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LibJS: Annotate Promise implementation with spec comments
I wanted to do this for a long time. The guts of Promise are pretty complex, and it's easier to understand with the spec right next to it. Also found a couple of issues along the way :^)
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7 changed files with 523 additions and 41 deletions
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@ -29,47 +29,78 @@ PromiseReactionJob::PromiseReactionJob(PromiseReaction& reaction, Value argument
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ThrowCompletionOr<Value> PromiseReactionJob::call()
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{
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auto& vm = this->vm();
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// a. Let promiseCapability be reaction.[[Capability]].
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auto& promise_capability = m_reaction.capability();
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// b. Let type be reaction.[[Type]].
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auto type = m_reaction.type();
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// c. Let handler be reaction.[[Handler]].
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auto handler = m_reaction.handler();
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Value handler_result;
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// d. If handler is empty, then
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if (!handler.has_value()) {
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dbgln_if(PROMISE_DEBUG, "[PromiseReactionJob @ {}]: Handler is empty", this);
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switch (type) {
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case PromiseReaction::Type::Fulfill:
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// i. If type is Fulfill, let handlerResult be NormalCompletion(argument).
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if (type == PromiseReaction::Type::Fulfill) {
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dbgln_if(PROMISE_DEBUG, "[PromiseReactionJob @ {}]: Reaction type is Type::Fulfill, setting handler result to {}", this, m_argument);
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handler_result = m_argument;
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break;
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case PromiseReaction::Type::Reject:
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}
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// ii. Else,
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else {
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// 1. Assert: type is Reject.
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VERIFY(type == PromiseReaction::Type::Reject);
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// 2. Let handlerResult be ThrowCompletion(argument).
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// NOTE: handler_result is set to exception value further below
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dbgln_if(PROMISE_DEBUG, "[PromiseReactionJob @ {}]: Reaction type is Type::Reject, throwing exception with argument {}", this, m_argument);
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vm.throw_exception(global_object(), m_argument);
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// handler_result is set to exception value further below
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break;
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}
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} else {
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}
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// e. Else, let handlerResult be HostCallJobCallback(handler, undefined, « argument »).
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else {
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dbgln_if(PROMISE_DEBUG, "[PromiseReactionJob @ {}]: Calling handler callback {} @ {} with argument {}", this, handler.value().callback->class_name(), handler.value().callback, m_argument);
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handler_result = call_job_callback(vm, handler.value(), js_undefined(), m_argument);
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}
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// f. If promiseCapability is undefined, then
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if (!promise_capability.has_value()) {
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// i. Assert: handlerResult is not an abrupt completion.
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VERIFY(!vm.exception());
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// ii. Return NormalCompletion(empty).
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dbgln_if(PROMISE_DEBUG, "[PromiseReactionJob @ {}]: Reaction has no PromiseCapability, returning empty value", this);
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// TODO: This can't return an empty value at the moment, because the implicit conversion to Completion would fail.
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// Change it back when this is using completions (`return normal_completion({})`)
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return js_undefined();
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}
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// g. Assert: promiseCapability is a PromiseCapability Record.
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// h. If handlerResult is an abrupt completion, then
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if (vm.exception()) {
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handler_result = vm.exception()->value();
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vm.clear_exception();
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vm.stop_unwind();
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// i. Let status be Call(promiseCapability.[[Reject]], undefined, « handlerResult.[[Value]] »).
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auto* reject_function = promise_capability.value().reject;
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dbgln_if(PROMISE_DEBUG, "[PromiseReactionJob @ {}]: Calling PromiseCapability's reject function @ {}", this, reject_function);
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return vm.call(*reject_function, js_undefined(), handler_result);
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} else {
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}
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// i. Else,
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else {
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// i. Let status be Call(promiseCapability.[[Resolve]], undefined, « handlerResult.[[Value]] »).
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auto* resolve_function = promise_capability.value().resolve;
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dbgln_if(PROMISE_DEBUG, "[PromiseReactionJob @ {}]: Calling PromiseCapability's resolve function @ {}", this, resolve_function);
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return vm.call(*resolve_function, js_undefined(), handler_result);
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}
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// j. Return Completion(status).
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}
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void PromiseReactionJob::visit_edges(Visitor& visitor)
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@ -97,16 +128,29 @@ PromiseResolveThenableJob::PromiseResolveThenableJob(Promise& promise_to_resolve
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ThrowCompletionOr<Value> PromiseResolveThenableJob::call()
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{
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auto& vm = this->vm();
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// a. Let resolvingFunctions be CreateResolvingFunctions(promiseToResolve).
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auto [resolve_function, reject_function] = m_promise_to_resolve.create_resolving_functions();
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// b. Let thenCallResult be HostCallJobCallback(then, thenable, « resolvingFunctions.[[Resolve]], resolvingFunctions.[[Reject]] »).
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dbgln_if(PROMISE_DEBUG, "[PromiseResolveThenableJob @ {}]: Calling then job callback for thenable {}", this, &m_thenable);
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auto then_call_result = call_job_callback(vm, m_then, m_thenable, &resolve_function, &reject_function);
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// c. If thenCallResult is an abrupt completion, then
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if (vm.exception()) {
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auto error = vm.exception()->value();
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vm.clear_exception();
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vm.stop_unwind();
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// i. Let status be Call(resolvingFunctions.[[Reject]], undefined, « thenCallResult.[[Value]] »).
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// FIXME: Actually do this... not sure why we don't? :yakfused:
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// ii. Return Completion(status).
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dbgln_if(PROMISE_DEBUG, "[PromiseResolveThenableJob @ {}]: An exception was thrown, returning error {}", this, error);
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return error;
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}
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// d. Return Completion(thenCallResult).
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dbgln_if(PROMISE_DEBUG, "[PromiseResolveThenableJob @ {}]: Returning then call result {}", this, then_call_result);
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return then_call_result;
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}
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