Allow yield expressions without a RHS.

src/preparser.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_PREPARSER_H
 #define V8_PREPARSER_H
 
 #include "src/v8.h"
 
 #include "src/func-name-inferrer.h"
@@ skipping 1774 matching lines @@
     fni_->Leave();
   }
 
   return factory()->NewAssignment(op, expression, right, pos);
 }
 
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParseYieldExpression(bool* ok) {
   // YieldExpression ::
-  //   'yield' '*'? AssignmentExpression
+  //   'yield' ([no line terminator] '*'? AssignmentExpression)?
   int pos = peek_position();
   Expect(Token::YIELD, CHECK_OK);
-  Yield::Kind kind =
-      Check(Token::MUL) ? Yield::DELEGATING : Yield::SUSPEND;
   ExpressionT generator_object =
       factory()->NewVariableProxy(function_state_->generator_object_variable());
-  ExpressionT expression =
-      ParseAssignmentExpression(false, CHECK_OK);
+  ExpressionT expression = Traits::EmptyExpression();
+  Yield::Kind kind = Yield::SUSPEND;
+  if (!scanner()->HasAnyLineTerminatorBeforeNext()) {
+    if (Check(Token::MUL)) kind = Yield::DELEGATING;
+    switch (peek()) {
+      case Token::EOS:
+      case Token::SEMICOLON:
+      case Token::RBRACE:
+      case Token::RBRACK:
+      case Token::RPAREN:
+      case Token::COLON:
+      case Token::COMMA:
+        // The above set of tokens is the complete set of tokens that can appear
+        // after an AssignmentExpression, and none of them can start an
+        // AssignmentExpression.  This allows us to avoid looking for an RHS for
+        // a Yield::SUSPEND operation, given only one look-ahead token.
+        if (kind == Yield::SUSPEND)
+          break;
+        ASSERT(kind == Yield::DELEGATING);
+        // Delegating yields require an RHS; fall through.
+      default:
+        expression = ParseAssignmentExpression(false, CHECK_OK);
+        break;
+    }
+  }
   typename Traits::Type::YieldExpression yield =
       factory()->NewYield(generator_object, expression, kind, pos);
   if (kind == Yield::DELEGATING) {
     yield->set_index(function_state_->NextHandlerIndex());
   }
   return yield;
 }
 
 
 // Precedence = 3
@@ skipping 392 matching lines @@
       parser()->ReportMessage("accessor_get_set");
     }
     *ok = false;
   }
 }
 
 
 } }  // v8::internal
 
 #endif  // V8_PREPARSER_H