// `AsyncGeneratorCompleteStep ( generator, completion, done [ , realm ] )`
///
/// More information:
/// - [ECMAScript reference][spec]
///
/// [spec]: https://tc39.es/ecma262/#sec-asyncgeneratorcompletestep
pub(crate) fn complete_step(
next: &AsyncGeneratorRequest,
completion: JsResult<JsValue>,
done: bool,
realm: Option<Realm>,
context: &mut Context,
) {
// 1. Let queue be generator.[[AsyncGeneratorQueue]].
// 2. Assert: queue is not empty.
// 3. Let next be the first element of queue.
// 4. Remove the first element from queue.
// 5. Let promiseCapability be next.[[Capability]].
let promise_capability = &next.capability;
// 6. Let value be completion.[[Value]].
match completion {
// 7. If completion.[[Type]] is throw, then
Err(e) => {
// a. Perform ! Call(promiseCapability.[[Reject]], undefined, « value »).
promise_capability
.reject()
.call(&JsValue::undefined(), &[e.to_opaque(context)], context)
.expect("cannot fail per spec");
}
// 8. Else,
Ok(value) => {
// a. Assert: completion.[[Type]] is normal.
// b. If realm is present, then
let iterator_result = if let Some(realm) = realm {
// i. Let oldRealm be the running execution context's Realm.
// ii. Set the running execution context's Realm to realm.
let old_realm = context.enter_realm(realm);
// iii. Let iteratorResult be CreateIterResultObject(value, done).
let iterator_result = create_iter_result_object(value, done, context);
// iv. Set the running execution context's Realm to oldRealm.
context.enter_realm(old_realm);
iterator_result
} else {
// c. Else,
// i. Let iteratorResult be CreateIterResultObject(value, done).
create_iter_result_object(value, done, context)
};
// d. Perform ! Call(promiseCapability.[[Resolve]], undefined, « iteratorResult »).
promise_capability
.resolve()
.call(&JsValue::undefined(), &[iterator_result], context)
.expect("cannot fail per spec");
}
}
}
/// `AsyncGeneratorResume ( generator, completion )`
///
/// More information:
/// - [ECMAScript reference][spec]
///
/// [spec]: https://tc39.es/ecma262/#sec-asyncgeneratorresume
pub(crate) fn resume(
generator: &JsObject,
state: AsyncGeneratorState,
mut generator_context: GeneratorContext,
completion: CompletionRecord,
context: &mut Context,
) {
// 1. Assert: generator.[[AsyncGeneratorState]] is either suspendedStart or suspendedYield.
assert!(
state == AsyncGeneratorState::SuspendedStart
|| state == AsyncGeneratorState::SuspendedYield
);
// 2. Let genContext be generator.[[AsyncGeneratorContext]].
// 3. Let callerContext be the running execution context.
// 4. Suspend callerContext.
// 5. Set generator.[[AsyncGeneratorState]] to executing.
generator
.downcast_mut::<Self>()
.expect("already checked before")
.state = AsyncGeneratorState::Executing;
let (value, resume_kind) = match completion {
CompletionRecord::Normal(val) => (val, GeneratorResumeKind::Normal),
CompletionRecord::Return(val) => (val, GeneratorResumeKind::Return),
CompletionRecord::Throw(err) => (err.to_opaque(context), GeneratorResumeKind::Throw),
};
// 6. Push genContext onto the execution context stack; genContext is now the running execution context.
let result = generator_context.resume(Some(value), resume_kind, context);
// 7. Resume the suspended evaluation of genContext using completion as the result of the operation that suspended it. Let result be the Completion Record returned by the resumed computation.
generator
.downcast_mut::<Self>()
.expect("already checked before")
.context = Some(generator_context);
// 8. Assert: result is never an abrupt completion.
assert!(!result.is_throw_completion());
// 9. Assert: When we return here, genContext has already been removed from the execution context stack and
// callerContext is the currently running execution context.
// 10. Return unused.
}
/// `AsyncGeneratorAwaitReturn ( generator )`
///
/// More information:
/// - [ECMAScript reference][spec]
///
/// [spec]: https://tc39.es/ecma262/#sec-asyncgeneratorawaitreturn
pub(crate) fn await_return(generator: JsObject, value: JsValue, context: &mut Context) {
// 1. Let queue be generator.[[AsyncGeneratorQueue]].
// 2. Assert: queue is not empty.
// 3. Let next be the first element of queue.
// 4. Let completion be Completion(next.[[Completion]]).
// Note: The spec is currently broken here.
// See: https://github.com/tc39/ecma262/pull/2683
// 6. Let promise be ? PromiseResolve(%Promise%, completion.[[Value]]).
let promise_completion = Promise::promise_resolve(
&context.intrinsics().constructors().promise().constructor(),
value,
context,
);
let promise = match promise_completion {
Ok(value) => value,
Err(value) => {
let mut gen = generator
.downcast_mut::<Self>()
.expect("already checked before");
gen.state = AsyncGeneratorState::Completed;
gen.context = None;
let next = gen.queue.pop_front().expect("queue must not be empty");
drop(gen);
Self::complete_step(&next, Err(value), true, None, context);
Self::drain_queue(&generator, context);
return;
}
};
// 7. Let fulfilledClosure be a new Abstract Closure with parameters (value) that captures generator and performs the following steps when called:
// 8. Let onFulfilled be CreateBuiltinFunction(fulfilledClosure, 1, "", « »).
let on_fulfilled = FunctionObjectBuilder::new(
context.realm(),
NativeFunction::from_copy_closure_with_captures(
|_this, args, generator, context| {
let next = {
let mut gen = generator
.downcast_mut::<Self>()
.expect("already checked before");
// a. Set generator.[[AsyncGeneratorState]] to completed.
gen.state = AsyncGeneratorState::Completed;
gen.context = None;
gen.queue.pop_front().expect("must have one entry")
};
// b. Let result be NormalCompletion(value).
let result = Ok(args.get_or_undefined(0).clone());
// c. Perform AsyncGeneratorCompleteStep(generator, result, true).
Self::complete_step(&next, result, true, None, context);
// d. Perform AsyncGeneratorDrainQueue(generator).
Self::drain_queue(generator, context);
// e. Return undefined.
Ok(JsValue::undefined())
},
generator.clone(),
),
)
.name("")
.length(1)
.build();
// 9. Let rejectedClosure be a new Abstract Closure with parameters (reason) that captures generator and performs the following steps when called:
// 10. Let onRejected be CreateBuiltinFunction(rejectedClosure, 1, "", « »).
let on_rejected = FunctionObjectBuilder::new(
context.realm(),
NativeFunction::from_copy_closure_with_captures(
|_this, args, generator, context| {
let mut gen = generator
.downcast_mut::<Self>()
.expect("already checked before");
// a. Set generator.[[AsyncGeneratorState]] to completed.
gen.state = AsyncGeneratorState::Completed;
gen.context = None;
// b. Let result be ThrowCompletion(reason).
let result = Err(JsError::from_opaque(args.get_or_undefined(0).clone()));
// c. Perform AsyncGeneratorCompleteStep(generator, result, true).
let next = gen.queue.pop_front().expect("must have one entry");
drop(gen);
Self::complete_step(&next, result, true, None, context);
// d. Perform AsyncGeneratorDrainQueue(generator).
Self::drain_queue(generator, context);
// e. Return undefined.
Ok(JsValue::undefined())
},
generator,
),
)
.name("")
.length(1)
.build();
// 11. Perform PerformPromiseThen(promise, onFulfilled, onRejected).
Promise::perform_promise_then(
&promise,
Some(on_fulfilled),
Some(on_rejected),
None,
context,
);
}
/// `AsyncGeneratorDrainQueue ( generator )`
///
/// More information:
/// - [ECMAScript reference][spec]
///
/// [spec]: https://tc39.es/ecma262/#sec-asyncgeneratordrainqueue
pub(crate) fn drain_queue(generator: &JsObject, context: &mut Context) {
let mut gen = generator
.downcast_mut::<Self>()
.expect("already checked before");
// 1. Assert: generator.[[AsyncGeneratorState]] is completed.
assert_eq!(gen.state, AsyncGeneratorState::Completed);
// 2. Let queue be generator.[[AsyncGeneratorQueue]].
let queue = &mut gen.queue;
// 3. If queue is empty, return unused.
if queue.is_empty() {
return;
}
// 4. Let done be false.
// 5. Repeat, while done is false,
loop {
// a. Let next be the first element of queue.
let next = queue.front().expect("must have entry");
// b. Let completion be Completion(next.[[Completion]]).
match next.completion.clone() {
// c. If completion.[[Type]] is return, then
CompletionRecord::Return(val) => {
// i. Set generator.[[AsyncGeneratorState]] to awaiting-return.
gen.state = AsyncGeneratorState::AwaitingReturn;
drop(gen);
// ii. Perform ! AsyncGeneratorAwaitReturn(generator).
Self::await_return(generator.clone(), val, context);
// iii. Set done to true.
break;
}
// d. Else,
completion => {
// i. If completion.[[Type]] is normal, then
// 1. Set completion to NormalCompletion(undefined).
let completion = completion.consume().map(|_| JsValue::undefined());
// ii. Perform AsyncGeneratorCompleteStep(generator, completion, true).
let next = queue.pop_front().expect("must have entry");
Self::complete_step(&next, completion, true, None, context);
// iii. If queue is empty, set done to true.
if queue.is_empty() {
break;
}
}
}
}
}
}