Mypal/js/src/regexp/regexp-shim.h

/* -*- 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/. */

// Copyright 2019 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef RegexpShim_h
#define RegexpShim_h

#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include "mozilla/MathAlgorithms.h"
#include "mozilla/Maybe.h"
#include "mozilla/SegmentedVector.h"
#include "mozilla/Types.h"

#include <algorithm>
#include <cctype>

#include "jit/Label.h"
#include "jit/shared/Assembler-shared.h"
#include "js/Value.h"
#include "regexp/RegExpTypes.h"
#include "regexp/util/flags.h"
#include "regexp/util/vector.h"
#include "regexp/util/zone.h"
#include "vm/NativeObject.h"

// Forward declaration of classes
namespace v8 {
namespace internal {

class Heap;
class Isolate;
class RegExpMatchInfo;
class RegExpStack;

}  // namespace internal
}  // namespace v8

#define V8_WARN_UNUSED_RESULT MOZ_MUST_USE
#define V8_EXPORT_PRIVATE MOZ_EXPORT
#define V8_FALLTHROUGH MOZ_FALLTHROUGH

#define FATAL(x) MOZ_CRASH(x)
#define UNREACHABLE() MOZ_CRASH("unreachable code")
#define UNIMPLEMENTED() MOZ_CRASH("unimplemented code")
#define STATIC_ASSERT(exp) static_assert(exp, #exp)

#define DCHECK MOZ_ASSERT
#define DCHECK_EQ(lhs, rhs) MOZ_ASSERT((lhs) == (rhs))
#define DCHECK_NE(lhs, rhs) MOZ_ASSERT((lhs) != (rhs))
#define DCHECK_GT(lhs, rhs) MOZ_ASSERT((lhs) > (rhs))
#define DCHECK_GE(lhs, rhs) MOZ_ASSERT((lhs) >= (rhs))
#define DCHECK_LT(lhs, rhs) MOZ_ASSERT((lhs) < (rhs))
#define DCHECK_LE(lhs, rhs) MOZ_ASSERT((lhs) <= (rhs))
#define DCHECK_NULL(val) MOZ_ASSERT((val) == nullptr)
#define DCHECK_NOT_NULL(val) MOZ_ASSERT((val) != nullptr)
#define DCHECK_IMPLIES(lhs, rhs) MOZ_ASSERT_IF(lhs, rhs)
#define CHECK MOZ_RELEASE_ASSERT
#define CHECK_LE(lhs, rhs) MOZ_RELEASE_ASSERT((lhs) <= (rhs))

template <class T>
static constexpr inline T Min(T t1, T t2) {
  return t1 < t2 ? t1 : t2;
}

template <class T>
static constexpr inline T Max(T t1, T t2) {
  return t1 > t2 ? t1 : t2;
}
#define MemCopy memcpy

// Origin:
// https://github.com/v8/v8/blob/855591a54d160303349a5f0a32fab15825c708d1/src/base/macros.h#L310-L319
// ptrdiff_t is 't' according to the standard, but MSVC uses 'I'.
#ifdef _MSC_VER
#  define V8PRIxPTRDIFF "Ix"
#  define V8PRIdPTRDIFF "Id"
#  define V8PRIuPTRDIFF "Iu"
#else
#  define V8PRIxPTRDIFF "tx"
#  define V8PRIdPTRDIFF "td"
#  define V8PRIuPTRDIFF "tu"
#endif

// Origin:
// https://github.com/v8/v8/blob/855591a54d160303349a5f0a32fab15825c708d1/src/base/macros.h#L27-L38
// The arraysize(arr) macro returns the # of elements in an array arr.
// The expression is a compile-time constant, and therefore can be
// used in defining new arrays, for example.  If you use arraysize on
// a pointer by mistake, you will get a compile-time error.
#define arraysize(array) (sizeof(ArraySizeHelper(array)))

// This template function declaration is used in defining arraysize.
// Note that the function doesn't need an implementation, as we only
// use its type.
template <typename T, size_t N>
char (&ArraySizeHelper(T (&array)[N]))[N];

// Explicitly declare the assignment operator as deleted.
#define DISALLOW_ASSIGN(TypeName) TypeName& operator=(const TypeName&) = delete

// Explicitly declare the copy constructor and assignment operator as deleted.
// This also deletes the implicit move constructor and implicit move assignment
// operator, but still allows to manually define them.
#define DISALLOW_COPY_AND_ASSIGN(TypeName) \
  TypeName(const TypeName&) = delete;      \
  DISALLOW_ASSIGN(TypeName)

// Explicitly declare all implicit constructors as deleted, namely the
// default constructor, copy constructor and operator= functions.
// This is especially useful for classes containing only static methods.
#define DISALLOW_IMPLICIT_CONSTRUCTORS(TypeName) \
  TypeName() = delete;                           \
  DISALLOW_COPY_AND_ASSIGN(TypeName)

namespace v8 {

// Origin:
// https://github.com/v8/v8/blob/855591a54d160303349a5f0a32fab15825c708d1/src/base/macros.h#L364-L367
template <typename T, typename U>
constexpr inline bool IsAligned(T value, U alignment) {
  return (value & (alignment - 1)) == 0;
}

using byte = uint8_t;
using Address = uintptr_t;
static const Address kNullAddress = 0;

// Latin1/UTF-16 constants
// Code-point values in Unicode 4.0 are 21 bits wide.
// Code units in UTF-16 are 16 bits wide.
using uc16 = char16_t;
using uc32 = int32_t;

namespace base {

// Origin:
// https://github.com/v8/v8/blob/855591a54d160303349a5f0a32fab15825c708d1/src/base/macros.h#L247-L258
// The USE(x, ...) template is used to silence C++ compiler warnings
// issued for (yet) unused variables (typically parameters).
// The arguments are guaranteed to be evaluated from left to right.
struct Use {
  template <typename T>
  Use(T&&) {}  // NOLINT(runtime/explicit)
};
#define USE(...)                                                   \
  do {                                                             \
    ::v8::base::Use unused_tmp_array_for_use_macro[]{__VA_ARGS__}; \
    (void)unused_tmp_array_for_use_macro;                          \
  } while (false)

// Origin:
// https://github.com/v8/v8/blob/855591a54d160303349a5f0a32fab15825c708d1/src/base/safe_conversions.h#L35-L39
// saturated_cast<> is analogous to static_cast<> for numeric types, except
// that the specified numeric conversion will saturate rather than overflow or
// underflow.
template <typename Dst, typename Src>
inline Dst saturated_cast(Src value);

// This is the only specialization that is needed for regexp code.
// Instead of pulling in dozens of lines of template goo
// to derive it, I used the implementation from uint8_clamped in
// ArrayBufferObject.h.
template <>
inline uint8_t saturated_cast<uint8_t, int>(int x) {
  return (x >= 0) ? ((x < 255) ? uint8_t(x) : 255) : 0;
}

#define LAZY_INSTANCE_INITIALIZER { mozilla::Nothing() }

template <typename T>
struct LazyInstanceImpl {
  mozilla::Maybe<T> value_;
  T* Pointer() {
    if (value_.isNothing()) {
      value_.emplace();
    }
    return value_.ptr();
  }
};

template <typename T>
class LazyInstance {
public:
  using type = LazyInstanceImpl<T>;
};


namespace bits {

inline uint64_t CountTrailingZeros(uint64_t value) {
  return mozilla::CountTrailingZeroes64(value);
}

inline size_t RoundUpToPowerOfTwo32(size_t value) {
  return mozilla::RoundUpPow2(value);
}

}  // namespace bits
}  // namespace base

namespace unibrow {

using uchar = unsigned int;

// Origin:
// https://github.com/v8/v8/blob/1f1e4cdb04c75eab77adbecd5f5514ddc3eb56cf/src/strings/unicode.h#L133-L150
class Latin1 {
 public:
  static const uc16 kMaxChar = 0xff;

  // Convert the character to Latin-1 case equivalent if possible.
  static inline uc16 TryConvertToLatin1(uc16 c) {
    // "GREEK CAPITAL LETTER MU" case maps to "MICRO SIGN".
    // "GREEK SMALL LETTER MU" case maps to "MICRO SIGN".
    if (c == 0x039C || c == 0x03BC) {
      return 0xB5;
    }
    // "LATIN CAPITAL LETTER Y WITH DIAERESIS" case maps to "LATIN SMALL LETTER
    // Y WITH DIAERESIS".
    if (c == 0x0178) {
      return 0xFF;
    }
    return c;
  }
};

// Origin:
// https://github.com/v8/v8/blob/b4bfbce6f91fc2cc72178af42bb3172c5f5eaebb/src/strings/unicode.h#L99-L131
class Utf16 {
 public:
  static inline bool IsLeadSurrogate(int code) {
    return js::unicode::IsLeadSurrogate(code);
  }
  static inline bool IsTrailSurrogate(int code) {
    return js::unicode::IsTrailSurrogate(code);
  }
  static inline uc16 LeadSurrogate(uint32_t char_code) {
    return js::unicode::LeadSurrogate(char_code);
  }
  static inline uc16 TrailSurrogate(uint32_t char_code) {
    return js::unicode::TrailSurrogate(char_code);
  }
  static inline uint32_t CombineSurrogatePair(char16_t lead, char16_t trail) {
    return js::unicode::UTF16Decode(lead, trail);
  }
  static const uchar kMaxNonSurrogateCharCode = 0xffff;
};

#ifndef V8_INTL_SUPPORT

// A cache used in case conversion.  It caches the value for characters
// that either have no mapping or map to a single character independent
// of context.  Characters that map to more than one character or that
// map differently depending on context are always looked up.
// Origin:
// https://github.com/v8/v8/blob/b4bfbce6f91fc2cc72178af42bb3172c5f5eaebb/src/strings/unicode.h#L64-L88
template <class T, int size = 256>
class Mapping {
 public:
  inline Mapping() = default;
  inline int get(uchar c, uchar n, uchar* result) {
    CacheEntry entry = entries_[c & kMask];
    if (entry.code_point_ == c) {
      if (entry.offset_ == 0) {
        return 0;
      } else {
        result[0] = c + entry.offset_;
        return 1;
      }
    } else {
      return CalculateValue(c, n, result);
    }
  }

 private:
  int CalculateValue(uchar c, uchar n, uchar* result) {
    bool allow_caching = true;
    int length = T::Convert(c, n, result, &allow_caching);
    if (allow_caching) {
      if (length == 1) {
        entries_[c & kMask] = CacheEntry(c, result[0] - c);
        return 1;
      } else {
        entries_[c & kMask] = CacheEntry(c, 0);
        return 0;
      }
    } else {
      return length;
    }
  }

  struct CacheEntry {
    inline CacheEntry() : code_point_(kNoChar), offset_(0) {}
    inline CacheEntry(uchar code_point, signed offset)
        : code_point_(code_point), offset_(offset) {}
    uchar code_point_;
    signed offset_;
    static const int kNoChar = (1 << 21) - 1;
  };
  static const int kSize = size;
  static const int kMask = kSize - 1;
  CacheEntry entries_[kSize];
};

// Origin:
// https://github.com/v8/v8/blob/b4bfbce6f91fc2cc72178af42bb3172c5f5eaebb/src/strings/unicode.h#L241-L252
struct Ecma262Canonicalize {
  static const int kMaxWidth = 1;
  static int Convert(uchar c, uchar n, uchar* result, bool* allow_caching_ptr);
};
struct Ecma262UnCanonicalize {
  static const int kMaxWidth = 4;
  static int Convert(uchar c, uchar n, uchar* result, bool* allow_caching_ptr);
};
struct CanonicalizationRange {
  static const int kMaxWidth = 1;
  static int Convert(uchar c, uchar n, uchar* result, bool* allow_caching_ptr);
};

#endif  // !V8_INTL_SUPPORT

struct Letter {
  static bool Is(uchar c);
};

}  // namespace unibrow

namespace internal {

#define PRINTF_FORMAT(x, y) MOZ_FORMAT_PRINTF(x, y)
void PRINTF_FORMAT(1, 2) PrintF(const char* format, ...);
void PRINTF_FORMAT(2, 3) PrintF(FILE* out, const char* format, ...);

// Superclass for classes only using static method functions.
// The subclass of AllStatic cannot be instantiated at all.
class AllStatic {
#ifdef DEBUG
 public:
  AllStatic() = delete;
#endif
};

// Superclass for classes managed with new and delete.
// In irregexp, this is only AlternativeGeneration (in regexp-compiler.cc)
// Compare:
// https://github.com/v8/v8/blob/7b3332844212d78ee87a9426f3a6f7f781a8fbfa/src/utils/allocation.cc#L88-L96
class Malloced {
 public:
  static void* operator new(size_t size) {
    js::AutoEnterOOMUnsafeRegion oomUnsafe;
    void* result = js_malloc(size);
    if (!result) {
      oomUnsafe.crash("Irregexp Malloced shim");
    }
    return result;
  }
  static void operator delete(void* p) { js_free(p); }
};

constexpr int32_t KB = 1024;
constexpr int32_t MB = 1024 * 1024;

#define kMaxInt JSVAL_INT_MAX
#define kMinInt JSVAL_INT_MIN
constexpr int kSystemPointerSize = sizeof(void*);

// The largest integer n such that n and n + 1 are both exactly
// representable as a Number value.  ES6 section 20.1.2.6
constexpr double kMaxSafeInteger = 9007199254740991.0;  // 2^53-1

constexpr int kBitsPerByte = 8;
constexpr int kBitsPerByteLog2 = 3;
constexpr int kUInt32Size = sizeof(uint32_t);
constexpr int kInt64Size = sizeof(int64_t);
constexpr int kUC16Size = sizeof(uc16);

inline constexpr bool IsDecimalDigit(uc32 c) { return c >= '0' && c <= '9'; }
inline bool is_uint24(int val) { return (val & 0x00ffffff) == val; }

inline bool IsIdentifierStart(uc32 c) {
  return js::unicode::IsIdentifierStart(uint32_t(c));
}
inline bool IsIdentifierPart(uc32 c) {
  return js::unicode::IsIdentifierPart(uint32_t(c));
}

// Wrappers to disambiguate char16_t and uc16.
struct AsUC16 {
  explicit AsUC16(char16_t v) : value(v) {}
  char16_t value;
};

struct AsUC32 {
  explicit AsUC32(int32_t v) : value(v) {}
  int32_t value;
};

std::ostream& operator<<(std::ostream& os, const AsUC16& c);
std::ostream& operator<<(std::ostream& os, const AsUC32& c);

// This class is used for the output of trace-regexp-parser.  V8 has
// an elaborate implementation to ensure that the output gets to the
// right place, even on Android. We just need something that will
// print output (ideally to stderr, to match the rest of our tracing
// code). This is an empty wrapper that will convert itself to
// std::cerr when used.
class StdoutStream {
public:
  operator std::ostream&() const;
  template <typename T> std::ostream& operator<<(T t);
};

// Reuse existing Maybe implementation
using mozilla::Maybe;

template <typename T>
Maybe<T> Just(const T& value) {
  return mozilla::Some(value);
}

template <typename T>
mozilla::Nothing Nothing() {
  return mozilla::Nothing();
}


template <typename T>
using PseudoHandle = mozilla::UniquePtr<T, JS::FreePolicy>;

// Origin:
// https://github.com/v8/v8/blob/855591a54d160303349a5f0a32fab15825c708d1/src/utils/utils.h#L600-L642
// Compare 8bit/16bit chars to 8bit/16bit chars.
// Used indirectly by regexp-interpreter.cc
template <typename lchar, typename rchar>
inline int CompareCharsUnsigned(const lchar* lhs, const rchar* rhs,
                                size_t chars) {
  const lchar* limit = lhs + chars;
  if (sizeof(*lhs) == sizeof(char) && sizeof(*rhs) == sizeof(char)) {
    // memcmp compares byte-by-byte, yielding wrong results for two-byte
    // strings on little-endian systems.
    return memcmp(lhs, rhs, chars);
  }
  while (lhs < limit) {
    int r = static_cast<int>(*lhs) - static_cast<int>(*rhs);
    if (r != 0) return r;
    ++lhs;
    ++rhs;
  }
  return 0;
}
template <typename lchar, typename rchar>
inline int CompareChars(const lchar* lhs, const rchar* rhs, size_t chars) {
  DCHECK_LE(sizeof(lchar), 2);
  DCHECK_LE(sizeof(rchar), 2);
  if (sizeof(lchar) == 1) {
    if (sizeof(rchar) == 1) {
      return CompareCharsUnsigned(reinterpret_cast<const uint8_t*>(lhs),
                                  reinterpret_cast<const uint8_t*>(rhs), chars);
    } else {
      return CompareCharsUnsigned(reinterpret_cast<const uint8_t*>(lhs),
                                  reinterpret_cast<const char16_t*>(rhs),
                                  chars);
    }
  } else {
    if (sizeof(rchar) == 1) {
      return CompareCharsUnsigned(reinterpret_cast<const char16_t*>(lhs),
                                  reinterpret_cast<const uint8_t*>(rhs), chars);
    } else {
      return CompareCharsUnsigned(reinterpret_cast<const char16_t*>(lhs),
                                  reinterpret_cast<const char16_t*>(rhs),
                                  chars);
    }
  }
}

// Origin:
// https://github.com/v8/v8/blob/855591a54d160303349a5f0a32fab15825c708d1/src/utils/utils.h#L40-L48
// Returns the value (0 .. 15) of a hexadecimal character c.
// If c is not a legal hexadecimal character, returns a value < 0.
// Used in regexp-parser.cc
inline int HexValue(uc32 c) {
  c -= '0';
  if (static_cast<unsigned>(c) <= 9) return c;
  c = (c | 0x20) - ('a' - '0');  // detect 0x11..0x16 and 0x31..0x36.
  if (static_cast<unsigned>(c) <= 5) return c + 10;
  return -1;
}

// V8::Object ~= JS::Value
class Object {
 public:
  // The default object constructor in V8 stores a nullptr,
  // which has its low bit clear and is interpreted as Smi(0).
  constexpr Object() : value_(JS::Int32Value(0)) {}

  // Conversions to/from SpiderMonkey types
  constexpr Object(JS::Value value) : value_(value) {}
  operator JS::Value() const { return value_; }

  // Used in regexp-macro-assembler.cc and regexp-interpreter.cc to
  // check the return value of isolate->stack_guard()->HandleInterrupts()
  // In V8, this will be either an exception object or undefined.
  // In SM, we store the exception in the context, so we can use our normal
  // idiom: return false iff we are throwing an exception.
  inline bool IsException(Isolate*) const { return !value_.toBoolean(); }

 protected:
  JS::Value value_;
};

class Smi : public Object {
 public:
  static Smi FromInt(int32_t value) {
    Smi smi;
    smi.value_ = JS::Int32Value(value);
    return smi;
  }
  static inline int32_t ToInt(const Object object) {
    return JS::Value(object).toInt32();
  }
};

// V8::HeapObject ~= JSObject
class HeapObject : public Object {
 public:
  inline static HeapObject cast(Object object) {
    HeapObject h;
    h.value_ = JS::Value(object);
    return h;
  }
};

// A fixed-size array with Objects (aka Values) as element types
// Only used for named captures. Allocated during parsing, so
// can't be a GC thing.
// TODO: implement.
class FixedArray : public HeapObject {
 public:
  inline void set(uint32_t index, Object value) {}
  inline static FixedArray cast(Object object) { MOZ_CRASH("TODO"); }
};

class ByteArrayData {
public:
  uint32_t length;
  uint8_t* data();
};

/*
 * Conceptually, ByteArrayData is a variable-size structure. To
 * implement this in a C++-approved way, we allocate a struct
 * containing the 32-bit length field, followed by additional memory
 * for the data. To access the data, we get a pointer to the next byte
 * after the length field and cast it to the correct type.
 */
inline uint8_t* ByteArrayData::data() {
  static_assert(alignof(uint8_t) <= alignof(ByteArrayData),
                "The trailing data must be aligned to start immediately "
                "after the header with no padding.");
  ByteArrayData* immediatelyAfter = this + 1;
  return reinterpret_cast<uint8_t*>(immediatelyAfter);
}

// A fixed-size array of bytes.
class ByteArray : public HeapObject {
  ByteArrayData* inner() const {
    return static_cast<ByteArrayData*>(value_.toPrivate());
  }
public:
  PseudoHandle<ByteArrayData> takeOwnership(Isolate* isolate);
  byte get(uint32_t index) {
    MOZ_ASSERT(index < length());
    return inner()->data()[index];
  }
  void set(uint32_t index, byte val) {
    MOZ_ASSERT(index < length());
    inner()->data()[index] = val;
  }
  uint32_t length() const { return inner()->length; }
  byte* GetDataStartAddress() { return inner()->data(); }

  static ByteArray cast(Object object) {
    ByteArray b;
    b.value_ = JS::Value(object);
    return b;
  }
};

// Like Handles in SM, V8 handles are references to marked pointers.
// Unlike SM, where Rooted pointers are created individually on the
// stack, the target of a V8 handle lives in an arena on the isolate
// (~= JSContext). Whenever a Handle is created, a new "root" is
// created at the end of the arena.
//
// HandleScopes are used to manage the lifetimes of these handles.  A
// HandleScope lives on the stack and stores the size of the arena at
// the time of its creation. When the function returns and the
// HandleScope is destroyed, the arena is truncated to its previous
// size, clearing all roots that were created since the creation of
// the HandleScope.
//
// In some cases, objects that are GC-allocated in V8 are not in SM.
// In particular, irregexp allocates ByteArrays during code generation
// to store lookup tables. This does not play nicely with the SM
// macroassembler's requirement that no GC allocations take place
// while it is on the stack. To work around this, this shim layer also
// provides the ability to create pseudo-handles, which are not
// managed by the GC but provide the same API to irregexp. The "root"
// of a pseudohandle is a unique pointer living in a second arena. If
// the allocated object should outlive the HandleScope, it must be
// manually moved out of the arena using takeOwnership.

class MOZ_STACK_CLASS HandleScope {
public:
  HandleScope(Isolate* isolate);
 ~HandleScope();

 private:
  size_t level_;
  size_t non_gc_level_;
  Isolate* isolate_;

  friend class Isolate;
};

// Origin:
// https://github.com/v8/v8/blob/5792f3587116503fc047d2f68c951c72dced08a5/src/handles/handles.h#L88-L171
template <typename T>
class MOZ_NONHEAP_CLASS Handle {
 public:
  Handle() : location_(nullptr) {}
  Handle(T object, Isolate* isolate);
  Handle(JS::Value value, Isolate* isolate);

  // Constructor for handling automatic up casting.
  template <typename S, typename = typename std::enable_if<
                            std::is_convertible<S*, T*>::value>::type>
  inline Handle(Handle<S> handle) : location_(handle.location_) {}

  template <typename S>
  inline static const Handle<T> cast(Handle<S> that) {
    return Handle<T>(that.location_);
  }

  inline bool is_null() const { return location_ == nullptr; }

  inline T operator*() const {
    return T::cast(Object(*location_));
  };

  // {ObjectRef} is returned by {Handle::operator->}. It should never be stored
  // anywhere or used in any other code; no one should ever have to spell out
  // {ObjectRef} in code. Its only purpose is to be dereferenced immediately by
  // "operator-> chaining". Returning the address of the field is valid because
  // this object's lifetime only ends at the end of the full statement.
  // Origin:
  // https://github.com/v8/v8/blob/03aaa4b3bf4cb01eee1f223b252e6869b04ab08c/src/handles/handles.h#L91-L105
  class MOZ_TEMPORARY_CLASS ObjectRef {
   public:
    T* operator->() { return &object_; }

   private:
    friend class Handle;
    explicit ObjectRef(T object) : object_(object) {}

    T object_;
  };
  inline ObjectRef operator->() const { return ObjectRef{**this}; }

  static Handle<T> fromHandleValue(JS::HandleValue handle) {
    return Handle(handle.address());
  }

 private:
  Handle(const JS::Value* location) : location_(location) {}

  template <typename>
  friend class Handle;
  template <typename>
  friend class MaybeHandle;

  const JS::Value* location_;
};

// A Handle can be converted into a MaybeHandle. Converting a MaybeHandle
// into a Handle requires checking that it does not point to nullptr.  This
// ensures nullptr checks before use.
//
// Also note that Handles do not provide default equality comparison or hashing
// operators on purpose. Such operators would be misleading, because intended
// semantics is ambiguous between Handle location and object identity.
// Origin:
// https://github.com/v8/v8/blob/5792f3587116503fc047d2f68c951c72dced08a5/src/handles/maybe-handles.h#L15-L78
template <typename T>
class MOZ_NONHEAP_CLASS MaybeHandle final {
 public:
  MaybeHandle() : location_(nullptr) {}

  // Constructor for handling automatic up casting from Handle.
  // Ex. Handle<JSArray> can be passed when MaybeHandle<Object> is expected.
  template <typename S, typename = typename std::enable_if<
                            std::is_convertible<S*, T*>::value>::type>
  MaybeHandle(Handle<S> handle) : location_(handle.location_) {}

  inline Handle<T> ToHandleChecked() const {
    MOZ_RELEASE_ASSERT(location_);
    return Handle<T>(location_);
  }

  // Convert to a Handle with a type that can be upcasted to.
  template <typename S>
  inline bool ToHandle(Handle<S>* out) const {
    if (location_) {
      *out = Handle<T>(location_);
      return true;
    } else {
      *out = Handle<T>();
      return false;
    }
  }

private:
  JS::Value* location_;
};

// From v8/src/handles/handles-inl.h

template <typename T>
inline Handle<T> handle(T object, Isolate* isolate) {
  return Handle<T>(object, isolate);
}

// RAII Guard classes

class DisallowHeapAllocation {
 public:
  DisallowHeapAllocation() {}
  operator const JS::AutoAssertNoGC&() const { return no_gc_; }

 private:
  const JS::AutoAssertNoGC no_gc_;
};

// This is used inside DisallowHeapAllocation regions to enable
// allocation just before throwing an exception, to allocate the
// exception object. Specifically, it only ever guards:
// - isolate->stack_guard()->HandleInterrupts()
// - isolate->StackOverflow()
// Those cases don't allocate in SpiderMonkey, so this can be a no-op.
class AllowHeapAllocation {
 public:
  // Empty constructor to avoid unused_variable warnings
  AllowHeapAllocation() {}
};

// Origin:
// https://github.com/v8/v8/blob/84f3877c15bc7f8956d21614da4311337525a3c8/src/objects/string.h#L83-L474
class String : public HeapObject {
 private:
  JSString* str() const { return value_.toString(); }

 public:
  String() : HeapObject() {}
  String(JSString* str) { value_ = JS::StringValue(str); }

  operator JSString*() const { return str(); }

  // Max char codes.
  static const int32_t kMaxOneByteCharCode = unibrow::Latin1::kMaxChar;
  static const uint32_t kMaxOneByteCharCodeU = unibrow::Latin1::kMaxChar;
  static const int kMaxUtf16CodeUnit = 0xffff;
  static const uc32 kMaxCodePoint = 0x10ffff;

  MOZ_ALWAYS_INLINE int length() const { return str()->length(); }
  bool IsFlat() { return str()->isLinear(); };

  // Origin:
  // https://github.com/v8/v8/blob/84f3877c15bc7f8956d21614da4311337525a3c8/src/objects/string.h#L95-L152
  class FlatContent {
   public:
    FlatContent(JSLinearString* string, const DisallowHeapAllocation& no_gc)
        : string_(string), no_gc_(no_gc) {}
    inline bool IsOneByte() const { return string_->hasLatin1Chars(); }
    inline bool IsTwoByte() const { return !string_->hasLatin1Chars(); }

    Vector<const uint8_t> ToOneByteVector() const {
      MOZ_ASSERT(IsOneByte());
      return Vector<const uint8_t>(string_->latin1Chars(no_gc_),
                                   string_->length());
    }
    Vector<const uc16> ToUC16Vector() const {
      MOZ_ASSERT(IsTwoByte());
      return Vector<const uc16>(string_->twoByteChars(no_gc_),
                                string_->length());
    }
   private:
    const JSLinearString* string_;
    const JS::AutoAssertNoGC& no_gc_;
  };
  FlatContent GetFlatContent(const DisallowHeapAllocation& no_gc) {
    MOZ_ASSERT(IsFlat());
    return FlatContent(&str()->asLinear(), no_gc);
  }

  static Handle<String> Flatten(Isolate* isolate, Handle<String> string);

  inline static String cast(Object object) {
    String s;
    s.value_ = JS::StringValue(JS::Value(object).toString());
    return s;
  }

  inline static bool IsOneByteRepresentationUnderneath(String string) {
    return string.str()->hasLatin1Chars();
  }
  inline bool IsOneByteRepresentation() const {
    return str()->hasLatin1Chars();
  }

  std::unique_ptr<char[]> ToCString();

  template <typename Char>
  Vector<const Char> GetCharVector(const DisallowHeapAllocation& no_gc);
};

template <>
inline Vector<const uint8_t> String::GetCharVector(
    const DisallowHeapAllocation& no_gc) {
  String::FlatContent flat = GetFlatContent(no_gc);
  MOZ_ASSERT(flat.IsOneByte());
  return flat.ToOneByteVector();
}

template <>
inline Vector<const uc16> String::GetCharVector(
    const DisallowHeapAllocation& no_gc) {
  String::FlatContent flat = GetFlatContent(no_gc);
  MOZ_ASSERT(flat.IsTwoByte());
  return flat.ToUC16Vector();
}

// A flat string reader provides random access to the contents of a
// string independent of the character width of the string.  The handle
// must be valid as long as the reader is being used.
// Origin:
// https://github.com/v8/v8/blob/84f3877c15bc7f8956d21614da4311337525a3c8/src/objects/string.h#L807-L825
class MOZ_STACK_CLASS FlatStringReader {
 public:
  FlatStringReader(JSLinearString* string)
    : length_(string->length()),
      is_latin1_(string->hasLatin1Chars()) {

    if (is_latin1_) {
      latin1_chars_ = string->latin1Chars(nogc_);
    } else {
      two_byte_chars_ = string->twoByteChars(nogc_);
    }
  }
  FlatStringReader(const char16_t* chars, size_t length)
    : two_byte_chars_(chars),
      length_(length),
      is_latin1_(false) {}

  int length() { return length_; }

  inline char16_t Get(size_t index) {
    MOZ_ASSERT(index < length_);
    if (is_latin1_) {
      return latin1_chars_[index];
    } else {
      return two_byte_chars_[index];
    }
  }

 private:
  union {
    const JS::Latin1Char *latin1_chars_;
    const char16_t* two_byte_chars_;
  };
  size_t length_;
  bool is_latin1_;
  JS::AutoCheckCannotGC nogc_;
};

class JSRegExp : public HeapObject {
 public:
  // ******************************************************
  // Methods that are called from inside the implementation
  // ******************************************************
  void TierUpTick() { /*inner()->tierUpTick();*/ }
  bool MarkedForTierUp() const {
    return false; /*inner()->markedForTierUp();*/
  }

  // TODO: hook these up
  Object Code(bool is_latin1) const { return Object(JS::UndefinedValue()); }
  Object Bytecode(bool is_latin1) const { return Object(JS::UndefinedValue()); }

  uint32_t BacktrackLimit() const {
    return 0; /*inner()->backtrackLimit();*/
  }

  static JSRegExp cast(Object object) {
    JSRegExp regexp;
    MOZ_ASSERT(JS::Value(object).toGCThing()->is<js::RegExpShared>());
    regexp.value_ = JS::PrivateGCThingValue(JS::Value(object).toGCThing());
    return regexp;
  }

  // ******************************
  // Static constants
  // ******************************

  // Meaning of Type:
  // NOT_COMPILED: Initial value. No data has been stored in the JSRegExp yet.
  // ATOM: A simple string to match against using an indexOf operation.
  // IRREGEXP: Compiled with Irregexp.
  enum Type { NOT_COMPILED, ATOM, IRREGEXP };

  // Maximum number of captures allowed.
  static constexpr int kMaxCaptures = 1 << 16;

  // **************************************************
  // JSRegExp::Flags
  // **************************************************

  struct FlagShiftBit {
    static constexpr int kGlobal = 0;
    static constexpr int kIgnoreCase = 1;
    static constexpr int kMultiline = 2;
    static constexpr int kSticky = 3;
    static constexpr int kUnicode = 4;
    static constexpr int kDotAll = 5;
    static constexpr int kInvalid = 6;
  };
  enum Flag : uint8_t {
    kNone = 0,
    kGlobal = 1 << FlagShiftBit::kGlobal,
    kIgnoreCase = 1 << FlagShiftBit::kIgnoreCase,
    kMultiline = 1 << FlagShiftBit::kMultiline,
    kSticky = 1 << FlagShiftBit::kSticky,
    kUnicode = 1 << FlagShiftBit::kUnicode,
    kDotAll = 1 << FlagShiftBit::kDotAll,
    kInvalid = 1 << FlagShiftBit::kInvalid,  // Not included in FlagCount.
  };
  using Flags = base::Flags<Flag>;
  static constexpr int kFlagCount = 6;

  static constexpr int kNoBacktrackLimit = 0;

private:
  js::RegExpShared* inner() {
    return value_.toGCThing()->as<js::RegExpShared>();
  }
};

class Histogram {
 public:
  inline void AddSample(int sample) {}
};

class Counters {
 public:
  Histogram* regexp_backtracks() { return &regexp_backtracks_; }

 private:
  Histogram regexp_backtracks_;
};

#define PROFILE(isolate, call) \
  do {                         \
  } while (false);

enum class AllocationType : uint8_t {
  kYoung,  // Allocate in the nursery
  kOld,    // Allocate in the tenured heap
};

using StackGuard = Isolate;
using Factory = Isolate;

class Isolate {
 public:
  //********** Isolate code **********//
  RegExpStack* regexp_stack() const { return regexpStack_; }
  byte* top_of_regexp_stack() const;

  // This is called from inside no-GC code. Instead of suppressing GC
  // to allocate the error, we return false from Execute and call
  // ReportOverRecursed in the caller.
  void StackOverflow() {}

#ifndef V8_INTL_SUPPORT
  unibrow::Mapping<unibrow::Ecma262UnCanonicalize>* jsregexp_uncanonicalize() {
    return &jsregexp_uncanonicalize_;
  }
  unibrow::Mapping<unibrow::Ecma262Canonicalize>*
  regexp_macro_assembler_canonicalize() {
    return &regexp_macro_assembler_canonicalize_;
  }
  unibrow::Mapping<unibrow::CanonicalizationRange>* jsregexp_canonrange() {
    return &jsregexp_canonrange_;
  }

private:
  unibrow::Mapping<unibrow::Ecma262UnCanonicalize> jsregexp_uncanonicalize_;
  unibrow::Mapping<unibrow::Ecma262Canonicalize>
  regexp_macro_assembler_canonicalize_;
  unibrow::Mapping<unibrow::CanonicalizationRange> jsregexp_canonrange_;
#endif // !V8_INTL_SUPPORT

public:
  // An empty stub for telemetry we don't support
  void IncreaseTotalRegexpCodeGenerated(Handle<HeapObject> code) {}

  Counters* counters() { return &counters_; }

  //********** Factory code **********//
  inline Factory* factory() { return this; }

  Handle<ByteArray> NewByteArray(
      int length, AllocationType allocation = AllocationType::kYoung);

  // Allocates a fixed array initialized with undefined values.
  Handle<FixedArray> NewFixedArray(int length);

  template <typename Char>
  Handle<String> InternalizeString(const Vector<const Char>& str);

  //********** Stack guard code **********//
  inline StackGuard* stack_guard() { return this; }
  Object HandleInterrupts() {
    return Object(JS::BooleanValue(cx()->handleInterrupt()));
  }

  JSContext* cx() const { return cx_; }

  void trace(JSTracer* trc);

  //********** Handle code **********//

  JS::Value* getHandleLocation(JS::Value value);

 private:

  mozilla::SegmentedVector<JS::Value> handleArena_;
  mozilla::SegmentedVector<PseudoHandle<void>> uniquePtrArena_;

  void* allocatePseudoHandle(size_t bytes);

public:
  template <typename T>
  PseudoHandle<T> takeOwnership(void* ptr);

private:
  void openHandleScope(HandleScope& scope) {
    scope.level_ = handleArena_.Length();
    scope.non_gc_level_ = uniquePtrArena_.Length();
  }
  void closeHandleScope(size_t prevLevel, size_t prevUniqueLevel) {
    size_t currLevel = handleArena_.Length();
    handleArena_.PopLastN(currLevel - prevLevel);

    size_t currUniqueLevel = uniquePtrArena_.Length();
    uniquePtrArena_.PopLastN(currUniqueLevel - prevUniqueLevel);
  }
  friend class HandleScope;

  JSContext* cx_;
  RegExpStack* regexpStack_;
  Counters counters_;
};

// Origin:
// https://github.com/v8/v8/blob/50dcf2af54ce27801a71c47c1be1d2c5e36b0dd6/src/execution/isolate.h#L1909-L1931
class StackLimitCheck {
 public:
  StackLimitCheck(Isolate* isolate) : cx_(isolate->cx()) {}

  // Use this to check for stack-overflows in C++ code.
  bool HasOverflowed() { return !CheckRecursionLimitDontReport(cx_); }

  // Use this to check for interrupt request in C++ code.
  bool InterruptRequested() { return cx_->hasAnyPendingInterrupt(); }

  // Use this to check for stack-overflow when entering runtime from JS code.
  bool JsHasOverflowed() {
    return !CheckRecursionLimitConservativeDontReport(cx_);
  }

 private:
  JSContext* cx_;
};

class Code : public HeapObject {
 public:
  uint8_t* raw_instruction_start() { return inner()->raw(); }

  static Code cast(Object object) {
    Code c;
    MOZ_ASSERT(JS::Value(object).toGCThing()->is<js::jit::JitCode>());
    c.value_ = JS::PrivateGCThingValue(JS::Value(object).toGCThing());
    return c;
  }
  js::jit::JitCode* inner() {
    return value_.toGCThing()->as<js::jit::JitCode>();
  }
};

enum class MessageTemplate { kStackOverflow };

class MessageFormatter {
 public:
  static const char* TemplateString(MessageTemplate index) {
    switch (index) {
      case MessageTemplate::kStackOverflow:
        return "too much recursion";
    }
  }
};

// Origin: https://github.com/v8/v8/blob/master/src/codegen/label.h
class Label {
 public:
  Label() : inner_(js::jit::Label()) {}

  js::jit::Label* inner() { return &inner_; }

  void Unuse() { inner_.reset(); }

  bool is_linked() { return inner_.used(); }
  bool is_bound() { return inner_.bound(); }
  bool is_unused() { return !inner_.used() && !inner_.bound(); }

  int pos() { return inner_.offset(); }
  void link_to(int pos) { inner_.use(pos); }
  void bind_to(int pos) { inner_.bind(pos); }

 private:
  js::jit::Label inner_;
  js::jit::CodeOffset patchOffset_;

  friend class SMRegExpMacroAssembler;
};

// TODO: Map flags to jitoptions
extern bool FLAG_correctness_fuzzer_suppressions;
extern bool FLAG_enable_regexp_unaligned_accesses;
extern bool FLAG_harmony_regexp_sequence;
extern bool FLAG_regexp_interpret_all;
extern bool FLAG_regexp_mode_modifiers;
extern bool FLAG_regexp_optimization;
extern bool FLAG_regexp_peephole_optimization;
extern bool FLAG_regexp_possessive_quantifier;
extern bool FLAG_regexp_tier_up;
extern bool FLAG_trace_regexp_assembler;
extern bool FLAG_trace_regexp_bytecodes;
extern bool FLAG_trace_regexp_parser;
extern bool FLAG_trace_regexp_peephole_optimization;

#define V8_USE_COMPUTED_GOTO 1
#define COMPILING_IRREGEXP_FOR_EXTERNAL_EMBEDDER

}  // namespace internal
}  // namespace v8

#endif  // RegexpShim_h