Adding upstream version 1:115.7.0.upstream/1%115.7.0upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1383 insertions, 0 deletions

diff --git a/js/src/builtin/JSON.cpp b/js/src/builtin/JSON.cpp
new file mode 100644
index 0000000000..7fde8de9b6
--- /dev/null
+++ b/js/src/builtin/JSON.cpp
@@ -0,0 +1,1383 @@
+/* -*- 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 "builtin/JSON.h"
+
+#include "mozilla/CheckedInt.h"
+#include "mozilla/FloatingPoint.h"
+#include "mozilla/Range.h"
+#include "mozilla/ScopeExit.h"
+
+#include <algorithm>
+
+#include "jsnum.h"
+#include "jstypes.h"
+
+#include "builtin/Array.h"
+#include "js/friend/ErrorMessages.h"  // js::GetErrorMessage, JSMSG_*
+#include "js/friend/StackLimits.h"    // js::AutoCheckRecursionLimit
+#include "js/Object.h"                // JS::GetBuiltinClass
+#include "js/PropertySpec.h"
+#include "js/StableStringChars.h"
+#include "js/TypeDecls.h"
+#include "js/Value.h"
+#include "util/StringBuffer.h"
+#include "vm/Interpreter.h"
+#include "vm/JSAtom.h"
+#include "vm/JSContext.h"
+#include "vm/JSObject.h"
+#include "vm/JSONParser.h"
+#include "vm/NativeObject.h"
+#include "vm/PlainObject.h"    // js::PlainObject
+#include "vm/WellKnownAtom.h"  // js_*_str
+#ifdef ENABLE_RECORD_TUPLE
+#  include "builtin/RecordObject.h"
+#  include "builtin/TupleObject.h"
+#  include "vm/RecordType.h"
+#endif
+
+#include "builtin/Array-inl.h"
+#include "vm/GeckoProfiler-inl.h"
+#include "vm/JSAtom-inl.h"
+#include "vm/NativeObject-inl.h"
+
+using namespace js;
+
+using mozilla::CheckedInt;
+using mozilla::Maybe;
+using mozilla::RangedPtr;
+
+using JS::AutoStableStringChars;
+
+/* ES5 15.12.3 Quote.
+ * Requires that the destination has enough space allocated for src after
+ * escaping (that is, `2 + 6 * (srcEnd - srcBegin)` characters).
+ */
+template <typename SrcCharT, typename DstCharT>
+static MOZ_ALWAYS_INLINE RangedPtr<DstCharT> InfallibleQuote(
+    RangedPtr<const SrcCharT> srcBegin, RangedPtr<const SrcCharT> srcEnd,
+    RangedPtr<DstCharT> dstPtr) {
+  // Maps characters < 256 to the value that must follow the '\\' in the quoted
+  // string. Entries with 'u' are handled as \\u00xy, and entries with 0 are not
+  // escaped in any way. Characters >= 256 are all assumed to be unescaped.
+  static const Latin1Char escapeLookup[256] = {
+      // clang-format off
+        'u', 'u', 'u', 'u', 'u', 'u', 'u', 'u', 'b', 't',
+        'n', 'u', 'f', 'r', 'u', 'u', 'u', 'u', 'u', 'u',
+        'u', 'u', 'u', 'u', 'u', 'u', 'u', 'u', 'u', 'u',
+        'u', 'u', 0,   0,  '\"', 0,   0,   0,   0,   0,
+        0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
+        0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
+        0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
+        0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
+        0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
+        0,   0,  '\\', // rest are all zeros
+      // clang-format on
+  };
+
+  /* Step 1. */
+  *dstPtr++ = '"';
+
+  auto ToLowerHex = [](uint8_t u) {
+    MOZ_ASSERT(u <= 0xF);
+    return "0123456789abcdef"[u];
+  };
+
+  /* Step 2. */
+  while (srcBegin != srcEnd) {
+    const SrcCharT c = *srcBegin++;
+
+    // Handle the Latin-1 cases.
+    if (MOZ_LIKELY(c < sizeof(escapeLookup))) {
+      Latin1Char escaped = escapeLookup[c];
+
+      // Directly copy non-escaped code points.
+      if (escaped == 0) {
+        *dstPtr++ = c;
+        continue;
+      }
+
+      // Escape the rest, elaborating Unicode escapes when needed.
+      *dstPtr++ = '\\';
+      *dstPtr++ = escaped;
+      if (escaped == 'u') {
+        *dstPtr++ = '0';
+        *dstPtr++ = '0';
+
+        uint8_t x = c >> 4;
+        MOZ_ASSERT(x < 10);
+        *dstPtr++ = '0' + x;
+
+        *dstPtr++ = ToLowerHex(c & 0xF);
+      }
+
+      continue;
+    }
+
+    // Non-ASCII non-surrogates are directly copied.
+    if (!unicode::IsSurrogate(c)) {
+      *dstPtr++ = c;
+      continue;
+    }
+
+    // So too for complete surrogate pairs.
+    if (MOZ_LIKELY(unicode::IsLeadSurrogate(c) && srcBegin < srcEnd &&
+                   unicode::IsTrailSurrogate(*srcBegin))) {
+      *dstPtr++ = c;
+      *dstPtr++ = *srcBegin++;
+      continue;
+    }
+
+    // But lone surrogates are Unicode-escaped.
+    char32_t as32 = char32_t(c);
+    *dstPtr++ = '\\';
+    *dstPtr++ = 'u';
+    *dstPtr++ = ToLowerHex(as32 >> 12);
+    *dstPtr++ = ToLowerHex((as32 >> 8) & 0xF);
+    *dstPtr++ = ToLowerHex((as32 >> 4) & 0xF);
+    *dstPtr++ = ToLowerHex(as32 & 0xF);
+  }
+
+  /* Steps 3-4. */
+  *dstPtr++ = '"';
+  return dstPtr;
+}
+
+template <typename SrcCharT, typename DstCharT>
+static size_t QuoteHelper(const JSLinearString& linear, StringBuffer& sb,
+                          size_t sbOffset) {
+  size_t len = linear.length();
+
+  JS::AutoCheckCannotGC nogc;
+  RangedPtr<const SrcCharT> srcBegin{linear.chars<SrcCharT>(nogc), len};
+  RangedPtr<DstCharT> dstBegin{sb.begin<DstCharT>(), sb.begin<DstCharT>(),
+                               sb.end<DstCharT>()};
+  RangedPtr<DstCharT> dstEnd =
+      InfallibleQuote(srcBegin, srcBegin + len, dstBegin + sbOffset);
+
+  return dstEnd - dstBegin;
+}
+
+static bool Quote(JSContext* cx, StringBuffer& sb, JSString* str) {
+  JSLinearString* linear = str->ensureLinear(cx);
+  if (!linear) {
+    return false;
+  }
+
+  if (linear->hasTwoByteChars() && !sb.ensureTwoByteChars()) {
+    return false;
+  }
+
+  // We resize the backing buffer to the maximum size we could possibly need,
+  // write the escaped string into it, and shrink it back to the size we ended
+  // up needing.
+
+  size_t len = linear->length();
+  size_t sbInitialLen = sb.length();
+
+  CheckedInt<size_t> reservedLen = CheckedInt<size_t>(len) * 6 + 2;
+  if (MOZ_UNLIKELY(!reservedLen.isValid())) {
+    ReportAllocationOverflow(cx);
+    return false;
+  }
+
+  if (!sb.growByUninitialized(reservedLen.value())) {
+    return false;
+  }
+
+  size_t newSize;
+
+  if (linear->hasTwoByteChars()) {
+    newSize = QuoteHelper<char16_t, char16_t>(*linear, sb, sbInitialLen);
+  } else if (sb.isUnderlyingBufferLatin1()) {
+    newSize = QuoteHelper<Latin1Char, Latin1Char>(*linear, sb, sbInitialLen);
+  } else {
+    newSize = QuoteHelper<Latin1Char, char16_t>(*linear, sb, sbInitialLen);
+  }
+
+  sb.shrinkTo(newSize);
+
+  return true;
+}
+
+namespace {
+
+using ObjectVector = GCVector<JSObject*, 8>;
+
+class StringifyContext {
+ public:
+  StringifyContext(JSContext* cx, StringBuffer& sb, const StringBuffer& gap,
+                   HandleObject replacer, const RootedIdVector& propertyList,
+                   bool maybeSafely)
+      : sb(sb),
+        gap(gap),
+        replacer(cx, replacer),
+        stack(cx, ObjectVector(cx)),
+        propertyList(propertyList),
+        depth(0),
+        maybeSafely(maybeSafely) {
+    MOZ_ASSERT_IF(maybeSafely, !replacer);
+    MOZ_ASSERT_IF(maybeSafely, gap.empty());
+  }
+
+  StringBuffer& sb;
+  const StringBuffer& gap;
+  RootedObject replacer;
+  Rooted<ObjectVector> stack;
+  const RootedIdVector& propertyList;
+  uint32_t depth;
+  bool maybeSafely;
+};
+
+} /* anonymous namespace */
+
+static bool Str(JSContext* cx, const Value& v, StringifyContext* scx);
+
+static bool WriteIndent(StringifyContext* scx, uint32_t limit) {
+  if (!scx->gap.empty()) {
+    if (!scx->sb.append('\n')) {
+      return false;
+    }
+
+    if (scx->gap.isUnderlyingBufferLatin1()) {
+      for (uint32_t i = 0; i < limit; i++) {
+        if (!scx->sb.append(scx->gap.rawLatin1Begin(),
+                            scx->gap.rawLatin1End())) {
+          return false;
+        }
+      }
+    } else {
+      for (uint32_t i = 0; i < limit; i++) {
+        if (!scx->sb.append(scx->gap.rawTwoByteBegin(),
+                            scx->gap.rawTwoByteEnd())) {
+          return false;
+        }
+      }
+    }
+  }
+
+  return true;
+}
+
+namespace {
+
+template <typename KeyType>
+class KeyStringifier {};
+
+template <>
+class KeyStringifier<uint32_t> {
+ public:
+  static JSString* toString(JSContext* cx, uint32_t index) {
+    return IndexToString(cx, index);
+  }
+};
+
+template <>
+class KeyStringifier<HandleId> {
+ public:
+  static JSString* toString(JSContext* cx, HandleId id) {
+    return IdToString(cx, id);
+  }
+};
+
+} /* anonymous namespace */
+
+/*
+ * ES5 15.12.3 Str, steps 2-4, extracted to enable preprocessing of property
+ * values when stringifying objects in JO.
+ */
+template <typename KeyType>
+static bool PreprocessValue(JSContext* cx, HandleObject holder, KeyType key,
+                            MutableHandleValue vp, StringifyContext* scx) {
+  // We don't want to do any preprocessing here if scx->maybeSafely,
+  // since the stuff we do here can have side-effects.
+  if (scx->maybeSafely) {
+    return true;
+  }
+
+  RootedString keyStr(cx);
+
+  // Step 2. Modified by BigInt spec 6.1 to check for a toJSON method on the
+  // BigInt prototype when the value is a BigInt, and to pass the BigInt
+  // primitive value as receiver.
+  if (vp.isObject() || vp.isBigInt()) {
+    RootedValue toJSON(cx);
+    RootedObject obj(cx, JS::ToObject(cx, vp));
+    if (!obj) {
+      return false;
+    }
+
+    if (!GetProperty(cx, obj, vp, cx->names().toJSON, &toJSON)) {
+      return false;
+    }
+
+    if (IsCallable(toJSON)) {
+      keyStr = KeyStringifier<KeyType>::toString(cx, key);
+      if (!keyStr) {
+        return false;
+      }
+
+      RootedValue arg0(cx, StringValue(keyStr));
+      if (!js::Call(cx, toJSON, vp, arg0, vp)) {
+        return false;
+      }
+    }
+  }
+
+  /* Step 3. */
+  if (scx->replacer && scx->replacer->isCallable()) {
+    MOZ_ASSERT(holder != nullptr,
+               "holder object must be present when replacer is callable");
+
+    if (!keyStr) {
+      keyStr = KeyStringifier<KeyType>::toString(cx, key);
+      if (!keyStr) {
+        return false;
+      }
+    }
+
+    RootedValue arg0(cx, StringValue(keyStr));
+    RootedValue replacerVal(cx, ObjectValue(*scx->replacer));
+    if (!js::Call(cx, replacerVal, holder, arg0, vp, vp)) {
+      return false;
+    }
+  }
+
+  /* Step 4. */
+  if (vp.get().isObject()) {
+    RootedObject obj(cx, &vp.get().toObject());
+
+    ESClass cls;
+    if (!JS::GetBuiltinClass(cx, obj, &cls)) {
+      return false;
+    }
+
+    if (cls == ESClass::Number) {
+      double d;
+      if (!ToNumber(cx, vp, &d)) {
+        return false;
+      }
+      vp.setNumber(d);
+    } else if (cls == ESClass::String) {
+      JSString* str = ToStringSlow<CanGC>(cx, vp);
+      if (!str) {
+        return false;
+      }
+      vp.setString(str);
+    } else if (cls == ESClass::Boolean || cls == ESClass::BigInt ||
+               IF_RECORD_TUPLE(
+                   obj->is<RecordObject>() || obj->is<TupleObject>(), false)) {
+      if (!Unbox(cx, obj, vp)) {
+        return false;
+      }
+    }
+  }
+
+  return true;
+}
+
+/*
+ * Determines whether a value which has passed by ES5 150.2.3 Str steps 1-4's
+ * gauntlet will result in Str returning |undefined|.  This function is used to
+ * properly omit properties resulting in such values when stringifying objects,
+ * while properly stringifying such properties as null when they're encountered
+ * in arrays.
+ */
+static inline bool IsFilteredValue(const Value& v) {
+  return v.isUndefined() || v.isSymbol() || IsCallable(v);
+}
+
+class CycleDetector {
+ public:
+  CycleDetector(StringifyContext* scx, HandleObject obj)
+      : stack_(&scx->stack), obj_(obj), appended_(false) {}
+
+  MOZ_ALWAYS_INLINE bool foundCycle(JSContext* cx) {
+    JSObject* obj = obj_;
+    for (JSObject* obj2 : stack_) {
+      if (MOZ_UNLIKELY(obj == obj2)) {
+        JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                                  JSMSG_JSON_CYCLIC_VALUE);
+        return false;
+      }
+    }
+    appended_ = stack_.append(obj);
+    return appended_;
+  }
+
+  ~CycleDetector() {
+    if (MOZ_LIKELY(appended_)) {
+      MOZ_ASSERT(stack_.back() == obj_);
+      stack_.popBack();
+    }
+  }
+
+ private:
+  MutableHandle<ObjectVector> stack_;
+  HandleObject obj_;
+  bool appended_;
+};
+
+#ifdef ENABLE_RECORD_TUPLE
+enum class JOType { Record, Object };
+template <JOType type = JOType::Object>
+#endif
+/* ES5 15.12.3 JO. */
+static bool JO(JSContext* cx, HandleObject obj, StringifyContext* scx) {
+  /*
+   * This method implements the JO algorithm in ES5 15.12.3, but:
+   *
+   *   * The algorithm is somewhat reformulated to allow the final string to
+   *     be streamed into a single buffer, rather than be created and copied
+   *     into place incrementally as the ES5 algorithm specifies it.  This
+   *     requires moving portions of the Str call in 8a into this algorithm
+   *     (and in JA as well).
+   */
+
+#ifdef ENABLE_RECORD_TUPLE
+  RecordType* rec;
+
+  if constexpr (type == JOType::Record) {
+    MOZ_ASSERT(obj->is<RecordType>());
+    rec = &obj->as<RecordType>();
+  } else {
+    MOZ_ASSERT(!IsExtendedPrimitive(*obj));
+  }
+#endif
+  MOZ_ASSERT_IF(scx->maybeSafely, obj->is<PlainObject>());
+
+  /* Steps 1-2, 11. */
+  CycleDetector detect(scx, obj);
+  if (!detect.foundCycle(cx)) {
+    return false;
+  }
+
+  if (!scx->sb.append('{')) {
+    return false;
+  }
+
+  /* Steps 5-7. */
+  Maybe<RootedIdVector> ids;
+  const RootedIdVector* props;
+  if (scx->replacer && !scx->replacer->isCallable()) {
+    // NOTE: We can't assert |IsArray(scx->replacer)| because the replacer
+    //       might have been a revocable proxy to an array.  Such a proxy
+    //       satisfies |IsArray|, but any side effect of JSON.stringify
+    //       could revoke the proxy so that |!IsArray(scx->replacer)|.  See
+    //       bug 1196497.
+    props = &scx->propertyList;
+  } else {
+    MOZ_ASSERT_IF(scx->replacer, scx->propertyList.length() == 0);
+    ids.emplace(cx);
+    if (!GetPropertyKeys(cx, obj, JSITER_OWNONLY, ids.ptr())) {
+      return false;
+    }
+    props = ids.ptr();
+  }
+
+  /* My kingdom for not-quite-initialized-from-the-start references. */
+  const RootedIdVector& propertyList = *props;
+
+  /* Steps 8-10, 13. */
+  bool wroteMember = false;
+  RootedId id(cx);
+  for (size_t i = 0, len = propertyList.length(); i < len; i++) {
+    if (!CheckForInterrupt(cx)) {
+      return false;
+    }
+
+    /*
+     * Steps 8a-8b.  Note that the call to Str is broken up into 1) getting
+     * the property; 2) processing for toJSON, calling the replacer, and
+     * handling boxed Number/String/Boolean objects; 3) filtering out
+     * values which process to |undefined|, and 4) stringifying all values
+     * which pass the filter.
+     */
+    id = propertyList[i];
+    RootedValue outputValue(cx);
+#ifdef DEBUG
+    if (scx->maybeSafely) {
+      PropertyResult prop;
+      if (!NativeLookupOwnPropertyNoResolve(cx, &obj->as<NativeObject>(), id,
+                                            &prop)) {
+        return false;
+      }
+      MOZ_ASSERT(prop.isNativeProperty() &&
+                 prop.propertyInfo().isDataDescriptor());
+    }
+#endif  // DEBUG
+
+#ifdef ENABLE_RECORD_TUPLE
+    if constexpr (type == JOType::Record) {
+      MOZ_ALWAYS_TRUE(rec->getOwnProperty(cx, id, &outputValue));
+    } else
+#endif
+    {
+      RootedValue objValue(cx, ObjectValue(*obj));
+      if (!GetProperty(cx, obj, objValue, id, &outputValue)) {
+        return false;
+      }
+    }
+    if (!PreprocessValue(cx, obj, HandleId(id), &outputValue, scx)) {
+      return false;
+    }
+    if (IsFilteredValue(outputValue)) {
+      continue;
+    }
+
+    /* Output a comma unless this is the first member to write. */
+    if (wroteMember && !scx->sb.append(',')) {
+      return false;
+    }
+    wroteMember = true;
+
+    if (!WriteIndent(scx, scx->depth)) {
+      return false;
+    }
+
+    JSString* s = IdToString(cx, id);
+    if (!s) {
+      return false;
+    }
+
+    if (!Quote(cx, scx->sb, s) || !scx->sb.append(':') ||
+        !(scx->gap.empty() || scx->sb.append(' ')) ||
+        !Str(cx, outputValue, scx)) {
+      return false;
+    }
+  }
+
+  if (wroteMember && !WriteIndent(scx, scx->depth - 1)) {
+    return false;
+  }
+
+  return scx->sb.append('}');
+}
+
+// For JSON.stringify and JSON.parse with a reviver function, we need to know
+// the length of an object for which JS::IsArray returned true. This must be
+// either an ArrayObject or a proxy wrapping one.
+static MOZ_ALWAYS_INLINE bool GetLengthPropertyForArrayLike(JSContext* cx,
+                                                            HandleObject obj,
+                                                            uint32_t* lengthp) {
+  if (MOZ_LIKELY(obj->is<ArrayObject>())) {
+    *lengthp = obj->as<ArrayObject>().length();
+    return true;
+  }
+#ifdef ENABLE_RECORD_TUPLE
+  if (obj->is<TupleType>()) {
+    *lengthp = obj->as<TupleType>().length();
+    return true;
+  }
+#endif
+
+  MOZ_ASSERT(obj->is<ProxyObject>());
+
+  uint64_t len = 0;
+  if (!GetLengthProperty(cx, obj, &len)) {
+    return false;
+  }
+
+  // A scripted proxy wrapping an array can return a length value larger than
+  // UINT32_MAX. Stringification will likely report an OOM in this case. Match
+  // other JS engines and report an early error in this case, although
+  // technically this is observable, for example when stringifying with a
+  // replacer function.
+  if (len > UINT32_MAX) {
+    ReportAllocationOverflow(cx);
+    return false;
+  }
+
+  *lengthp = uint32_t(len);
+  return true;
+}
+
+/* ES5 15.12.3 JA. */
+static bool JA(JSContext* cx, HandleObject obj, StringifyContext* scx) {
+  /*
+   * This method implements the JA algorithm in ES5 15.12.3, but:
+   *
+   *   * The algorithm is somewhat reformulated to allow the final string to
+   *     be streamed into a single buffer, rather than be created and copied
+   *     into place incrementally as the ES5 algorithm specifies it.  This
+   *     requires moving portions of the Str call in 8a into this algorithm
+   *     (and in JO as well).
+   */
+
+  /* Steps 1-2, 11. */
+  CycleDetector detect(scx, obj);
+  if (!detect.foundCycle(cx)) {
+    return false;
+  }
+
+  if (!scx->sb.append('[')) {
+    return false;
+  }
+
+  /* Step 6. */
+  uint32_t length;
+  if (!GetLengthPropertyForArrayLike(cx, obj, &length)) {
+    return false;
+  }
+
+  /* Steps 7-10. */
+  if (length != 0) {
+    /* Steps 4, 10b(i). */
+    if (!WriteIndent(scx, scx->depth)) {
+      return false;
+    }
+
+    /* Steps 7-10. */
+    RootedValue outputValue(cx);
+    for (uint32_t i = 0; i < length; i++) {
+      if (!CheckForInterrupt(cx)) {
+        return false;
+      }
+
+      /*
+       * Steps 8a-8c.  Again note how the call to the spec's Str method
+       * is broken up into getting the property, running it past toJSON
+       * and the replacer and maybe unboxing, and interpreting some
+       * values as |null| in separate steps.
+       */
+#ifdef DEBUG
+      if (scx->maybeSafely) {
+        /*
+         * Trying to do a JS_AlreadyHasOwnElement runs the risk of
+         * hitting OOM on jsid creation.  Let's just assert sanity for
+         * small enough indices.
+         */
+        MOZ_ASSERT(obj->is<ArrayObject>());
+        MOZ_ASSERT(obj->is<NativeObject>());
+        Rooted<NativeObject*> nativeObj(cx, &obj->as<NativeObject>());
+        if (i <= PropertyKey::IntMax) {
+          MOZ_ASSERT(
+              nativeObj->containsDenseElement(i) != nativeObj->isIndexed(),
+              "the array must either be small enough to remain "
+              "fully dense (and otherwise un-indexed), *or* "
+              "all its initially-dense elements were sparsified "
+              "and the object is indexed");
+        } else {
+          MOZ_ASSERT(nativeObj->isIndexed());
+        }
+      }
+#endif
+      if (!GetElement(cx, obj, i, &outputValue)) {
+        return false;
+      }
+      if (!PreprocessValue(cx, obj, i, &outputValue, scx)) {
+        return false;
+      }
+      if (IsFilteredValue(outputValue)) {
+        if (!scx->sb.append("null")) {
+          return false;
+        }
+      } else {
+        if (!Str(cx, outputValue, scx)) {
+          return false;
+        }
+      }
+
+      /* Steps 3, 4, 10b(i). */
+      if (i < length - 1) {
+        if (!scx->sb.append(',')) {
+          return false;
+        }
+        if (!WriteIndent(scx, scx->depth)) {
+          return false;
+        }
+      }
+    }
+
+    /* Step 10(b)(iii). */
+    if (!WriteIndent(scx, scx->depth - 1)) {
+      return false;
+    }
+  }
+
+  return scx->sb.append(']');
+}
+
+static bool Str(JSContext* cx, const Value& v, StringifyContext* scx) {
+  /* Step 11 must be handled by the caller. */
+  MOZ_ASSERT(!IsFilteredValue(v));
+
+  /*
+   * This method implements the Str algorithm in ES5 15.12.3, but:
+   *
+   *   * We move property retrieval (step 1) into callers to stream the
+   *     stringification process and avoid constantly copying strings.
+   *   * We move the preprocessing in steps 2-4 into a helper function to
+   *     allow both JO and JA to use this method.  While JA could use it
+   *     without this move, JO must omit any |undefined|-valued property per
+   *     so it can't stream out a value using the Str method exactly as
+   *     defined by ES5.
+   *   * We move step 11 into callers, again to ease streaming.
+   */
+
+  /* Step 8. */
+  if (v.isString()) {
+    return Quote(cx, scx->sb, v.toString());
+  }
+
+  /* Step 5. */
+  if (v.isNull()) {
+    return scx->sb.append("null");
+  }
+
+  /* Steps 6-7. */
+  if (v.isBoolean()) {
+    return v.toBoolean() ? scx->sb.append("true") : scx->sb.append("false");
+  }
+
+  /* Step 9. */
+  if (v.isNumber()) {
+    if (v.isDouble()) {
+      if (!std::isfinite(v.toDouble())) {
+        MOZ_ASSERT(!scx->maybeSafely,
+                   "input JS::ToJSONMaybeSafely must not include "
+                   "reachable non-finite numbers");
+        return scx->sb.append("null");
+      }
+    }
+
+    return NumberValueToStringBuffer(v, scx->sb);
+  }
+
+  /* Step 10 in the BigInt proposal. */
+  if (v.isBigInt()) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_BIGINT_NOT_SERIALIZABLE);
+    return false;
+  }
+
+  AutoCheckRecursionLimit recursion(cx);
+  if (!recursion.check(cx)) {
+    return false;
+  }
+
+  /* Step 10. */
+  MOZ_ASSERT(v.hasObjectPayload());
+  RootedObject obj(cx, &v.getObjectPayload());
+
+  MOZ_ASSERT(
+      !scx->maybeSafely || obj->is<PlainObject>() || obj->is<ArrayObject>(),
+      "input to JS::ToJSONMaybeSafely must not include reachable "
+      "objects that are neither arrays nor plain objects");
+
+  scx->depth++;
+  auto dec = mozilla::MakeScopeExit([&] { scx->depth--; });
+
+#ifdef ENABLE_RECORD_TUPLE
+  if (v.isExtendedPrimitive()) {
+    if (obj->is<RecordType>()) {
+      return JO<JOType::Record>(cx, obj, scx);
+    }
+    if (obj->is<TupleType>()) {
+      return JA(cx, obj, scx);
+    }
+    MOZ_CRASH("Unexpected extended primitive - boxes cannot be stringified.");
+  }
+#endif
+
+  bool isArray;
+  if (!IsArray(cx, obj, &isArray)) {
+    return false;
+  }
+
+  return isArray ? JA(cx, obj, scx) : JO(cx, obj, scx);
+}
+
+/* ES6 24.3.2. */
+bool js::Stringify(JSContext* cx, MutableHandleValue vp, JSObject* replacer_,
+                   const Value& space_, StringBuffer& sb,
+                   StringifyBehavior stringifyBehavior) {
+  RootedObject replacer(cx, replacer_);
+  RootedValue space(cx, space_);
+
+  MOZ_ASSERT_IF(stringifyBehavior == StringifyBehavior::RestrictedSafe,
+                space.isNull());
+  MOZ_ASSERT_IF(stringifyBehavior == StringifyBehavior::RestrictedSafe,
+                vp.isObject());
+  /**
+   * This uses MOZ_ASSERT, since it's actually asserting something jsapi
+   * consumers could get wrong, so needs a better error message.
+   */
+  MOZ_ASSERT(stringifyBehavior == StringifyBehavior::Normal ||
+                 vp.toObject().is<PlainObject>() ||
+                 vp.toObject().is<ArrayObject>(),
+             "input to JS::ToJSONMaybeSafely must be a plain object or array");
+
+  /* Step 4. */
+  RootedIdVector propertyList(cx);
+  if (replacer) {
+    bool isArray;
+    if (replacer->isCallable()) {
+      /* Step 4a(i): use replacer to transform values.  */
+    } else if (!IsArray(cx, replacer, &isArray)) {
+      return false;
+    } else if (isArray) {
+      /* Step 4b(iii). */
+
+      /* Step 4b(iii)(2-3). */
+      uint32_t len;
+      if (!GetLengthPropertyForArrayLike(cx, replacer, &len)) {
+        return false;
+      }
+
+      // Cap the initial size to a moderately small value.  This avoids
+      // ridiculous over-allocation if an array with bogusly-huge length
+      // is passed in.  If we end up having to add elements past this
+      // size, the set will naturally resize to accommodate them.
+      const uint32_t MaxInitialSize = 32;
+      Rooted<GCHashSet<jsid>> idSet(
+          cx, GCHashSet<jsid>(cx, std::min(len, MaxInitialSize)));
+
+      /* Step 4b(iii)(4). */
+      uint32_t k = 0;
+
+      /* Step 4b(iii)(5). */
+      RootedValue item(cx);
+      for (; k < len; k++) {
+        if (!CheckForInterrupt(cx)) {
+          return false;
+        }
+
+        /* Step 4b(iii)(5)(a-b). */
+        if (!GetElement(cx, replacer, k, &item)) {
+          return false;
+        }
+
+        /* Step 4b(iii)(5)(c-g). */
+        RootedId id(cx);
+        if (item.isNumber() || item.isString()) {
+          if (!PrimitiveValueToId<CanGC>(cx, item, &id)) {
+            return false;
+          }
+        } else {
+          ESClass cls;
+          if (!GetClassOfValue(cx, item, &cls)) {
+            return false;
+          }
+
+          if (cls != ESClass::String && cls != ESClass::Number) {
+            continue;
+          }
+
+          JSAtom* atom = ToAtom<CanGC>(cx, item);
+          if (!atom) {
+            return false;
+          }
+
+          id.set(AtomToId(atom));
+        }
+
+        /* Step 4b(iii)(5)(g). */
+        auto p = idSet.lookupForAdd(id);
+        if (!p) {
+          /* Step 4b(iii)(5)(g)(i). */
+          if (!idSet.add(p, id) || !propertyList.append(id)) {
+            return false;
+          }
+        }
+      }
+    } else {
+      replacer = nullptr;
+    }
+  }
+
+  /* Step 5. */
+  if (space.isObject()) {
+    RootedObject spaceObj(cx, &space.toObject());
+
+    ESClass cls;
+    if (!JS::GetBuiltinClass(cx, spaceObj, &cls)) {
+      return false;
+    }
+
+    if (cls == ESClass::Number) {
+      double d;
+      if (!ToNumber(cx, space, &d)) {
+        return false;
+      }
+      space = NumberValue(d);
+    } else if (cls == ESClass::String) {
+      JSString* str = ToStringSlow<CanGC>(cx, space);
+      if (!str) {
+        return false;
+      }
+      space = StringValue(str);
+    }
+  }
+
+  StringBuffer gap(cx);
+
+  if (space.isNumber()) {
+    /* Step 6. */
+    double d;
+    MOZ_ALWAYS_TRUE(ToInteger(cx, space, &d));
+    d = std::min(10.0, d);
+    if (d >= 1 && !gap.appendN(' ', uint32_t(d))) {
+      return false;
+    }
+  } else if (space.isString()) {
+    /* Step 7. */
+    JSLinearString* str = space.toString()->ensureLinear(cx);
+    if (!str) {
+      return false;
+    }
+    size_t len = std::min(size_t(10), str->length());
+    if (!gap.appendSubstring(str, 0, len)) {
+      return false;
+    }
+  } else {
+    /* Step 8. */
+    MOZ_ASSERT(gap.empty());
+  }
+
+  Rooted<PlainObject*> wrapper(cx);
+  RootedId emptyId(cx, NameToId(cx->names().empty));
+  if (replacer && replacer->isCallable()) {
+    // We can skip creating the initial wrapper object if no replacer
+    // function is present.
+
+    /* Step 9. */
+    wrapper = NewPlainObject(cx);
+    if (!wrapper) {
+      return false;
+    }
+
+    /* Steps 10-11. */
+    if (!NativeDefineDataProperty(cx, wrapper, emptyId, vp, JSPROP_ENUMERATE)) {
+      return false;
+    }
+  }
+
+  /* Step 12. */
+  StringifyContext scx(cx, sb, gap, replacer, propertyList,
+                       stringifyBehavior == StringifyBehavior::RestrictedSafe);
+  if (!PreprocessValue(cx, wrapper, HandleId(emptyId), vp, &scx)) {
+    return false;
+  }
+  if (IsFilteredValue(vp)) {
+    return true;
+  }
+
+  return Str(cx, vp, &scx);
+}
+
+/* ES5 15.12.2 Walk. */
+static bool Walk(JSContext* cx, HandleObject holder, HandleId name,
+                 HandleValue reviver, MutableHandleValue vp) {
+  AutoCheckRecursionLimit recursion(cx);
+  if (!recursion.check(cx)) {
+    return false;
+  }
+
+  /* Step 1. */
+  RootedValue val(cx);
+  if (!GetProperty(cx, holder, holder, name, &val)) {
+    return false;
+  }
+
+  /* Step 2. */
+  if (val.isObject()) {
+    RootedObject obj(cx, &val.toObject());
+
+    bool isArray;
+    if (!IsArray(cx, obj, &isArray)) {
+      return false;
+    }
+
+    if (isArray) {
+      /* Step 2a(ii). */
+      uint32_t length;
+      if (!GetLengthPropertyForArrayLike(cx, obj, &length)) {
+        return false;
+      }
+
+      /* Step 2a(i), 2a(iii-iv). */
+      RootedId id(cx);
+      RootedValue newElement(cx);
+      for (uint32_t i = 0; i < length; i++) {
+        if (!CheckForInterrupt(cx)) {
+          return false;
+        }
+
+        if (!IndexToId(cx, i, &id)) {
+          return false;
+        }
+
+        /* Step 2a(iii)(1). */
+        if (!Walk(cx, obj, id, reviver, &newElement)) {
+          return false;
+        }
+
+        ObjectOpResult ignored;
+        if (newElement.isUndefined()) {
+          /* Step 2a(iii)(2). The spec deliberately ignores strict failure. */
+          if (!DeleteProperty(cx, obj, id, ignored)) {
+            return false;
+          }
+        } else {
+          /* Step 2a(iii)(3). The spec deliberately ignores strict failure. */
+          Rooted<PropertyDescriptor> desc(
+              cx, PropertyDescriptor::Data(newElement,
+                                           {JS::PropertyAttribute::Configurable,
+                                            JS::PropertyAttribute::Enumerable,
+                                            JS::PropertyAttribute::Writable}));
+          if (!DefineProperty(cx, obj, id, desc, ignored)) {
+            return false;
+          }
+        }
+      }
+    } else {
+      /* Step 2b(i). */
+      RootedIdVector keys(cx);
+      if (!GetPropertyKeys(cx, obj, JSITER_OWNONLY, &keys)) {
+        return false;
+      }
+
+      /* Step 2b(ii). */
+      RootedId id(cx);
+      RootedValue newElement(cx);
+      for (size_t i = 0, len = keys.length(); i < len; i++) {
+        if (!CheckForInterrupt(cx)) {
+          return false;
+        }
+
+        /* Step 2b(ii)(1). */
+        id = keys[i];
+        if (!Walk(cx, obj, id, reviver, &newElement)) {
+          return false;
+        }
+
+        ObjectOpResult ignored;
+        if (newElement.isUndefined()) {
+          /* Step 2b(ii)(2). The spec deliberately ignores strict failure. */
+          if (!DeleteProperty(cx, obj, id, ignored)) {
+            return false;
+          }
+        } else {
+          /* Step 2b(ii)(3). The spec deliberately ignores strict failure. */
+          Rooted<PropertyDescriptor> desc(
+              cx, PropertyDescriptor::Data(newElement,
+                                           {JS::PropertyAttribute::Configurable,
+                                            JS::PropertyAttribute::Enumerable,
+                                            JS::PropertyAttribute::Writable}));
+          if (!DefineProperty(cx, obj, id, desc, ignored)) {
+            return false;
+          }
+        }
+      }
+    }
+  }
+
+  /* Step 3. */
+  RootedString key(cx, IdToString(cx, name));
+  if (!key) {
+    return false;
+  }
+
+  RootedValue keyVal(cx, StringValue(key));
+  return js::Call(cx, reviver, holder, keyVal, val, vp);
+}
+
+static bool Revive(JSContext* cx, HandleValue reviver, MutableHandleValue vp) {
+  Rooted<PlainObject*> obj(cx, NewPlainObject(cx));
+  if (!obj) {
+    return false;
+  }
+
+  if (!DefineDataProperty(cx, obj, cx->names().empty, vp)) {
+    return false;
+  }
+
+  Rooted<jsid> id(cx, NameToId(cx->names().empty));
+  return Walk(cx, obj, id, reviver, vp);
+}
+
+template <typename CharT>
+bool ParseJSON(JSContext* cx, const mozilla::Range<const CharT> chars,
+               MutableHandleValue vp) {
+  Rooted<JSONParser<CharT>> parser(
+      cx,
+      JSONParser<CharT>(cx, chars, JSONParser<CharT>::ParseType::JSONParse));
+  return parser.parse(vp);
+}
+
+template <typename CharT>
+bool js::ParseJSONWithReviver(JSContext* cx,
+                              const mozilla::Range<const CharT> chars,
+                              HandleValue reviver, MutableHandleValue vp) {
+  /* 15.12.2 steps 2-3. */
+  if (!ParseJSON(cx, chars, vp)) {
+    return false;
+  }
+
+  /* 15.12.2 steps 4-5. */
+  if (IsCallable(reviver)) {
+    return Revive(cx, reviver, vp);
+  }
+  return true;
+}
+
+template bool js::ParseJSONWithReviver(
+    JSContext* cx, const mozilla::Range<const Latin1Char> chars,
+    HandleValue reviver, MutableHandleValue vp);
+
+template bool js::ParseJSONWithReviver(
+    JSContext* cx, const mozilla::Range<const char16_t> chars,
+    HandleValue reviver, MutableHandleValue vp);
+
+static bool json_toSource(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  args.rval().setString(cx->names().JSON);
+  return true;
+}
+
+/* ES5 15.12.2. */
+static bool json_parse(JSContext* cx, unsigned argc, Value* vp) {
+  AutoJSMethodProfilerEntry pseudoFrame(cx, "JSON", "parse");
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  /* Step 1. */
+  JSString* str = (args.length() >= 1) ? ToString<CanGC>(cx, args[0])
+                                       : cx->names().undefined;
+  if (!str) {
+    return false;
+  }
+
+  JSLinearString* linear = str->ensureLinear(cx);
+  if (!linear) {
+    return false;
+  }
+
+  AutoStableStringChars linearChars(cx);
+  if (!linearChars.init(cx, linear)) {
+    return false;
+  }
+
+  HandleValue reviver = args.get(1);
+
+  /* Steps 2-5. */
+  return linearChars.isLatin1()
+             ? ParseJSONWithReviver(cx, linearChars.latin1Range(), reviver,
+                                    args.rval())
+             : ParseJSONWithReviver(cx, linearChars.twoByteRange(), reviver,
+                                    args.rval());
+}
+
+#ifdef ENABLE_RECORD_TUPLE
+bool BuildImmutableProperty(JSContext* cx, HandleValue value, HandleId name,
+                            HandleValue reviver,
+                            MutableHandleValue immutableRes) {
+  MOZ_ASSERT(!name.isSymbol());
+
+  // Step 1
+  if (value.isObject()) {
+    RootedValue childValue(cx), newElement(cx);
+    RootedId childName(cx);
+
+    // Step 1.a-1.b
+    if (value.toObject().is<ArrayObject>()) {
+      Rooted<ArrayObject*> arr(cx, &value.toObject().as<ArrayObject>());
+
+      // Step 1.b.iii
+      uint32_t len = arr->length();
+
+      TupleType* tup = TupleType::createUninitialized(cx, len);
+      if (!tup) {
+        return false;
+      }
+      immutableRes.setExtendedPrimitive(*tup);
+
+      // Step 1.b.iv
+      for (uint32_t i = 0; i < len; i++) {
+        // Step 1.b.iv.1
+        childName.set(PropertyKey::Int(i));
+
+        // Step 1.b.iv.2
+        if (!GetProperty(cx, arr, value, childName, &childValue)) {
+          return false;
+        }
+
+        // Step 1.b.iv.3
+        if (!BuildImmutableProperty(cx, childValue, childName, reviver,
+                                    &newElement)) {
+          return false;
+        }
+        MOZ_ASSERT(newElement.isPrimitive());
+
+        // Step 1.b.iv.5
+        if (!tup->initializeNextElement(cx, newElement)) {
+          return false;
+        }
+      }
+
+      // Step 1.b.v
+      tup->finishInitialization(cx);
+    } else {
+      RootedObject obj(cx, &value.toObject());
+
+      // Step 1.c.i - We only get the property keys rather than the
+      // entries, but the difference is not observable from user code
+      // because `obj` is a plan object not exposed externally
+      RootedIdVector props(cx);
+      if (!GetPropertyKeys(cx, obj, JSITER_OWNONLY, &props)) {
+        return false;
+      }
+
+      RecordType* rec = RecordType::createUninitialized(cx, props.length());
+      if (!rec) {
+        return false;
+      }
+      immutableRes.setExtendedPrimitive(*rec);
+
+      for (uint32_t i = 0; i < props.length(); i++) {
+        // Step 1.c.iii.1
+        childName.set(props[i]);
+
+        // Step 1.c.iii.2
+        if (!GetProperty(cx, obj, value, childName, &childValue)) {
+          return false;
+        }
+
+        // Step 1.c.iii.3
+        if (!BuildImmutableProperty(cx, childValue, childName, reviver,
+                                    &newElement)) {
+          return false;
+        }
+        MOZ_ASSERT(newElement.isPrimitive());
+
+        // Step 1.c.iii.5
+        if (!newElement.isUndefined()) {
+          // Step 1.c.iii.5.a-b
+          rec->initializeNextProperty(cx, childName, newElement);
+        }
+      }
+
+      // Step 1.c.iv
+      rec->finishInitialization(cx);
+    }
+  } else {
+    // Step 2.a
+    immutableRes.set(value);
+  }
+
+  // Step 3
+  if (IsCallable(reviver)) {
+    RootedValue keyVal(cx, StringValue(IdToString(cx, name)));
+
+    // Step 3.a
+    if (!Call(cx, reviver, UndefinedHandleValue, keyVal, immutableRes,
+              immutableRes)) {
+      return false;
+    }
+
+    // Step 3.b
+    if (!immutableRes.isPrimitive()) {
+      JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                                JSMSG_RECORD_TUPLE_NO_OBJECT);
+      return false;
+    }
+  }
+
+  return true;
+}
+
+static bool json_parseImmutable(JSContext* cx, unsigned argc, Value* vp) {
+  AutoJSMethodProfilerEntry pseudoFrame(cx, "JSON", "parseImmutable");
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  /* Step 1. */
+  JSString* str = (args.length() >= 1) ? ToString<CanGC>(cx, args[0])
+                                       : cx->names().undefined;
+  if (!str) {
+    return false;
+  }
+
+  JSLinearString* linear = str->ensureLinear(cx);
+  if (!linear) {
+    return false;
+  }
+
+  AutoStableStringChars linearChars(cx);
+  if (!linearChars.init(cx, linear)) {
+    return false;
+  }
+
+  HandleValue reviver = args.get(1);
+  RootedValue unfiltered(cx);
+
+  if (linearChars.isLatin1()) {
+    if (!ParseJSON(cx, linearChars.latin1Range(), &unfiltered)) {
+      return false;
+    }
+  } else {
+    if (!ParseJSON(cx, linearChars.twoByteRange(), &unfiltered)) {
+      return false;
+    }
+  }
+
+  RootedId id(cx, NameToId(cx->names().empty));
+  return BuildImmutableProperty(cx, unfiltered, id, reviver, args.rval());
+}
+#endif
+
+/* ES6 24.3.2. */
+bool json_stringify(JSContext* cx, unsigned argc, Value* vp) {
+  AutoJSMethodProfilerEntry pseudoFrame(cx, "JSON", "stringify");
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  RootedObject replacer(cx,
+                        args.get(1).isObject() ? &args[1].toObject() : nullptr);
+  RootedValue value(cx, args.get(0));
+  RootedValue space(cx, args.get(2));
+
+  JSStringBuilder sb(cx);
+  if (!Stringify(cx, &value, replacer, space, sb, StringifyBehavior::Normal)) {
+    return false;
+  }
+
+  // XXX This can never happen to nsJSON.cpp, but the JSON object
+  // needs to support returning undefined. So this is a little awkward
+  // for the API, because we want to support streaming writers.
+  if (!sb.empty()) {
+    JSString* str = sb.finishString();
+    if (!str) {
+      return false;
+    }
+    args.rval().setString(str);
+  } else {
+    args.rval().setUndefined();
+  }
+
+  return true;
+}
+
+static const JSFunctionSpec json_static_methods[] = {
+    JS_FN(js_toSource_str, json_toSource, 0, 0),
+    JS_FN("parse", json_parse, 2, 0), JS_FN("stringify", json_stringify, 3, 0),
+#ifdef ENABLE_RECORD_TUPLE
+    JS_FN("parseImmutable", json_parseImmutable, 2, 0),
+#endif
+    JS_FS_END};
+
+static const JSPropertySpec json_static_properties[] = {
+    JS_STRING_SYM_PS(toStringTag, "JSON", JSPROP_READONLY), JS_PS_END};
+
+static JSObject* CreateJSONObject(JSContext* cx, JSProtoKey key) {
+  RootedObject proto(cx, &cx->global()->getObjectPrototype());
+  return NewTenuredObjectWithGivenProto(cx, &JSONClass, proto);
+}
+
+static const ClassSpec JSONClassSpec = {
+    CreateJSONObject, nullptr, json_static_methods, json_static_properties};
+
+const JSClass js::JSONClass = {js_JSON_str,
+                               JSCLASS_HAS_CACHED_PROTO(JSProto_JSON),
+                               JS_NULL_CLASS_OPS, &JSONClassSpec};