Make the condition for when this is predeclared easier to understand.

src/ast/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/ast/scopes.h"
 
 #include <set>
 
 #include "src/accessors.h"
 #include "src/bootstrapper.h"
@@ skipping 111 matching lines @@
   outer_scope_->AddInnerScope(this);
 }
 
 Scope::Snapshot::Snapshot(Scope* scope)
     : outer_scope_(scope),
       top_inner_scope_(scope->inner_scope_),
       top_unresolved_(scope->unresolved_),
       top_local_(scope->GetClosureScope()->locals_.length()),
       top_decl_(scope->GetClosureScope()->decls_.length()) {}
 
-DeclarationScope::DeclarationScope(Zone* zone)
+DeclarationScope::DeclarationScope(Zone* zone,
+                                   AstValueFactory* ast_value_factory)
     : Scope(zone),
       function_kind_(kNormalFunction),
       params_(4, zone),
       sloppy_block_function_map_(zone) {
   SetDefaults();
+

[marja, 2016/08/31 12:27:48]

Nit: how about DCHECK_EQ(scope_type, SCRIPT_SCOPE) here, just for documenting
the intention...

+  // Make sure that if we don't find the global 'this', it won't be declared as
+  // a regular dynamic global by predeclaring it with the right variable kind.
+  DeclareDynamicGlobal(ast_value_factory->this_string(), Variable::THIS);
 }
 
 DeclarationScope::DeclarationScope(Zone* zone, Scope* outer_scope,
                                    ScopeType scope_type,
                                    FunctionKind function_kind)
     : Scope(zone, outer_scope, scope_type),
       function_kind_(function_kind),
       params_(4, zone),
       sloppy_block_function_map_(zone) {
+  DCHECK_NE(scope_type, SCRIPT_SCOPE);
   SetDefaults();
   asm_function_ = outer_scope_->IsAsmModule();
 }
 
 ModuleScope::ModuleScope(DeclarationScope* script_scope,
                          AstValueFactory* ast_value_factory)
     : DeclarationScope(ast_value_factory->zone(), script_scope, MODULE_SCOPE) {
   Zone* zone = ast_value_factory->zone();
   module_descriptor_ = new (zone) ModuleDescriptor(zone);
   set_language_mode(STRICT);
@@ skipping 18 matching lines @@
   num_heap_slots_ = scope_info->ContextLength();
   DCHECK_LE(Context::MIN_CONTEXT_SLOTS, num_heap_slots_);
 }
 
 DeclarationScope::DeclarationScope(Zone* zone, ScopeType scope_type,
                                    Handle<ScopeInfo> scope_info)
     : Scope(zone, scope_type, scope_info),
       function_kind_(scope_info->function_kind()),
       params_(0, zone),
       sloppy_block_function_map_(zone) {
+  DCHECK_NE(scope_type, SCRIPT_SCOPE);
   SetDefaults();
 }
 
 Scope::Scope(Zone* zone, const AstRawString* catch_variable_name)
     : zone_(zone),
       outer_scope_(nullptr),
       variables_(zone),
       locals_(0, zone),
       decls_(0, zone),
       scope_type_(CATCH_SCOPE) {
@@ skipping 218 matching lines @@
   DeclarationScope* scope = info->literal()->scope();
 
   // We are compiling one of three cases:
   // 1) top-level code,
   // 2) a function/eval/module on the top-level
   // 3) a function/eval in a scope that was already resolved.
   DCHECK(scope->scope_type() == SCRIPT_SCOPE ||
          scope->outer_scope()->scope_type() == SCRIPT_SCOPE ||
          scope->outer_scope()->already_resolved_);
 
-  // If there's a chance that there's a reference to global 'this', predeclare
-  // it as a dynamic global on the script scope.
-  if (scope->GetReceiverScope()->is_script_scope()) {
-    info->script_scope()->DeclareDynamicGlobal(
-        info->ast_value_factory()->this_string(), Variable::THIS);
-  }
-
   scope->AllocateVariables(info, mode);
 
 #ifdef DEBUG
   if (info->script_is_native() ? FLAG_print_builtin_scopes
                                : FLAG_print_scopes) {
     scope->Print();
   }
   scope->CheckScopePositions();
   scope->CheckZones();
 #endif
@@ skipping 1215 matching lines @@
   Variable* function =
       is_function_scope() ? AsDeclarationScope()->function_var() : nullptr;
   bool is_function_var_in_context =
       function != nullptr && function->IsContextSlot();
   return num_heap_slots() - Context::MIN_CONTEXT_SLOTS -
          (is_function_var_in_context ? 1 : 0);
 }
 
 }  // namespace internal
 }  // namespace v8