Eliminate remaining case of ambiguous context level info

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 8706 matching lines @@
     new_loop_var = true;
     loop_var_type = ParseConstFinalVarOrType(
        I->type_checks() ? ClassFinalizer::kCanonicalize :
                                   ClassFinalizer::kIgnore);
   }
   TokenPosition loop_var_pos = TokenPos();
   const String* loop_var_name = ExpectIdentifier("variable name expected");
 
   // Parse stream expression.
   ExpectToken(Token::kIN);
+
+  // Open a block for the iterator variable and the try-finally statement
+  // that contains the loop. Ensure that the block starts 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).
+  OpenBlock();
+  const Block* await_for_block = current_block_;
+
   const TokenPosition stream_expr_pos = TokenPos();
   AstNode* stream_expr =
       ParseAwaitableExpr(kAllowConst, kConsumeCascades, NULL);
   ExpectToken(Token::kRPAREN);
 
-  // Open a block for the iterator variable and the try-finally
-  // statement that contains the loop.
-  OpenBlock();
-  const Block* loop_block = current_block_;
-
   // Build creation of implicit StreamIterator.
   // var :for-in-iter = new StreamIterator(stream_expr).
   const Class& stream_iterator_cls =
       Class::ZoneHandle(Z, I->object_store()->stream_iterator_class());
   ASSERT(!stream_iterator_cls.IsNull());
   const Function& iterator_ctor =
       Function::ZoneHandle(Z, stream_iterator_cls.LookupFunction(
           Symbols::StreamIteratorConstructor()));
   ASSERT(!iterator_ctor.IsNull());
   ArgumentListNode* ctor_args = new (Z) ArgumentListNode(stream_expr_pos);
@@ skipping 229 matching lines @@
 
   AstNode* try_catch_node =
       new(Z) TryCatchNode(await_for_pos,
                          try_block,
                          context_var,
                          catch_clause,
                          finally_clause,
                          try_index,
                          finally_clause);
 
-  ASSERT(current_block_ == loop_block);
-  loop_block->statements->Add(try_catch_node);
+  ASSERT(current_block_ == await_for_block);
+  await_for_block->statements->Add(try_catch_node);
 
   return CloseBlock();  // Implicit block around while loop.
 }
 
 
 AstNode* Parser::ParseForInStatement(TokenPosition forin_pos,
                                      SourceLabel* label) {
   TRACE_PARSER("ParseForInStatement");
   bool loop_var_is_final = (CurrentToken() == Token::kFINAL);
   if (CurrentToken() == Token::kCONST) {
@@ skipping 5654 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