Set correct token position range for statement block containing moveNext call of

runtime/vm/parser.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/parser.h"
 #include "vm/flags.h"
 
 #ifndef DART_PRECOMPILED_RUNTIME
 
 #include "lib/invocation_mirror.h"
@@ skipping 9010 matching lines @@
     // The case without a type is handled above, so require a type here.
     // Delay creation of the local variable until we know its actual
     // position, which is inside the loop body.
     new_loop_var = true;
     loop_var_type = ParseConstFinalVarOrType(
         I->type_checks() ? ClassFinalizer::kCanonicalize :
                                    ClassFinalizer::kIgnore);
     loop_var_name = ExpectIdentifier("variable name expected");
   }
   ExpectToken(Token::kIN);
+
+  OpenBlock();  // Implicit block around while loop.

[hausner, 2016/07/29 17:59:35]

Maybe add a comment that explains why we open a block that textually starts in
the middle of the for-in expression. I think you can copy the explanation in the
CL:

Ensure that the block token range contains the call to moveNext and it
also starts the block at a different token position than the following loop
block. Both blocks can allocate contexts and if they have a matching token
position
range, it can be an issue (cf. bug 26941)

[regis, 2016/07/29 21:31:47]

Done.

+
   const TokenPosition collection_pos = TokenPos();
   AstNode* collection_expr =
       ParseAwaitableExpr(kAllowConst, kConsumeCascades, NULL);
   ExpectToken(Token::kRPAREN);
 
-  OpenBlock();  // Implicit block around while loop.
-
   // Generate implicit iterator variable and add to scope.
   // We could set the type of the implicit iterator variable to Iterator<T>
   // where T is the type of the for loop variable. However, the type error
   // would refer to the compiler generated iterator and could confuse the user.
   // It is better to leave the iterator untyped and postpone the type error
   // until the loop variable is assigned to.
   const AbstractType& iterator_type = Object::dynamic_type();
   LocalVariable* iterator_var = new(Z) LocalVariable(
       collection_pos, Symbols::ForInIter(), iterator_type);
   current_block_->scope->AddVariable(iterator_var);
@@ skipping 5612 matching lines @@
     const ArgumentListNode& function_args,
     const LocalVariable* temp_for_last_arg,
     bool is_super_invocation) {
   UNREACHABLE();
   return NULL;
 }
 
 }  // namespace dart
 
 #endif  // DART_PRECOMPILED_RUNTIME