Source/JavaScriptCore/runtime/JSScope.cpp - WebKit - Git at Google

 /*
  * Copyright (C) 2012-2017 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */

 #include "config.h"
 #include "JSScope.h"

 #include "AbstractModuleRecord.h"
 #include "Exception.h"
 #include "JSGlobalObject.h"
 #include "JSLexicalEnvironment.h"
 #include "JSModuleEnvironment.h"
 #include "JSWithScope.h"
 #include "JSCInlines.h"
 #include "VariableEnvironment.h"

 namespace JSC {

 STATIC_ASSERT_IS_TRIVIALLY_DESTRUCTIBLE(JSScope);

 const ClassInfo JSScope::s_info = { "Scope", &Base::s_info, nullptr, nullptr, CREATE_METHOD_TABLE(JSScope) };

 void JSScope::visitChildren(JSCell* cell, SlotVisitor& visitor)
 {
     JSScope* thisObject = jsCast<JSScope*>(cell);
     ASSERT_GC_OBJECT_INHERITS(thisObject, info());
     Base::visitChildren(thisObject, visitor);
     visitor.append(thisObject->m_next);
 }

 // Returns true if we found enough information to terminate optimization.
 static inline bool abstractAccess(ExecState* exec, JSScope* scope, const Identifier& ident, GetOrPut getOrPut, size_t depth, bool& needsVarInjectionChecks, ResolveOp& op, InitializationMode initializationMode)
 {
     VM& vm = exec->vm();
     auto throwScope = DECLARE_THROW_SCOPE(vm);

     if (scope->isJSLexicalEnvironment()) {
         JSLexicalEnvironment* lexicalEnvironment = jsCast<JSLexicalEnvironment*>(scope);

         SymbolTable* symbolTable = lexicalEnvironment->symbolTable();
         {
             ConcurrentJSLocker locker(symbolTable->m_lock);
             auto iter = symbolTable->find(locker, ident.impl());
             if (iter != symbolTable->end(locker)) {
                 SymbolTableEntry& entry = iter->value;
                 ASSERT(!entry.isNull());
                 if (entry.isReadOnly() && getOrPut == Put) {
                     // We know the property will be at this lexical environment scope, but we don't know how to cache it.
                     op = ResolveOp(Dynamic, 0, 0, 0, 0, 0);
                     return true;
                 }

                 op = ResolveOp(makeType(ClosureVar, needsVarInjectionChecks), depth, 0, lexicalEnvironment, entry.watchpointSet(), entry.scopeOffset().offset());
                 return true;
             }
         }

         if (scope->type() == ModuleEnvironmentType) {
             JSModuleEnvironment* moduleEnvironment = jsCast<JSModuleEnvironment*>(scope);
             AbstractModuleRecord* moduleRecord = moduleEnvironment->moduleRecord();
             AbstractModuleRecord::Resolution resolution = moduleRecord->resolveImport(exec, ident);
             RETURN_IF_EXCEPTION(throwScope, false);
             if (resolution.type == AbstractModuleRecord::Resolution::Type::Resolved) {
                 AbstractModuleRecord* importedRecord = resolution.moduleRecord;
                 JSModuleEnvironment* importedEnvironment = importedRecord->moduleEnvironment();
                 SymbolTable* symbolTable = importedEnvironment->symbolTable();
                 ConcurrentJSLocker locker(symbolTable->m_lock);
                 auto iter = symbolTable->find(locker, resolution.localName.impl());
                 ASSERT(iter != symbolTable->end(locker));
                 SymbolTableEntry& entry = iter->value;
                 ASSERT(!entry.isNull());
                 op = ResolveOp(makeType(ModuleVar, needsVarInjectionChecks), depth, 0, importedEnvironment, entry.watchpointSet(), entry.scopeOffset().offset(), resolution.localName.impl());
                 return true;
             }
         }

         if (symbolTable->usesNonStrictEval())
             needsVarInjectionChecks = true;
         return false;
     }

     if (scope->isGlobalLexicalEnvironment()) {
         JSGlobalLexicalEnvironment* globalLexicalEnvironment = jsCast<JSGlobalLexicalEnvironment*>(scope);
         SymbolTable* symbolTable = globalLexicalEnvironment->symbolTable();
         ConcurrentJSLocker locker(symbolTable->m_lock);
         auto iter = symbolTable->find(locker, ident.impl());
         if (iter != symbolTable->end(locker)) {
             SymbolTableEntry& entry = iter->value;
             ASSERT(!entry.isNull());
             if (getOrPut == Put && entry.isReadOnly() && !isInitialization(initializationMode)) {
                 // We know the property will be at global lexical environment, but we don't know how to cache it.
                 op = ResolveOp(Dynamic, 0, 0, 0, 0, 0);
                 return true;
             }

             // We can force const Initialization to always go down the fast path. It is provably impossible to construct
             // a program that needs a var injection check here. You can convince yourself of this as follows:
             // Any other let/const/class would be a duplicate of this in the global scope, so we would never get here in that situation.
             // Also, if we had an eval in the global scope that defined a const, it would also be a duplicate of this const, and so it would
             // also throw an error. Therefore, we're *the only* thing that can assign to this "const" slot for the first (and only) time. Also,
             // we will never have a Dynamic ResolveType here because if we were inside a "with" statement, that would mean the "const" definition
             // isn't a global, it would be a local to the "with" block.
             // We still need to make the slow path correct for when we need to fire a watchpoint.
             ResolveType resolveType = initializationMode == InitializationMode::ConstInitialization ? GlobalLexicalVar : makeType(GlobalLexicalVar, needsVarInjectionChecks);
             op = ResolveOp(
                 resolveType, depth, 0, 0, entry.watchpointSet(),
                 reinterpret_cast<uintptr_t>(globalLexicalEnvironment->variableAt(entry.scopeOffset()).slot()));
             return true;
         }

         return false;
     }

     if (scope->isGlobalObject()) {
         JSGlobalObject* globalObject = jsCast<JSGlobalObject*>(scope);
         {
             SymbolTable* symbolTable = globalObject->symbolTable();
             ConcurrentJSLocker locker(symbolTable->m_lock);
             auto iter = symbolTable->find(locker, ident.impl());
             if (iter != symbolTable->end(locker)) {
                 SymbolTableEntry& entry = iter->value;
                 ASSERT(!entry.isNull());
                 if (getOrPut == Put && entry.isReadOnly()) {
                     // We know the property will be at global scope, but we don't know how to cache it.
                     op = ResolveOp(Dynamic, 0, 0, 0, 0, 0);
                     return true;
                 }

                 op = ResolveOp(
                     makeType(GlobalVar, needsVarInjectionChecks), depth, 0, 0, entry.watchpointSet(),
                     reinterpret_cast<uintptr_t>(globalObject->variableAt(entry.scopeOffset()).slot()));
                 return true;
             }
         }

         PropertySlot slot(globalObject, PropertySlot::InternalMethodType::VMInquiry);
         bool hasOwnProperty = globalObject->getOwnPropertySlot(globalObject, exec, ident, slot);
         if (!hasOwnProperty) {
             op = ResolveOp(makeType(UnresolvedProperty, needsVarInjectionChecks), 0, 0, 0, 0, 0);
             return true;
         }

         Structure* structure = globalObject->structure(vm);
         if (!slot.isCacheableValue()
             || !structure->propertyAccessesAreCacheable()
             || (structure->hasReadOnlyOrGetterSetterPropertiesExcludingProto() && getOrPut == Put)) {
             // We know the property will be at global scope, but we don't know how to cache it.
             ASSERT(!scope->next());
             op = ResolveOp(makeType(GlobalProperty, needsVarInjectionChecks), 0, 0, 0, 0, 0);
             return true;
         }


         WatchpointState state = structure->ensurePropertyReplacementWatchpointSet(vm, slot.cachedOffset())->state();
         if (state == IsWatched && getOrPut == Put) {
             // The field exists, but because the replacement watchpoint is still intact. This is
             // kind of dangerous. We have two options:
             // 1) Invalidate the watchpoint set. That would work, but it's possible that this code
             //    path never executes - in which case this would be unwise.
             // 2) Have the invalidation happen at run-time. All we have to do is leave the code
             //    uncached. The only downside is slightly more work when this does execute.
             // We go with option (2) here because it seems less evil.
             op = ResolveOp(makeType(GlobalProperty, needsVarInjectionChecks), depth, 0, 0, 0, 0);
         } else
             op = ResolveOp(makeType(GlobalProperty, needsVarInjectionChecks), depth, structure, 0, 0, slot.cachedOffset());
         return true;
     }

     op = ResolveOp(Dynamic, 0, 0, 0, 0, 0);
     return true;
 }

 JSObject* JSScope::objectAtScope(JSScope* scope)
 {
     JSObject* object = scope;
     if (object->type() == WithScopeType)
         return jsCast<JSWithScope*>(object)->object();

     return object;
 }

 // When an exception occurs, the result of isUnscopable becomes false.
 static inline bool isUnscopable(ExecState* exec, JSScope* scope, JSObject* object, const Identifier& ident)
 {
     VM& vm = exec->vm();
     auto throwScope = DECLARE_THROW_SCOPE(vm);
     if (scope->type() != WithScopeType)
         return false;

     JSValue unscopables = object->get(exec, vm.propertyNames->unscopablesSymbol);
     RETURN_IF_EXCEPTION(throwScope, false);
     if (!unscopables.isObject())
         return false;
     JSValue blocked = jsCast<JSObject*>(unscopables)->get(exec, ident);
     RETURN_IF_EXCEPTION(throwScope, false);

     return blocked.toBoolean(exec);
 }

 template<typename ReturnPredicateFunctor, typename SkipPredicateFunctor>
 ALWAYS_INLINE JSObject* JSScope::resolve(ExecState* exec, JSScope* scope, const Identifier& ident, ReturnPredicateFunctor returnPredicate, SkipPredicateFunctor skipPredicate)
 {
     VM& vm = exec->vm();
     auto throwScope = DECLARE_THROW_SCOPE(vm);
     ScopeChainIterator end = scope->end();
     ScopeChainIterator it = scope->begin();
     while (1) {
         JSScope* scope = it.scope();
         JSObject* object = it.get();

         // Global scope.
         if (++it == end) {
             JSScope* globalScopeExtension = scope->globalObject(vm)->globalScopeExtension();
             if (UNLIKELY(globalScopeExtension)) {
                 bool hasProperty = object->hasProperty(exec, ident);
                 RETURN_IF_EXCEPTION(throwScope, nullptr);
                 if (hasProperty)
                     return object;
                 JSObject* extensionScopeObject = JSScope::objectAtScope(globalScopeExtension);
                 hasProperty = extensionScopeObject->hasProperty(exec, ident);
                 RETURN_IF_EXCEPTION(throwScope, nullptr);
                 if (hasProperty)
                     return extensionScopeObject;
             }
             return object;
         }

         if (skipPredicate(scope))
             continue;

         bool hasProperty = object->hasProperty(exec, ident);
         RETURN_IF_EXCEPTION(throwScope, nullptr);
         if (hasProperty) {
             bool unscopable = isUnscopable(exec, scope, object, ident);
             EXCEPTION_ASSERT(!throwScope.exception() || !unscopable);
             if (!unscopable)
                 return object;
         }

         if (returnPredicate(scope))
             return object;
     }
 }

 JSValue JSScope::resolveScopeForHoistingFuncDeclInEval(ExecState* exec, JSScope* scope, const Identifier& ident)
 {
     VM& vm = exec->vm();
     auto throwScope = DECLARE_THROW_SCOPE(vm);

     auto returnPredicate = [&] (JSScope* scope) -> bool {
         return scope->isVarScope();
     };
     auto skipPredicate = [&] (JSScope* scope) -> bool {
         return scope->isWithScope();
     };
     JSObject* object = resolve(exec, scope, ident, returnPredicate, skipPredicate);
     RETURN_IF_EXCEPTION(throwScope, { });

     bool result = false;
     if (JSScope* scope = jsDynamicCast<JSScope*>(vm, object)) {
         if (SymbolTable* scopeSymbolTable = scope->symbolTable(vm)) {
             result = scope->isGlobalObject()
                 ? JSObject::isExtensible(object, exec)
                 : scopeSymbolTable->scopeType() == SymbolTable::ScopeType::VarScope;
         }
     }

     return result ? JSValue(object) : jsUndefined();
 }

 JSObject* JSScope::resolve(ExecState* exec, JSScope* scope, const Identifier& ident)
 {
     auto predicate1 = [&] (JSScope*) -> bool {
         return false;
     };
     auto predicate2 = [&] (JSScope*) -> bool {
         return false;
     };
     return resolve(exec, scope, ident, predicate1, predicate2);
 }

 ResolveOp JSScope::abstractResolve(ExecState* exec, size_t depthOffset, JSScope* scope, const Identifier& ident, GetOrPut getOrPut, ResolveType unlinkedType, InitializationMode initializationMode)
 {
     VM& vm = exec->vm();
     auto throwScope = DECLARE_THROW_SCOPE(vm);

     ResolveOp op(Dynamic, 0, 0, 0, 0, 0);
     if (unlinkedType == Dynamic)
         return op;

     bool needsVarInjectionChecks = JSC::needsVarInjectionChecks(unlinkedType);
     size_t depth = depthOffset;
     for (; scope; scope = scope->next()) {
         bool success = abstractAccess(exec, scope, ident, getOrPut, depth, needsVarInjectionChecks, op, initializationMode);
         RETURN_IF_EXCEPTION(throwScope, ResolveOp(Dynamic, 0, 0, 0, 0, 0));
         if (success)
             break;
         ++depth;
     }

     return op;
 }

 void JSScope::collectClosureVariablesUnderTDZ(JSScope* scope, VariableEnvironment& result)
 {
     for (; scope; scope = scope->next()) {
         if (!scope->isLexicalScope() && !scope->isCatchScope())
             continue;

         if (scope->isModuleScope()) {
             AbstractModuleRecord* moduleRecord = jsCast<JSModuleEnvironment*>(scope)->moduleRecord();
             for (const auto& pair : moduleRecord->importEntries())
                 result.add(pair.key);
         }

         SymbolTable* symbolTable = jsCast<JSSymbolTableObject*>(scope)->symbolTable();
         ASSERT(symbolTable->scopeType() == SymbolTable::ScopeType::LexicalScope || symbolTable->scopeType() == SymbolTable::ScopeType::CatchScope);
         ConcurrentJSLocker locker(symbolTable->m_lock);
         for (auto end = symbolTable->end(locker), iter = symbolTable->begin(locker); iter != end; ++iter)
             result.add(iter->key);
     }
 }

 bool JSScope::isVarScope()
 {
     if (type() != LexicalEnvironmentType)
         return false;
     return jsCast<JSLexicalEnvironment*>(this)->symbolTable()->scopeType() == SymbolTable::ScopeType::VarScope;
 }

 bool JSScope::isLexicalScope()
 {
     if (!isJSLexicalEnvironment())
         return false;
     return jsCast<JSLexicalEnvironment*>(this)->symbolTable()->scopeType() == SymbolTable::ScopeType::LexicalScope;
 }

 bool JSScope::isModuleScope()
 {
     return type() == ModuleEnvironmentType;
 }

 bool JSScope::isCatchScope()
 {
     if (type() != LexicalEnvironmentType)
         return false;
     return jsCast<JSLexicalEnvironment*>(this)->symbolTable()->scopeType() == SymbolTable::ScopeType::CatchScope;
 }

 bool JSScope::isFunctionNameScopeObject()
 {
     if (type() != LexicalEnvironmentType)
         return false;
     return jsCast<JSLexicalEnvironment*>(this)->symbolTable()->scopeType() == SymbolTable::ScopeType::FunctionNameScope;
 }

 bool JSScope::isNestedLexicalScope()
 {
     if (!isJSLexicalEnvironment())
         return false;
     return jsCast<JSLexicalEnvironment*>(this)->symbolTable()->isNestedLexicalScope();
 }

 JSScope* JSScope::constantScopeForCodeBlock(ResolveType type, CodeBlock* codeBlock)
 {
     switch (type) {
     case GlobalProperty:
     case GlobalVar:
     case GlobalPropertyWithVarInjectionChecks:
     case GlobalVarWithVarInjectionChecks:
         return codeBlock->globalObject();
     case GlobalLexicalVarWithVarInjectionChecks:
     case GlobalLexicalVar:
         return codeBlock->globalObject()->globalLexicalEnvironment();
     default:
         return nullptr;
     }

     RELEASE_ASSERT_NOT_REACHED();
     return nullptr;
 }

 SymbolTable* JSScope::symbolTable(VM& vm)
 {
     if (JSSymbolTableObject* symbolTableObject = jsDynamicCast<JSSymbolTableObject*>(vm, this))
         return symbolTableObject->symbolTable();

     return nullptr;
 }

 JSValue JSScope::toThis(JSCell*, ExecState* exec, ECMAMode ecmaMode)
 {
     if (ecmaMode == StrictMode)
         return jsUndefined();
     return exec->globalThisValue();
 }

 } // namespace JSC
	/*
	* Copyright (C) 2012-2017 Apple Inc. All Rights Reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution.
	*
	* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
	* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
	* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
	* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
	* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
	* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
	* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
	* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/

	#include "config.h"
	#include "JSScope.h"

	#include "AbstractModuleRecord.h"
	#include "Exception.h"
	#include "JSGlobalObject.h"
	#include "JSLexicalEnvironment.h"
	#include "JSModuleEnvironment.h"
	#include "JSWithScope.h"
	#include "JSCInlines.h"
	#include "VariableEnvironment.h"

	namespace JSC {

	STATIC_ASSERT_IS_TRIVIALLY_DESTRUCTIBLE(JSScope);

	const ClassInfo JSScope::s_info = { "Scope", &Base::s_info, nullptr, nullptr, CREATE_METHOD_TABLE(JSScope) };

	void JSScope::visitChildren(JSCell* cell, SlotVisitor& visitor)
	{
	JSScope* thisObject = jsCast<JSScope*>(cell);
	ASSERT_GC_OBJECT_INHERITS(thisObject, info());
	Base::visitChildren(thisObject, visitor);
	visitor.append(thisObject->m_next);
	}

	// Returns true if we found enough information to terminate optimization.
	static inline bool abstractAccess(ExecState* exec, JSScope* scope, const Identifier& ident, GetOrPut getOrPut, size_t depth, bool& needsVarInjectionChecks, ResolveOp& op, InitializationMode initializationMode)
	{
	VM& vm = exec->vm();
	auto throwScope = DECLARE_THROW_SCOPE(vm);

	if (scope->isJSLexicalEnvironment()) {
	JSLexicalEnvironment* lexicalEnvironment = jsCast<JSLexicalEnvironment*>(scope);

	SymbolTable* symbolTable = lexicalEnvironment->symbolTable();
	{
	ConcurrentJSLocker locker(symbolTable->m_lock);
	auto iter = symbolTable->find(locker, ident.impl());
	if (iter != symbolTable->end(locker)) {
	SymbolTableEntry& entry = iter->value;
	ASSERT(!entry.isNull());
	if (entry.isReadOnly() && getOrPut == Put) {
	// We know the property will be at this lexical environment scope, but we don't know how to cache it.
	op = ResolveOp(Dynamic, 0, 0, 0, 0, 0);
	return true;
	}

	op = ResolveOp(makeType(ClosureVar, needsVarInjectionChecks), depth, 0, lexicalEnvironment, entry.watchpointSet(), entry.scopeOffset().offset());
	return true;
	}
	}

	if (scope->type() == ModuleEnvironmentType) {
	JSModuleEnvironment* moduleEnvironment = jsCast<JSModuleEnvironment*>(scope);
	AbstractModuleRecord* moduleRecord = moduleEnvironment->moduleRecord();
	AbstractModuleRecord::Resolution resolution = moduleRecord->resolveImport(exec, ident);
	RETURN_IF_EXCEPTION(throwScope, false);
	if (resolution.type == AbstractModuleRecord::Resolution::Type::Resolved) {
	AbstractModuleRecord* importedRecord = resolution.moduleRecord;
	JSModuleEnvironment* importedEnvironment = importedRecord->moduleEnvironment();
	SymbolTable* symbolTable = importedEnvironment->symbolTable();
	ConcurrentJSLocker locker(symbolTable->m_lock);
	auto iter = symbolTable->find(locker, resolution.localName.impl());
	ASSERT(iter != symbolTable->end(locker));
	SymbolTableEntry& entry = iter->value;
	ASSERT(!entry.isNull());
	op = ResolveOp(makeType(ModuleVar, needsVarInjectionChecks), depth, 0, importedEnvironment, entry.watchpointSet(), entry.scopeOffset().offset(), resolution.localName.impl());
	return true;
	}
	}

	if (symbolTable->usesNonStrictEval())
	needsVarInjectionChecks = true;
	return false;
	}

	if (scope->isGlobalLexicalEnvironment()) {
	JSGlobalLexicalEnvironment* globalLexicalEnvironment = jsCast<JSGlobalLexicalEnvironment*>(scope);
	SymbolTable* symbolTable = globalLexicalEnvironment->symbolTable();
	ConcurrentJSLocker locker(symbolTable->m_lock);
	auto iter = symbolTable->find(locker, ident.impl());
	if (iter != symbolTable->end(locker)) {
	SymbolTableEntry& entry = iter->value;
	ASSERT(!entry.isNull());
	if (getOrPut == Put && entry.isReadOnly() && !isInitialization(initializationMode)) {
	// We know the property will be at global lexical environment, but we don't know how to cache it.
	op = ResolveOp(Dynamic, 0, 0, 0, 0, 0);
	return true;
	}

	// We can force const Initialization to always go down the fast path. It is provably impossible to construct
	// a program that needs a var injection check here. You can convince yourself of this as follows:
	// Any other let/const/class would be a duplicate of this in the global scope, so we would never get here in that situation.
	// Also, if we had an eval in the global scope that defined a const, it would also be a duplicate of this const, and so it would
	// also throw an error. Therefore, we're the only thing that can assign to this "const" slot for the first (and only) time. Also,
	// we will never have a Dynamic ResolveType here because if we were inside a "with" statement, that would mean the "const" definition
	// isn't a global, it would be a local to the "with" block.
	// We still need to make the slow path correct for when we need to fire a watchpoint.
	ResolveType resolveType = initializationMode == InitializationMode::ConstInitialization ? GlobalLexicalVar : makeType(GlobalLexicalVar, needsVarInjectionChecks);
	op = ResolveOp(
	resolveType, depth, 0, 0, entry.watchpointSet(),
	reinterpret_cast<uintptr_t>(globalLexicalEnvironment->variableAt(entry.scopeOffset()).slot()));
	return true;
	}

	return false;
	}

	if (scope->isGlobalObject()) {
	JSGlobalObject* globalObject = jsCast<JSGlobalObject*>(scope);
	{
	SymbolTable* symbolTable = globalObject->symbolTable();
	ConcurrentJSLocker locker(symbolTable->m_lock);
	auto iter = symbolTable->find(locker, ident.impl());
	if (iter != symbolTable->end(locker)) {
	SymbolTableEntry& entry = iter->value;
	ASSERT(!entry.isNull());
	if (getOrPut == Put && entry.isReadOnly()) {
	// We know the property will be at global scope, but we don't know how to cache it.
	op = ResolveOp(Dynamic, 0, 0, 0, 0, 0);
	return true;
	}

	op = ResolveOp(
	makeType(GlobalVar, needsVarInjectionChecks), depth, 0, 0, entry.watchpointSet(),
	reinterpret_cast<uintptr_t>(globalObject->variableAt(entry.scopeOffset()).slot()));
	return true;
	}
	}

	PropertySlot slot(globalObject, PropertySlot::InternalMethodType::VMInquiry);
	bool hasOwnProperty = globalObject->getOwnPropertySlot(globalObject, exec, ident, slot);
	if (!hasOwnProperty) {
	op = ResolveOp(makeType(UnresolvedProperty, needsVarInjectionChecks), 0, 0, 0, 0, 0);
	return true;
	}

	Structure* structure = globalObject->structure(vm);
	if (!slot.isCacheableValue()
	\|\| !structure->propertyAccessesAreCacheable()
	\|\| (structure->hasReadOnlyOrGetterSetterPropertiesExcludingProto() && getOrPut == Put)) {
	// We know the property will be at global scope, but we don't know how to cache it.
	ASSERT(!scope->next());
	op = ResolveOp(makeType(GlobalProperty, needsVarInjectionChecks), 0, 0, 0, 0, 0);
	return true;
	}


	WatchpointState state = structure->ensurePropertyReplacementWatchpointSet(vm, slot.cachedOffset())->state();
	if (state == IsWatched && getOrPut == Put) {
	// The field exists, but because the replacement watchpoint is still intact. This is
	// kind of dangerous. We have two options:
	// 1) Invalidate the watchpoint set. That would work, but it's possible that this code
	// path never executes - in which case this would be unwise.
	// 2) Have the invalidation happen at run-time. All we have to do is leave the code
	// uncached. The only downside is slightly more work when this does execute.
	// We go with option (2) here because it seems less evil.
	op = ResolveOp(makeType(GlobalProperty, needsVarInjectionChecks), depth, 0, 0, 0, 0);
	} else
	op = ResolveOp(makeType(GlobalProperty, needsVarInjectionChecks), depth, structure, 0, 0, slot.cachedOffset());
	return true;
	}

	op = ResolveOp(Dynamic, 0, 0, 0, 0, 0);
	return true;
	}

	JSObject* JSScope::objectAtScope(JSScope* scope)
	{
	JSObject* object = scope;
	if (object->type() == WithScopeType)
	return jsCast<JSWithScope*>(object)->object();

	return object;
	}

	// When an exception occurs, the result of isUnscopable becomes false.
	static inline bool isUnscopable(ExecState* exec, JSScope* scope, JSObject* object, const Identifier& ident)
	{
	VM& vm = exec->vm();
	auto throwScope = DECLARE_THROW_SCOPE(vm);
	if (scope->type() != WithScopeType)
	return false;

	JSValue unscopables = object->get(exec, vm.propertyNames->unscopablesSymbol);
	RETURN_IF_EXCEPTION(throwScope, false);
	if (!unscopables.isObject())
	return false;
	JSValue blocked = jsCast<JSObject*>(unscopables)->get(exec, ident);
	RETURN_IF_EXCEPTION(throwScope, false);

	return blocked.toBoolean(exec);
	}

	template<typename ReturnPredicateFunctor, typename SkipPredicateFunctor>
	ALWAYS_INLINE JSObject* JSScope::resolve(ExecState* exec, JSScope* scope, const Identifier& ident, ReturnPredicateFunctor returnPredicate, SkipPredicateFunctor skipPredicate)
	{
	VM& vm = exec->vm();
	auto throwScope = DECLARE_THROW_SCOPE(vm);
	ScopeChainIterator end = scope->end();
	ScopeChainIterator it = scope->begin();
	while (1) {
	JSScope* scope = it.scope();
	JSObject* object = it.get();

	// Global scope.
	if (++it == end) {
	JSScope* globalScopeExtension = scope->globalObject(vm)->globalScopeExtension();
	if (UNLIKELY(globalScopeExtension)) {
	bool hasProperty = object->hasProperty(exec, ident);
	RETURN_IF_EXCEPTION(throwScope, nullptr);
	if (hasProperty)
	return object;
	JSObject* extensionScopeObject = JSScope::objectAtScope(globalScopeExtension);
	hasProperty = extensionScopeObject->hasProperty(exec, ident);
	RETURN_IF_EXCEPTION(throwScope, nullptr);
	if (hasProperty)
	return extensionScopeObject;
	}
	return object;
	}

	if (skipPredicate(scope))
	continue;

	bool hasProperty = object->hasProperty(exec, ident);
	RETURN_IF_EXCEPTION(throwScope, nullptr);
	if (hasProperty) {
	bool unscopable = isUnscopable(exec, scope, object, ident);
	EXCEPTION_ASSERT(!throwScope.exception() \|\| !unscopable);
	if (!unscopable)
	return object;
	}

	if (returnPredicate(scope))
	return object;
	}
	}

	JSValue JSScope::resolveScopeForHoistingFuncDeclInEval(ExecState* exec, JSScope* scope, const Identifier& ident)
	{
	VM& vm = exec->vm();
	auto throwScope = DECLARE_THROW_SCOPE(vm);

	auto returnPredicate = [&] (JSScope* scope) -> bool {
	return scope->isVarScope();
	};
	auto skipPredicate = [&] (JSScope* scope) -> bool {
	return scope->isWithScope();
	};
	JSObject* object = resolve(exec, scope, ident, returnPredicate, skipPredicate);
	RETURN_IF_EXCEPTION(throwScope, { });

	bool result = false;
	if (JSScope* scope = jsDynamicCast<JSScope*>(vm, object)) {
	if (SymbolTable* scopeSymbolTable = scope->symbolTable(vm)) {
	result = scope->isGlobalObject()
	? JSObject::isExtensible(object, exec)
	: scopeSymbolTable->scopeType() == SymbolTable::ScopeType::VarScope;
	}
	}

	return result ? JSValue(object) : jsUndefined();
	}

	JSObject* JSScope::resolve(ExecState* exec, JSScope* scope, const Identifier& ident)
	{
	auto predicate1 = [&] (JSScope*) -> bool {
	return false;
	};
	auto predicate2 = [&] (JSScope*) -> bool {
	return false;
	};
	return resolve(exec, scope, ident, predicate1, predicate2);
	}

	ResolveOp JSScope::abstractResolve(ExecState* exec, size_t depthOffset, JSScope* scope, const Identifier& ident, GetOrPut getOrPut, ResolveType unlinkedType, InitializationMode initializationMode)
	{
	VM& vm = exec->vm();
	auto throwScope = DECLARE_THROW_SCOPE(vm);

	ResolveOp op(Dynamic, 0, 0, 0, 0, 0);
	if (unlinkedType == Dynamic)
	return op;

	bool needsVarInjectionChecks = JSC::needsVarInjectionChecks(unlinkedType);
	size_t depth = depthOffset;
	for (; scope; scope = scope->next()) {
	bool success = abstractAccess(exec, scope, ident, getOrPut, depth, needsVarInjectionChecks, op, initializationMode);
	RETURN_IF_EXCEPTION(throwScope, ResolveOp(Dynamic, 0, 0, 0, 0, 0));
	if (success)
	break;
	++depth;
	}

	return op;
	}

	void JSScope::collectClosureVariablesUnderTDZ(JSScope* scope, VariableEnvironment& result)
	{
	for (; scope; scope = scope->next()) {
	if (!scope->isLexicalScope() && !scope->isCatchScope())
	continue;

	if (scope->isModuleScope()) {
	AbstractModuleRecord* moduleRecord = jsCast<JSModuleEnvironment*>(scope)->moduleRecord();
	for (const auto& pair : moduleRecord->importEntries())
	result.add(pair.key);
	}

	SymbolTable* symbolTable = jsCast<JSSymbolTableObject*>(scope)->symbolTable();
	ASSERT(symbolTable->scopeType() == SymbolTable::ScopeType::LexicalScope \|\| symbolTable->scopeType() == SymbolTable::ScopeType::CatchScope);
	ConcurrentJSLocker locker(symbolTable->m_lock);
	for (auto end = symbolTable->end(locker), iter = symbolTable->begin(locker); iter != end; ++iter)
	result.add(iter->key);
	}
	}

	bool JSScope::isVarScope()
	{
	if (type() != LexicalEnvironmentType)
	return false;
	return jsCast<JSLexicalEnvironment*>(this)->symbolTable()->scopeType() == SymbolTable::ScopeType::VarScope;
	}

	bool JSScope::isLexicalScope()
	{
	if (!isJSLexicalEnvironment())
	return false;
	return jsCast<JSLexicalEnvironment*>(this)->symbolTable()->scopeType() == SymbolTable::ScopeType::LexicalScope;
	}

	bool JSScope::isModuleScope()
	{
	return type() == ModuleEnvironmentType;
	}

	bool JSScope::isCatchScope()
	{
	if (type() != LexicalEnvironmentType)
	return false;
	return jsCast<JSLexicalEnvironment*>(this)->symbolTable()->scopeType() == SymbolTable::ScopeType::CatchScope;
	}

	bool JSScope::isFunctionNameScopeObject()
	{
	if (type() != LexicalEnvironmentType)
	return false;
	return jsCast<JSLexicalEnvironment*>(this)->symbolTable()->scopeType() == SymbolTable::ScopeType::FunctionNameScope;
	}

	bool JSScope::isNestedLexicalScope()
	{
	if (!isJSLexicalEnvironment())
	return false;
	return jsCast<JSLexicalEnvironment*>(this)->symbolTable()->isNestedLexicalScope();
	}

	JSScope* JSScope::constantScopeForCodeBlock(ResolveType type, CodeBlock* codeBlock)
	{
	switch (type) {
	case GlobalProperty:
	case GlobalVar:
	case GlobalPropertyWithVarInjectionChecks:
	case GlobalVarWithVarInjectionChecks:
	return codeBlock->globalObject();
	case GlobalLexicalVarWithVarInjectionChecks:
	case GlobalLexicalVar:
	return codeBlock->globalObject()->globalLexicalEnvironment();
	default:
	return nullptr;
	}

	RELEASE_ASSERT_NOT_REACHED();
	return nullptr;
	}

	SymbolTable* JSScope::symbolTable(VM& vm)
	{
	if (JSSymbolTableObject* symbolTableObject = jsDynamicCast<JSSymbolTableObject*>(vm, this))
	return symbolTableObject->symbolTable();

	return nullptr;
	}

	JSValue JSScope::toThis(JSCell, ExecState exec, ECMAMode ecmaMode)
	{
	if (ecmaMode == StrictMode)
	return jsUndefined();
	return exec->globalThisValue();
	}

	} // namespace JSC