Reject uses of lexical for-loop variable on the RHS.

src/parser.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2773 matching lines @@
     if (peek() == Token::VAR || peek() == Token::CONST) {
       bool is_const = peek() == Token::CONST;
       Handle<String> name;
       Block* variable_statement =
           ParseVariableDeclarations(kForStatement, NULL, NULL, &name, CHECK_OK);
 
       if (peek() == Token::IN && !name.is_null()) {
         Interface* interface =
             is_const ? Interface::NewConst() : Interface::NewValue();
         VariableProxy* each =
             top_scope_->NewUnresolved(factory(), name, interface);

[Michael Starzinger, 2012/10/05 08:42:36]

For consistency we could also move this loop variable and interface down.

[rossberg, 2012/10/05 09:15:02]

Done.

         ForInStatement* loop = factory()->NewForInStatement(labels);
         Target target(&this->target_stack_, loop);
 
         Expect(Token::IN, CHECK_OK);
         Expression* enumerable = ParseExpression(true, CHECK_OK);
         Expect(Token::RPAREN, CHECK_OK);
 
         Statement* body = ParseStatement(NULL, CHECK_OK);
         loop->Initialize(each, enumerable, body);
         Block* result = factory()->NewBlock(NULL, 2, false);
@@ skipping 26 matching lines @@
         //   for (x' in e) {
         //     let x;
         //     x = x';
         //     b;
         //   }
 
         // TODO(keuchel): Move the temporary variable to the block scope, after
         // implementing stack allocated block scoped variables.
         Variable* temp = top_scope_->DeclarationScope()->NewTemporary(name);
         VariableProxy* temp_proxy = factory()->NewVariableProxy(temp);
         Interface* interface = Interface::NewValue();

[Michael Starzinger, 2012/10/05 08:42:36]

Can we also move the interface down right before the loop variable is created?

[rossberg, 2012/10/05 09:15:02]

Inlined instead.

-        VariableProxy* each =
-            top_scope_->NewUnresolved(factory(), name, interface);
         ForInStatement* loop = factory()->NewForInStatement(labels);
         Target target(&this->target_stack_, loop);
 
+        // The expression does not see the loop variable.
         Expect(Token::IN, CHECK_OK);
+        top_scope_ = saved_scope;
         Expression* enumerable = ParseExpression(true, CHECK_OK);
+        top_scope_ = for_scope;
         Expect(Token::RPAREN, CHECK_OK);
 
         Statement* body = ParseStatement(NULL, CHECK_OK);
         Block* body_block = factory()->NewBlock(NULL, 3, false);
+        VariableProxy* each =
+            top_scope_->NewUnresolved(factory(), name, interface);
         Assignment* assignment = factory()->NewAssignment(
             Token::ASSIGN, each, temp_proxy, RelocInfo::kNoPosition);
         Statement* assignment_statement =
             factory()->NewExpressionStatement(assignment);
         body_block->AddStatement(variable_statement, zone());
         body_block->AddStatement(assignment_statement, zone());
         body_block->AddStatement(body, zone());
         loop->Initialize(temp_proxy, enumerable, body_block);
         top_scope_ = saved_scope;
         for_scope->set_end_position(scanner().location().end_pos);
@@ skipping 3105 matching lines @@
       ASSERT(info->isolate()->has_pending_exception());
     } else {
       result = parser.ParseProgram();
     }
   }
   info->SetFunction(result);
   return (result != NULL);
 }
 
 } }  // namespace v8::internal