Include parent field/list index in retaining path.

runtime/vm/object_graph_test.cc

 // Copyright (c) 2014, 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 "platform/assert.h"
 #include "vm/object_graph.h"
 #include "vm/unit_test.h"
 
 namespace dart {
 
@@ skipping 27 matching lines @@
 };
 
 
 TEST_CASE(ObjectGraph) {
   Isolate* isolate = Isolate::Current();
   // Create a simple object graph with objects a, b, c, d:
   //  a+->b+->c
   //  +   +
   //  |   v
   //  +-->d
-  Array& a = Array::Handle(Array::New(2, Heap::kNew));
+  Array& a = Array::Handle(Array::New(12, Heap::kNew));
   Array& b = Array::Handle(Array::New(2, Heap::kOld));
   Array& c = Array::Handle(Array::New(0, Heap::kOld));
   Array& d = Array::Handle(Array::New(0, Heap::kOld));
-  a.SetAt(0, b);
+  a.SetAt(10, b);
   b.SetAt(0, c);
   b.SetAt(1, d);
-  a.SetAt(1, d);
+  a.SetAt(11, d);
   intptr_t a_size = a.raw()->Size();
   intptr_t b_size = b.raw()->Size();
   intptr_t c_size = c.raw()->Size();
   intptr_t d_size = d.raw()->Size();
   {
     // No more allocation; raw pointers ahead.
     NoGCScope no_gc_scope;
     RawObject* b_raw = b.raw();
     // Clear handles to cut unintended retained paths.
     b = Array::null();
@@ skipping 20 matching lines @@
       graph.IterateObjects(&without);
       EXPECT_EQ(2, with.count() - without.count());
       EXPECT_EQ(b_size + c_size,
                 with.size() - without.size());
     }
     EXPECT_EQ(a_size + b_size + c_size + d_size,
               graph.SizeRetainedByInstance(a));
   }
   {
     // Get hold of c again.
-    b ^= a.At(0);
+    b ^= a.At(10);
     c ^= b.At(0);
     b = Array::null();
     ObjectGraph graph(isolate);
     // A retaining path should end like this: c <- b <- a <- ...
     {
       HANDLESCOPE(isolate);
       // Test null, empty, and length 1 array.
       intptr_t null_length = graph.RetainingPath(&c, Object::null_array());
       intptr_t empty_length = graph.RetainingPath(&c, Object::empty_array());
       Array& path = Array::Handle(Array::New(1, Heap::kNew));
       intptr_t one_length = graph.RetainingPath(&c, path);
       EXPECT_EQ(null_length, empty_length);
       EXPECT_EQ(null_length, one_length);
       EXPECT_LE(3, null_length);
     }
     {
       HANDLESCOPE(isolate);

[Cutch, 2014/06/30 15:56:34]

Can we add a test with a custom class:

class Foo {
  var field1;
  var field2;
}

and verify the offset from parent is correct for both fields?

[koda, 2014/06/30 16:20:04]

I intend to add such a test in service_test when interpreting the offset as a
field in the JSON response.

I could extend this CL to also translate the offset to a field id. What do you
think?

-      Array& path = Array::Handle(Array::New(3, Heap::kNew));
+      Array& path = Array::Handle(Array::New(6, Heap::kNew));
       intptr_t length = graph.RetainingPath(&c, path);
       EXPECT_LE(3, length);
       Array& expected_c = Array::Handle();
       expected_c ^= path.At(0);
+      // c is the first element in b.
+      Smi& offset_from_parent = Smi::Handle();
+      offset_from_parent ^= path.At(1);
+      EXPECT_EQ(Array::element_offset(0),
+                offset_from_parent.Value() * kWordSize);
       Array& expected_b = Array::Handle();
-      expected_b ^= path.At(1);
+      expected_b ^= path.At(2);
+      // b is the element with index 10 in a.
+      offset_from_parent ^= path.At(3);
+      EXPECT_EQ(Array::element_offset(10),
+                offset_from_parent.Value() * kWordSize);
       Array& expected_a = Array::Handle();
-      expected_a ^= path.At(2);
+      expected_a ^= path.At(4);
       EXPECT(expected_c.raw() == c.raw());
-      EXPECT(expected_b.raw() == a.At(0));
+      EXPECT(expected_b.raw() == a.At(10));
       EXPECT(expected_a.raw() == a.raw());
     }
   }
 }
 
 }  // namespace dart