The Tor Browser: js/src/vm/ScopeObject.h@6474c204b198 (annotated)

js/src/vm/ScopeObject.h@6474c204b198 (annotated)

js/src/vm/ScopeObject.h

Wed, 31 Dec 2014 06:09:35 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:09:35 +0100
changeset 0: 6474c204b198
permissions: -rw-r--r--

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
  * vim: set ts=8 sts=4 et sw=4 tw=99:
  * 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 vm_ScopeObject_h
 #define vm_ScopeObject_h
 #include "jscntxt.h"
 #include "jsobj.h"
 #include "jsweakmap.h"
 #include "gc/Barrier.h"
 #include "vm/ProxyObject.h"
 namespace js {
 namespace frontend { struct Definition; }
 class StaticWithObject;
 /*****************************************************************************/
 /*
  * All function scripts have an "enclosing static scope" that refers to the
  * innermost enclosing let or function in the program text. This allows full
  * reconstruction of the lexical scope for debugging or compiling efficient
  * access to variables in enclosing scopes. The static scope is represented at
  * runtime by a tree of compiler-created objects representing each scope:
  *  - a StaticBlockObject is created for 'let' and 'catch' scopes
  *  - a JSFunction+JSScript+Bindings trio is created for function scopes
  * (These objects are primarily used to clone objects scopes for the
  * dynamic scope chain.)
  *
  * There is an additional scope for named lambdas. E.g., in:
  *
  *   (function f() { var x; function g() { } })
  *
  * g's innermost enclosing scope will first be the function scope containing
  * 'x', enclosed by a scope containing only the name 'f'. (This separate scope
  * is necessary due to the fact that declarations in the function scope shadow
  * (dynamically, in the case of 'eval') the lambda name.)
  *
  * There are two limitations to the current lexical nesting information:
  *
  *  - 'with' is completely absent; this isn't a problem for the current use
  *    cases since 'with' causes every static scope to be on the dynamic scope
  *    chain (so the debugger can find everything) and inhibits all upvar
  *    optimization.
  *
  *  - The "enclosing static scope" chain stops at 'eval'. For example in:
  *      let (x) { eval("function f() {}") }
  *    f does not have an enclosing static scope. This is fine for current uses
  *    for the same reason as 'with'.
  *
  * (See also AssertDynamicScopeMatchesStaticScope.)
  */
 template <AllowGC allowGC>
 class StaticScopeIter
 {
     typename MaybeRooted<JSObject*, allowGC>::RootType obj;
     bool onNamedLambda;
   public:
     StaticScopeIter(ExclusiveContext *cx, JSObject *obj)
       : obj(cx, obj), onNamedLambda(false)
     {
         JS_STATIC_ASSERT(allowGC == CanGC);
         JS_ASSERT_IF(obj, obj->is<StaticBlockObject>() || obj->is<StaticWithObject>() ||
                      obj->is<JSFunction>());
     }
     StaticScopeIter(JSObject *obj)
       : obj((ExclusiveContext *) nullptr, obj), onNamedLambda(false)
     {
         JS_STATIC_ASSERT(allowGC == NoGC);
         JS_ASSERT_IF(obj, obj->is<StaticBlockObject>() || obj->is<StaticWithObject>() ||
                      obj->is<JSFunction>());
     }
     bool done() const;
     void operator++(int);
     /* Return whether this static scope will be on the dynamic scope chain. */
     bool hasDynamicScopeObject() const;
     Shape *scopeShape() const;
     enum Type { WITH, BLOCK, FUNCTION, NAMED_LAMBDA };
     Type type() const;
     StaticBlockObject &block() const;
     StaticWithObject &staticWith() const;
     JSScript *funScript() const;
 };
 /*****************************************************************************/
 /*
  * A "scope coordinate" describes how to get from head of the scope chain to a
  * given lexically-enclosing variable. A scope coordinate has two dimensions:
  *  - hops: the number of scope objects on the scope chain to skip
  *  - slot: the slot on the scope object holding the variable's value
  */
 class ScopeCoordinate
 {
     uint32_t hops_;
     uint32_t slot_;
     /*
      * Technically, hops_/slot_ are SCOPECOORD_(HOPS|SLOT)_BITS wide.  Since
      * ScopeCoordinate is a temporary value, don't bother with a bitfield as
      * this only adds overhead.
      */
     static_assert(SCOPECOORD_HOPS_BITS <= 32, "We have enough bits below");
     static_assert(SCOPECOORD_SLOT_BITS <= 32, "We have enough bits below");
   public:
     inline ScopeCoordinate(jsbytecode *pc)
       : hops_(GET_SCOPECOORD_HOPS(pc)), slot_(GET_SCOPECOORD_SLOT(pc + SCOPECOORD_HOPS_LEN))
     {
         JS_ASSERT(JOF_OPTYPE(*pc) == JOF_SCOPECOORD);
     }
     inline ScopeCoordinate() {}
     void setHops(uint32_t hops) { JS_ASSERT(hops < SCOPECOORD_HOPS_LIMIT); hops_ = hops; }
     void setSlot(uint32_t slot) { JS_ASSERT(slot < SCOPECOORD_SLOT_LIMIT); slot_ = slot; }
     uint32_t hops() const { JS_ASSERT(hops_ < SCOPECOORD_HOPS_LIMIT); return hops_; }
     uint32_t slot() const { JS_ASSERT(slot_ < SCOPECOORD_SLOT_LIMIT); return slot_; }
 };
 /*
  * Return a shape representing the static scope containing the variable
  * accessed by the ALIASEDVAR op at 'pc'.
  */
 extern Shape *
 ScopeCoordinateToStaticScopeShape(JSScript *script, jsbytecode *pc);
 /* Return the name being accessed by the given ALIASEDVAR op. */
 extern PropertyName *
 ScopeCoordinateName(ScopeCoordinateNameCache &cache, JSScript *script, jsbytecode *pc);
 /* Return the function script accessed by the given ALIASEDVAR op, or nullptr. */
 extern JSScript *
 ScopeCoordinateFunctionScript(JSScript *script, jsbytecode *pc);
 /*****************************************************************************/
 /*
  * Scope objects
  *
  * Scope objects are technically real JSObjects but only belong on the scope
  * chain (that is, fp->scopeChain() or fun->environment()). The hierarchy of
  * scope objects is:
  *
  *   JSObject                   Generic object
  *     \
  *   ScopeObject                Engine-internal scope
  *     \   \   \
  *      \   \  DeclEnvObject    Holds name of recursive/heavyweight named lambda
  *       \   \
  *        \  CallObject         Scope of entire function or strict eval
  *         \
  *   NestedScopeObject          Scope created for a statement
  *     \   \  \
  *      \   \ StaticWithObject  Template for "with" object in static scope chain
  *       \   \
  *        \  DynamicWithObject  Run-time "with" object on scope chain
  *         \
  *   BlockObject                Shared interface of cloned/static block objects
  *     \   \
  *      \  ClonedBlockObject    let, switch, catch, for
  *       \
  *       StaticBlockObject      See NB
  *
  * This hierarchy represents more than just the interface hierarchy: reserved
  * slots in base classes are fixed for all derived classes. Thus, for example,
  * ScopeObject::enclosingScope() can simply access a fixed slot without further
  * dynamic type information.
  *
  * NB: Static block objects are a special case: these objects are created at
  * compile time to hold the shape/binding information from which block objects
  * are cloned at runtime. These objects should never escape into the wild and
  * support a restricted set of ScopeObject operations.
  *
  * See also "Debug scope objects" below.
  */
 class ScopeObject : public JSObject
 {
   protected:
     static const uint32_t SCOPE_CHAIN_SLOT = 0;
   public:
     /*
      * Since every scope chain terminates with a global object and GlobalObject
      * does not derive ScopeObject (it has a completely different layout), the
      * enclosing scope of a ScopeObject is necessarily non-null.
      */
     inline JSObject &enclosingScope() const {
         return getFixedSlot(SCOPE_CHAIN_SLOT).toObject();
     }
     void setEnclosingScope(HandleObject obj);
     /*
      * Get or set an aliased variable contained in this scope. Unaliased
      * variables should instead access the stack frame. Aliased variable access
      * is primarily made through JOF_SCOPECOORD ops which is why these members
      * take a ScopeCoordinate instead of just the slot index.
      */
     inline const Value &aliasedVar(ScopeCoordinate sc);
     inline void setAliasedVar(JSContext *cx, ScopeCoordinate sc, PropertyName *name, const Value &v);
     /* For jit access. */
     static size_t offsetOfEnclosingScope() {
         return getFixedSlotOffset(SCOPE_CHAIN_SLOT);
     }
     static size_t enclosingScopeSlot() {
         return SCOPE_CHAIN_SLOT;
     }
 };
 class CallObject : public ScopeObject
 {
     static const uint32_t CALLEE_SLOT = 1;
     static CallObject *
     create(JSContext *cx, HandleScript script, HandleObject enclosing, HandleFunction callee);
   public:
     static const Class class_;
     /* These functions are internal and are exposed only for JITs. */
     /*
      * Construct a bare-bones call object given a shape, a non-singleton type,
      * and slots pointer.  The call object must be further initialized to be
      * usable.
      */
     static CallObject *
     create(JSContext *cx, HandleShape shape, HandleTypeObject type, HeapSlot *slots);
     /*
      * Construct a bare-bones call object given a shape and slots pointer, and
      * make it have singleton type.  The call object must be initialized to be
      * usable.
      */
     static CallObject *
     createSingleton(JSContext *cx, HandleShape shape, HeapSlot *slots);
     static CallObject *
     createTemplateObject(JSContext *cx, HandleScript script, gc::InitialHeap heap);
     static const uint32_t RESERVED_SLOTS = 2;
     static CallObject *createForFunction(JSContext *cx, HandleObject enclosing, HandleFunction callee);
     static CallObject *createForFunction(JSContext *cx, AbstractFramePtr frame);
     static CallObject *createForStrictEval(JSContext *cx, AbstractFramePtr frame);
     /* True if this is for a strict mode eval frame. */
     bool isForEval() const {
         JS_ASSERT(getFixedSlot(CALLEE_SLOT).isObjectOrNull());
         JS_ASSERT_IF(getFixedSlot(CALLEE_SLOT).isObject(),
                      getFixedSlot(CALLEE_SLOT).toObject().is<JSFunction>());
         return getFixedSlot(CALLEE_SLOT).isNull();
     }
     /*
      * Returns the function for which this CallObject was created. (This may
      * only be called if !isForEval.)
      */
     JSFunction &callee() const {
         return getFixedSlot(CALLEE_SLOT).toObject().as<JSFunction>();
     }
     /* Get/set the aliased variable referred to by 'bi'. */
     const Value &aliasedVar(AliasedFormalIter fi) {
         return getSlot(fi.scopeSlot());
     }
     inline void setAliasedVar(JSContext *cx, AliasedFormalIter fi, PropertyName *name,
                               const Value &v);
     /*
      * When an aliased var (var accessed by nested closures) is also aliased by
      * the arguments object, it must of course exist in one canonical location
      * and that location is always the CallObject. For this to work, the
      * ArgumentsObject stores special MagicValue in its array for forwarded-to-
      * CallObject variables. This MagicValue's payload is the slot of the
      * CallObject to access.
      */
     const Value &aliasedVarFromArguments(const Value &argsValue) {
         return getSlot(argsValue.magicUint32());
     }
     inline void setAliasedVarFromArguments(JSContext *cx, const Value &argsValue, jsid id,
                                            const Value &v);
     /* For jit access. */
     static size_t offsetOfCallee() {
         return getFixedSlotOffset(CALLEE_SLOT);
     }
     static size_t calleeSlot() {
         return CALLEE_SLOT;
     }
 };
 class DeclEnvObject : public ScopeObject
 {
     // Pre-allocated slot for the named lambda.
     static const uint32_t LAMBDA_SLOT = 1;
   public:
     static const uint32_t RESERVED_SLOTS = 2;
     static const gc::AllocKind FINALIZE_KIND = gc::FINALIZE_OBJECT2_BACKGROUND;
     static const Class class_;
     static DeclEnvObject *
     createTemplateObject(JSContext *cx, HandleFunction fun, gc::InitialHeap heap);
     static DeclEnvObject *create(JSContext *cx, HandleObject enclosing, HandleFunction callee);
     static inline size_t lambdaSlot() {
         return LAMBDA_SLOT;
     }
 };
 class NestedScopeObject : public ScopeObject
 {
   public:
     /*
      * A refinement of enclosingScope that returns nullptr if the enclosing
      * scope is not a NestedScopeObject.
      */
     inline NestedScopeObject *enclosingNestedScope() const;
     // Return true if this object is a compile-time scope template.
     inline bool isStatic() { return !getProto(); }
     // Return the static scope corresponding to this scope chain object.
     inline NestedScopeObject* staticScope() {
         JS_ASSERT(!isStatic());
         return &getProto()->as<NestedScopeObject>();
     }
     // At compile-time it's possible for the scope chain to be null.
     JSObject *enclosingScopeForStaticScopeIter() {
         return getReservedSlot(SCOPE_CHAIN_SLOT).toObjectOrNull();
     }
     void initEnclosingNestedScope(JSObject *obj) {
         JS_ASSERT(getReservedSlot(SCOPE_CHAIN_SLOT).isUndefined());
         setReservedSlot(SCOPE_CHAIN_SLOT, ObjectOrNullValue(obj));
     }
     /*
      * The parser uses 'enclosingNestedScope' as the prev-link in the
      * pc->staticScope stack. Note: in the case of hoisting, this prev-link will
      * not ultimately be the same as enclosingNestedScope;
      * initEnclosingNestedScope must be called separately in the
      * emitter. 'reset' is just for asserting stackiness.
      */
     void initEnclosingNestedScopeFromParser(NestedScopeObject *prev) {
         setReservedSlot(SCOPE_CHAIN_SLOT, ObjectOrNullValue(prev));
     }
     void resetEnclosingNestedScopeFromParser() {
         setReservedSlot(SCOPE_CHAIN_SLOT, UndefinedValue());
     }
 };
 // With scope template objects on the static scope chain.
 class StaticWithObject : public NestedScopeObject
 {
   public:
     static const unsigned RESERVED_SLOTS = 1;
     static const gc::AllocKind FINALIZE_KIND = gc::FINALIZE_OBJECT2_BACKGROUND;
     static const Class class_;
     static StaticWithObject *create(ExclusiveContext *cx);
 };
 // With scope objects on the run-time scope chain.
 class DynamicWithObject : public NestedScopeObject
 {
     static const unsigned OBJECT_SLOT = 1;
     static const unsigned THIS_SLOT = 2;
   public:
     static const unsigned RESERVED_SLOTS = 3;
     static const gc::AllocKind FINALIZE_KIND = gc::FINALIZE_OBJECT4_BACKGROUND;
     static const Class class_;
     static DynamicWithObject *
     create(JSContext *cx, HandleObject object, HandleObject enclosing, HandleObject staticWith);
     StaticWithObject& staticWith() const {
         return getProto()->as<StaticWithObject>();
     }
     /* Return the 'o' in 'with (o)'. */
     JSObject &object() const {
         return getReservedSlot(OBJECT_SLOT).toObject();
     }
     /* Return object for the 'this' class hook. */
     JSObject &withThis() const {
         return getReservedSlot(THIS_SLOT).toObject();
     }
 };
 class BlockObject : public NestedScopeObject
 {
   protected:
     static const unsigned DEPTH_SLOT = 1;
   public:
     static const unsigned RESERVED_SLOTS = 2;
     static const gc::AllocKind FINALIZE_KIND = gc::FINALIZE_OBJECT4_BACKGROUND;
     static const Class class_;
     /* Return the abstract stack depth right before entering this nested scope. */
     uint32_t stackDepth() const {
         return getReservedSlot(DEPTH_SLOT).toPrivateUint32();
     }
     /* Return the number of variables associated with this block. */
     uint32_t numVariables() const {
         // TODO: propertyCount() is O(n), use O(1) lastProperty()->slot() instead
         return propertyCount();
     }
   protected:
     /* Blocks contain an object slot for each slot i: 0 <= i < slotCount. */
     const Value &slotValue(unsigned i) {
         return getSlotRef(RESERVED_SLOTS + i);
     }
     void setSlotValue(unsigned i, const Value &v) {
         setSlot(RESERVED_SLOTS + i, v);
     }
 };
 class StaticBlockObject : public BlockObject
 {
     static const unsigned LOCAL_OFFSET_SLOT = 1;
   public:
     static StaticBlockObject *create(ExclusiveContext *cx);
     /* See StaticScopeIter comment. */
     JSObject *enclosingStaticScope() const {
         return getFixedSlot(SCOPE_CHAIN_SLOT).toObjectOrNull();
     }
     /*
      * Return the index (in the range [0, numVariables()) corresponding to the
      * given shape of a block object.
      */
     uint32_t shapeToIndex(const Shape &shape) {
         uint32_t slot = shape.slot();
         JS_ASSERT(slot - RESERVED_SLOTS < numVariables());
         return slot - RESERVED_SLOTS;
     }
     /*
      * A refinement of enclosingStaticScope that returns nullptr if the enclosing
      * static scope is a JSFunction.
      */
     inline StaticBlockObject *enclosingBlock() const;
     uint32_t localOffset() {
         return getReservedSlot(LOCAL_OFFSET_SLOT).toPrivateUint32();
     }
     // Return the local corresponding to the 'var'th binding where 'var' is in the
     // range [0, numVariables()).
     uint32_t blockIndexToLocalIndex(uint32_t index) {
         JS_ASSERT(index < numVariables());
         return getReservedSlot(LOCAL_OFFSET_SLOT).toPrivateUint32() + index;
     }
     // Return the slot corresponding to local variable 'local', where 'local' is
     // in the range [localOffset(), localOffset() + numVariables()).  The result is
     // in the range [RESERVED_SLOTS, RESERVED_SLOTS + numVariables()).
     uint32_t localIndexToSlot(uint32_t local) {
         JS_ASSERT(local >= localOffset());
         local -= localOffset();
         JS_ASSERT(local < numVariables());
         return RESERVED_SLOTS + local;
     }
     /*
      * A let binding is aliased if accessed lexically by nested functions or
      * dynamically through dynamic name lookup (eval, with, function::, etc).
      */
     bool isAliased(unsigned i) {
         return slotValue(i).isTrue();
     }
     /*
      * A static block object is cloned (when entering the block) iff some
      * variable of the block isAliased.
      */
     bool needsClone() {
         return !getFixedSlot(RESERVED_SLOTS).isFalse();
     }
     /* Frontend-only functions ***********************************************/
     /* Initialization functions for above fields. */
     void setAliased(unsigned i, bool aliased) {
         JS_ASSERT_IF(i > 0, slotValue(i-1).isBoolean());
         setSlotValue(i, BooleanValue(aliased));
         if (aliased && !needsClone()) {
             setSlotValue(0, MagicValue(JS_BLOCK_NEEDS_CLONE));
             JS_ASSERT(needsClone());
         }
     }
     void setLocalOffset(uint32_t offset) {
         JS_ASSERT(getReservedSlot(LOCAL_OFFSET_SLOT).isUndefined());
         initReservedSlot(LOCAL_OFFSET_SLOT, PrivateUint32Value(offset));
     }
     /*
      * Frontend compilation temporarily uses the object's slots to link
      * a let var to its associated Definition parse node.
      */
     void setDefinitionParseNode(unsigned i, frontend::Definition *def) {
         JS_ASSERT(slotValue(i).isUndefined());
         setSlotValue(i, PrivateValue(def));
     }
     frontend::Definition *definitionParseNode(unsigned i) {
         Value v = slotValue(i);
         return reinterpret_cast<frontend::Definition *>(v.toPrivate());
     }
     /*
      * While ScopeCoordinate can generally reference up to 2^24 slots, block objects have an
      * additional limitation that all slot indices must be storable as uint16_t short-ids in the
      * associated Shape. If we could remove the block dependencies on shape->shortid, we could
      * remove INDEX_LIMIT.
      */
     static const unsigned LOCAL_INDEX_LIMIT = JS_BIT(16);
     static Shape *addVar(ExclusiveContext *cx, Handle<StaticBlockObject*> block, HandleId id,
                          unsigned index, bool *redeclared);
 };
 class ClonedBlockObject : public BlockObject
 {
   public:
     static ClonedBlockObject *create(JSContext *cx, Handle<StaticBlockObject *> block,
                                      AbstractFramePtr frame);
     /* The static block from which this block was cloned. */
     StaticBlockObject &staticBlock() const {
         return getProto()->as<StaticBlockObject>();
     }
     /* Assuming 'put' has been called, return the value of the ith let var. */
     const Value &var(unsigned i, MaybeCheckAliasing checkAliasing = CHECK_ALIASING) {
         JS_ASSERT_IF(checkAliasing, staticBlock().isAliased(i));
         return slotValue(i);
     }
     void setVar(unsigned i, const Value &v, MaybeCheckAliasing checkAliasing = CHECK_ALIASING) {
         JS_ASSERT_IF(checkAliasing, staticBlock().isAliased(i));
         setSlotValue(i, v);
     }
     /* Copy in all the unaliased formals and locals. */
     void copyUnaliasedValues(AbstractFramePtr frame);
 };
 template<XDRMode mode>
 bool
 XDRStaticBlockObject(XDRState<mode> *xdr, HandleObject enclosingScope,
                      StaticBlockObject **objp);
 template<XDRMode mode>
 bool
 XDRStaticWithObject(XDRState<mode> *xdr, HandleObject enclosingScope,
                     StaticWithObject **objp);
 extern JSObject *
 CloneNestedScopeObject(JSContext *cx, HandleObject enclosingScope, Handle<NestedScopeObject*> src);
 /*****************************************************************************/
 class ScopeIterKey;
 class ScopeIterVal;
 /*
  * A scope iterator describes the active scopes enclosing the current point of
  * execution for a single frame, proceeding from inner to outer. Here, "frame"
  * means a single activation of: a function, eval, or global code. By design,
  * ScopeIter exposes *all* scopes, even those that have been optimized away
  * (i.e., no ScopeObject was created when entering the scope and thus there is
  * no ScopeObject on fp->scopeChain representing the scope).
  *
  * Note: ScopeIter iterates over all scopes *within* a frame which means that
  * all scopes are ScopeObjects. In particular, the GlobalObject enclosing
  * global code (and any random objects passed as scopes to Execute) will not
  * be included.
  */
 class ScopeIter
 {
     friend class ScopeIterKey;
     friend class ScopeIterVal;
   public:
     enum Type { Call, Block, With, StrictEvalScope };
   private:
     JSContext *cx;
     AbstractFramePtr frame_;
     RootedObject cur_;
     Rooted<NestedScopeObject *> staticScope_;
     Type type_;
     bool hasScopeObject_;
     void settle();
     /* ScopeIter does not have value semantics. */
     ScopeIter(const ScopeIter &si) MOZ_DELETE;
     ScopeIter(JSContext *cx) MOZ_DELETE;
   public:
     /* Constructing from a copy of an existing ScopeIter. */
     ScopeIter(const ScopeIter &si, JSContext *cx
               MOZ_GUARD_OBJECT_NOTIFIER_PARAM);
     /* Constructing from AbstractFramePtr places ScopeIter on the innermost scope. */
     ScopeIter(AbstractFramePtr frame, jsbytecode *pc, JSContext *cx
               MOZ_GUARD_OBJECT_NOTIFIER_PARAM);
     /*
      * Without a stack frame, the resulting ScopeIter is done() with
      * enclosingScope() as given.
      */
     ScopeIter(JSObject &enclosingScope, JSContext *cx
               MOZ_GUARD_OBJECT_NOTIFIER_PARAM);
     ScopeIter(const ScopeIterVal &hashVal, JSContext *cx
               MOZ_GUARD_OBJECT_NOTIFIER_PARAM);
     bool done() const { return !frame_; }
     /* If done(): */
     JSObject &enclosingScope() const { JS_ASSERT(done()); return *cur_; }
     /* If !done(): */
     ScopeIter &operator++();
     AbstractFramePtr frame() const { JS_ASSERT(!done()); return frame_; }
     Type type() const { JS_ASSERT(!done()); return type_; }
     bool hasScopeObject() const { JS_ASSERT(!done()); return hasScopeObject_; }
     ScopeObject &scope() const;
     NestedScopeObject* staticScope() const { return staticScope_; }
     StaticBlockObject &staticBlock() const {
         JS_ASSERT(type() == Block);
         return staticScope_->as<StaticBlockObject>();
     }
     MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
 };
 class ScopeIterKey
 {
     friend class ScopeIterVal;
     AbstractFramePtr frame_;
     JSObject *cur_;
     NestedScopeObject *staticScope_;
     ScopeIter::Type type_;
     bool hasScopeObject_;
   public:
     ScopeIterKey(const ScopeIter &si)
       : frame_(si.frame()), cur_(si.cur_), staticScope_(si.staticScope_), type_(si.type_),
         hasScopeObject_(si.hasScopeObject_) {}
     AbstractFramePtr frame() const { return frame_; }
     JSObject *cur() const { return cur_; }
     NestedScopeObject *staticScope() const { return staticScope_; }
     ScopeIter::Type type() const { return type_; }
     bool hasScopeObject() const { return hasScopeObject_; }
     JSObject *enclosingScope() const { return cur_; }
     JSObject *&enclosingScope() { return cur_; }
     /* For use as hash policy */
     typedef ScopeIterKey Lookup;
     static HashNumber hash(ScopeIterKey si);
     static bool match(ScopeIterKey si1, ScopeIterKey si2);
     bool operator!=(const ScopeIterKey &other) const {
         return frame_ != other.frame_ ||
                cur_ != other.cur_ ||
                staticScope_ != other.staticScope_ ||
                type_ != other.type_;
     }
     static void rekey(ScopeIterKey &k, const ScopeIterKey& newKey) {
         k = newKey;
     }
 };
 class ScopeIterVal
 {
     friend class ScopeIter;
     friend class DebugScopes;
     AbstractFramePtr frame_;
     RelocatablePtr<JSObject> cur_;
     RelocatablePtr<NestedScopeObject> staticScope_;
     ScopeIter::Type type_;
     bool hasScopeObject_;
     static void staticAsserts();
   public:
     ScopeIterVal(const ScopeIter &si)
       : frame_(si.frame()), cur_(si.cur_), staticScope_(si.staticScope_), type_(si.type_),
         hasScopeObject_(si.hasScopeObject_) {}
     AbstractFramePtr frame() const { return frame_; }
 };
 /*****************************************************************************/
 /*
  * Debug scope objects
  *
  * The debugger effectively turns every opcode into a potential direct eval.
  * Naively, this would require creating a ScopeObject for every call/block
  * scope and using JSOP_GETALIASEDVAR for every access. To optimize this, the
  * engine assumes there is no debugger and optimizes scope access and creation
  * accordingly. When the debugger wants to perform an unexpected eval-in-frame
  * (or other, similar dynamic-scope-requiring operations), fp->scopeChain is
  * now incomplete: it may not contain all, or any, of the ScopeObjects to
  * represent the current scope.
  *
  * To resolve this, the debugger first calls GetDebugScopeFor(Function|Frame)
  * to synthesize a "debug scope chain". A debug scope chain is just a chain of
  * objects that fill in missing scopes and protect the engine from unexpected
  * access. (The latter means that some debugger operations, like redefining a
  * lexical binding, can fail when a true eval would succeed.) To do both of
  * these things, GetDebugScopeFor* creates a new proxy DebugScopeObject to sit
  * in front of every existing ScopeObject.
  *
  * GetDebugScopeFor* ensures the invariant that the same DebugScopeObject is
  * always produced for the same underlying scope (optimized or not!). This is
  * maintained by some bookkeeping information stored in DebugScopes.
  */
 extern JSObject *
 GetDebugScopeForFunction(JSContext *cx, HandleFunction fun);
 extern JSObject *
 GetDebugScopeForFrame(JSContext *cx, AbstractFramePtr frame, jsbytecode *pc);
 /* Provides debugger access to a scope. */
 class DebugScopeObject : public ProxyObject
 {
     /*
      * The enclosing scope on the dynamic scope chain. This slot is analogous
      * to the SCOPE_CHAIN_SLOT of a ScopeObject.
      */
     static const unsigned ENCLOSING_EXTRA = 0;
     /*
      * NullValue or a dense array holding the unaliased variables of a function
      * frame that has been popped.
      */
     static const unsigned SNAPSHOT_EXTRA = 1;
   public:
     static DebugScopeObject *create(JSContext *cx, ScopeObject &scope, HandleObject enclosing);
     ScopeObject &scope() const;
     JSObject &enclosingScope() const;
     /* May only be called for proxies to function call objects. */
     JSObject *maybeSnapshot() const;
     void initSnapshot(JSObject &snapshot);
     /* Currently, the 'declarative' scopes are Call and Block. */
     bool isForDeclarative() const;
     // Get a property by 'id', but returns sentinel values instead of throwing
     // on exceptional cases.
     bool getMaybeSentinelValue(JSContext *cx, HandleId id, MutableHandleValue vp);
 };
 /* Maintains per-compartment debug scope bookkeeping information. */
 class DebugScopes
 {
     /* The map from (non-debug) scopes to debug scopes. */
     typedef WeakMap<EncapsulatedPtrObject, RelocatablePtrObject> ObjectWeakMap;
     ObjectWeakMap proxiedScopes;
     static MOZ_ALWAYS_INLINE void proxiedScopesPostWriteBarrier(JSRuntime *rt, ObjectWeakMap *map,
                                                                const EncapsulatedPtrObject &key);
     /*
      * The map from live frames which have optimized-away scopes to the
      * corresponding debug scopes.
      */
     typedef HashMap<ScopeIterKey,
                     ReadBarriered<DebugScopeObject>,
                     ScopeIterKey,
                     RuntimeAllocPolicy> MissingScopeMap;
     MissingScopeMap missingScopes;
     class MissingScopesRef;
     static MOZ_ALWAYS_INLINE void missingScopesPostWriteBarrier(JSRuntime *rt, MissingScopeMap *map,
                                                                const ScopeIterKey &key);
     /*
      * The map from scope objects of live frames to the live frame. This map
      * updated lazily whenever the debugger needs the information. In between
      * two lazy updates, liveScopes becomes incomplete (but not invalid, onPop*
      * removes scopes as they are popped). Thus, two consecutive debugger lazy
      * updates of liveScopes need only fill in the new scopes.
      */
     typedef HashMap<ScopeObject *,
                     ScopeIterVal,
                     DefaultHasher<ScopeObject *>,
                     RuntimeAllocPolicy> LiveScopeMap;
     LiveScopeMap liveScopes;
     static MOZ_ALWAYS_INLINE void liveScopesPostWriteBarrier(JSRuntime *rt, LiveScopeMap *map,
                                                             ScopeObject *key);
   public:
     DebugScopes(JSContext *c);
     ~DebugScopes();
   private:
     bool init();
     static DebugScopes *ensureCompartmentData(JSContext *cx);
   public:
     void mark(JSTracer *trc);
     void sweep(JSRuntime *rt);
 #if defined(JSGC_GENERATIONAL) && defined(JS_GC_ZEAL)
     void checkHashTablesAfterMovingGC(JSRuntime *rt);
 #endif
     static DebugScopeObject *hasDebugScope(JSContext *cx, ScopeObject &scope);
     static bool addDebugScope(JSContext *cx, ScopeObject &scope, DebugScopeObject &debugScope);
     static DebugScopeObject *hasDebugScope(JSContext *cx, const ScopeIter &si);
     static bool addDebugScope(JSContext *cx, const ScopeIter &si, DebugScopeObject &debugScope);
     static bool updateLiveScopes(JSContext *cx);
     static ScopeIterVal *hasLiveScope(ScopeObject &scope);
     // In debug-mode, these must be called whenever exiting a scope that might
     // have stack-allocated locals.
     static void onPopCall(AbstractFramePtr frame, JSContext *cx);
     static void onPopBlock(JSContext *cx, const ScopeIter &si);
     static void onPopBlock(JSContext *cx, AbstractFramePtr frame, jsbytecode *pc);
     static void onPopWith(AbstractFramePtr frame);
     static void onPopStrictEvalScope(AbstractFramePtr frame);
     static void onCompartmentLeaveDebugMode(JSCompartment *c);
 };
 }  /* namespace js */
 template<>
 inline bool
 JSObject::is<js::NestedScopeObject>() const
 {
     return is<js::BlockObject>() || is<js::StaticWithObject>() || is<js::DynamicWithObject>();
 }
 template<>
 inline bool
 JSObject::is<js::ScopeObject>() const
 {
     return is<js::CallObject>() || is<js::DeclEnvObject>() || is<js::NestedScopeObject>();
 }
 template<>
 inline bool
 JSObject::is<js::DebugScopeObject>() const
 {
     extern bool js_IsDebugScopeSlow(js::ProxyObject *proxy);
     // Note: don't use is<ProxyObject>() here -- it also matches subclasses!
     return hasClass(&js::ProxyObject::uncallableClass_) &&
            js_IsDebugScopeSlow(&const_cast<JSObject*>(this)->as<js::ProxyObject>());
 }
 template<>
 inline bool
 JSObject::is<js::ClonedBlockObject>() const
 {
     return is<js::BlockObject>() && !!getProto();
 }
 template<>
 inline bool
 JSObject::is<js::StaticBlockObject>() const
 {
     return is<js::BlockObject>() && !getProto();
 }
 inline JSObject *
 JSObject::enclosingScope()
 {
     return is<js::ScopeObject>()
            ? &as<js::ScopeObject>().enclosingScope()
            : is<js::DebugScopeObject>()
            ? &as<js::DebugScopeObject>().enclosingScope()
            : getParent();
 }
 namespace js {
 inline const Value &
 ScopeObject::aliasedVar(ScopeCoordinate sc)
 {
     JS_ASSERT(is<CallObject>() || is<ClonedBlockObject>());
     return getSlot(sc.slot());
 }
 inline NestedScopeObject *
 NestedScopeObject::enclosingNestedScope() const
 {
     JSObject *obj = getReservedSlot(SCOPE_CHAIN_SLOT).toObjectOrNull();
     return obj && obj->is<NestedScopeObject>() ? &obj->as<NestedScopeObject>() : nullptr;
 }
 #ifdef DEBUG
 bool
 AnalyzeEntrainedVariables(JSContext *cx, HandleScript script);
 #endif
 } // namespace js
 #endif /* vm_ScopeObject_h */

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js/src/vm/ScopeObject.h