[esnext] implement frontend changes for async/await proposal

src/parsing/parser-base.h

 // 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.
 
 #ifndef V8_PARSING_PARSER_BASE_H
 #define V8_PARSING_PARSER_BASE_H
 
 #include "src/ast/scopes.h"
 #include "src/bailout-reason.h"
 #include "src/hashmap.h"
@@ skipping 11 matching lines @@
   kFunctionNameIsStrictReserved,
   kSkipFunctionNameCheck,
   kFunctionNameValidityUnknown
 };
 
 enum AllowLabelledFunctionStatement {
   kAllowLabelledFunctionStatement,
   kDisallowLabelledFunctionStatement,
 };
 
+enum class ParseFunctionFlags {

[Dan Ehrenberg, 2016/05/05 01:14:40]

Cute overloading idiom. We could do this elsewhere, like PropertyAttributes.
Even define the overloading once in a templated way.

+  kIsNormal = 0,
+  kIsGenerator = 1,
+  kIsAsync = 2,
+  kIsDefault = 4
+};
+
+static inline ParseFunctionFlags operator|(ParseFunctionFlags lhs,
+                                           ParseFunctionFlags rhs) {
+  typedef unsigned char T;
+  return static_cast<ParseFunctionFlags>(static_cast<T>(lhs) |
+                                         static_cast<T>(rhs));
+}
+
+static inline ParseFunctionFlags& operator|=(ParseFunctionFlags& lhs,
+                                             const ParseFunctionFlags& rhs) {
+  lhs = lhs | rhs;
+  return lhs;
+}
+
+static inline bool operator&(ParseFunctionFlags bitfield,
+                             ParseFunctionFlags mask) {
+  typedef unsigned char T;
+  return static_cast<T>(bitfield) & static_cast<T>(mask);
+}
+
 struct FormalParametersBase {
   explicit FormalParametersBase(Scope* scope) : scope(scope) {}
   Scope* scope;
   bool has_rest = false;
   bool is_simple = true;
   int materialized_literals_count = 0;
 };
 
 
 // Common base class shared between parser and pre-parser. Traits encapsulate
@@ skipping 68 matching lines @@
         zone_(zone),
         scanner_(scanner),
         stack_overflow_(false),
         allow_lazy_(false),
         allow_natives_(false),
         allow_tailcalls_(false),
         allow_harmony_restrictive_declarations_(false),
         allow_harmony_do_expressions_(false),
         allow_harmony_for_in_(false),
         allow_harmony_function_name_(false),
-        allow_harmony_function_sent_(false) {}
+        allow_harmony_function_sent_(false),
+        allow_harmony_async_await_(false) {}
 
 #define ALLOW_ACCESSORS(name)                           \
   bool allow_##name() const { return allow_##name##_; } \
   void set_allow_##name(bool allow) { allow_##name##_ = allow; }
 
 #define SCANNER_ACCESSORS(name)                                  \
   bool allow_##name() const { return scanner_->allow_##name(); } \
   void set_allow_##name(bool allow) {                            \
     return scanner_->set_allow_##name(allow);                    \
   }
 
   ALLOW_ACCESSORS(lazy);
   ALLOW_ACCESSORS(natives);
   ALLOW_ACCESSORS(tailcalls);
   ALLOW_ACCESSORS(harmony_restrictive_declarations);
   ALLOW_ACCESSORS(harmony_do_expressions);
   ALLOW_ACCESSORS(harmony_for_in);
   ALLOW_ACCESSORS(harmony_function_name);
   ALLOW_ACCESSORS(harmony_function_sent);
+  ALLOW_ACCESSORS(harmony_async_await);
   SCANNER_ACCESSORS(harmony_exponentiation_operator);
 
 #undef SCANNER_ACCESSORS
 #undef ALLOW_ACCESSORS
 
   uintptr_t stack_limit() const { return stack_limit_; }
 
  protected:
   enum AllowRestrictedIdentifiers {
     kAllowRestrictedIdentifiers,
@@ skipping 115 matching lines @@
       this_location_ = location;
     }
     void set_super_location(Scanner::Location location) {
       super_location_ = location;
     }
     void set_return_location(Scanner::Location location) {
       return_location_ = location;
     }
 
     bool is_generator() const { return IsGeneratorFunction(kind_); }
+    bool is_async_function() const { return IsAsyncFunction(kind_); }
 
     FunctionKind kind() const { return kind_; }
     FunctionState* outer() const { return outer_function_state_; }
 
     void set_generator_object_variable(
         typename Traits::Type::GeneratorVariable* variable) {
       DCHECK(variable != NULL);
       DCHECK(is_generator());
       generator_object_variable_ = variable;
     }
@@ skipping 287 matching lines @@
       return true;
     }
     return false;
   }
 
   bool PeekContextualKeyword(Vector<const char> keyword) {
     return peek() == Token::IDENTIFIER &&
            scanner()->is_next_contextual_keyword(keyword);
   }
 
+  bool PeekAheadContextualKeyword(Vector<const char> keyword) {
+    return PeekAhead() == Token::IDENTIFIER &&
+           scanner()->is_next_next_contextual_keyword(keyword);
+  }
+
   void ExpectMetaProperty(Vector<const char> property_name,
                           const char* full_name, int pos, bool* ok);
 
   void ExpectContextualKeyword(Vector<const char> keyword, bool* ok) {
     Expect(Token::IDENTIFIER, ok);
     if (!*ok) return;
     if (!scanner()->is_literal_contextual_keyword(keyword)) {
       ReportUnexpectedToken(scanner()->current_token());
       *ok = false;
     }
@@ skipping 70 matching lines @@
       return 0;  // 0 precedence will terminate binary expression parsing
     return Token::Precedence(token);
   }
 
   typename Traits::Type::Factory* factory() {
     return function_state_->factory();
   }
 
   LanguageMode language_mode() { return scope_->language_mode(); }
   bool is_generator() const { return function_state_->is_generator(); }
+  bool is_async_function() const {
+    return function_state_->is_async_function();
+  }
 
   // Report syntax errors.
   void ReportMessage(MessageTemplate::Template message, const char* arg = NULL,
                      ParseErrorType error_type = kSyntaxError) {
     Scanner::Location source_location = scanner()->location();
     Traits::ReportMessageAt(source_location, message, arg, error_type);
   }
 
   void ReportMessageAt(Scanner::Location location,
                        MessageTemplate::Template message,
@@ skipping 66 matching lines @@
       *ok = false;
     } else if (is_strict(language_mode) &&
                !classifier->is_valid_strict_mode_formal_parameters()) {
       ReportClassifierError(classifier->strict_mode_formal_parameter_error());
       *ok = false;
     }
   }
 
   void ValidateArrowFormalParameters(const ExpressionClassifier* classifier,
                                      ExpressionT expr,
-                                     bool parenthesized_formals, bool* ok) {
+                                     bool parenthesized_formals, bool is_async,
+                                     bool* ok) {
     if (classifier->is_valid_binding_pattern()) {
       // A simple arrow formal parameter: IDENTIFIER => BODY.
       if (!this->IsIdentifier(expr)) {
         Traits::ReportMessageAt(scanner()->location(),
                                 MessageTemplate::kUnexpectedToken,
                                 Token::String(scanner()->current_token()));
         *ok = false;
       }
     } else if (!classifier->is_valid_arrow_formal_parameters()) {
       // If after parsing the expr, we see an error but the expression is
       // neither a valid binding pattern nor a valid parenthesized formal
       // parameter list, show the "arrow formal parameters" error if the formals
       // started with a parenthesis, and the binding pattern error otherwise.
       const typename ExpressionClassifier::Error& error =
           parenthesized_formals ? classifier->arrow_formal_parameters_error()
                                 : classifier->binding_pattern_error();
       ReportClassifierError(error);
       *ok = false;
     }
+    if (is_async && !classifier->is_valid_async_arrow_formal_parameters()) {
+      const typename ExpressionClassifier::Error& error =
+          classifier->async_arrow_formal_parameters_error();
+      ReportClassifierError(error);
+      *ok = false;
+    }
   }
 
   void ValidateLetPattern(const ExpressionClassifier* classifier, bool* ok) {
     if (!classifier->is_valid_let_pattern()) {
       ReportClassifierError(classifier->let_pattern_error());
       *ok = false;
     }
   }
 
   void CheckNoTailCallExpressions(const ExpressionClassifier* classifier,
@@ skipping 53 matching lines @@
     return ParseIdentifierOrStrictReservedWord(this->is_generator(),
                                                is_strict_reserved, ok);
   }
 
   IdentifierT ParseIdentifierName(bool* ok);
 
   ExpressionT ParseRegExpLiteral(bool seen_equal,
                                  ExpressionClassifier* classifier, bool* ok);
 
   ExpressionT ParsePrimaryExpression(ExpressionClassifier* classifier,
-                                     bool* ok);
+                                     bool* is_async, bool* ok);
+  ExpressionT ParsePrimaryExpression(ExpressionClassifier* classifier,
+                                     bool* ok) {
+    bool is_async;
+    return ParsePrimaryExpression(classifier, &is_async, ok);
+  }
   ExpressionT ParseExpression(bool accept_IN, bool* ok);
   ExpressionT ParseExpression(bool accept_IN, ExpressionClassifier* classifier,
                               bool* ok);
   ExpressionT ParseArrayLiteral(ExpressionClassifier* classifier, bool* ok);
   ExpressionT ParsePropertyName(IdentifierT* name, bool* is_get, bool* is_set,
-                                bool* is_computed_name,
+                                bool* is_await, bool* is_computed_name,
                                 ExpressionClassifier* classifier, bool* ok);
   ExpressionT ParseObjectLiteral(ExpressionClassifier* classifier, bool* ok);
   ObjectLiteralPropertyT ParsePropertyDefinition(
       ObjectLiteralCheckerBase* checker, bool in_class, bool has_extends,
       bool is_static, bool* is_computed_name, bool* has_seen_constructor,
       ExpressionClassifier* classifier, IdentifierT* name, bool* ok);
   typename Traits::Type::ExpressionList ParseArguments(
+      Scanner::Location* first_spread_pos, bool maybe_arrow,
+      ExpressionClassifier* classifier, bool* ok);
+  typename Traits::Type::ExpressionList ParseArguments(
       Scanner::Location* first_spread_pos, ExpressionClassifier* classifier,
-      bool* ok);
+      bool* ok) {
+    return ParseArguments(first_spread_pos, false, classifier, ok);
+  }
 
   ExpressionT ParseAssignmentExpression(bool accept_IN,
                                         ExpressionClassifier* classifier,
                                         bool* ok);
   ExpressionT ParseYieldExpression(bool accept_IN,
                                    ExpressionClassifier* classifier, bool* ok);
   ExpressionT ParseTailCallExpression(ExpressionClassifier* classifier,
                                       bool* ok);
   ExpressionT ParseConditionalExpression(bool accept_IN,
                                          ExpressionClassifier* classifier,
                                          bool* ok);
   ExpressionT ParseBinaryExpression(int prec, bool accept_IN,
                                     ExpressionClassifier* classifier, bool* ok);
   ExpressionT ParseUnaryExpression(ExpressionClassifier* classifier, bool* ok);
   ExpressionT ParsePostfixExpression(ExpressionClassifier* classifier,
                                      bool* ok);
   ExpressionT ParseLeftHandSideExpression(ExpressionClassifier* classifier,
                                           bool* ok);
   ExpressionT ParseMemberWithNewPrefixesExpression(
-      ExpressionClassifier* classifier, bool* ok);
-  ExpressionT ParseMemberExpression(ExpressionClassifier* classifier, bool* ok);
+      ExpressionClassifier* classifier, bool* is_async, bool* ok);
+  ExpressionT ParseMemberExpression(ExpressionClassifier* classifier,
+                                    bool* is_async, bool* ok);
   ExpressionT ParseMemberExpressionContinuation(
-      ExpressionT expression, ExpressionClassifier* classifier, bool* ok);
+      ExpressionT expression, bool* is_async, ExpressionClassifier* classifier,
+      bool* ok);
   ExpressionT ParseArrowFunctionLiteral(bool accept_IN,
                                         const FormalParametersT& parameters,
+                                        bool is_async,
                                         const ExpressionClassifier& classifier,
                                         bool* ok);
   ExpressionT ParseTemplateLiteral(ExpressionT tag, int start,
                                    ExpressionClassifier* classifier, bool* ok);
   void AddTemplateExpression(ExpressionT);
   ExpressionT ParseSuperExpression(bool is_new,
                                    ExpressionClassifier* classifier, bool* ok);
   ExpressionT ParseNewTargetExpression(bool* ok);
 
   void ParseFormalParameter(FormalParametersT* parameters,
@@ skipping 122 matching lines @@
   bool stack_overflow_;
 
   bool allow_lazy_;
   bool allow_natives_;
   bool allow_tailcalls_;
   bool allow_harmony_restrictive_declarations_;
   bool allow_harmony_do_expressions_;
   bool allow_harmony_for_in_;
   bool allow_harmony_function_name_;
   bool allow_harmony_function_sent_;
+  bool allow_harmony_async_await_;
 };
 
 template <class Traits>
 ParserBase<Traits>::FunctionState::FunctionState(
     FunctionState** function_state_stack, Scope** scope_stack, Scope* scope,
     FunctionKind kind, typename Traits::Type::Factory* factory)
     : next_materialized_literal_index_(0),
       expected_property_count_(0),
       this_location_(Scanner::Location::invalid()),
       return_location_(Scanner::Location::invalid()),
@@ skipping 140 matching lines @@
     }
     if (this->IsArguments(name)) {
       scope_->RecordArgumentsUsage();
       classifier->RecordStrictModeFormalParameterError(
           scanner()->location(), MessageTemplate::kStrictEvalArguments);
       if (is_strict(language_mode())) {
         classifier->RecordBindingPatternError(
             scanner()->location(), MessageTemplate::kStrictEvalArguments);
       }
     }
+    if (this->IsAwait(name)) {
+      if (is_async_function()) {
+        classifier->RecordPatternError(
+            scanner()->location(), MessageTemplate::kAwaitBindingIdentifier);
+      }
+      classifier->RecordAsyncArrowFormalParametersError(
+          scanner()->location(), MessageTemplate::kAwaitBindingIdentifier);

[Dan Ehrenberg, 2016/05/05 01:14:40]

"await is only treated as a FutureReservedWord when Module is the goal symbol of
the syntactic grammar." (from ES2015)
"await is always parsed as an AwaitExpression but is a Syntax Error via static
semantics." (from the async await spec)

I'm not sure what either of these ends up having to do with arrow functions...
I'm a bit confused by the grammars.

[caitp (gmail), 2016/05/05 01:36:57]

Ideally we'd have a variety of versions of this message for the different causes
(but that's a bit harder in v8 than in JSC).

Basically, in an async function, you can't use `await` as a parameter name (or
as a BindingIdentifier within the function body) --- so that's what the error is
meant to communicate.

+    }
 
     if (classifier->duplicate_finder() != nullptr &&
         scanner()->FindSymbol(classifier->duplicate_finder(), 1) != 0) {
       classifier->RecordDuplicateFormalParameterError(scanner()->location());
     }
     return name;
   } else if (is_sloppy(language_mode()) &&
              (next == Token::FUTURE_STRICT_RESERVED_WORD ||
               next == Token::ESCAPED_STRICT_RESERVED_WORD ||
               next == Token::LET || next == Token::STATIC ||
@@ skipping 32 matching lines @@
              next == Token::STATIC || (next == Token::YIELD && !is_generator)) {
     *is_strict_reserved = true;
   } else {
     ReportUnexpectedToken(next);
     *ok = false;
     return Traits::EmptyIdentifier();
   }
 
   IdentifierT name = this->GetSymbol(scanner());
   if (this->IsArguments(name)) scope_->RecordArgumentsUsage();
+

[Dan Ehrenberg, 2016/05/05 01:14:40]

Spurious whitespace change.

[caitp (gmail), 2016/05/05 01:36:57]

Acknowledged.

   return name;
 }
 
 template <class Traits>
 typename ParserBase<Traits>::IdentifierT
 ParserBase<Traits>::ParseIdentifierName(bool* ok) {
   Token::Value next = Next();
   if (next != Token::IDENTIFIER && next != Token::ENUM &&
       next != Token::AWAIT && next != Token::LET && next != Token::STATIC &&
       next != Token::YIELD && next != Token::FUTURE_STRICT_RESERVED_WORD &&
@@ skipping 43 matching lines @@
 #define DUMMY )  // to make indentation work
 #undef DUMMY
 
 // Used in functions where the return type is not ExpressionT.
 #define CHECK_OK_CUSTOM(x) ok); \
   if (!*ok) return this->x(); \
   ((void)0
 #define DUMMY )  // to make indentation work
 #undef DUMMY
 
-

[Dan Ehrenberg, 2016/05/05 01:14:40]

Spurious whitespace change.

 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParsePrimaryExpression(ExpressionClassifier* classifier,
-                                           bool* ok) {
+                                           bool* is_async, bool* ok) {
   // PrimaryExpression ::
   //   'this'
   //   'null'
   //   'true'
   //   'false'
   //   Identifier
   //   Number
   //   String
   //   ArrayLiteral
   //   ObjectLiteral
   //   RegExpLiteral
   //   ClassLiteral
   //   '(' Expression ')'
   //   TemplateLiteral
   //   do Block
+  //   AsyncFunctionExpression
 
   int beg_pos = peek_position();
   switch (peek()) {
     case Token::THIS: {
       BindingPatternUnexpectedToken(classifier);
       Consume(Token::THIS);
       return this->ThisExpression(scope_, factory(), beg_pos);
     }
 
     case Token::NULL_LITERAL:
     case Token::TRUE_LITERAL:
     case Token::FALSE_LITERAL:
       BindingPatternUnexpectedToken(classifier);
       return this->ExpressionFromLiteral(Next(), beg_pos, scanner(), factory());
     case Token::SMI:
     case Token::NUMBER:
       BindingPatternUnexpectedToken(classifier);
       return this->ExpressionFromLiteral(Next(), beg_pos, scanner(), factory());
 
     case Token::IDENTIFIER:
+      if (allow_harmony_async_await() &&
+          PeekContextualKeyword(CStrVector("async")) &&
+          !scanner()->HasAnyLineTerminatorAfterNext()) {
+        if (PeekAhead() == Token::FUNCTION) {
+          Consume(Token::IDENTIFIER);
+          return this->ParseAsyncFunctionExpression(CHECK_OK);
+        }
+        // CoverCallExpressionAndAsyncArrowHead
+        *is_async = true;
+      }
+    /* Falls through */
     case Token::LET:
     case Token::STATIC:
     case Token::YIELD:
     case Token::AWAIT:
     case Token::ESCAPED_STRICT_RESERVED_WORD:
     case Token::FUTURE_STRICT_RESERVED_WORD: {
       // Using eval or arguments in this context is OK even in strict mode.
       IdentifierT name = ParseAndClassifyIdentifier(classifier, CHECK_OK);
       return this->ExpressionFromIdentifier(
           name, beg_pos, scanner()->location().end_pos, scope_, factory());
@@ skipping 250 matching lines @@
 
   ExpressionT result = factory()->NewArrayLiteral(values, first_spread_index,
                                                   literal_index, pos);
   if (first_spread_index >= 0) {
     result = factory()->NewRewritableExpression(result);
     Traits::QueueNonPatternForRewriting(result);
   }
   return result;
 }
 
-
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT ParserBase<Traits>::ParsePropertyName(
-    IdentifierT* name, bool* is_get, bool* is_set, bool* is_computed_name,
-    ExpressionClassifier* classifier, bool* ok) {
+    IdentifierT* name, bool* is_get, bool* is_set, bool* is_await,
+    bool* is_computed_name, ExpressionClassifier* classifier, bool* ok) {
   Token::Value token = peek();
   int pos = peek_position();
 
   // For non computed property names we normalize the name a bit:
   //
   //   "12" -> 12
   //   12.3 -> "12.3"
   //   12.30 -> "12.3"
   //   identifier -> "identifier"
   //
@@ skipping 24 matching lines @@
       Traits::RewriteNonPattern(&computed_name_classifier, CHECK_OK);
       classifier->Accumulate(&computed_name_classifier,
                              ExpressionClassifier::ExpressionProductions);
       Expect(Token::RBRACK, CHECK_OK);
       return expression;
     }
 
     default:
       *name = ParseIdentifierName(CHECK_OK);
       scanner()->IsGetOrSet(is_get, is_set);
+      if (this->IsAwait(*name)) {
+        *is_await = true;
+      }
       break;
   }
 
   uint32_t index;
   return this->IsArrayIndex(*name, &index)
              ? factory()->NewNumberLiteral(index, pos)
              : factory()->NewStringLiteral(*name, pos);
 }
 
 
 template <class Traits>
 typename ParserBase<Traits>::ObjectLiteralPropertyT
 ParserBase<Traits>::ParsePropertyDefinition(
     ObjectLiteralCheckerBase* checker, bool in_class, bool has_extends,
     bool is_static, bool* is_computed_name, bool* has_seen_constructor,
     ExpressionClassifier* classifier, IdentifierT* name, bool* ok) {
   DCHECK(!in_class || is_static || has_seen_constructor != nullptr);
   ExpressionT value = this->EmptyExpression();
   bool is_get = false;
   bool is_set = false;
+  bool is_await = false;
   bool is_generator = Check(Token::MUL);
 
   Token::Value name_token = peek();
+
+  bool is_async = allow_harmony_async_await() && !is_generator &&
+                  name_token == Token::IDENTIFIER &&
+                  PeekContextualKeyword(CStrVector("async")) &&
+                  !scanner()->HasAnyLineTerminatorAfterNext() &&
+                  PeekAhead() != Token::LPAREN;
+
   int next_beg_pos = scanner()->peek_location().beg_pos;
   int next_end_pos = scanner()->peek_location().end_pos;
-  ExpressionT name_expression =
-      ParsePropertyName(name, &is_get, &is_set, is_computed_name, classifier,
-                        CHECK_OK_CUSTOM(EmptyObjectLiteralProperty));
+  ExpressionT name_expression = ParsePropertyName(
+      name, &is_get, &is_set, &is_await, is_computed_name, classifier,
+      CHECK_OK_CUSTOM(EmptyObjectLiteralProperty));
 
   if (fni_ != nullptr && !*is_computed_name) {
     this->PushLiteralName(fni_, *name);
   }
 
   if (!in_class && !is_generator) {
     DCHECK(!is_static);
 
     if (peek() == Token::COLON) {
       // PropertyDefinition
@@ skipping 24 matching lines @@
       // CoverInitializedName
       //    IdentifierReference Initializer?
       if (classifier->duplicate_finder() != nullptr &&
           scanner()->FindSymbol(classifier->duplicate_finder(), 1) != 0) {
         classifier->RecordDuplicateFormalParameterError(scanner()->location());
       }
       if (name_token == Token::LET) {
         classifier->RecordLetPatternError(
             scanner()->location(), MessageTemplate::kLetInLexicalBinding);
       }
-
+      if (is_await && is_async_function()) {
+        classifier->RecordPatternError(
+            Scanner::Location(next_beg_pos, next_end_pos),
+            MessageTemplate::kAwaitBindingIdentifier);
+      }
       ExpressionT lhs = this->ExpressionFromIdentifier(
           *name, next_beg_pos, next_end_pos, scope_, factory());
       CheckDestructuringElement(lhs, classifier, next_beg_pos, next_end_pos);
 
       if (peek() == Token::ASSIGN) {
         Consume(Token::ASSIGN);
         ExpressionClassifier rhs_classifier(this);
         ExpressionT rhs = this->ParseAssignmentExpression(
             true, &rhs_classifier, CHECK_OK_CUSTOM(EmptyObjectLiteralProperty));
         Traits::RewriteNonPattern(&rhs_classifier,
@@ skipping 17 matching lines @@
           name_expression, value, ObjectLiteralProperty::COMPUTED, false,
           false);
     }
   }
 
   // Method definitions are never valid in patterns.
   classifier->RecordPatternError(
       Scanner::Location(next_beg_pos, scanner()->location().end_pos),
       MessageTemplate::kInvalidDestructuringTarget);
 
+  if (is_async) {
+    DCHECK(!is_generator);
+    DCHECK(!is_get);
+    DCHECK(!is_set);
+    bool dont_care;
+    name_expression = ParsePropertyName(
+        name, &dont_care, &dont_care, &dont_care, is_computed_name, classifier,
+        CHECK_OK_CUSTOM(EmptyObjectLiteralProperty));
+  }
+
   if (is_generator || peek() == Token::LPAREN) {
     // MethodDefinition
     //    PropertyName '(' StrictFormalParameters ')' '{' FunctionBody '}'
     //    '*' PropertyName '(' StrictFormalParameters ')' '{' FunctionBody '}'
     if (!*is_computed_name) {
       checker->CheckProperty(name_token, kMethodProperty, is_static,
                              is_generator,
                              CHECK_OK_CUSTOM(EmptyObjectLiteralProperty));
     }
 
-    FunctionKind kind = is_generator ? FunctionKind::kConciseGeneratorMethod
-                                     : FunctionKind::kConciseMethod;
+    FunctionKind kind = is_generator
+                            ? FunctionKind::kConciseGeneratorMethod
+                            : is_async ? FunctionKind::kAsyncConciseMethod
+                                       : FunctionKind::kConciseMethod;
 
     if (in_class && !is_static && this->IsConstructor(*name)) {
       *has_seen_constructor = true;
       kind = has_extends ? FunctionKind::kSubclassConstructor
                          : FunctionKind::kBaseConstructor;
     }
 
     value = this->ParseFunctionLiteral(
         *name, scanner()->location(), kSkipFunctionNameCheck, kind,
         RelocInfo::kNoPosition, FunctionLiteral::kAccessorOrMethod,
@@ skipping 17 matching lines @@
 
   if (is_get || is_set) {
     // MethodDefinition (Accessors)
     //    get PropertyName '(' ')' '{' FunctionBody '}'
     //    set PropertyName '(' PropertySetParameterList ')' '{' FunctionBody '}'
     *name = this->EmptyIdentifier();
     bool dont_care = false;
     name_token = peek();
 
     name_expression = ParsePropertyName(
-        name, &dont_care, &dont_care, is_computed_name, classifier,
+        name, &dont_care, &dont_care, &dont_care, is_computed_name, classifier,
         CHECK_OK_CUSTOM(EmptyObjectLiteralProperty));
 
     if (!*is_computed_name) {
       checker->CheckProperty(name_token, kAccessorProperty, is_static,
                              is_generator,
                              CHECK_OK_CUSTOM(EmptyObjectLiteralProperty));
     }
 
     typename Traits::Type::FunctionLiteral value = this->ParseFunctionLiteral(
         *name, scanner()->location(), kSkipFunctionNameCheck,
@@ skipping 74 matching lines @@
 
   // Computation of literal_index must happen before pre parse bailout.
   int literal_index = function_state_->NextMaterializedLiteralIndex();
 
   return factory()->NewObjectLiteral(properties,
                                      literal_index,
                                      number_of_boilerplate_properties,
                                      pos);
 }
 
-
 template <class Traits>
 typename Traits::Type::ExpressionList ParserBase<Traits>::ParseArguments(
-    Scanner::Location* first_spread_arg_loc, ExpressionClassifier* classifier,
-    bool* ok) {
+    Scanner::Location* first_spread_arg_loc, bool maybe_arrow,
+    ExpressionClassifier* classifier, bool* ok) {
   // Arguments ::
   //   '(' (AssignmentExpression)*[','] ')'
 
   Scanner::Location spread_arg = Scanner::Location::invalid();
   typename Traits::Type::ExpressionList result =
       this->NewExpressionList(4, zone_);
   Expect(Token::LPAREN, CHECK_OK_CUSTOM(NullExpressionList));
   bool done = (peek() == Token::RPAREN);
   bool was_unspread = false;
   int unspread_sequences_count = 0;
@@ skipping 35 matching lines @@
     }
   }
   Scanner::Location location = scanner_->location();
   if (Token::RPAREN != Next()) {
     ReportMessageAt(location, MessageTemplate::kUnterminatedArgList);
     *ok = false;
     return this->NullExpressionList();
   }
   *first_spread_arg_loc = spread_arg;
 
-  if (spread_arg.IsValid()) {
+  if ((!maybe_arrow || peek() != Token::ARROW) && spread_arg.IsValid()) {
     // Unspread parameter sequences are translated into array literals in the
     // parser. Ensure that the number of materialized literals matches between
     // the parser and preparser
     Traits::MaterializeUnspreadArgumentsLiterals(unspread_sequences_count);
   }
 
   return result;
 }
 
 // Precedence = 2
@@ skipping 11 matching lines @@
   int lhs_beg_pos = peek_position();
 
   if (peek() == Token::YIELD && is_generator()) {
     return this->ParseYieldExpression(accept_IN, classifier, ok);
   }
 
   FuncNameInferrer::State fni_state(fni_);
   ParserBase<Traits>::Checkpoint checkpoint(this);
   ExpressionClassifier arrow_formals_classifier(this,
                                                 classifier->duplicate_finder());
+
+  bool is_async = allow_harmony_async_await() && peek() == Token::IDENTIFIER &&
+                  PeekContextualKeyword(CStrVector("async")) &&
+                  !scanner()->HasAnyLineTerminatorAfterNext();
+
   bool parenthesized_formals = peek() == Token::LPAREN;
-  if (!parenthesized_formals) {
+  if (!is_async && !parenthesized_formals) {
     ArrowFormalParametersUnexpectedToken(&arrow_formals_classifier);
   }
   ExpressionT expression = this->ParseConditionalExpression(
       accept_IN, &arrow_formals_classifier, CHECK_OK);
+
+  if (is_async && peek_any_identifier() && PeekAhead() == Token::ARROW) {
+    // async Identifier => AsyncConciseBody
+    IdentifierT name =
+        ParseAndClassifyIdentifier(&arrow_formals_classifier, CHECK_OK);
+    expression = this->ExpressionFromIdentifier(
+        name, position(), scanner()->location().end_pos, scope_, factory());
+  }
+
   if (peek() == Token::ARROW) {
     classifier->RecordPatternError(scanner()->peek_location(),
                                    MessageTemplate::kUnexpectedToken,
                                    Token::String(Token::ARROW));
     ValidateArrowFormalParameters(&arrow_formals_classifier, expression,
-                                  parenthesized_formals, CHECK_OK);
+                                  parenthesized_formals, is_async, CHECK_OK);
     // This reads strangely, but is correct: it checks whether any
     // sub-expression of the parameter list failed to be a valid formal
     // parameter initializer. Since YieldExpressions are banned anywhere
     // in an arrow parameter list, this is correct.
     // TODO(adamk): Rename "FormalParameterInitializerError" to refer to
     // "YieldExpression", which is its only use.
     ValidateFormalParameterInitializer(&arrow_formals_classifier, ok);
+
     Scanner::Location loc(lhs_beg_pos, scanner()->location().end_pos);
     Scope* scope =
         this->NewScope(scope_, FUNCTION_SCOPE, 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.
     scope_->PropagateUsageFlagsToScope(scope);
     FormalParametersT parameters(scope);
     if (!arrow_formals_classifier.is_simple_parameter_list()) {
       scope->SetHasNonSimpleParameters();
       parameters.is_simple = false;
     }
 
     checkpoint.Restore(&parameters.materialized_literals_count);
 
     scope->set_start_position(lhs_beg_pos);
     Scanner::Location duplicate_loc = Scanner::Location::invalid();
     this->ParseArrowFunctionFormalParameterList(&parameters, expression, loc,
                                                 &duplicate_loc, CHECK_OK);
     if (duplicate_loc.IsValid()) {
       arrow_formals_classifier.RecordDuplicateFormalParameterError(
           duplicate_loc);
     }
     expression = this->ParseArrowFunctionLiteral(
-        accept_IN, parameters, arrow_formals_classifier, CHECK_OK);
+        accept_IN, parameters, is_async, arrow_formals_classifier, CHECK_OK);
 
     if (fni_ != nullptr) fni_->Infer();
 
     return expression;
   }
 
   if (this->IsValidReferenceExpression(expression)) {
     arrow_formals_classifier.ForgiveAssignmentPatternError();
   }
 
   // "expression" was not itself an arrow function parameter list, but it might
   // form part of one.  Propagate speculative formal parameter error locations.
   // Do not merge pending non-pattern expressions yet!
   classifier->Accumulate(
       &arrow_formals_classifier,
       ExpressionClassifier::StandardProductions |
-      ExpressionClassifier::FormalParametersProductions |
-      ExpressionClassifier::CoverInitializedNameProduction,
+          ExpressionClassifier::FormalParametersProductions |
+          ExpressionClassifier::CoverInitializedNameProduction |
+          ExpressionClassifier::AsyncArrowFormalParametersProduction,
       false);
 
   if (!Token::IsAssignmentOp(peek())) {
     // Parsed conditional expression only (no assignment).
     // Now pending non-pattern expressions must be merged.
     classifier->MergeNonPatterns(&arrow_formals_classifier);
     return expression;
   }
 
   // Now pending non-pattern expressions must be discarded.
@@ skipping 282 matching lines @@
   //   PostfixExpression
   //   'delete' UnaryExpression
   //   'void' UnaryExpression
   //   'typeof' UnaryExpression
   //   '++' UnaryExpression
   //   '--' UnaryExpression
   //   '+' UnaryExpression
   //   '-' UnaryExpression
   //   '~' UnaryExpression
   //   '!' UnaryExpression
+  //   [+Await] AwaitExpression[?Yield]
 
   Token::Value op = peek();
   if (Token::IsUnaryOp(op)) {
     BindingPatternUnexpectedToken(classifier);
     ArrowFormalParametersUnexpectedToken(classifier);
 
     op = Next();
     int pos = position();
     ExpressionT expression = ParseUnaryExpression(classifier, CHECK_OK);
     CheckNoTailCallExpressions(classifier, CHECK_OK);
@@ skipping 27 matching lines @@
         expression, beg_pos, scanner()->location().end_pos,
         MessageTemplate::kInvalidLhsInPrefixOp, CHECK_OK);
     this->MarkExpressionAsAssigned(expression);
     Traits::RewriteNonPattern(classifier, CHECK_OK);
 
     return factory()->NewCountOperation(op,
                                         true /* prefix */,
                                         expression,
                                         position());
 
+  } else if (is_async_function() && peek() == Token::AWAIT) {
+    int beg_pos = peek_position();
+    Consume(Token::AWAIT);
+    ExpressionT value = ParseUnaryExpression(classifier, CHECK_OK);
+
+    classifier->RecordFormalParameterInitializerError(
+        Scanner::Location(beg_pos, scanner()->location().end_pos),
+        MessageTemplate::kAwaitExpressionFormalParameter);
+
+    return Traits::RewriteAwaitExpression(value, beg_pos);
   } else {
     return this->ParsePostfixExpression(classifier, ok);
   }
 }
 
 
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParsePostfixExpression(ExpressionClassifier* classifier,
                                            bool* ok) {
@@ skipping 29 matching lines @@
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParseLeftHandSideExpression(
     ExpressionClassifier* classifier, bool* ok) {
   // LeftHandSideExpression ::
   //   (NewExpression | MemberExpression) ...
 
   if (FLAG_harmony_explicit_tailcalls && peek() == Token::CONTINUE) {
     return this->ParseTailCallExpression(classifier, ok);
   }
 
-  ExpressionT result =
-      this->ParseMemberWithNewPrefixesExpression(classifier, CHECK_OK);
+  bool is_async = false;
+  ExpressionT result = this->ParseMemberWithNewPrefixesExpression(
+      classifier, &is_async, CHECK_OK);
 
   while (true) {
     switch (peek()) {
       case Token::LBRACK: {
         CheckNoTailCallExpressions(classifier, CHECK_OK);
         Traits::RewriteNonPattern(classifier, CHECK_OK);
         BindingPatternUnexpectedToken(classifier);
         ArrowFormalParametersUnexpectedToken(classifier);
         Consume(Token::LBRACK);
         int pos = position();
         ExpressionT index = ParseExpression(true, classifier, CHECK_OK);
         Traits::RewriteNonPattern(classifier, CHECK_OK);
         result = factory()->NewProperty(result, index, pos);
         Expect(Token::RBRACK, CHECK_OK);
         break;
       }
 
       case Token::LPAREN: {
         CheckNoTailCallExpressions(classifier, CHECK_OK);
+        int pos;
         Traits::RewriteNonPattern(classifier, CHECK_OK);
         BindingPatternUnexpectedToken(classifier);
-        ArrowFormalParametersUnexpectedToken(classifier);
-
-        int pos;
         if (scanner()->current_token() == Token::IDENTIFIER ||
             scanner()->current_token() == Token::SUPER) {
           // For call of an identifier we want to report position of
           // the identifier as position of the call in the stack trace.
           pos = position();
         } else {
           // For other kinds of calls we record position of the parenthesis as
           // position of the call. Note that this is extremely important for
           // expressions of the form function(){...}() for which call position
           // should not point to the closing brace otherwise it will intersect
           // with positions recorded for function literal and confuse debugger.
           pos = peek_position();
           // Also the trailing parenthesis are a hint that the function will
           // be called immediately. If we happen to have parsed a preceding
           // function literal eagerly, we can also compile it eagerly.
           if (result->IsFunctionLiteral() && mode() == PARSE_EAGERLY) {
             result->AsFunctionLiteral()->set_should_eager_compile();
           }
         }
         Scanner::Location spread_pos;
         typename Traits::Type::ExpressionList args =
-            ParseArguments(&spread_pos, classifier, CHECK_OK);
+            ParseArguments(&spread_pos, is_async, classifier, CHECK_OK);
+
+        if (V8_UNLIKELY(is_async && peek() == Token::ARROW)) {
+          if (args->length()) {
+            // async ( Arguments ) => ...
+            return Traits::ExpressionListToExpression(args);
+          }
+          // async () => ...
+          return factory()->NewEmptyParentheses(pos);
+        }
+
+        ArrowFormalParametersUnexpectedToken(classifier);
 
         // Keep track of eval() calls since they disable all local variable
         // optimizations.
         // The calls that need special treatment are the
         // direct eval calls. These calls are all of the form eval(...), with
         // no explicit receiver.
         // These calls are marked as potentially direct eval calls. Whether
         // they are actually direct calls to eval is determined at run time.
         this->CheckPossibleEvalCall(result, scope_);
 
@@ skipping 40 matching lines @@
         result = ParseTemplateLiteral(result, position(), classifier, CHECK_OK);
         break;
       }
 
       default:
         return result;
     }
   }
 }
 
-
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParseMemberWithNewPrefixesExpression(
-    ExpressionClassifier* classifier, bool* ok) {
+    ExpressionClassifier* classifier, bool* is_async, bool* ok) {
   // NewExpression ::
   //   ('new')+ MemberExpression
   //
   // NewTarget ::
   //   'new' '.' 'target'
 
   // The grammar for new expressions is pretty warped. We can have several 'new'
   // keywords following each other, and then a MemberExpression. When we see '('
   // after the MemberExpression, it's associated with the rightmost unassociated
   // 'new' to create a NewExpression with arguments. However, a NewExpression
@@ skipping 12 matching lines @@
     ArrowFormalParametersUnexpectedToken(classifier);
     Consume(Token::NEW);
     int new_pos = position();
     ExpressionT result = this->EmptyExpression();
     if (peek() == Token::SUPER) {
       const bool is_new = true;
       result = ParseSuperExpression(is_new, classifier, CHECK_OK);
     } else if (peek() == Token::PERIOD) {
       return ParseNewTargetExpression(CHECK_OK);
     } else {
-      result = this->ParseMemberWithNewPrefixesExpression(classifier, CHECK_OK);
+      result = this->ParseMemberWithNewPrefixesExpression(classifier, is_async,
+                                                          CHECK_OK);
     }
     Traits::RewriteNonPattern(classifier, CHECK_OK);
     if (peek() == Token::LPAREN) {
       // NewExpression with arguments.
       Scanner::Location spread_pos;
       typename Traits::Type::ExpressionList args =
           this->ParseArguments(&spread_pos, classifier, CHECK_OK);
 
       if (spread_pos.IsValid()) {
         args = Traits::PrepareSpreadArguments(args);
         result = Traits::SpreadCallNew(result, args, new_pos);
       } else {
         result = factory()->NewCallNew(result, args, new_pos);
       }
       // The expression can still continue with . or [ after the arguments.
-      result =
-          this->ParseMemberExpressionContinuation(result, classifier, CHECK_OK);
+      result = this->ParseMemberExpressionContinuation(result, is_async,
+                                                       classifier, CHECK_OK);
       return result;
     }
     // NewExpression without arguments.
     return factory()->NewCallNew(result, this->NewExpressionList(0, zone_),
                                  new_pos);
   }
   // No 'new' or 'super' keyword.
-  return this->ParseMemberExpression(classifier, ok);
+  return this->ParseMemberExpression(classifier, is_async, ok);
 }
 
-
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParseMemberExpression(ExpressionClassifier* classifier,
-                                          bool* ok) {
+                                          bool* is_async, bool* ok) {
   // MemberExpression ::
   //   (PrimaryExpression | FunctionLiteral | ClassLiteral)
   //     ('[' Expression ']' | '.' Identifier | Arguments | TemplateLiteral)*
 
   // The '[' Expression ']' and '.' Identifier parts are parsed by
   // ParseMemberExpressionContinuation, and the Arguments part is parsed by the
   // caller.
 
   // Parse the initial primary or function expression.
   ExpressionT result = this->EmptyExpression();
@@ skipping 36 matching lines @@
         name, function_name_location,
         is_strict_reserved_name ? kFunctionNameIsStrictReserved
                                 : kFunctionNameValidityUnknown,
         is_generator ? FunctionKind::kGeneratorFunction
                      : FunctionKind::kNormalFunction,
         function_token_position, function_type, language_mode(), CHECK_OK);
   } else if (peek() == Token::SUPER) {
     const bool is_new = false;
     result = ParseSuperExpression(is_new, classifier, CHECK_OK);
   } else {
-    result = ParsePrimaryExpression(classifier, CHECK_OK);
+    result = ParsePrimaryExpression(classifier, is_async, CHECK_OK);
   }
 
-  result = ParseMemberExpressionContinuation(result, classifier, CHECK_OK);
+  result =
+      ParseMemberExpressionContinuation(result, is_async, classifier, CHECK_OK);
   return result;
 }
 
 
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParseSuperExpression(bool is_new,
                                          ExpressionClassifier* classifier,
                                          bool* ok) {
   Expect(Token::SUPER, CHECK_OK);
@@ skipping 46 matching lines @@
   if (!scope_->ReceiverScope()->is_function_scope()) {
     ReportMessageAt(scanner()->location(),
                     MessageTemplate::kUnexpectedNewTarget);
     *ok = false;
     return this->EmptyExpression();
   }
 
   return this->NewTargetExpression(scope_, factory(), pos);
 }
 
-
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParseMemberExpressionContinuation(
-    ExpressionT expression, ExpressionClassifier* classifier, bool* ok) {
+    ExpressionT expression, bool* is_async, ExpressionClassifier* classifier,
+    bool* ok) {
   // Parses this part of MemberExpression:
   // ('[' Expression ']' | '.' Identifier | TemplateLiteral)*
   while (true) {
     switch (peek()) {
       case Token::LBRACK: {
+        *is_async = false;
         Traits::RewriteNonPattern(classifier, CHECK_OK);
         BindingPatternUnexpectedToken(classifier);
         ArrowFormalParametersUnexpectedToken(classifier);
 
         Consume(Token::LBRACK);
         int pos = position();
         ExpressionT index = this->ParseExpression(true, classifier, CHECK_OK);
         Traits::RewriteNonPattern(classifier, CHECK_OK);
         expression = factory()->NewProperty(expression, index, pos);
         if (fni_ != NULL) {
           this->PushPropertyName(fni_, index);
         }
         Expect(Token::RBRACK, CHECK_OK);
         break;
       }
       case Token::PERIOD: {
+        *is_async = false;
         Traits::RewriteNonPattern(classifier, CHECK_OK);
         BindingPatternUnexpectedToken(classifier);
         ArrowFormalParametersUnexpectedToken(classifier);
 
         Consume(Token::PERIOD);
         int pos = position();
         IdentifierT name = ParseIdentifierName(CHECK_OK);
         expression = factory()->NewProperty(
             expression, factory()->NewStringLiteral(name, pos), pos);
         if (fni_ != NULL) {
           this->PushLiteralName(fni_, name);
         }
         break;
       }
       case Token::TEMPLATE_SPAN:
       case Token::TEMPLATE_TAIL: {
+        *is_async = false;
         Traits::RewriteNonPattern(classifier, CHECK_OK);
         BindingPatternUnexpectedToken(classifier);
         ArrowFormalParametersUnexpectedToken(classifier);
         int pos;
         if (scanner()->current_token() == Token::IDENTIFIER) {
           pos = position();
         } else {
           pos = peek_position();
           if (expression->IsFunctionLiteral() && mode() == PARSE_EAGERLY) {
             // If the tag function looks like an IIFE, set_parenthesized() to
@@ skipping 148 matching lines @@
     case Token::STATIC:
     case Token::LET:  // Yes, you can do let let = ... in sloppy mode
     case Token::YIELD:
     case Token::AWAIT:
       return true;
     default:
       return false;
   }
 }
 
-
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParseArrowFunctionLiteral(
-    bool accept_IN, const FormalParametersT& formal_parameters,
+    bool accept_IN, const FormalParametersT& formal_parameters, bool is_async,
     const ExpressionClassifier& formals_classifier, bool* ok) {
   if (peek() == Token::ARROW && scanner_->HasAnyLineTerminatorBeforeNext()) {
     // ASI inserts `;` after arrow parameters if a line terminator is found.
     // `=> ...` is never a valid expression, so report as syntax error.
     // If next token is not `=>`, it's a syntax error anyways.
     ReportUnexpectedTokenAt(scanner_->peek_location(), Token::ARROW);
     *ok = false;
     return this->EmptyExpression();
   }
 
   typename Traits::Type::StatementList body;
   int num_parameters = formal_parameters.scope->num_parameters();
   int materialized_literal_count = -1;
   int expected_property_count = -1;
   Scanner::Location super_loc;
 
   {
     typename Traits::Type::Factory function_factory(ast_value_factory());
-    FunctionState function_state(&function_state_, &scope_,
-                                 formal_parameters.scope, kArrowFunction,
-                                 &function_factory);
+    FunctionState function_state(
+        &function_state_, &scope_, formal_parameters.scope,
+        is_async ? kAsyncArrowFunction : kArrowFunction, &function_factory);
 
     function_state.SkipMaterializedLiterals(
         formal_parameters.materialized_literals_count);
 
     this->ReindexLiterals(formal_parameters);
 
     Expect(Token::ARROW, CHECK_OK);
 
     if (peek() == Token::LBRACE) {
       // Multiple statement body
@@ skipping 287 matching lines @@
     has_seen_constructor_ = true;
     return;
   }
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_PARSING_PARSER_BASE_H