/*
* Copyright (c) 2021, Ali Mohammad Pur <mpfard@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/TypeCasts.h>
#include <LibJS/Runtime/AsyncFunctionDriverWrapper.h>
#include <LibJS/Runtime/GlobalObject.h>
#include <LibJS/Runtime/NativeFunction.h>
#include <LibJS/Runtime/PromiseCapability.h>
#include <LibJS/Runtime/PromiseConstructor.h>
#include <LibJS/Runtime/VM.h>
#include <LibJS/Runtime/ValueInlines.h>
namespace JS {
GC_DEFINE_ALLOCATOR(AsyncFunctionDriverWrapper);
GC::Ref<Promise> AsyncFunctionDriverWrapper::create(Realm& realm, GeneratorObject* generator_object)
{
auto top_level_promise = Promise::create(realm);
// Note: The top_level_promise is also kept alive by this Wrapper
auto wrapper = realm.create<AsyncFunctionDriverWrapper>(realm, *generator_object, *top_level_promise);
// Prime the generator:
// This runs until the first `await value;`
wrapper->continue_async_execution(realm.vm(), js_undefined(), true, IsInitialExecution::Yes);
return top_level_promise;
}
AsyncFunctionDriverWrapper::AsyncFunctionDriverWrapper(Realm& realm, GC::Ref<GeneratorObject> generator_object, GC::Ref<Promise> top_level_promise)
: Promise(realm.intrinsics().promise_prototype())
, m_generator_object(generator_object)
, m_top_level_promise(top_level_promise)
{
}
// 27.7.5.3 Await ( value ), https://tc39.es/ecma262/#await
ThrowCompletionOr<void> AsyncFunctionDriverWrapper::await(JS::Value value)
{
auto& vm = this->vm();
auto& realm = *vm.current_realm();
// 1. Let asyncContext be the running execution context.
if (!m_suspended_execution_context)
m_suspended_execution_context = vm.running_execution_context().copy();
// 2. Let promise be ? PromiseResolve(%Promise%, value).
auto* promise_object = TRY(promise_resolve(vm, realm.intrinsics().promise_constructor(), value));
// 3. Let fulfilledClosure be a new Abstract Closure with parameters (v) that captures asyncContext and performs the
// following steps when called:
auto fulfilled_closure = [this](VM& vm) -> ThrowCompletionOr<Value> {
auto value = vm.argument(0);
// a. Let prevContext be the running execution context.
auto& prev_context = vm.running_execution_context();
// FIXME: b. Suspend prevContext.
// c. Push asyncContext onto the execution context stack; asyncContext is now the running execution context.
TRY(vm.push_execution_context(*m_suspended_execution_context, {}));
// d. Resume the suspended evaluation of asyncContext using NormalCompletion(v) as the result of the operation that
// suspended it.
continue_async_execution(vm, value, true);
// e. Assert: When we reach this step, asyncContext has already been removed from the execution context stack and
// prevContext is the currently running execution context.
VERIFY(&vm.running_execution_context() == &prev_context);
// f. Return undefined.
return js_undefined();
};
// 4. Let onFulfilled be CreateBuiltinFunction(fulfilledClosure, 1, "", « »).
auto on_fulfilled = NativeFunction::create(realm, move(fulfilled_closure), 1, "");
// 5. Let rejectedClosure be a new Abstract Closure with parameters (reason) that captures asyncContext and performs the
// following steps when called:
auto rejected_closure = [this](VM& vm) -> ThrowCompletionOr<Value> {
auto reason = vm.argument(0);
// a. Let prevContext be the running execution context.
auto& prev_context = vm.running_execution_context();
// FIXME: b. Suspend prevContext.
// c. Push asyncContext onto the execution context stack; asyncContext is now the running execution context.
TRY(vm.push_execution_context(*m_suspended_execution_context, {}));
// d. Resume the suspended evaluation of asyncContext using ThrowCompletion(reason) as the result of the operation that
// suspended it.
continue_async_execution(vm, reason, false);
// e. Assert: When we reach this step, asyncContext has already been removed from the execution context stack and
// prevContext is the currently running execution context.
VERIFY(&vm.running_execution_context() == &prev_context);
// f. Return undefined.
return js_undefined();
};
// 6. Let onRejected be CreateBuiltinFunction(rejectedClosure, 1, "", « »).
auto on_rejected = NativeFunction::create(realm, move(rejected_closure), 1, "");
// 7. Perform PerformPromiseThen(promise, onFulfilled, onRejected).
m_current_promise = verify_cast<Promise>(promise_object);
m_current_promise->perform_then(on_fulfilled, on_rejected, {});
// 8. Remove asyncContext from the execution context stack and restore the execution context that is at the top of the
// execution context stack as the running execution context.
// NOTE: This is done later on for us in continue_async_execution.
// NOTE: None of these are necessary. 10-12 are handled by step d of the above lambdas.
// 9. Let callerContext be the running execution context.
// 10. Resume callerContext passing empty. If asyncContext is ever resumed again, let completion be the Completion Record with which it is resumed.
// 11. Assert: If control reaches here, then asyncContext is the running execution context again.
// 12. Return completion.
return {};
}
void AsyncFunctionDriverWrapper::continue_async_execution(VM& vm, Value value, bool is_successful, IsInitialExecution is_initial_execution)
{
auto generator_result = is_successful
? m_generator_object->resume(vm, value, {})
: m_generator_object->resume_abrupt(vm, throw_completion(value), {});
auto result = [&, this]() -> ThrowCompletionOr<void> {
while (true) {
if (generator_result.is_throw_completion())
return generator_result.throw_completion();
auto result = generator_result.release_value();
VERIFY(result.is_object());
auto promise_value = TRY(result.get(vm, vm.names.value));
if (TRY(result.get(vm, vm.names.done)).to_boolean()) {
// When returning a promise, we need to unwrap it.
if (promise_value.is_object() && is<Promise>(promise_value.as_object())) {
auto& returned_promise = static_cast<Promise&>(promise_value.as_object());
if (returned_promise.state() == Promise::State::Fulfilled) {
m_top_level_promise->fulfill(returned_promise.result());
return {};
}
if (returned_promise.state() == Promise::State::Rejected)
return throw_completion(returned_promise.result());
// The promise is still pending but there's nothing more to do here.
return {};
}
// We hit a `return value;`
m_top_level_promise->fulfill(promise_value);
return {};
}
// We hit `await Promise`
auto await_result = this->await(promise_value);
if (await_result.is_throw_completion()) {
generator_result = m_generator_object->resume_abrupt(vm, await_result.release_error(), {});
continue;
}
return {};
}
}();
if (result.is_throw_completion()) {
m_top_level_promise->reject(result.throw_completion().value().value_or(js_undefined()));
}
// For the initial execution, the execution context will be popped for us later on by ECMAScriptFunctionObject.
if (is_initial_execution == IsInitialExecution::No)
vm.pop_execution_context();
}
void AsyncFunctionDriverWrapper::visit_edges(Cell::Visitor& visitor)
{
Base::visit_edges(visitor);
visitor.visit(m_generator_object);
visitor.visit(m_top_level_promise);
if (m_current_promise)
visitor.visit(m_current_promise);
if (m_suspended_execution_context)
m_suspended_execution_context->visit_edges(visitor);
}
}