ForOfIterator.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sts=4 et sw=4 tw=99:
 * 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 "jsapi.h"

#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, iterableObj, 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_);
    if (cx_->isExceptionPending()) {
        if (!GetAndClearException(cx_, &completionException)) {
            completionException.setUndefined();
        }
    }

    // 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);
        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);
}