[esnext] prototype runtime implementation for async functions

src/parsing/parser-base.h

Index: src/parsing/parser-base.h
diff --git a/src/parsing/parser-base.h b/src/parsing/parser-base.h
index f4cfc4974ccfec9470fdfec7bdd8ea1df5cec62c..d84465e8403a091c021e0bdb800e1ab7b49e51a6 100644
--- a/src/parsing/parser-base.h
+++ b/src/parsing/parser-base.h
@@ -36,6 +36,12 @@ enum class ParseFunctionFlags {
   kIsDefault = 4
 };
 
+enum class FunctionBody {
+  Normal,
+  ArrowBlock = Normal,
+  ArrowConcise,
+};
+
 static inline ParseFunctionFlags operator|(ParseFunctionFlags lhs,
                                            ParseFunctionFlags rhs) {
   typedef unsigned char T;
@@ -260,7 +266,7 @@ class ParserBase : public Traits {
     void set_generator_object_variable(
         typename Traits::Type::GeneratorVariable* variable) {
       DCHECK(variable != NULL);
-      DCHECK(is_generator());
+      DCHECK(is_generator() || is_async_function());
       generator_object_variable_ = variable;
     }
     typename Traits::Type::GeneratorVariable* generator_object_variable()
@@ -2013,8 +2019,9 @@ ParserBase<Traits>::ParseAssignmentExpression(bool accept_IN,
     ValidateArrowFormalParameters(&arrow_formals_classifier, expression,
                                   parenthesized_formals, is_async, CHECK_OK);
     Scanner::Location loc(lhs_beg_pos, scanner()->location().end_pos);
-    Scope* scope =
-        this->NewScope(scope_, FUNCTION_SCOPE, FunctionKind::kArrowFunction);
+    Scope* scope = this->NewScope(scope_, FUNCTION_SCOPE,
+                                  is_async ? FunctionKind::kAsyncArrowFunction
+                                           : FunctionKind::kArrowFunction);
     // Because the arrow's parameters were parsed in the outer scope, any
     // usage flags that might have been triggered there need to be copied
     // to the arrow scope.
@@ -2941,11 +2948,12 @@ ParserBase<Traits>::ParseArrowFunctionLiteral(
   int expected_property_count = -1;
   Scanner::Location super_loc;
 
+  FunctionKind arrow_kind = is_async ? kAsyncArrowFunction : kArrowFunction;
   {
     typename Traits::Type::Factory function_factory(ast_value_factory());
-    FunctionState function_state(
-        &function_state_, &scope_, formal_parameters.scope,
-        is_async ? kAsyncArrowFunction : kArrowFunction, &function_factory);
+    FunctionState function_state(&function_state_, &scope_,
+                                 formal_parameters.scope, arrow_kind,
+                                 &function_factory);
 
     function_state.SkipMaterializedLiterals(
         formal_parameters.materialized_literals_count);
@@ -2970,7 +2978,7 @@ ParserBase<Traits>::ParseArrowFunctionLiteral(
       } else {
         body = this->ParseEagerFunctionBody(
             this->EmptyIdentifier(), RelocInfo::kNoPosition, formal_parameters,
-            kArrowFunction, FunctionLiteral::kAnonymousExpression, CHECK_OK);
+            arrow_kind, FunctionLiteral::kAnonymousExpression, CHECK_OK);
         materialized_literal_count =
             function_state.materialized_literal_count();
         expected_property_count = function_state.expected_property_count();
@@ -2980,12 +2988,18 @@ ParserBase<Traits>::ParseArrowFunctionLiteral(
       int pos = position();
       parenthesized_function_ = false;
       ExpressionClassifier classifier(this);
-      ExpressionT expression =
-          ParseAssignmentExpression(accept_IN, &classifier, CHECK_OK);
-      Traits::RewriteNonPattern(&classifier, CHECK_OK);
       body = this->NewStatementList(1, zone());
-      this->AddParameterInitializationBlock(formal_parameters, body, CHECK_OK);
-      body->Add(factory()->NewReturnStatement(expression, pos), zone());
+      this->AddParameterInitializationBlock(formal_parameters, body, is_async,
+                                            CHECK_OK);
+      if (is_async) {
+        this->ParseAsyncArrowSingleExpressionBody(body, accept_IN, &classifier,
+                                                  pos, CHECK_OK);
+      } else {
+        ExpressionT expression =
+            ParseAssignmentExpression(accept_IN, &classifier, CHECK_OK);
+        Traits::RewriteNonPattern(&classifier, CHECK_OK);
+        body->Add(factory()->NewReturnStatement(expression, pos), zone());
+      }
       materialized_literal_count = function_state.materialized_literal_count();
       expected_property_count = function_state.expected_property_count();
     }
@@ -3016,7 +3030,7 @@ ParserBase<Traits>::ParseArrowFunctionLiteral(
       materialized_literal_count, expected_property_count, num_parameters,
       FunctionLiteral::kNoDuplicateParameters,
       FunctionLiteral::kAnonymousExpression,
-      FunctionLiteral::kShouldLazyCompile, FunctionKind::kArrowFunction,
+      FunctionLiteral::kShouldLazyCompile, arrow_kind,
       formal_parameters.scope->start_position());
 
   function_literal->set_function_token_position(