src/vm/ForOfIterator.cpp

/* -*- 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/. */

#include "js/ForOfIterator.h"
#include "js/friend/ErrorMessages.h"  // js::GetErrorMessage, JSMSG_*
#include "vm/Interpreter.h"
#include "vm/JSContext.h"
#include "vm/JSObject.h"
#include "vm/PIC.h"
#include "vm/Realm.h"

#include "vm/JSObject-inl.h"

using namespace js;
using JS::ForOfIterator;

bool ForOfIterator::init(HandleValue iterable,
                         NonIterableBehavior nonIterableBehavior) {
  JSContext* cx = cx_;
  RootedObject iterableObj(cx, ToObject(cx, iterable));
  if (!iterableObj) {
    return false;
  }

  MOZ_ASSERT(index == NOT_ARRAY);

  // Check the PIC first for a match.
  if (iterableObj->is<ArrayObject>()) {
    ForOfPIC::Chain* stubChain = ForOfPIC::getOrCreate(cx);
    if (!stubChain) {
      return false;
    }

    bool optimized;
    if (!stubChain->tryOptimizeArray(cx, iterableObj.as<ArrayObject>(),
                                     &optimized)) {
      return false;
    }

    if (optimized) {
      // Got optimized stub.  Array is optimizable.
      index = 0;
      iterator = iterableObj;
      nextMethod.setUndefined();
      return true;
    }
  }

  MOZ_ASSERT(index == NOT_ARRAY);

  RootedValue callee(cx);
  RootedId iteratorId(cx, SYMBOL_TO_JSID(cx->wellKnownSymbols().iterator));
  if (!GetProperty(cx, iterableObj, iterable, iteratorId, &callee)) {
    return false;
  }

  // If obj[@@iterator] is undefined and we were asked to allow non-iterables,
  // bail out now without setting iterator.  This will make valueIsIterable(),
  // which our caller should check, return false.
  if (nonIterableBehavior == AllowNonIterable && callee.isUndefined()) {
    return true;
  }

  // Throw if obj[@@iterator] isn't callable.
  // js::Invoke is about to check for this kind of error anyway, but it would
  // throw an inscrutable error message about |method| rather than this nice
  // one about |obj|.
  if (!callee.isObject() || !callee.toObject().isCallable()) {
    UniqueChars bytes =
        DecompileValueGenerator(cx, JSDVG_SEARCH_STACK, iterable, nullptr);
    if (!bytes) {
      return false;
    }
    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr, JSMSG_NOT_ITERABLE,
                             bytes.get());
    return false;
  }

  RootedValue res(cx);
  if (!js::Call(cx, callee, iterable, &res)) {
    return false;
  }

  if (!res.isObject()) {
    return ThrowCheckIsObject(cx, CheckIsObjectKind::GetIterator);
  }

  RootedObject iteratorObj(cx, &res.toObject());
  if (!GetProperty(cx, iteratorObj, iteratorObj, cx->names().next, &res)) {
    return false;
  }

  iterator = iteratorObj;
  nextMethod = res;
  return true;
}

inline bool ForOfIterator::nextFromOptimizedArray(MutableHandleValue vp,
                                                  bool* done) {
  MOZ_ASSERT(index != NOT_ARRAY);

  if (!CheckForInterrupt(cx_)) {
    return false;
  }

  ArrayObject* arr = &iterator->as<ArrayObject>();

  if (index >= arr->length()) {
    vp.setUndefined();
    *done = true;
    return true;
  }
  *done = false;

  // Try to get array element via direct access.
  if (index < arr->getDenseInitializedLength()) {
    vp.set(arr->getDenseElement(index));
    if (!vp.isMagic(JS_ELEMENTS_HOLE)) {
      ++index;
      return true;
    }
  }

  return GetElement(cx_, iterator, iterator, index++, vp);
}

bool ForOfIterator::next(MutableHandleValue vp, bool* done) {
  MOZ_ASSERT(iterator);
  if (index != NOT_ARRAY) {
    return nextFromOptimizedArray(vp, done);
  }

  RootedValue v(cx_);
  if (!js::Call(cx_, nextMethod, iterator, &v)) {
    return false;
  }

  if (!v.isObject()) {
    return ThrowCheckIsObject(cx_, CheckIsObjectKind::IteratorNext);
  }

  RootedObject resultObj(cx_, &v.toObject());
  if (!GetProperty(cx_, resultObj, resultObj, cx_->names().done, &v)) {
    return false;
  }

  *done = ToBoolean(v);
  if (*done) {
    vp.setUndefined();
    return true;
  }

  return GetProperty(cx_, resultObj, resultObj, cx_->names().value, vp);
}

// ES 2017 draft 0f10dba4ad18de92d47d421f378233a2eae8f077 7.4.6.
// When completion.[[Type]] is throw.
void ForOfIterator::closeThrow() {
  MOZ_ASSERT(iterator);

  RootedValue completionException(cx_);
  RootedSavedFrame completionExceptionStack(cx_);
  if (cx_->isExceptionPending()) {
    if (!GetAndClearExceptionAndStack(cx_, &completionException,
                                      &completionExceptionStack)) {
      completionException.setUndefined();
      completionExceptionStack = nullptr;
    }
  }

  // Steps 1-2 (implicit)

  // Step 3 (partial).
  RootedValue returnVal(cx_);
  if (!GetProperty(cx_, iterator, iterator, cx_->names().return_, &returnVal)) {
    return;
  }

  // Step 4.
  if (returnVal.isUndefined()) {
    cx_->setPendingException(completionException, completionExceptionStack);
    return;
  }

  // Step 3 (remaining part)
  if (!returnVal.isObject()) {
    JS_ReportErrorNumberASCII(cx_, GetErrorMessage, nullptr,
                              JSMSG_RETURN_NOT_CALLABLE);
    return;
  }
  RootedObject returnObj(cx_, &returnVal.toObject());
  if (!returnObj->isCallable()) {
    JS_ReportErrorNumberASCII(cx_, GetErrorMessage, nullptr,
                              JSMSG_RETURN_NOT_CALLABLE);
    return;
  }

  // Step 5.
  RootedValue innerResultValue(cx_);
  if (!js::Call(cx_, returnVal, iterator, &innerResultValue)) {
    if (cx_->isExceptionPending()) {
      cx_->clearPendingException();
    }
  }

  // Step 6.
  cx_->setPendingException(completionException, completionExceptionStack);
}