Implement proper scoping for "this" in arrow functions

src/scopes.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/scopes.h"
 
 #include "src/accessors.h"
 #include "src/bootstrapper.h"
@@ skipping 13 matching lines @@
 //       use. Because a Variable holding a handle with the same location exists
 //       this is ensured.
 
 VariableMap::VariableMap(Zone* zone)
     : ZoneHashMap(ZoneHashMap::PointersMatch, 8, ZoneAllocationPolicy(zone)),
       zone_(zone) {}
 VariableMap::~VariableMap() {}
 
 
 Variable* VariableMap::Declare(Scope* scope, const AstRawString* name,
-                               VariableMode mode, bool is_valid_lhs,
-                               Variable::Kind kind,
+                               VariableMode mode, Variable::Kind kind,
                                InitializationFlag initialization_flag,
                                MaybeAssignedFlag maybe_assigned_flag) {
   // AstRawStrings are unambiguous, i.e., the same string is always represented
   // by the same AstRawString*.
   // FIXME(marja): fix the type of Lookup.
   Entry* p = ZoneHashMap::Lookup(const_cast<AstRawString*>(name), name->hash(),
                                  true, ZoneAllocationPolicy(zone()));
   if (p->value == NULL) {
     // The variable has not been declared yet -> insert it.
     DCHECK(p->key == name);
-    p->value = new (zone()) Variable(scope, name, mode, is_valid_lhs, kind,
+    p->value = new (zone()) Variable(scope, name, mode, kind,
                                      initialization_flag, maybe_assigned_flag);
   }
   return reinterpret_cast<Variable*>(p->value);
 }
 
 
 Variable* VariableMap::Lookup(const AstRawString* name) {
   Entry* p = ZoneHashMap::Lookup(const_cast<AstRawString*>(name), name->hash(),
                                  false, ZoneAllocationPolicy(NULL));
   if (p != NULL) {
@@ skipping 67 matching lines @@
       already_resolved_(true),
       ast_value_factory_(value_factory),
       zone_(zone) {
   SetDefaults(CATCH_SCOPE, NULL, Handle<ScopeInfo>::null());
   AddInnerScope(inner_scope);
   ++num_var_or_const_;
   num_heap_slots_ = Context::MIN_CONTEXT_SLOTS;
   Variable* variable = variables_.Declare(this,
                                           catch_variable_name,
                                           VAR,
-                                          true,  // Valid left-hand side.
                                           Variable::NORMAL,
                                           kCreatedInitialized);
   AllocateHeapSlot(variable);
 }
 
 
 void Scope::SetDefaults(ScopeType scope_type,
                         Scope* outer_scope,
                         Handle<ScopeInfo> scope_info) {
   outer_scope_ = outer_scope;
@@ skipping 148 matching lines @@
   // Declare convenience variables.
   // Declare and allocate receiver (even for the script scope, and even
   // if naccesses_ == 0).
   // NOTE: When loading parameters in the script scope, we must take
   // care not to access them as properties of the global object, but
   // instead load them directly from the stack. Currently, the only
   // such parameter is 'this' which is passed on the stack when
   // invoking scripts
   if (is_declaration_scope()) {
     DCHECK(!subclass_constructor || is_function_scope());
-    Variable* var = variables_.Declare(
-        this, ast_value_factory_->this_string(),
-        subclass_constructor ? CONST : VAR, false, Variable::THIS,
-        subclass_constructor ? kNeedsInitialization : kCreatedInitialized);
-    var->AllocateTo(Variable::PARAMETER, -1);
-    receiver_ = var;
+    if (has_this_declaration()) {
+      Variable* var = variables_.Declare(
+          this, ast_value_factory_->this_string(),
+          subclass_constructor ? CONST : VAR, Variable::THIS,
+          subclass_constructor ? kNeedsInitialization : kCreatedInitialized);
+      receiver_ = var;
+    }
 
     if (subclass_constructor) {
-      new_target_ = variables_.Declare(
-          this, ast_value_factory_->new_target_string(), CONST, false,
-          Variable::NEW_TARGET, kCreatedInitialized);
+      new_target_ =
+          variables_.Declare(this, ast_value_factory_->new_target_string(),
+                             CONST, Variable::NEW_TARGET, kCreatedInitialized);
       new_target_->AllocateTo(Variable::PARAMETER, -2);
       new_target_->set_is_used();
     }
-  } else {
-    DCHECK(outer_scope() != NULL);
-    receiver_ = outer_scope()->receiver();
   }
 
   if (is_function_scope()) {
     // Declare 'arguments' variable which exists in all functions.
     // Note that it might never be accessed, in which case it won't be
     // allocated during variable allocation.
     variables_.Declare(this,
                        ast_value_factory_->arguments_string(),
                        VAR,
-                       true,
                        Variable::ARGUMENTS,
                        kCreatedInitialized);
   }
 }
 
 
 Scope* Scope::FinalizeBlockScope() {
   DCHECK(is_block_scope());
   DCHECK(internals_.is_empty());
   DCHECK(temps_.is_empty());
@@ skipping 55 matching lines @@
 
     mode = DYNAMIC;
     location = Variable::LOOKUP;
     init_flag = kCreatedInitialized;
     // Be conservative and flag parameters as maybe assigned. Better information
     // would require ScopeInfo to serialize the maybe_assigned bit also for
     // parameters.
     maybe_assigned_flag = kMaybeAssigned;
   }
 
-  Variable* var = variables_.Declare(this, name, mode, true, Variable::NORMAL,
+  Variable* var = variables_.Declare(this, name, mode, Variable::NORMAL,
                                      init_flag, maybe_assigned_flag);
   var->AllocateTo(location, index);
   return var;
 }
 
 
 Variable* Scope::LookupFunctionVar(const AstRawString* name,
                                    AstNodeFactory* factory) {
   if (function_ != NULL && function_->proxy()->raw_name() == name) {
     return function_->proxy()->var();
   } else if (!scope_info_.is_null()) {
     // If we are backed by a scope info, try to lookup the variable there.
     VariableMode mode;
     int index = scope_info_->FunctionContextSlotIndex(*(name->string()), &mode);
     if (index < 0) return NULL;
-    Variable* var = new(zone()) Variable(
-        this, name, mode, true /* is valid LHS */,
-        Variable::NORMAL, kCreatedInitialized);
+    Variable* var = new (zone())
+        Variable(this, name, mode, Variable::NORMAL, kCreatedInitialized);
     VariableProxy* proxy = factory->NewVariableProxy(var);
     VariableDeclaration* declaration = factory->NewVariableDeclaration(
         proxy, mode, this, RelocInfo::kNoPosition);
     DeclareFunctionVar(declaration);
     var->AllocateTo(Variable::CONTEXT, index);
     return var;
   } else {
     return NULL;
   }
 }
 
 
 Variable* Scope::Lookup(const AstRawString* name) {
   for (Scope* scope = this;
        scope != NULL;
        scope = scope->outer_scope()) {
     Variable* var = scope->LookupLocal(name);
     if (var != NULL) return var;
   }
   return NULL;
 }
 
 
 Variable* Scope::DeclareParameter(const AstRawString* name, VariableMode mode,
                                   bool is_rest) {
   DCHECK(!already_resolved());
   DCHECK(is_function_scope());
-  Variable* var = variables_.Declare(this, name, mode, true, Variable::NORMAL,
+  Variable* var = variables_.Declare(this, name, mode, Variable::NORMAL,
                                      kCreatedInitialized);
   if (is_rest) {
     DCHECK_NULL(rest_parameter_);
     rest_parameter_ = var;
     rest_index_ = num_parameters();
   }
   params_.Add(var, zone());
   return var;
 }
 
 
 Variable* Scope::DeclareLocal(const AstRawString* name, VariableMode mode,
                               InitializationFlag init_flag,
                               MaybeAssignedFlag maybe_assigned_flag) {
   DCHECK(!already_resolved());
   // This function handles VAR, LET, and CONST modes.  DYNAMIC variables are
   // introduces during variable allocation, INTERNAL variables are allocated
   // explicitly, and TEMPORARY variables are allocated via NewTemporary().
   DCHECK(IsDeclaredVariableMode(mode));
   ++num_var_or_const_;
-  return variables_.Declare(this, name, mode, true, Variable::NORMAL, init_flag,
+  return variables_.Declare(this, name, mode, Variable::NORMAL, init_flag,
                             maybe_assigned_flag);
 }
 
 
 Variable* Scope::DeclareDynamicGlobal(const AstRawString* name) {
   DCHECK(is_script_scope());
   return variables_.Declare(this,
                             name,
                             DYNAMIC_GLOBAL,
-                            true,
                             Variable::NORMAL,
                             kCreatedInitialized);
 }
 
 
 void Scope::RemoveUnresolved(VariableProxy* var) {
   // Most likely (always?) any variable we want to remove
   // was just added before, so we search backwards.
   for (int i = unresolved_.length(); i-- > 0;) {
     if (unresolved_[i] == var) {
       unresolved_.Remove(i);
       return;
     }
   }
 }
 
 
 Variable* Scope::NewInternal(const AstRawString* name) {
   DCHECK(!already_resolved());
   Variable* var = new(zone()) Variable(this,
                                        name,
                                        INTERNAL,
-                                       false,
                                        Variable::NORMAL,
                                        kCreatedInitialized);
   internals_.Add(var, zone());
   return var;
 }
 
 
 Variable* Scope::NewTemporary(const AstRawString* name) {
   DCHECK(!already_resolved());
   Variable* var = new(zone()) Variable(this,
                                        name,
                                        TEMPORARY,
-                                       true,
                                        Variable::NORMAL,
                                        kCreatedInitialized);
   temps_.Add(var, zone());
   return var;
 }
 
 
 void Scope::AddDeclaration(Declaration* declaration) {
   decls_.Add(declaration, zone());
 }
@@ skipping 426 matching lines @@
   if (dynamics_ == NULL) dynamics_ = new (zone()) DynamicScopePart(zone());
   VariableMap* map = dynamics_->GetMap(mode);
   Variable* var = map->Lookup(name);
   if (var == NULL) {
     // Declare a new non-local.
     InitializationFlag init_flag = (mode == VAR)
         ? kCreatedInitialized : kNeedsInitialization;
     var = map->Declare(NULL,
                        name,
                        mode,
-                       true,
                        Variable::NORMAL,
                        init_flag);
     // Allocate it by giving it a dynamic lookup.
     var->AllocateTo(Variable::LOOKUP, -1);
   }
   return var;
 }
 
 
 Variable* Scope::LookupRecursive(VariableProxy* proxy,
@@ skipping 179 matching lines @@
   // via an eval() call.  This is only possible if the variable has a
   // visible name.
   if ((var->is_this() || var->is_new_target() || !var->raw_name()->IsEmpty()) &&
       (var->has_forced_context_allocation() || scope_calls_eval_ ||
        inner_scope_calls_eval_ || scope_contains_with_ || is_catch_scope() ||
        is_block_scope() || is_module_scope() || is_script_scope())) {
     var->set_is_used();
     if (scope_calls_eval_ || inner_scope_calls_eval_) var->set_maybe_assigned();
   }
   // Global variables do not need to be allocated.
-  return !var->IsGlobalObjectProperty() && var->is_used();
+  return var->is_this() || (var->is_used() && !var->IsGlobalObjectProperty());
 }
 
 
 bool Scope::MustAllocateInContext(Variable* var) {
   // If var is accessed from an inner scope, or if there is a possibility
   // that it might be accessed from the current or an inner scope (through
   // an eval() call or a runtime with lookup), it must be allocated in the
   // context.
   //
   // Exceptions: If the scope as a whole has forced context allocation, all
@@ skipping 70 matching lines @@
   // order is relevant!
   for (int i = params_.length() - 1; i >= 0; --i) {
     Variable* var = params_[i];
     if (var == rest_parameter_) continue;
 
     DCHECK(var->scope() == this);
     if (uses_sloppy_arguments || has_forced_context_allocation()) {
       // Force context allocation of the parameter.
       var->ForceContextAllocation();
     }
+    AllocateParameter(var, i);
+  }
+}
 
-    if (MustAllocate(var)) {
-      if (MustAllocateInContext(var)) {
-        DCHECK(var->IsUnallocated() || var->IsContextSlot());
-        if (var->IsUnallocated()) {
-          AllocateHeapSlot(var);
-        }
-      } else {
-        DCHECK(var->IsUnallocated() || var->IsParameter());
-        if (var->IsUnallocated()) {
-          var->AllocateTo(Variable::PARAMETER, i);
-        }
+
+void Scope::AllocateParameter(Variable* var, int index) {
+  if (MustAllocate(var)) {
+    if (MustAllocateInContext(var)) {
+      DCHECK(var->IsUnallocated() || var->IsContextSlot());
+      if (var->IsUnallocated()) {
+        AllocateHeapSlot(var);
+      }
+    } else {
+      DCHECK(var->IsUnallocated() || var->IsParameter());
+      if (var->IsUnallocated()) {
+        var->AllocateTo(Variable::PARAMETER, index);
       }
     }
   }
 }
 
 
+void Scope::AllocateReceiver() {
+  DCHECK_EQ(receiver()->scope(), this);
+
+  if (is_script_scope()) {
+    receiver()->AllocateTo(Variable::PARAMETER, -1);
+  } else {
+    if (has_forced_context_allocation()) {
+      receiver()->ForceContextAllocation();
+    }
+    AllocateParameter(receiver(), -1);
+  }
+}
+
+
 void Scope::AllocateNonParameterLocal(Isolate* isolate, Variable* var) {
   DCHECK(var->scope() == this);
   DCHECK(!var->IsVariable(isolate->factory()->dot_result_string()) ||
          !var->IsStackLocal());
   if (var->IsUnallocated() && MustAllocate(var)) {
     if (MustAllocateInContext(var)) {
       AllocateHeapSlot(var);
     } else {
       AllocateStackSlot(var);
     }
@@ skipping 47 matching lines @@
   // If scope is already resolved, we still need to allocate
   // variables in inner scopes which might not had been resolved yet.
   if (already_resolved()) return;
   // The number of slots required for variables.
   num_stack_slots_ = 0;
   num_heap_slots_ = Context::MIN_CONTEXT_SLOTS;
 
   // Allocate variables for this scope.
   // Parameters must be allocated first, if any.
   if (is_function_scope()) AllocateParameterLocals(isolate);
+  if (has_this_declaration()) AllocateReceiver();
   AllocateNonParameterLocals(isolate);
 
   // Force allocation of a context for this scope if necessary. For a 'with'
   // scope and for a function scope that makes an 'eval' call we need a context,
   // even if no local variables were statically allocated in the scope.
   // Likewise for modules.
   bool must_have_context = is_with_scope() || is_module_scope() ||
       (is_function_scope() && calls_eval());
 
   // If we didn't allocate any locals in the local context, then we only
@@ skipping 30 matching lines @@
 }
 
 
 int Scope::ContextLocalCount() const {
   if (num_heap_slots() == 0) return 0;
   return num_heap_slots() - Context::MIN_CONTEXT_SLOTS -
       (function_ != NULL && function_->proxy()->var()->IsContextSlot() ? 1 : 0);
 }
 
 } }  // namespace v8::internal