[esnext] implement frontend changes for async/await proposal

src/parsing/preparser.cc

Index: src/parsing/preparser.cc
diff --git a/src/parsing/preparser.cc b/src/parsing/preparser.cc
index 68372f841a7ea7811129db20ff93046c174dbbf2..2912d13ad927078ccb3d66821389d8927d4dafa7 100644
--- a/src/parsing/preparser.cc
+++ b/src/parsing/preparser.cc
@@ -67,6 +67,12 @@ PreParserIdentifier PreParserTraits::GetSymbol(Scanner* scanner) {
   if (scanner->LiteralMatches("constructor", 11)) {
     return PreParserIdentifier::Constructor();
   }
+  if (scanner->LiteralMatches("async", 5)) {
+    return PreParserIdentifier::Async();
+  }

[Dan Ehrenberg, 2016/05/06 00:08:56]

My hunch is that the parser and preparser would work out better if async were
lexed like await--in the scanner, rather than having special behavior in the
parser, with the parser then going back and treating it as an identifier when
appropriate. But either way is functional apparently.

[caitp (gmail), 2016/05/06 00:31:03]

Im not entirely sure this change is really needed anymore, actually. I think
PeekContextualKeyword makes this redundant now, maybe.

+  if (scanner->LiteralMatches("await", 5)) {
+    return PreParserIdentifier::Await();
+  }

[Dan Ehrenberg, 2016/05/06 00:08:56]

This looks like dead code. I think this case is handled by 43-44.

[caitp (gmail), 2016/05/06 00:31:03]

yes, its no longer needed since Mikes CL, will delete

   return PreParserIdentifier::Default();
 }
 
@@ -193,6 +199,15 @@ PreParser::Statement PreParser::ParseStatementListItem(bool* ok) {
         return ParseVariableStatement(kStatementListItem, ok);
       }
       break;
+    case Token::IDENTIFIER:
+      if (allow_harmony_async_await() &&
+          PeekContextualKeyword(CStrVector("async")) &&
+          PeekAhead() == Token::FUNCTION &&
+          !scanner()->HasAnyLineTerminatorAfterNext()) {
+        Consume(Token::IDENTIFIER);
+        return ParseAsyncFunctionDeclaration(ok);
+      }
+    /* falls through */
     default:
       break;
   }
@@ -397,6 +412,31 @@ PreParser::Statement PreParser::ParseHoistableDeclaration(
   return Statement::FunctionDeclaration();
 }
 
+PreParser::Statement PreParser::ParseAsyncFunctionDeclaration(bool* ok) {
+  // AsyncFunctionDeclaration ::
+  //   async [no LineTerminator here] function BindingIdentifier[Await]
+  //       ( FormalParameters[Await] ) { AsyncFunctionBody }
+  DCHECK_EQ(scanner()->current_token(), Token::IDENTIFIER);
+  DCHECK(scanner()->is_literal_contextual_keyword(CStrVector("async")));
+  int pos = position();
+  Expect(Token::FUNCTION, CHECK_OK);
+  bool is_strict_reserved = false;
+  Identifier name =
+      ParseIdentifierOrStrictReservedWord(&is_strict_reserved, CHECK_OK);
+  if (V8_UNLIKELY(is_async_function() && this->IsAwait(name))) {
+    ReportMessageAt(scanner()->location(),
+                    MessageTemplate::kAwaitBindingIdentifier);
+    *ok = false;
+    return Statement::Default();
+  }
+  ParseFunctionLiteral(name, scanner()->location(),
+                       is_strict_reserved ? kFunctionNameIsStrictReserved
+                                          : kFunctionNameValidityUnknown,
+                       FunctionKind::kAsyncFunction, pos,
+                       FunctionLiteral::kDeclaration, language_mode(),
+                       CHECK_OK);
+  return Statement::FunctionDeclaration();
+}
 
 PreParser::Statement PreParser::ParseHoistableDeclaration(bool* ok) {
   // FunctionDeclaration ::
@@ -1111,6 +1151,37 @@ PreParser::Expression PreParser::ParseFunctionLiteral(
   return Expression::Default();
 }
 
+PreParser::Expression PreParser::ParseAsyncFunctionExpression(bool* ok) {
+  // AsyncFunctionDeclaration ::
+  //   async [no LineTerminator here] function ( FormalParameters[Await] )
+  //       { AsyncFunctionBody }
+  //
+  //   async [no LineTerminator here] function BindingIdentifier[Await]
+  //       ( FormalParameters[Await] ) { AsyncFunctionBody }
+  int pos = position();
+  Expect(Token::FUNCTION, CHECK_OK);
+  bool is_strict_reserved = false;
+  Identifier name;
+  FunctionLiteral::FunctionType type = FunctionLiteral::kAnonymousExpression;
+
+  if (peek_any_identifier()) {
+    type = FunctionLiteral::kNamedExpression;
+    name = ParseIdentifierOrStrictReservedWord(&is_strict_reserved, CHECK_OK);
+    if (this->IsAwait(name)) {
+      ReportMessageAt(scanner()->location(),
+                      MessageTemplate::kAwaitBindingIdentifier);
+      *ok = false;
+      return Expression::Default();
+    }
+  }
+
+  ParseFunctionLiteral(name, scanner()->location(),
+                       is_strict_reserved ? kFunctionNameIsStrictReserved
+                                          : kFunctionNameValidityUnknown,
+                       FunctionKind::kAsyncFunction, pos, type, language_mode(),
+                       CHECK_OK);
+  return Expression::Default();
+}
 
 void PreParser::ParseLazyFunctionLiteralBody(bool* ok,
                                              Scanner::BookmarkScope* bookmark) {