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.
   // 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