[async-await] (simpler) fix for Return in try/finally in async functions

src/ast/scopes.cc

Index: src/ast/scopes.cc
diff --git a/src/ast/scopes.cc b/src/ast/scopes.cc
index bd91e16a5220cccfab9ccb59f7eee7464dedac52..48f163aff7c40903090d523086fff2129c0a9a26 100644
--- a/src/ast/scopes.cc
+++ b/src/ast/scopes.cc
@@ -297,7 +297,7 @@ void DeclarationScope::SetDefaults() {
   new_target_ = nullptr;
   function_ = nullptr;
   arguments_ = nullptr;
-  this_function_ = nullptr;
+  rare_data_ = nullptr;
   should_eager_compile_ = false;
   was_lazily_parsed_ = false;
 #ifdef DEBUG
@@ -682,7 +682,7 @@ void DeclarationScope::DeclareDefaultFunctionVariables(
 
   if (IsConciseMethod(function_kind_) || IsClassConstructor(function_kind_) ||
       IsAccessorFunction(function_kind_)) {
-    this_function_ =
+    EnsureRareData()->this_function =
         Declare(zone(), ast_value_factory->this_function_string(), CONST);
   }
 }
@@ -703,6 +703,24 @@ Variable* DeclarationScope::DeclareFunctionVar(const AstRawString* name) {
   return function_;
 }
 
+Variable* DeclarationScope::DeclareGeneratorObjectVar(
+    const AstRawString* name) {
+  DCHECK(is_function_scope() || is_module_scope());
+  DCHECK_NULL(generator_object_var());
+
+  Variable* result = EnsureRareData()->generator_object = NewTemporary(name);
+  result->set_is_used();
+  return result;
+}
+
+Variable* DeclarationScope::DeclarePromiseVar(const AstRawString* name) {
+  DCHECK(is_function_scope());
+  DCHECK_NULL(promise_var());
+  Variable* result = EnsureRareData()->promise = NewTemporary(name);
+  result->set_is_used();
+  return result;
+}
+
 bool Scope::HasBeenRemoved() const {
   if (sibling() == this) {
     DCHECK_NULL(inner_scope_);
@@ -2110,9 +2128,8 @@ void DeclarationScope::AllocateLocals() {
     new_target_ = nullptr;
   }
 
-  if (this_function_ != nullptr && !MustAllocate(this_function_)) {
-    this_function_ = nullptr;
-  }
+  NullifyRareVariableIf(RareVariable::kThisFunction,
+                        [=](Variable* var) { return !MustAllocate(var); });
 }
 
 void ModuleScope::AllocateModuleVariables() {