Fix context chaining to prevent memory leak (issue 7681).

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/bigint_operations.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
 #include "vm/compiler_stats.h"
@@ skipping 168 matching lines @@
   // Allocate parameters and local variables, either in the local frame or
   // in the context(s).
   LocalScope* context_owner = NULL;  // No context needed yet.
   int next_free_frame_index =
       scope->AllocateVariables(first_parameter_index_,
                                num_params,
                                first_stack_local_index_,
                                scope,
                                &context_owner);
 
-  // If this function is not a closure function and if it contains captured
-  // variables, the context needs to be saved on entry and restored on exit.
+  // If this function allocates context variables, but none of its enclosing
+  // functions do, the context on entry is not linked as parent of the allocated
+  // context but saved on entry and restored on exit as to prevent memory leaks.

[Ivan Posva, 2013/01/07 22:19:11]

Please update the bug, but do not close it as we still need to ensure the
closures which do not need chained contexts do not remember the current context
on allocation.

[regis, 2013/01/07 22:24:01]

Done.

   // Add and allocate a local variable to this purpose.
-  if ((context_owner != NULL) && !function().IsClosureFunction()) {
-    LocalVariable* context_var =
-        new LocalVariable(function().token_pos(),
-                          Symbols::SavedEntryContextVar(),
-                          Type::ZoneHandle(Type::DynamicType()));
-    context_var->set_index(next_free_frame_index--);
-    scope->AddVariable(context_var);
-    set_saved_context_var(context_var);
+  if (context_owner != NULL) {
+    const ContextScope& context_scope =
+        ContextScope::Handle(function().context_scope());
+    if (context_scope.IsNull() || (context_scope.num_variables() == 0)) {
+      LocalVariable* context_var =
+          new LocalVariable(function().token_pos(),
+                            Symbols::SavedEntryContextVar(),
+                            Type::ZoneHandle(Type::DynamicType()));
+      context_var->set_index(next_free_frame_index--);
+      scope->AddVariable(context_var);
+      set_saved_context_var(context_var);
+    }
   }
 
   // Frame indices are relative to the frame pointer and are decreasing.
   ASSERT(next_free_frame_index <= first_stack_local_index_);
   num_stack_locals_ = first_stack_local_index_ - next_free_frame_index;
 }
 
 
 struct Parser::Block : public ZoneAllocated {
   Block(Block* outer_block, LocalScope* local_scope, SequenceNode* seq)
@@ skipping 9492 matching lines @@
 void Parser::SkipQualIdent() {
   ASSERT(IsIdentifier());
   ConsumeToken();
   if (CurrentToken() == Token::kPERIOD) {
     ConsumeToken();  // Consume the kPERIOD token.
     ExpectIdentifier("identifier expected after '.'");
   }
 }
 
 }  // namespace dart