src/builtins/array-findlast.tq

// Copyright 2021 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.

namespace array {
// https://tc39.es/proposal-array-find-from-last/index.html#sec-array.prototype.findlast
transitioning builtin ArrayFindLastLoopContinuation(implicit context: Context)(
    predicate: Callable, thisArg: JSAny, o: JSReceiver,
    initialK: Number): JSAny {
  // 5. Repeat, while k >= 0
  for (let k: Number = initialK; k >= 0; k--) {
    // 5a. Let Pk be ! ToString(𝔽(k)).
    // k is guaranteed to be a positive integer, hence ToString is
    // side-effect free and HasProperty/GetProperty do the conversion inline.

    // 5b. Let kValue be ? Get(O, Pk).
    const value: JSAny = GetProperty(o, k);

    // 5c. Let testResult be ! ToBoolean(? Call(predicate, thisArg, « kValue,
    // 𝔽(k), O »)).
    const testResult: JSAny = Call(context, predicate, thisArg, value, k, o);

    // 5d. If testResult is true, return kValue.
    if (ToBoolean(testResult)) {
      return value;
    }

    // 5e. Set k to k - 1. (done by the loop).
  }

  // 6. Return undefined.
  return Undefined;
}

// https://tc39.es/proposal-array-find-from-last/index.html#sec-array.prototype.findlast
transitioning macro FastArrayFindLast(implicit context: Context)(
    o: JSReceiver, len: Number, predicate: Callable, thisArg: JSAny): JSAny
    labels Bailout(Number) {
  const smiLen = Cast<Smi>(len) otherwise goto Bailout(len - 1);
  // 4. Let k be len - 1.
  let k: Smi = smiLen - 1;
  const fastO = Cast<FastJSArray>(o) otherwise goto Bailout(k);
  let fastOW = NewFastJSArrayWitness(fastO);

  // 5. Repeat, while k ≥ 0
  // Build a fast loop over the smi array.
  for (; k >= 0; k--) {
    fastOW.Recheck() otherwise goto Bailout(k);

    // Ensure that we haven't walked beyond a possibly updated length.
    if (k >= fastOW.Get().length) goto Bailout(k);

    // 5a. Let Pk be ! ToString(𝔽(k)).
    // k is guaranteed to be a positive integer, hence there is no need to
    // cast ToString for LoadElementOrUndefined.

    // 5b. Let kValue be ? Get(O, Pk).
    const value: JSAny = fastOW.LoadElementOrUndefined(k);
    // 5c. Let testResult be ! ToBoolean(? Call(predicate, thisArg, « kValue,
    // 𝔽(k), O »)).
    const testResult: JSAny =
        Call(context, predicate, thisArg, value, k, fastOW.Get());
    // 5d. If testResult is true, return kValue.
    if (ToBoolean(testResult)) {
      return value;
    }

    // 5e. Set k to k - 1. (done by the loop).
  }

  // 6. Return undefined.
  return Undefined;
}

// https://tc39.es/proposal-array-find-from-last/index.html#sec-array.prototype.findlast
transitioning javascript builtin
ArrayPrototypeFindLast(
    js-implicit context: NativeContext, receiver: JSAny)(...arguments): JSAny {
  try {
    RequireObjectCoercible(receiver, 'Array.prototype.findLast');

    // 1. Let O be ? ToObject(this value).
    const o: JSReceiver = ToObject_Inline(context, receiver);

    // 2. Let len be ? LengthOfArrayLike(O).
    const len: Number = GetLengthProperty(o);

    // 3. If IsCallable(predicate) is false, throw a TypeError exception.
    if (arguments.length == 0) {
      goto NotCallableError;
    }
    const predicate = Cast<Callable>(arguments[0]) otherwise NotCallableError;

    // If a thisArg parameter is provided, it will be used as the this value for
    // each invocation of predicate. If it is not provided, undefined is used
    // instead.
    const thisArg: JSAny = arguments[1];

    // Special cases.
    try {
      return FastArrayFindLast(o, len, predicate, thisArg)
          otherwise Bailout;
    } label Bailout(k: Number) deferred {
      return ArrayFindLastLoopContinuation(predicate, thisArg, o, k);
    }
  } label NotCallableError deferred {
    ThrowTypeError(MessageTemplate::kCalledNonCallable, arguments[0]);
  }
}
}