Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 571 insertions, 0 deletions

diff --git a/js/src/vm/AsyncIteration.h b/js/src/vm/AsyncIteration.h
new file mode 100644
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef vm_AsyncIteration_h
+#define vm_AsyncIteration_h
+
+#include "builtin/Promise.h"  // js::PromiseHandler
+#include "builtin/SelfHostingDefines.h"
+#include "js/Class.h"
+#include "vm/GeneratorObject.h"
+#include "vm/JSObject.h"
+#include "vm/List.h"
+#include "vm/PromiseObject.h"
+
+// [SMDOC] Async generators
+//
+// # Start
+//
+// When an async generator is called, it synchronously runs until the
+// JSOp::InitialYield and then suspends, just like a sync generator, and returns
+// an async generator object (js::AsyncGeneratorObject).
+//
+//
+// # Request queue
+//
+// When next/return/throw is called on the async generator object,
+// js::AsyncGeneratorEnqueue performs the following:
+//   * Create a new AsyncGeneratorRequest and enqueue it in the generator
+//     object's request queue.
+//   * Resume the generator with the oldest request, if the generator is
+//     suspended (see "Resume" section below)
+//   * Return the promise for the request
+//
+// This is done in js::AsyncGeneratorEnqueue, which corresponds to
+// AsyncGeneratorEnqueue in the spec,
+// and js::AsyncGeneratorResumeNext corresponds to the following:
+//   * AsyncGeneratorResolve
+//   * AsyncGeneratorReject
+//   * AsyncGeneratorResumeNext
+//
+// The returned promise is resolved when the resumption for the request
+// completes with yield/throw/return, in js::AsyncGeneratorResolve and
+// js::AsyncGeneratorReject.
+// They correspond to AsyncGeneratorResolve and AsyncGeneratorReject in the
+// spec.
+//
+//
+// # Await
+//
+// Async generator's `await` is implemented differently than async function's
+// `await`.
+//
+// The bytecode is the following:
+// (ignoring CanSkipAwait; see the comment in AsyncFunction.h for more details)
+//
+// ```
+//   (operand here)                  # VALUE
+//   GetAliasedVar ".generator"      # VALUE .generator
+//   Await 0                         # RVAL GENERATOR RESUMEKIND
+//
+//   AfterYield                      # RVAL GENERATOR RESUMEKIND
+//   CheckResumeKind                 # RVAL
+// ```
+//
+// Async generators don't use JSOp::AsyncAwait, and that part is handled
+// in js::AsyncGeneratorResume, and js::AsyncGeneratorAwait called there.
+//
+// Both JSOp::Await and JSOp::Yield behave in the exactly same way,
+// and js::AsyncGeneratorResume checks the last opcode and branches for
+// await/yield/return cases.
+//
+//
+// # Reaction jobs and resume after await
+//
+// This is almost same as for async functions (see AsyncFunction.h).
+//
+// The reaction record for the job is marked as "this is for async generator"
+// (see js::AsyncGeneratorAwait), and handled specially in
+// js::PromiseReactionJob, which calls js::AsyncGeneratorPromiseReactionJob.
+//
+//
+// # Yield
+//
+// `yield` is implemented with the following bytecode sequence:
+// (Ignoring CanSkipAwait for simplicity)
+//
+// ```
+//   (operand here)                  # VALUE
+//   GetAliasedVar ".generator"      # VALUE .generator
+//   Await 1                         # RVAL GENERATOR RESUMEKIND
+//   AfterYield                      # RVAL GENERATOR RESUMEKIND
+//   CheckResumeKind                 # RVAL
+//
+//   GetAliasedVar ".generator"      # RVAL .generator
+//   Yield 2                         # RVAL2 GENERATOR RESUMEKIND
+//
+//   AfterYield                      # RVAL2 GENERATOR RESUMEKIND
+//   CheckResumeKind                 # RVAL2
+// ```
+//
+// The 1st part (JSOp::Await + JSOp::CheckResumeKind) performs an implicit
+// `await`, as specified in AsyncGeneratorYield step 5.
+//
+// AsyncGeneratorYield ( value )
+// https://tc39.es/ecma262/#sec-asyncgeneratoryield
+//
+//   5. Set value to ? Await(value).
+//
+// The 2nd part (JSOp::Yield) suspends execution and yields the result of
+// `await`, as specified in AsyncGeneratorYield steps 1-4, 6-7, 9-10.
+//
+// AsyncGeneratorYield ( value )
+// https://tc39.es/ecma262/#sec-asyncgeneratoryield
+//
+//   1. Let genContext be the running execution context.
+//   2. Assert: genContext is the execution context of a generator.
+//   3. Let generator be the value of the Generator component of genContext.
+//   4. Assert: GetGeneratorKind() is async.
+//   ..
+//   6. Set generator.[[AsyncGeneratorState]] to suspendedYield.
+//   7. Remove genContext 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.
+//   8. ...
+//   9. Return ! AsyncGeneratorResolve(generator, value, false).
+//   10. NOTE: This returns to the evaluation of the operation that had most
+//       previously resumed evaluation of genContext.
+//
+// The last part (JSOp::CheckResumeKind) checks the resumption type and
+// resumes/throws/returns the execution, as specified in AsyncGeneratorYield
+// step 8.
+//
+//   8. Set the code evaluation state of genContext such that when evaluation is
+//      resumed with a Completion resumptionValue the following steps will be
+//      performed:
+//     a. If resumptionValue.[[Type]] is not return, return
+//        Completion(resumptionValue).
+//     b. Let awaited be Await(resumptionValue.[[Value]]).
+//     c. If awaited.[[Type]] is throw, return Completion(awaited).
+//     d. Assert: awaited.[[Type]] is normal.
+//     e. Return Completion { [[Type]]: return, [[Value]]: awaited.[[Value]],
+//        [[Target]]: empty }.
+//     f. NOTE: When one of the above steps returns, it returns to the
+//        evaluation of the YieldExpression production that originally called
+//        this abstract operation.
+//
+// Resumption with `AsyncGenerator.prototype.return` is handled differently.
+// See "Resumption with return" section below.
+//
+//
+// # Return
+//
+// `return` with operand is implemented with the following bytecode sequence:
+// (Ignoring CanSkipAwait for simplicity)
+//
+// ```
+//   (operand here)                  # VALUE
+//   GetAliasedVar ".generator"      # VALUE .generator
+//   Await 0                         # RVAL GENERATOR RESUMEKIND
+//   AfterYield                      # RVAL GENERATOR RESUMEKIND
+//   CheckResumeKind                 # RVAL
+//
+//   SetRval                         #
+//   GetAliasedVar ".generator"      # .generator
+//   FinalYieldRval                  #
+// ```
+//
+// The 1st part (JSOp::Await + JSOp::CheckResumeKind) performs implicit
+// `await`, as specified in ReturnStatement's Evaluation step 3.
+//
+// ReturnStatement: return Expression;
+// https://tc39.es/ecma262/#sec-return-statement-runtime-semantics-evaluation
+//
+//   3. If ! GetGeneratorKind() is async, set exprValue to ? Await(exprValue).
+//
+// And the 2nd part corresponds to AsyncGeneratorStart steps 5.a-e, 5.g.
+//
+// AsyncGeneratorStart ( generator, generatorBody )
+// https://tc39.es/ecma262/#sec-asyncgeneratorstart
+//
+//   5. Set the code evaluation state of genContext such that when evaluation
+//      is resumed for that execution context the following steps will be
+//      performed:
+//     a. Let result be the result of evaluating generatorBody.
+//     b. Assert: If we return here, the async generator either threw an
+//        exception or performed either an implicit or explicit return.
+//     c. Remove genContext 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.
+//     d. Set generator.[[AsyncGeneratorState]] to completed.
+//     e. If result is a normal completion, let resultValue be undefined.
+//     ...
+//     g. Return ! AsyncGeneratorResolve(generator, resultValue, true).
+//
+// `return` without operand or implicit return is implicit with the following
+// bytecode sequence:
+//
+// ```
+//   Undefined                       # undefined
+//   SetRval                         #
+//   GetAliasedVar ".generator"      # .generator
+//   FinalYieldRval                  #
+// ```
+//
+// This is also AsyncGeneratorStart steps 5.a-e, 5.g.
+//
+//
+// # Throw
+//
+// Unlike async function, async generator doesn't use implicit try-catch,
+// but the throw completion is handled by js::AsyncGeneratorResume,
+// and js::AsyncGeneratorThrown is called there.
+//
+//   5. ...
+//     f. Else,
+//       i. Let resultValue be result.[[Value]].
+//       ii. If result.[[Type]] is not return, then
+//         1. Return ! AsyncGeneratorReject(generator, resultValue).
+//
+//
+// # Resumption with return
+//
+// Resumption with return completion is handled in js::AsyncGeneratorResumeNext.
+//
+// If the generator is suspended, it doesn't immediately resume the generator
+// script itself, but handles implicit `await` it in
+// js::AsyncGeneratorResumeNext.
+// (See PromiseHandlerAsyncGeneratorYieldReturnAwaitedFulfilled and
+// PromiseHandlerAsyncGeneratorYieldReturnAwaitedRejected), and resumes the
+// generator with the result of await.
+// And the return completion is finally handled in JSOp::CheckResumeKind
+// after JSOp::Yield.
+//
+// This corresponds to AsyncGeneratorYield step 8.
+//
+// AsyncGeneratorYield ( value )
+// https://tc39.es/ecma262/#sec-asyncgeneratoryield
+//
+//   8. Set the code evaluation state of genContext such that when evaluation
+//      is resumed with a Completion resumptionValue the following steps will
+//      be performed:
+//     ..
+//     b. Let awaited be Await(resumptionValue.[[Value]]).
+//     c. If awaited.[[Type]] is throw, return Completion(awaited).
+//     d. Assert: awaited.[[Type]] is normal.
+//     e. Return Completion { [[Type]]: return, [[Value]]: awaited.[[Value]],
+//        [[Target]]: empty }.
+//
+// If the generator is already completed, it awaits on the return value,
+// (See PromiseHandlerAsyncGeneratorResumeNextReturnFulfilled and
+//  PromiseHandlerAsyncGeneratorResumeNextReturnRejected), and resolves the
+// request's promise with the value.
+//
+// It corresponds to AsyncGeneratorResumeNext step 10.b.i.
+//
+// AsyncGeneratorResumeNext ( generator )
+// https://tc39.es/ecma262/#sec-asyncgeneratorresumenext
+//
+//   10. If completion is an abrupt completion, then
+//     ..
+//     b. If state is completed, then
+//       i. If completion.[[Type]] is return, then
+//         1. Set generator.[[AsyncGeneratorState]] to awaiting-return.
+//         2. Let promise be ? PromiseResolve(%Promise%, completion.[[Value]]).
+//         3. Let stepsFulfilled be the algorithm steps defined in
+//            AsyncGeneratorResumeNext Return Processor Fulfilled Functions.
+//         4. Let onFulfilled be ! CreateBuiltinFunction(stepsFulfilled, «
+//            [[Generator]] »).
+//         5. Set onFulfilled.[[Generator]] to generator.
+//         6. Let stepsRejected be the algorithm steps defined in
+//            AsyncGeneratorResumeNext Return Processor Rejected Functions.
+//         7. Let onRejected be ! CreateBuiltinFunction(stepsRejected, «
+//            [[Generator]] »).
+//         8. Set onRejected.[[Generator]] to generator.
+//         9. Perform ! PerformPromiseThen(promise, onFulfilled, onRejected).
+//         10. Return undefined.
+//
+
+namespace js {
+
+class AsyncGeneratorObject;
+enum class CompletionKind : uint8_t;
+
+extern const JSClass AsyncGeneratorFunctionClass;
+
+[[nodiscard]] bool AsyncGeneratorPromiseReactionJob(
+    JSContext* cx, PromiseHandler handler,
+    Handle<AsyncGeneratorObject*> generator, HandleValue argument);
+
+bool AsyncGeneratorNext(JSContext* cx, unsigned argc, Value* vp);
+bool AsyncGeneratorReturn(JSContext* cx, unsigned argc, Value* vp);
+bool AsyncGeneratorThrow(JSContext* cx, unsigned argc, Value* vp);
+
+// AsyncGeneratorRequest record in the spec.
+// Stores the info from AsyncGenerator#{next,return,throw}.
+//
+// This object is reused across multiple requests as an optimization, and
+// stored in the Slot_CachedRequest slot.
+class AsyncGeneratorRequest : public NativeObject {
+ private:
+  enum AsyncGeneratorRequestSlots {
+    // Int32 value with CompletionKind.
+    //   Normal: next
+    //   Return: return
+    //   Throw:  throw
+    Slot_CompletionKind = 0,
+
+    // The value passed to AsyncGenerator#{next,return,throw}.
+    Slot_CompletionValue,
+
+    // The promise returned by AsyncGenerator#{next,return,throw}.
+    Slot_Promise,
+
+    Slots,
+  };
+
+  void init(CompletionKind completionKind, const Value& completionValue,
+            PromiseObject* promise) {
+    setFixedSlot(Slot_CompletionKind,
+                 Int32Value(static_cast<int32_t>(completionKind)));
+    setFixedSlot(Slot_CompletionValue, completionValue);
+    setFixedSlot(Slot_Promise, ObjectValue(*promise));
+  }
+
+  // Clear the request data for reuse.
+  void clearData() {
+    setFixedSlot(Slot_CompletionValue, NullValue());
+    setFixedSlot(Slot_Promise, NullValue());
+  }
+
+  friend AsyncGeneratorObject;
+
+ public:
+  static const JSClass class_;
+
+  static AsyncGeneratorRequest* create(JSContext* cx,
+                                       CompletionKind completionKind,
+                                       HandleValue completionValue,
+                                       Handle<PromiseObject*> promise);
+
+  CompletionKind completionKind() const {
+    return static_cast<CompletionKind>(
+        getFixedSlot(Slot_CompletionKind).toInt32());
+  }
+  JS::Value completionValue() const {
+    return getFixedSlot(Slot_CompletionValue);
+  }
+  PromiseObject* promise() const {
+    return &getFixedSlot(Slot_Promise).toObject().as<PromiseObject>();
+  }
+};
+
+class AsyncGeneratorObject : public AbstractGeneratorObject {
+ private:
+  enum AsyncGeneratorObjectSlots {
+    // Int32 value containing one of the |State| fields from below.
+    Slot_State = AbstractGeneratorObject::RESERVED_SLOTS,
+
+    // * null value if this async generator has no requests
+    // * AsyncGeneratorRequest if this async generator has only one request
+    // * list object if this async generator has 2 or more requests
+    Slot_QueueOrRequest,
+
+    // Cached AsyncGeneratorRequest for later use.
+    // undefined if there's no cache.
+    Slot_CachedRequest,
+
+    Slots
+  };
+
+ public:
+  enum State {
+    // "suspendedStart" in the spec.
+    // Suspended after invocation.
+    State_SuspendedStart,
+
+    // "suspendedYield" in the spec
+    // Suspended with `yield` expression.
+    State_SuspendedYield,
+
+    // "executing" in the spec.
+    // Resumed from initial suspend or yield, and either running the script
+    // or awaiting for `await` expression.
+    State_Executing,
+
+    // Part of "executing" in the spec.
+    // Awaiting on the value passed by AsyncGenerator#return which is called
+    // while executing.
+    State_AwaitingYieldReturn,
+
+    // "awaiting-return" in the spec.
+    // Awaiting on the value passed by AsyncGenerator#return which is called
+    // after completed.
+    State_AwaitingReturn,
+
+    // "completed" in the spec.
+    // The generator is completed.
+    State_Completed
+  };
+
+  State state() const {
+    return static_cast<State>(getFixedSlot(Slot_State).toInt32());
+  }
+  void setState(State state_) { setFixedSlot(Slot_State, Int32Value(state_)); }
+
+ private:
+  // Queue is implemented in 2 ways.  If only one request is queued ever,
+  // request is stored directly to the slot.  Once 2 requests are queued, a
+  // list is created and requests are appended into it, and the list is
+  // stored to the slot.
+
+  bool isSingleQueue() const {
+    return getFixedSlot(Slot_QueueOrRequest).isNull() ||
+           getFixedSlot(Slot_QueueOrRequest)
+               .toObject()
+               .is<AsyncGeneratorRequest>();
+  }
+  bool isSingleQueueEmpty() const {
+    return getFixedSlot(Slot_QueueOrRequest).isNull();
+  }
+  void setSingleQueueRequest(AsyncGeneratorRequest* request) {
+    setFixedSlot(Slot_QueueOrRequest, ObjectValue(*request));
+  }
+  void clearSingleQueueRequest() {
+    setFixedSlot(Slot_QueueOrRequest, NullValue());
+  }
+  AsyncGeneratorRequest* singleQueueRequest() const {
+    return &getFixedSlot(Slot_QueueOrRequest)
+                .toObject()
+                .as<AsyncGeneratorRequest>();
+  }
+
+  ListObject* queue() const {
+    return &getFixedSlot(Slot_QueueOrRequest).toObject().as<ListObject>();
+  }
+  void setQueue(ListObject* queue_) {
+    setFixedSlot(Slot_QueueOrRequest, ObjectValue(*queue_));
+  }
+
+ public:
+  static const JSClass class_;
+  static const JSClassOps classOps_;
+
+  static AsyncGeneratorObject* create(JSContext* cx, HandleFunction asyncGen);
+
+  bool isSuspendedStart() const { return state() == State_SuspendedStart; }
+  bool isSuspendedYield() const { return state() == State_SuspendedYield; }
+  bool isExecuting() const { return state() == State_Executing; }
+  bool isAwaitingYieldReturn() const {
+    return state() == State_AwaitingYieldReturn;
+  }
+  bool isAwaitingReturn() const { return state() == State_AwaitingReturn; }
+  bool isCompleted() const { return state() == State_Completed; }
+
+  void setSuspendedStart() { setState(State_SuspendedStart); }
+  void setSuspendedYield() { setState(State_SuspendedYield); }
+  void setExecuting() { setState(State_Executing); }
+  void setAwaitingYieldReturn() { setState(State_AwaitingYieldReturn); }
+  void setAwaitingReturn() { setState(State_AwaitingReturn); }
+  void setCompleted() { setState(State_Completed); }
+
+  [[nodiscard]] static bool enqueueRequest(
+      JSContext* cx, Handle<AsyncGeneratorObject*> generator,
+      Handle<AsyncGeneratorRequest*> request);
+
+  static AsyncGeneratorRequest* dequeueRequest(
+      JSContext* cx, Handle<AsyncGeneratorObject*> generator);
+
+  static AsyncGeneratorRequest* peekRequest(
+      Handle<AsyncGeneratorObject*> generator);
+
+  bool isQueueEmpty() const {
+    if (isSingleQueue()) {
+      return isSingleQueueEmpty();
+    }
+    return queue()->getDenseInitializedLength() == 0;
+  }
+
+  // This function does either of the following:
+  //   * return a cached request object with the slots updated
+  //   * create a new request object with the slots set
+  static AsyncGeneratorRequest* createRequest(
+      JSContext* cx, Handle<AsyncGeneratorObject*> generator,
+      CompletionKind completionKind, HandleValue completionValue,
+      Handle<PromiseObject*> promise);
+
+  // Stores the given request to the generator's cache after clearing its data
+  // slots.  The cached request will be reused in the subsequent createRequest
+  // call.
+  void cacheRequest(AsyncGeneratorRequest* request) {
+    if (hasCachedRequest()) {
+      return;
+    }
+
+    request->clearData();
+    setFixedSlot(Slot_CachedRequest, ObjectValue(*request));
+  }
+
+ private:
+  bool hasCachedRequest() const {
+    return getFixedSlot(Slot_CachedRequest).isObject();
+  }
+
+  AsyncGeneratorRequest* takeCachedRequest() {
+    auto request = &getFixedSlot(Slot_CachedRequest)
+                        .toObject()
+                        .as<AsyncGeneratorRequest>();
+    clearCachedRequest();
+    return request;
+  }
+
+  void clearCachedRequest() { setFixedSlot(Slot_CachedRequest, NullValue()); }
+};
+
+JSObject* CreateAsyncFromSyncIterator(JSContext* cx, HandleObject iter,
+                                      HandleValue nextMethod);
+
+class AsyncFromSyncIteratorObject : public NativeObject {
+ private:
+  enum AsyncFromSyncIteratorObjectSlots {
+    // Object that implements the sync iterator protocol.
+    Slot_Iterator = 0,
+
+    // The `next` property of the iterator object.
+    Slot_NextMethod = 1,
+
+    Slots
+  };
+
+  void init(JSObject* iterator, const Value& nextMethod) {
+    setFixedSlot(Slot_Iterator, ObjectValue(*iterator));
+    setFixedSlot(Slot_NextMethod, nextMethod);
+  }
+
+ public:
+  static const JSClass class_;
+
+  static JSObject* create(JSContext* cx, HandleObject iter,
+                          HandleValue nextMethod);
+
+  JSObject* iterator() const { return &getFixedSlot(Slot_Iterator).toObject(); }
+
+  const Value& nextMethod() const { return getFixedSlot(Slot_NextMethod); }
+};
+
+class AsyncIteratorObject : public NativeObject {
+ public:
+  static const JSClass class_;
+  static const JSClass protoClass_;
+};
+
+// Iterator Helpers proposal
+class AsyncIteratorHelperObject : public NativeObject {
+ public:
+  static const JSClass class_;
+
+  enum { GeneratorSlot, SlotCount };
+
+  static_assert(GeneratorSlot == ASYNC_ITERATOR_HELPER_GENERATOR_SLOT,
+                "GeneratorSlot must match self-hosting define for generator "
+                "object slot.");
+};
+
+AsyncIteratorHelperObject* NewAsyncIteratorHelper(JSContext* cx);
+
+}  // namespace js
+
+#endif /* vm_AsyncIteration_h */