[esnext] implement frontend changes for async/await proposal

src/parsing/expression-classifier.h

Index: src/parsing/expression-classifier.h
diff --git a/src/parsing/expression-classifier.h b/src/parsing/expression-classifier.h
index 71fa3d3e89b16018137605ed014740e5027beca4..86e4a4caf9c8caeb46762e58bb6b8adf69a3d054 100644
--- a/src/parsing/expression-classifier.h
+++ b/src/parsing/expression-classifier.h
@@ -39,6 +39,7 @@ class ExpressionClassifier {
     ArrowFormalParametersProduction = 1 << 6,
     LetPatternProduction = 1 << 7,
     CoverInitializedNameProduction = 1 << 8,
+    AsyncArrowFormalParametersProduction = 1 << 9,
 
     ExpressionProductions =
         (ExpressionProduction | FormalParameterInitializerProduction),
@@ -49,7 +50,8 @@ class ExpressionClassifier {
     StandardProductions = ExpressionProductions | PatternProductions,
     AllProductions =
         (StandardProductions | FormalParametersProductions |
-         ArrowFormalParametersProduction | CoverInitializedNameProduction)
+         ArrowFormalParametersProduction | CoverInitializedNameProduction |
+         AsyncArrowFormalParametersProduction)
   };
 
   enum FunctionProperties { NonSimpleParameter = 1 << 0 };
@@ -110,6 +112,10 @@ class ExpressionClassifier {
 
   bool is_valid_let_pattern() const { return is_valid(LetPatternProduction); }
 
+  bool is_valid_async_arrow_formal_parameters() const {
+    return is_valid(AsyncArrowFormalParametersProduction);
+  }
+
   const Error& expression_error() const { return expression_error_; }
 
   const Error& formal_parameter_initializer_error() const {
@@ -143,6 +149,10 @@ class ExpressionClassifier {
     return cover_initialized_name_error_;
   }
 
+  const Error& async_arrow_formal_parameters_error() const {
+    return async_arrow_formal_parameters_error_;
+  }
+
   bool is_simple_parameter_list() const {
     return !(function_properties_ & NonSimpleParameter);
   }
@@ -219,6 +229,16 @@ class ExpressionClassifier {
     arrow_formal_parameters_error_.arg = arg;
   }
 
+  void RecordAsyncArrowFormalParametersError(const Scanner::Location& loc,
+                                             MessageTemplate::Template message,
+                                             const char* arg = nullptr) {
+    if (!is_valid_async_arrow_formal_parameters()) return;
+    invalid_productions_ |= AsyncArrowFormalParametersProduction;
+    async_arrow_formal_parameters_error_.location = loc;
+    async_arrow_formal_parameters_error_.message = message;
+    async_arrow_formal_parameters_error_.arg = arg;
+  }
+
   void RecordDuplicateFormalParameterError(const Scanner::Location& loc) {
     if (!is_valid_formal_parameter_list_without_duplicates()) return;
     invalid_productions_ |= DistinctFormalParametersProduction;
@@ -305,6 +325,9 @@ class ExpressionClassifier {
         let_pattern_error_ = inner->let_pattern_error_;
       if (errors & CoverInitializedNameProduction)
         cover_initialized_name_error_ = inner->cover_initialized_name_error_;
+      if (errors & AsyncArrowFormalParametersProduction)
+        async_arrow_formal_parameters_error_ =
+            inner->async_arrow_formal_parameters_error_;
     }
 
     // As an exception to the above, the result continues to be a valid arrow
@@ -349,6 +372,7 @@ class ExpressionClassifier {
   Error strict_mode_formal_parameter_error_;
   Error let_pattern_error_;
   Error cover_initialized_name_error_;
+  Error async_arrow_formal_parameters_error_;
   DuplicateFinder* duplicate_finder_;
 };