Source/JavaScriptCore/runtime/JSStringJoiner.h

/*
 * Copyright (C) 2012-2022 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 * 1. Redistributions of source code must retain the above copyright
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 *    notice, this list of conditions and the following disclaimer in the
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 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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#pragma once

#include "ExceptionHelpers.h"
#include "JSCJSValue.h"
#include "JSGlobalObject.h"

namespace JSC {

class JSStringJoiner {
public:
    JSStringJoiner(JSGlobalObject*, LChar separator, size_t stringCount);
    JSStringJoiner(JSGlobalObject*, StringView separator, size_t stringCount);
    ~JSStringJoiner();

    void append(JSGlobalObject*, JSValue);
    void appendNumber(VM&, int32_t);
    void appendNumber(VM&, double);
    bool appendWithoutSideEffects(JSGlobalObject*, JSValue);
    void appendEmptyString();

    JSValue join(JSGlobalObject*);

private:
    void append(StringViewWithUnderlyingString&&);
    void append8Bit(const String&);
    unsigned joinedLength(JSGlobalObject*) const;

    LChar m_singleCharacterSeparator;
    StringView m_separator;
    Vector<StringViewWithUnderlyingString> m_strings;
    CheckedUint32 m_accumulatedStringsLength;
    bool m_isAll8Bit { true };
};

inline JSStringJoiner::JSStringJoiner(JSGlobalObject* globalObject, StringView separator, size_t stringCount)
    : m_separator(separator)
    , m_isAll8Bit(m_separator.is8Bit())
{
    VM& vm = globalObject->vm();
    auto scope = DECLARE_THROW_SCOPE(vm);
    if (UNLIKELY(!m_strings.tryReserveCapacity(stringCount)))
        throwOutOfMemoryError(globalObject, scope);
}

inline JSStringJoiner::JSStringJoiner(JSGlobalObject* globalObject, LChar separator, size_t stringCount)
    : m_singleCharacterSeparator(separator)
    , m_separator { &m_singleCharacterSeparator, 1 }
{
    VM& vm = globalObject->vm();
    auto scope = DECLARE_THROW_SCOPE(vm);
    if (UNLIKELY(!m_strings.tryReserveCapacity(stringCount)))
        throwOutOfMemoryError(globalObject, scope);
}

ALWAYS_INLINE void JSStringJoiner::append(StringViewWithUnderlyingString&& string)
{
    m_accumulatedStringsLength += string.view.length();
    m_isAll8Bit = m_isAll8Bit && string.view.is8Bit();
    m_strings.uncheckedAppend(WTFMove(string));
}

ALWAYS_INLINE void JSStringJoiner::append8Bit(const String& string)
{
    ASSERT(string.is8Bit());
    m_accumulatedStringsLength += string.length();
    m_strings.uncheckedAppend({ string, string });
}

ALWAYS_INLINE void JSStringJoiner::appendEmptyString()
{
    m_strings.uncheckedAppend({ { }, { } });
}

ALWAYS_INLINE bool JSStringJoiner::appendWithoutSideEffects(JSGlobalObject* globalObject, JSValue value)
{
    // The following code differs from using the result of JSValue::toString in the following ways:
    // 1) It's inlined more than JSValue::toString is.
    // 2) It includes conversion to WTF::String in a way that avoids allocating copies of substrings.
    // 3) It doesn't create a JSString for numbers, true, or false.
    // 4) It turns undefined and null into the empty string instead of "undefined" and "null".
    // 5) It uses optimized code paths for all the cases known to be 8-bit and for the empty string.
    // If we might make an effectful calls, return false. Otherwise return true.

    if (value.isCell()) {
        JSString* jsString;
        // FIXME: Support JSBigInt in side-effect-free append.
        // https://bugs.webkit.org/show_bug.cgi?id=211173
        if (!value.asCell()->isString())
            return false;
        jsString = asString(value);
        append(jsString->viewWithUnderlyingString(globalObject));
        return true;
    }

    if (value.isInt32()) {
        appendNumber(globalObject->vm(), value.asInt32());
        return true;
    }
    if (value.isDouble()) {
        appendNumber(globalObject->vm(), value.asDouble());
        return true;
    }
    if (value.isTrue()) {
        append8Bit(globalObject->vm().propertyNames->trueKeyword.string());
        return true;
    }
    if (value.isFalse()) {
        append8Bit(globalObject->vm().propertyNames->falseKeyword.string());
        return true;
    }

#if USE(BIGINT32)
    if (value.isBigInt32()) {
        appendNumber(globalObject->vm(), value.bigInt32AsInt32());
        return true;
    }
#endif

    ASSERT(value.isUndefinedOrNull());
    appendEmptyString();
    return true;
}

ALWAYS_INLINE void JSStringJoiner::append(JSGlobalObject* globalObject, JSValue value)
{
    VM& vm = globalObject->vm();
    auto scope = DECLARE_THROW_SCOPE(vm);

    bool success = appendWithoutSideEffects(globalObject, value);
    if (!success) {
        JSString* jsString = value.toString(globalObject);
        RETURN_IF_EXCEPTION(scope, void());
        RELEASE_AND_RETURN(scope, append(jsString->viewWithUnderlyingString(globalObject)));
    }
}

ALWAYS_INLINE void JSStringJoiner::appendNumber(VM& vm, int32_t value)
{
    append8Bit(vm.numericStrings.add(value));
}

ALWAYS_INLINE void JSStringJoiner::appendNumber(VM& vm, double value)
{
    append8Bit(vm.numericStrings.add(value));
}

} // namespace JSC