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/* -*- 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 */
#include "vm/ToSource.h"
#include "mozilla/Assertions.h" // MOZ_ASSERT
#include "mozilla/FloatingPoint.h" // mozilla::IsNegativeZero
#include <iterator> // std::size
#include <stdint.h> // uint32_t
#include "jsfriendapi.h" // CheckRecursionLimit
#include "builtin/Array.h" // ArrayToSource
#include "builtin/Boolean.h" // BooleanToString
#include "builtin/Object.h" // ObjectToSource
#include "gc/Allocator.h" // CanGC
#include "js/Class.h" // ESClass
#include "js/friend/StackLimits.h" // js::CheckRecursionLimit
#include "js/Object.h" // JS::GetBuiltinClass
#include "js/Symbol.h" // SymbolCode, JS::WellKnownSymbolLimit
#include "js/TypeDecls.h" // Rooted{Function, Object, String, Value}, HandleValue, Latin1Char
#include "js/Utility.h" // UniqueChars
#include "js/Value.h" // JS::Value
#include "util/StringBuffer.h" // JSStringBuilder
#include "vm/ArrayObject.h" // ArrayObject
#include "vm/ErrorObject.h" // ErrorObject, ErrorToSource
#include "vm/Interpreter.h" // Call
#include "vm/JSContext.h" // JSContext
#include "vm/JSFunction.h" // JSFunction, fun_toStringHelper
#include "vm/Printer.h" // QuoteString
#include "vm/SelfHosting.h" // CallSelfHostedFunction
#include "vm/Stack.h" // FixedInvokeArgs
#include "vm/StringType.h" // NewStringCopy{N,Z}, ToString
#include "vm/SymbolType.h" // Symbol
#include "vm/JSContext-inl.h" // JSContext::check
#include "vm/JSObject-inl.h" // IsCallable
#include "vm/ObjectOperations-inl.h" // GetProperty
using namespace js;
using mozilla::IsNegativeZero;
using JS::GetBuiltinClass;
* Convert a JSString to its source expression; returns null after reporting an
* error, otherwise returns a new string reference. No Handle needed since the
* input is dead after the GC.
static JSString* StringToSource(JSContext* cx, JSString* str) {
UniqueChars chars = QuoteString(cx, str, '"');
if (!chars) {
return nullptr;
return NewStringCopyZ<CanGC>(cx, chars.get());
static JSString* SymbolToSource(JSContext* cx, JS::Symbol* symbol) {
using JS::SymbolCode;
RootedString desc(cx, symbol->description());
SymbolCode code = symbol->code();
if (symbol->isWellKnownSymbol()) {
// Well-known symbol.
return desc;
if (code == SymbolCode::PrivateNameSymbol) {
return desc;
MOZ_ASSERT(code == SymbolCode::InSymbolRegistry ||
code == SymbolCode::UniqueSymbol);
JSStringBuilder buf(cx);
if (code == SymbolCode::InSymbolRegistry ? !buf.append("Symbol.for(")
: !buf.append("Symbol(")) {
return nullptr;
if (desc) {
UniqueChars quoted = QuoteString(cx, desc, '"');
if (!quoted || !buf.append(quoted.get(), strlen(quoted.get()))) {
return nullptr;
if (!buf.append(')')) {
return nullptr;
return buf.finishString();
static JSString* BoxedToSource(JSContext* cx, HandleObject obj,
const char* constructor) {
RootedValue value(cx);
if (!Unbox(cx, obj, &value)) {
return nullptr;
RootedString str(cx, ValueToSource(cx, value));
if (!str) {
return nullptr;
JSStringBuilder buf(cx);
if (!buf.append("new ") || !buf.append(constructor, strlen(constructor)) ||
!buf.append('(') || !buf.append(str) || !buf.append(')')) {
return nullptr;
return buf.finishString();
JSString* js::ValueToSource(JSContext* cx, HandleValue v) {
if (!CheckRecursionLimit(cx)) {
return nullptr;
switch (v.type()) {
case JS::ValueType::Undefined:
return cx->names().void0;
case JS::ValueType::String:
return StringToSource(cx, v.toString());
case JS::ValueType::Symbol:
return SymbolToSource(cx, v.toSymbol());
case JS::ValueType::Null:
return cx->names().null;
case JS::ValueType::Boolean:
return BooleanToString(cx, v.toBoolean());
case JS::ValueType::Double:
/* Special case to preserve negative zero, _contra_ toString. */
if (IsNegativeZero(v.toDouble())) {
static const Latin1Char negativeZero[] = {'-', '0'};
return NewStringCopyN<CanGC>(cx, negativeZero, std::size(negativeZero));
case JS::ValueType::Int32:
return ToString<CanGC>(cx, v);
case JS::ValueType::BigInt: {
RootedString str(cx, ToString<CanGC>(cx, v));
if (!str) {
return nullptr;
RootedString n(cx, cx->staticStrings().getUnit('n'));
return ConcatStrings<CanGC>(cx, str, n);
case JS::ValueType::Object: {
RootedValue fval(cx);
RootedObject obj(cx, &v.toObject());
if (!GetProperty(cx, obj, obj, cx->names().toSource, &fval)) {
return nullptr;
if (IsCallable(fval)) {
RootedValue v(cx);
if (!js::Call(cx, fval, obj, &v)) {
return nullptr;
return ToString<CanGC>(cx, v);
ESClass cls;
if (!GetBuiltinClass(cx, obj, &cls)) {
return nullptr;
// All ToSource functions must be able to handle wrapped objects!
switch (cls) {
case ESClass::Function:
return fun_toStringHelper(cx, obj, true);
case ESClass::Array:
return ArrayToSource(cx, obj);
case ESClass::Error:
return ErrorToSource(cx, obj);
case ESClass::RegExp: {
FixedInvokeArgs<0> args(cx);
RootedValue rval(cx);
if (!CallSelfHostedFunction(cx, cx->names().RegExpToString, v, args,
&rval)) {
return nullptr;
return ToString<CanGC>(cx, rval);
case ESClass::Boolean:
return BoxedToSource(cx, obj, "Boolean");
case ESClass::Number:
return BoxedToSource(cx, obj, "Number");
case ESClass::String:
return BoxedToSource(cx, obj, "String");
case ESClass::Date:
return BoxedToSource(cx, obj, "Date");
return ObjectToSource(cx, obj);
case JS::ValueType::PrivateGCThing:
case JS::ValueType::Magic:
"internal value types shouldn't leak into places "
"wanting source representations");
return nullptr;
MOZ_ASSERT_UNREACHABLE("shouldn't see an unrecognized value type");
return nullptr;