src/builtins/weak-ref.tq

// Copyright 2020 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include 'src/builtins/builtins-collections-gen.h'

namespace runtime {

extern runtime JSWeakRefAddToKeptObjects(
    implicit context: Context)(JSReceiver|Symbol): void;

}  // namespace runtime

namespace weakref {

// https://tc39.es/ecma262/#sec-weak-ref-target
@incrementUseCounter('v8::Isolate::kWeakReferences')
transitioning javascript builtin WeakRefConstructor(
    js-implicit context: NativeContext, receiver: JSAny, newTarget: JSAny,
    target: JSFunction)(...arguments): JSWeakRef {
  // 1. If NewTarget is undefined, throw a TypeError exception.
  if (newTarget == Undefined) {
    ThrowTypeError(MessageTemplate::kConstructorNotFunction, 'WeakRef');
  }

  if (arguments.actual_count == 0) {
    ThrowTypeError(MessageTemplate::kInvalidWeakRefsWeakRefConstructorTarget);
  }

  // 2. If CanBeHeldWeakly(weakTarget) is false, throw a TypeError exception.
  GotoIfCannotBeHeldWeakly(arguments[0]) otherwise ThrowTypeError(
      MessageTemplate::kInvalidWeakRefsWeakRefConstructorTarget);
  const weakTarget = UnsafeCast<(JSReceiver | Symbol)>(arguments[0]);

  // 3. Let weakRef be ? OrdinaryCreateFromConstructor(NewTarget,
  // "%WeakRefPrototype%", « [[WeakRefTarget]] »).
  const map = GetDerivedMap(target, UnsafeCast<JSReceiver>(newTarget));
  const weakRef = UnsafeCast<JSWeakRef>(AllocateFastOrSlowJSObjectFromMap(map));
  // 4. Perfom ! AddToKeptObjects(target).
  runtime::JSWeakRefAddToKeptObjects(weakTarget);
  // 5. Set weakRef.[[WeakRefTarget]] to target.
  weakRef.target = weakTarget;
  // 6. Return weakRef.
  return weakRef;
}

transitioning javascript builtin WeakRefDeref(
    js-implicit context: NativeContext, receiver: JSAny)(): JSAny {
  // 1. Let weakRef be the this value.
  // 2. Perform ? RequireInternalSlot(weakRef, [[WeakRefTarget]]).
  const weakRef = Cast<JSWeakRef>(receiver) otherwise
  ThrowTypeError(
      MessageTemplate::kIncompatibleMethodReceiver, 'WeakRef.prototype.deref',
      receiver);
  // 3. Let target be the value of weakRef.[[WeakRefTarget]].
  const target = weakRef.target;
  // 4. If target is not empty,
  //   a. Perform ! AddToKeptObjects(target).
  //   b. Return target.
  // 5. Return undefined.
  if (target != Undefined) {
    // JSWeakRefAddToKeptObjects might allocate and cause a GC, but it
    // won't clear `target` since we hold it here on the stack.
    runtime::JSWeakRefAddToKeptObjects(
        UnsafeCast<(JSReceiver | Symbol)>(target));
  }
  return target;
}

}  // namespace weakrefs