path: root/js/src/frontend/ObjectEmitter.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * 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/. */

#ifndef frontend_ObjectEmitter_h
#define frontend_ObjectEmitter_h

#include "mozilla/Attributes.h"  // MOZ_MUST_USE, MOZ_STACK_CLASS, MOZ_ALWAYS_INLINE, MOZ_RAII
#include "mozilla/Maybe.h"  // Maybe

#include <stddef.h>  // size_t, ptrdiff_t
#include <stdint.h>  // uint32_t

#include "jsopcode.h"                // JSOp
#include "jsfun.h"                   // JSFunction
#include "jsscript.h"                // FunctionAsyncKind

#include "frontend/EmitterScope.h"   // EmitterScope
#include "frontend/NameOpEmitter.h"   // NameOpEmitter
#include "frontend/TDZCheckCache.h"  // TDZCheckCache
#include "js/RootingAPI.h"           // JS::Handle, JS::Rooted
#include "vm/String.h"               // JSAtom
#include "vm/NativeObject.h"         // PlainObject
#include "vm/Scope.h"                // LexicalScope

namespace js {

namespace frontend {

struct BytecodeEmitter;
class SharedContext;

// Class for emitting bytecode for object and class properties.
// See ObjectEmitter and ClassEmitter for usage.
class MOZ_STACK_CLASS PropertyEmitter
{
  public:
    enum class Kind {
        // Prototype property.
        Prototype,

        // Class static property.
        Static
    };

  protected:
    BytecodeEmitter* bce_;

    // True if the object is class.
    // Set by ClassEmitter.
    bool isClass_ = false;

    // True if the property is class static method.
    bool isStatic_ = false;

    // True if the property has computed or index key.
    bool isIndexOrComputed_ = false;

    // An object which keeps the shape of this object literal.
    // This fields is reset to nullptr whenever the object literal turns out to
    // have at least one numeric, computed, spread or __proto__ property, or
    // the object becomes dictionary mode.
    // This field is used only in ObjectEmitter.
    JS::Rooted<PlainObject*> obj_;

#ifdef DEBUG
    // The state of this emitter.
    //
    // +-------+
    // | Start |-+
    // +-------+ |
    //           |
    // +---------+
    // |
    // |  +------------------------------------------------------------+
    // |  |                                                            |
    // |  | [normal property/method/accessor]                          |
    // |  v   prepareForPropValue  +-----------+              +------+ |
    // +->+----------------------->| PropValue |-+         +->| Init |-+
    //    |                        +-----------+ |         |  +------+
    //    |                                      |         |
    //    |  +----------------------------------+          +-----------+
    //    |  |                                                         |
    //    |  +-+---------------------------------------+               |
    //    |    |                                       |               |
    //    |    | [method with super]                   |               |
    //    |    |   emitInitHomeObject +-------------+  v               |
    //    |    +--------------------->| InitHomeObj |->+               |
    //    |                           +-------------+  |               |
    //    |                                            |               |
    //    |    +-------------------------------------- +               |
    //    |    |                                                       |
    //    |    | emitInitProp                                          |
    //    |    | emitInitGetter                                        |
    //    |    | emitInitSetter                                        |
    //    |    +------------------------------------------------------>+
    //    |                                                            ^
    //    | [index property/method/accessor]                           |
    //    |   prepareForIndexPropKey  +----------+                     |
    //    +-------------------------->| IndexKey |-+                   |
    //    |                           +----------+ |                   |
    //    |                                        |                   |
    //    |  +-------------------------------------+                   |
    //    |  |                                                         |
    //    |  | prepareForIndexPropValue +------------+                 |
    //    |  +------------------------->| IndexValue |-+               |
    //    |                             +------------+ |               |
    //    |                                            |               |
    //    |    +---------------------------------------+               |
    //    |    |                                                       |
    //    |    +-+--------------------------------------------------+  |
    //    |      |                                                  |  |
    //    |      | [method with super]                              |  |
    //    |      |   emitInitHomeObject +---------------------+     v  |
    //    |      +--------------------->| InitHomeObjForIndex |---->+  |
    //    |                             +---------------------+     |  |
    //    |                                                         |  |
    //    |      +--------------------------------------------------+  |
    //    |      |                                                     |
    //    |      | emitInitIndexProp                                   |
    //    |      | emitInitIndexGetter                                 |
    //    |      | emitInitIndexSetter                                 |
    //    |      +---------------------------------------------------->+
    //    |                                                            |
    //    | [computed property/method/accessor]                        |
    //    |   prepareForComputedPropKey  +-------------+               |
    //    +----------------------------->| ComputedKey |-+             |
    //    |                              +-------------+ |             |
    //    |                                              |             |
    //    |  +-------------------------------------------+             |
    //    |  |                                                         |
    //    |  | prepareForComputedPropValue +---------------+           |
    //    |  +---------------------------->| ComputedValue |-+         |
    //    |                                +---------------+ |         |
    //    |                                                  |         |
    //    |    +---------------------------------------------+         |
    //    |    |                                                       |
    //    |    +-+--------------------------------------------------+  |
    //    |      |                                                  |  |
    //    |      | [method with super]                              |  |
    //    |      |   emitInitHomeObject +------------------------+  v  |
    //    |      +--------------------->| InitHomeObjForComputed |->+  |
    //    |                             +------------------------+  |  |
    //    |                                                         |  |
    //    |      +--------------------------------------------------+  |
    //    |      |                                                     |
    //    |      | emitInitComputedProp                                |
    //    |      | emitInitComputedGetter                              |
    //    |      | emitInitComputedSetter                              |
    //    |      +---------------------------------------------------->+
    //    |                                                            ^
    //    |                                                            |
    //    | [__proto__]                                                |
    //    |   prepareForProtoValue  +------------+ emitMutateProto     |
    //    +------------------------>| ProtoValue |-------------------->+
    //    |                         +------------+                     ^
    //    |                                                            |
    //    | [...prop]                                                  |
    //    |   prepareForSpreadOperand +---------------+ emitSpread     |
    //    +-------------------------->| SpreadOperand |----------------+
    //                                +---------------+
    enum class PropertyState {
        // The initial state.
        Start,

        // After calling prepareForPropValue.
        PropValue,

        // After calling emitInitHomeObject, from PropValue.
        InitHomeObj,

        // After calling prepareForIndexPropKey.
        IndexKey,

        // prepareForIndexPropValue.
        IndexValue,

        // After calling emitInitHomeObject, from IndexValue.
        InitHomeObjForIndex,

        // After calling prepareForComputedPropKey.
        ComputedKey,

        // prepareForComputedPropValue.
        ComputedValue,

        // After calling emitInitHomeObject, from ComputedValue.
        InitHomeObjForComputed,

        // After calling prepareForProtoValue.
        ProtoValue,

        // After calling prepareForSpreadOperand.
        SpreadOperand,

        // After calling one of emitInitProp, emitInitGetter, emitInitSetter,
        // emitInitIndexOrComputedProp, emitInitIndexOrComputedGetter,
        // emitInitIndexOrComputedSetter, emitMutateProto, or emitSpread.
        Init,
    };
    PropertyState propertyState_ = PropertyState::Start;
#endif

  public:
    explicit PropertyEmitter(BytecodeEmitter* bce);

    // Parameters are the offset in the source code for each character below:
    //
    // { __proto__: protoValue }
    //   ^
    //   |
    //   keyPos
    MOZ_MUST_USE bool prepareForProtoValue(
        const mozilla::Maybe<uint32_t>& keyPos);
    MOZ_MUST_USE bool emitMutateProto();

    // { ...obj }
    //   ^
    //   |
    //   spreadPos
    MOZ_MUST_USE bool prepareForSpreadOperand(
        const mozilla::Maybe<uint32_t>& spreadPos);
    MOZ_MUST_USE bool emitSpread();

    // { key: value }
    //   ^
    //   |
    //   keyPos
    MOZ_MUST_USE bool prepareForPropValue(const mozilla::Maybe<uint32_t>& keyPos,
                                          Kind kind = Kind::Prototype);

    // { 1: value }
    //   ^
    //   |
    //   keyPos
    MOZ_MUST_USE bool prepareForIndexPropKey(
        const mozilla::Maybe<uint32_t>& keyPos, Kind kind = Kind::Prototype);
    MOZ_MUST_USE bool prepareForIndexPropValue();

    // { [ key ]: value }
    //   ^
    //   |
    //   keyPos
    MOZ_MUST_USE bool prepareForComputedPropKey(
        const mozilla::Maybe<uint32_t>& keyPos, Kind kind = Kind::Prototype);
    MOZ_MUST_USE bool prepareForComputedPropValue();

    MOZ_MUST_USE bool emitInitHomeObject(
        FunctionAsyncKind kind = FunctionAsyncKind::SyncFunction);

    // @param key
    //        Property key
    // @param isPropertyAnonFunctionOrClass
    //        True if the property value is an anonymous function or
    //        an anonymous class
    // @param anonFunction
    //        The anonymous function object for property value
    MOZ_MUST_USE bool emitInitProp(
        JS::Handle<JSAtom*> key, bool isPropertyAnonFunctionOrClass = false,
        JS::Handle<JSFunction*> anonFunction = nullptr);
    MOZ_MUST_USE bool emitInitGetter(JS::Handle<JSAtom*> key);
    MOZ_MUST_USE bool emitInitSetter(JS::Handle<JSAtom*> key);

    MOZ_MUST_USE bool emitInitIndexProp(
        bool isPropertyAnonFunctionOrClass = false);
    MOZ_MUST_USE bool emitInitIndexGetter();
    MOZ_MUST_USE bool emitInitIndexSetter();

    MOZ_MUST_USE bool emitInitComputedProp(
        bool isPropertyAnonFunctionOrClass = false);
    MOZ_MUST_USE bool emitInitComputedGetter();
    MOZ_MUST_USE bool emitInitComputedSetter();

  private:
    MOZ_MUST_USE MOZ_ALWAYS_INLINE bool prepareForProp(
        const mozilla::Maybe<uint32_t>& keyPos, bool isStatic, bool isComputed);

    // @param op
    //        Opcode for initializing property
    // @param prefixKind
    //        None, Get, or Set
    // @param key
    //        Atom of the property if the property key is not computed
    // @param isPropertyAnonFunctionOrClass
    //        True if the property is either an anonymous function or an
    //        anonymous class
    // @param anonFunction
    //        Anonymous function object for the property
    MOZ_MUST_USE bool emitInit(JSOp op, JS::Handle<JSAtom*> key,
                               bool isPropertyAnonFunctionOrClass,
                               JS::Handle<JSFunction*> anonFunction);
    MOZ_MUST_USE bool emitInitIndexOrComputed(JSOp op,
                                              FunctionPrefixKind prefixKind,
                                              bool isPropertyAnonFunctionOrClass);

    MOZ_MUST_USE bool emitPopClassConstructor();
};

// Class for emitting bytecode for object literal.
//
// Usage: (check for the return value is omitted for simplicity)
//
//   `{}`
//     ObjectEmitter oe(this);
//     oe.emitObject(0);
//     oe.emitEnd();
//
//   `{ prop: 10 }`
//     ObjectEmitter oe(this);
//     oe.emitObject(1);
//
//     oe.prepareForPropValue(Some(offset_of_prop));
//     emit(10);
//     oe.emitInitProp(atom_of_prop);
//
//     oe.emitEnd();
//
//   `{ prop: function() {} }`, when property value is anonymous function
//     ObjectEmitter oe(this);
//     oe.emitObject(1);
//
//     oe.prepareForPropValue(Some(offset_of_prop));
//     emit(function);
//     oe.emitInitProp(atom_of_prop, true, function_object);
//
//     oe.emitEnd();
//
//   `{ get prop() { ... }, set prop(v) { ... } }`
//     ObjectEmitter oe(this);
//     oe.emitObject(2);
//
//     oe.prepareForPropValue(Some(offset_of_prop));
//     emit(function_for_getter);
//     oe.emitInitGetter(atom_of_prop);
//
//     oe.prepareForPropValue(Some(offset_of_prop));
//     emit(function_for_setter);
//     oe.emitInitSetter(atom_of_prop);
//
//     oe.emitEnd();
//
//   `{ 1: 10, get 2() { ... }, set 3(v) { ... } }`
//     ObjectEmitter oe(this);
//     oe.emitObject(3);
//
//     oe.prepareForIndexPropKey(Some(offset_of_prop));
//     emit(1);
//     oe.prepareForIndexPropValue();
//     emit(10);
//     oe.emitInitIndexedProp(atom_of_prop);
//
//     oe.prepareForIndexPropKey(Some(offset_of_opening_bracket));
//     emit(2);
//     oe.prepareForIndexPropValue();
//     emit(function_for_getter);
//     oe.emitInitIndexGetter();
//
//     oe.prepareForIndexPropKey(Some(offset_of_opening_bracket));
//     emit(3);
//     oe.prepareForIndexPropValue();
//     emit(function_for_setter);
//     oe.emitInitIndexSetter();
//
//     oe.emitEnd();
//
//   `{ [prop1]: 10, get [prop2]() { ... }, set [prop3](v) { ... } }`
//     ObjectEmitter oe(this);
//     oe.emitObject(3);
//
//     oe.prepareForComputedPropKey(Some(offset_of_opening_bracket));
//     emit(prop1);
//     oe.prepareForComputedPropValue();
//     emit(10);
//     oe.emitInitComputedProp();
//
//     oe.prepareForComputedPropKey(Some(offset_of_opening_bracket));
//     emit(prop2);
//     oe.prepareForComputedPropValue();
//     emit(function_for_getter);
//     oe.emitInitComputedGetter();
//
//     oe.prepareForComputedPropKey(Some(offset_of_opening_bracket));
//     emit(prop3);
//     oe.prepareForComputedPropValue();
//     emit(function_for_setter);
//     oe.emitInitComputedSetter();
//
//     oe.emitEnd();
//
//   `{ __proto__: obj }`
//     ObjectEmitter oe(this);
//     oe.emitObject(1);
//     oe.prepareForProtoValue(Some(offset_of___proto__));
//     emit(obj);
//     oe.emitMutateProto();
//     oe.emitEnd();
//
//   `{ ...obj }`
//     ObjectEmitter oe(this);
//     oe.emitObject(1);
//     oe.prepareForSpreadOperand(Some(offset_of_triple_dots));
//     emit(obj);
//     oe.emitSpread();
//     oe.emitEnd();
//
class MOZ_STACK_CLASS ObjectEmitter : public PropertyEmitter
{
  private:
    // The offset of JSOP_NEWINIT, which is replced by JSOP_NEWOBJECT later
    // when the object is known to have a fixed shape.
    ptrdiff_t top_ = 0;

#ifdef DEBUG
    // The state of this emitter.
    //
    // +-------+ emitObject +--------+
    // | Start |----------->| Object |-+
    // +-------+            +--------+ |
    //                                 |
    //   +-----------------------------+
    //   |
    //   | (do PropertyEmitter operation)  emitEnd  +-----+
    //   +-------------------------------+--------->| End |
    //                                              +-----+
    enum class ObjectState {
        // The initial state.
        Start,

        // After calling emitObject.
        Object,

        // After calling emitEnd.
        End,
    };
    ObjectState objectState_ = ObjectState::Start;
#endif

  public:
    explicit ObjectEmitter(BytecodeEmitter* bce);

    MOZ_MUST_USE bool emitObject(size_t propertyCount);
    MOZ_MUST_USE bool emitEnd();
};

// Save and restore the strictness.
// Used by class declaration/expression to temporarily enable strict mode.
class MOZ_RAII AutoSaveLocalStrictMode
{
    SharedContext* sc_;
    bool savedStrictness_;

  public:
    explicit AutoSaveLocalStrictMode(SharedContext* sc);
    ~AutoSaveLocalStrictMode();

    // Force restore the strictness now.
    void restore();
};

// Class for emitting bytecode for JS class.
//
// Usage: (check for the return value is omitted for simplicity)
//
//   `class {}`
//     ClassEmitter ce(this);
//     ce.emitScope(scopeBindings);
//     ce.emitClass();
//
//     ce.emitInitDefaultConstructor(Some(offset_of_class),
//                                   Some(offset_of_closing_bracket));
//
//     ce.emitEnd(ClassEmitter::Kind::Expression);
//
//   `class { constructor() { ... } }`
//     ClassEmitter ce(this);
//     ce.emitScope(scopeBindings);
//     ce.emitClass();
//
//     emit(function_for_constructor);
//     ce.emitInitConstructor(/* needsHomeObject = */ false);
//
//     ce.emitEnd(ClassEmitter::Kind::Expression);
//
//   `class X { constructor() { ... } }`
//     ClassEmitter ce(this);
//     ce.emitScope(scopeBindings);
//     ce.emitClass(atom_of_X);
//
//     ce.emitInitDefaultConstructor(Some(offset_of_class),
//                                   Some(offset_of_closing_bracket));
//
//     ce.emitEnd(ClassEmitter::Kind::Expression);
//
//   `class X { constructor() { ... } }`
//     ClassEmitter ce(this);
//     ce.emitScope(scopeBindings);
//     ce.emitClass(atom_of_X);
//
//     emit(function_for_constructor);
//     ce.emitInitConstructor(/* needsHomeObject = */ false);
//
//     ce.emitEnd(ClassEmitter::Kind::Expression);
//
//   `class X extends Y { constructor() { ... } }`
//     ClassEmitter ce(this);
//     ce.emitScope(scopeBindings);
//
//     emit(Y);
//     ce.emitDerivedClass(atom_of_X);
//
//     emit(function_for_constructor);
//     ce.emitInitConstructor(/* needsHomeObject = */ false);
//
//     ce.emitEnd(ClassEmitter::Kind::Expression);
//
//   `class X extends Y { constructor() { ... super.f(); ... } }`
//     ClassEmitter ce(this);
//     ce.emitScope(scopeBindings);
//
//     emit(Y);
//     ce.emitDerivedClass(atom_of_X);
//
//     emit(function_for_constructor);
//     // pass true if constructor contains super.prop access
//     ce.emitInitConstructor(/* needsHomeObject = */ true);
//
//     ce.emitEnd(ClassEmitter::Kind::Expression);
//
//   `class X extends Y { field0 = expr0; ... }`
//     ClassEmitter ce(this);
//     ce.emitScope(scopeBindings);
//     emit(Y);
//     ce.emitDerivedClass(atom_of_X, nullptr, false);
//
//     ce.prepareForFieldInitializers(fields.length());
//     for (auto field : fields) {
//       emit(field.initializer_method());
//       ce.emitStoreFieldInitializer();
//     }
//     ce.emitFieldInitializersEnd();
//
//     emit(function_for_constructor);
//     ce.emitInitConstructor(/* needsHomeObject = */ false);
//     ce.emitEnd(ClassEmitter::Kind::Expression);
//
//   `class X { field0 = super.method(); ... }`
//     // after emitClass/emitDerivedClass
//     ce.prepareForFieldInitializers(1);
//     for (auto field : fields) {
//       emit(field.initializer_method());
//       if (field.initializer_contains_super_or_eval()) {
//         ce.emitFieldInitializerHomeObject();
//       }
//       ce.emitStoreFieldInitializer();
//     }
//     ce.emitFieldInitializersEnd();
//
//   `m() {}` in class
//     // after emitInitConstructor/emitInitDefaultConstructor
//     ce.prepareForPropValue(Some(offset_of_m));
//     emit(function_for_m);
//     ce.emitInitProp(atom_of_m);
//
//   `m() { super.f(); }` in class
//     // after emitInitConstructor/emitInitDefaultConstructor
//     ce.prepareForPropValue(Some(offset_of_m));
//     emit(function_for_m);
//     ce.emitInitHomeObject();
//     ce.emitInitProp(atom_of_m);
//
//   `async m() { super.f(); }` in class
//     // after emitInitConstructor/emitInitDefaultConstructor
//     ce.prepareForPropValue(Some(offset_of_m));
//     emit(function_for_m);
//     ce.emitInitHomeObject(FunctionAsyncKind::Async);
//     ce.emitInitProp(atom_of_m);
//
//   `get p() { super.f(); }` in class
//     // after emitInitConstructor/emitInitDefaultConstructor
//     ce.prepareForPropValue(Some(offset_of_p));
//     emit(function_for_p);
//     ce.emitInitHomeObject();
//     ce.emitInitGetter(atom_of_m);
//
//   `static m() {}` in class
//     // after emitInitConstructor/emitInitDefaultConstructor
//     ce.prepareForPropValue(Some(offset_of_m),
//                            PropertyEmitter::Kind::Static);
//     emit(function_for_m);
//     ce.emitInitProp(atom_of_m);
//
//   `static get [p]() { super.f(); }` in class
//     // after emitInitConstructor/emitInitDefaultConstructor
//     ce.prepareForComputedPropValue(Some(offset_of_m),
//                                    PropertyEmitter::Kind::Static);
//     emit(p);
//     ce.prepareForComputedPropValue();
//     emit(function_for_m);
//     ce.emitInitHomeObject();
//     ce.emitInitComputedGetter();
//
class MOZ_STACK_CLASS ClassEmitter : public PropertyEmitter
{
  public:
    enum class Kind {
        // Class expression.
        Expression,

        // Class declaration.
        Declaration,
    };

  private:
    // Pseudocode for class declarations:
    //
    //     class extends BaseExpression {
    //       constructor() { ... }
    //       ...
    //       }
    //
    //
    //   if defined <BaseExpression> {
    //     let heritage = BaseExpression;
    //
    //     if (heritage !== null) {
    //       funProto = heritage;
    //       objProto = heritage.prototype;
    //     } else {
    //       funProto = %FunctionPrototype%;
    //       objProto = null;
    //     }
    //   } else {
    //     objProto = %ObjectPrototype%;
    //   }
    //
    //   let homeObject = ObjectCreate(objProto);
    //
    //   if defined <constructor> {
    //     if defined <BaseExpression> {
    //       cons = DefineMethod(<constructor>, proto=homeObject,
    //       funProto=funProto);
    //     } else {
    //       cons = DefineMethod(<constructor>, proto=homeObject);
    //     }
    //   } else {
    //     if defined <BaseExpression> {
    //       cons = DefaultDerivedConstructor(proto=homeObject,
    //       funProto=funProto);
    //     } else {
    //       cons = DefaultConstructor(proto=homeObject);
    //     }
    //   }
    //
    //   cons.prototype = homeObject;
    //   homeObject.constructor = cons;
    //
    //   EmitPropertyList(...)

    bool isDerived_ = false;

    mozilla::Maybe<TDZCheckCache> tdzCache_;
    mozilla::Maybe<EmitterScope> innerScope_;
    AutoSaveLocalStrictMode strictMode_;

#ifdef DEBUG
    // The state of this emitter.
    //
    // +-------+
    // | Start |-+------------------------>+-+
    // +-------+ |                         ^ |
    //           | [has scope]             | |
    //           |   emitScope   +-------+ | |
    //           +-------------->| Scope |-+ |
    //                           +-------+   |
    //                                       |
    //   +-----------------------------------+
    //   |
    //   |   emitClass           +-------+
    //   +-+----------------->+->| Class |-+
    //     |                  ^  +-------+ |
    //     | emitDerivedClass |            |
    //     +------------------+            |
    //                                     |
    //     +-------------------------------+
    //     |
    //     |  prepareForFieldInitializers(isStatic = false)
    //     +---------------+
    //     |               |
    //     |      +--------v------------------+
    //     |      | InstanceFieldInitializers |
    //     |      +---------------------------+
    //     |               |
    //                     | emitFieldInitializersEnd
    //     |               |
    //     |      +--------v---------------------+
    //     |      | InstanceFieldInitializersEnd |
    //     |      +------------------------------+
    //     |               |
    //     +<--------------+
    //     |
    //     |
    //     |   emitInitConstructor           +-----------------+
    //     +-+--------------------------->+->| InitConstructor |-+
    //       |                            ^  +-----------------+ |
    //       | emitInitDefaultConstructor |                      |
    //       +----------------------------+                      |
    //                                                           |
    //     +-----------------------------------------------------+
    //     |
    //     |  prepareForFieldInitializers(isStatic = true)
    //     +---------------+
    //     |               |
    //     |      +--------v----------------+
    //     |      | StaticFieldInitializers |
    //     |      +-------------------------+
    //     |               |
    //     |               | emitFieldInitializersEnd
    //     |               |
    //     |      +--------v-------------------+
    //     |      | StaticFieldInitializersEnd |
    //     |      +----------------------------+
    //     |               |
    //     +<--------------+
    //     |
    //     | (do PropertyEmitter operation)
    //     +--------------------------------+
    //                                      |
    //     +-------------+    emitBinding   |
    //     |  BoundName  |<-----------------+
    //     +--+----------+
    //        |
    //        | emitEnd
    //        |
    //     +--v----+
    //     |  End  |
    //     +-------+
    //
    enum class ClassState {
        // The initial state.
        Start,

        // After calling emitScope.
        Scope,

        // After calling emitClass or emitDerivedClass.
        Class,

        // After calling emitInitConstructor or emitInitDefaultConstructor.
        InitConstructor,

        // After calling prepareForFieldInitializers(isStatic = false).
        InstanceFieldInitializers,

        // After calling emitFieldInitializersEnd.
        InstanceFieldInitializersEnd,

        // After calling prepareForFieldInitializers(isStatic = true).
        StaticFieldInitializers,

        // After calling emitFieldInitializersEnd.
        StaticFieldInitializersEnd,

        // After calling emitBinding.
        BoundName,

        // After calling emitEnd.
        End,
    };
    ClassState classState_ = ClassState::Start;

    // The state of the fields emitter.
    //
    // clang-format off
    //
    //   +-------+
    //   | Start +<-----------------------------+
    //   +-------+                              |
    //       |                                  |
    //       | prepareForFieldInitializer       | emitStoreFieldInitializer
    //       v                                  |
    // +-------------+                          |
    // | Initializer +------------------------->+
    // +-------------+                          |
    //       |                                  |
    //       | emitFieldInitializerHomeObject   |
    //       v                                  |
    // +---------------------------+            |
    // | InitializerWithHomeObject +------------+
    // +---------------------------+
    //
    // clang-format on
    enum class FieldState {
        // After calling prepareForFieldInitializers
        // and 0 or more calls to emitStoreFieldInitializer.
        Start,

        // After calling prepareForFieldInitializer
        Initializer,

        // After calling emitFieldInitializerHomeObject
        InitializerWithHomeObject,
    };
    FieldState fieldState_ = FieldState::Start;

    size_t numFields_ = 0;
#endif

    JS::Rooted<JSAtom*> name_;
    mozilla::Maybe<NameOpEmitter> initializersAssignment_;
    size_t fieldIndex_ = 0;

  public:
    explicit ClassEmitter(BytecodeEmitter* bce);

    MOZ_MUST_USE bool emitScope(JS::Handle<LexicalScope::Data*> scopeBindings);

    // @param name
    //        Name of the class (nullptr if this is anonymous class)
    MOZ_MUST_USE bool emitClass(JS::Handle<JSAtom*> name);
    MOZ_MUST_USE bool emitDerivedClass(JS::Handle<JSAtom*> name);

    // @param needsHomeObject
    //        True if the constructor contains `super.foo`
    MOZ_MUST_USE bool emitInitConstructor(bool needsHomeObject);

    // Parameters are the offset in the source code for each character below:
    //
    //   class X { foo() {} }
    //   ^                  ^
    //   |                  |
    //   |                  classEnd
    //   |
    //   classStart
    //
    MOZ_MUST_USE bool emitInitDefaultConstructor(
        const mozilla::Maybe<uint32_t>& classStart,
        const mozilla::Maybe<uint32_t>& classEnd);

    MOZ_MUST_USE bool prepareForFieldInitializers(size_t numFields, bool isStatic);
    MOZ_MUST_USE bool prepareForFieldInitializer();
    MOZ_MUST_USE bool emitFieldInitializerHomeObject(bool isStatic);
    MOZ_MUST_USE bool emitStoreFieldInitializer();
    MOZ_MUST_USE bool emitFieldInitializersEnd();

    MOZ_MUST_USE bool emitBinding();

    MOZ_MUST_USE bool emitEnd(Kind kind);

  private:
    void setName(JS::Handle<JSAtom*> name);
    MOZ_MUST_USE bool initProtoAndCtor();
};

} /* namespace frontend */
} /* namespace js */

#endif /* frontend_ObjectEmitter_h */