[esnext] implement frontend changes for async/await proposal

src/parsing/preparser.cc

 // Copyright 2011 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.
 
 #include <cmath>
 
 #include "src/allocation.h"
 #include "src/base/logging.h"
 #include "src/conversions-inl.h"
 #include "src/conversions.h"
@@ skipping 49 matching lines @@
   }
   if (scanner->UnescapedLiteralMatches("undefined", 9)) {
     return PreParserIdentifier::Undefined();
   }
   if (scanner->LiteralMatches("prototype", 9)) {
     return PreParserIdentifier::Prototype();
   }
   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();
 }
 
 
 PreParserIdentifier PreParserTraits::GetNumberAsSymbol(Scanner* scanner) {
   return PreParserIdentifier::Default();
 }
 
 
 PreParserExpression PreParserTraits::ExpressionFromString(
@@ skipping 106 matching lines @@
       return ParseHoistableDeclaration(ok);
     case Token::CLASS:
       return ParseClassDeclaration(ok);
     case Token::CONST:
       return ParseVariableStatement(kStatementListItem, ok);
     case Token::LET:
       if (IsNextLetKeyword()) {
         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;
   }
   return ParseStatement(kAllowLabelledFunctionStatement, ok);
 }
 
 
 void PreParser::ParseStatementList(int end_token, bool* ok,
                                    Scanner::BookmarkScope* bookmark) {
   // SourceElements ::
@@ skipping 184 matching lines @@
   ParseFunctionLiteral(name, scanner()->location(),
                        is_strict_reserved ? kFunctionNameIsStrictReserved
                                           : kFunctionNameValidityUnknown,
                        is_generator ? FunctionKind::kGeneratorFunction
                                     : FunctionKind::kNormalFunction,
                        pos, FunctionLiteral::kDeclaration, language_mode(),
                        CHECK_OK);
   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 ::
   //   'function' Identifier '(' FormalParameterListopt ')' '{' FunctionBody '}'
   // GeneratorDeclaration ::
   //   'function' '*' Identifier '(' FormalParameterListopt ')'
   //      '{' FunctionBody '}'
   Expect(Token::FUNCTION, CHECK_OK);
   int pos = position();
   bool is_generator = Check(Token::MUL);
@@ skipping 694 matching lines @@
                            allow_duplicate_parameters, CHECK_OK);
 
   if (is_strict(language_mode)) {
     int end_position = scanner()->location().end_pos;
     CheckStrictOctalLiteral(start_position, end_position, CHECK_OK);
   }
 
   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) {
   int body_start = position();
   ParseStatementList(Token::RBRACE, ok, bookmark);
   if (!*ok) return;
   if (bookmark && bookmark->HasBeenReset()) return;
 
   // Position right after terminal '}'.
   DCHECK_EQ(Token::RBRACE, scanner()->peek());
@@ skipping 100 matching lines @@
   }
   Expect(Token::RBRACE, CHECK_OK);
   return PreParserExpression::Default();
 }
 
 #undef CHECK_OK
 
 
 }  // namespace internal
 }  // namespace v8