Add Dart_PropagateError.

runtime/vm/ast.cc

Index: runtime/vm/ast.cc
===================================================================
--- runtime/vm/ast.cc	(revision 3415)
+++ runtime/vm/ast.cc	(working copy)
@@ -438,15 +438,21 @@
   }
   GrowableArray<const Object*> arguments;
   const Array& kNoArgumentNames = Array::Handle();
-  const Instance& field_value =
-      Instance::ZoneHandle(DartEntry::InvokeStatic(getter_func,
+  const Object& result =
+      Object::ZoneHandle(DartEntry::InvokeStatic(getter_func,
                                                    arguments,
                                                    kNoArgumentNames));

[siva, 2012/01/31 00:52:34]

Does result have to be a ZoneHandle? We are not returning this handle from the
function.

[turnidge, 2012/01/31 21:56:31]

Done.

-  if (field_value.IsUnhandledException()) {
+  if (result.IsError()) {
+    // TODO(turnidge): We could get better error messages by returning
+    // the Error object directly to the parser.  This will involve
+    // replumbing all of the EvalConstExpr methods.
     return NULL;
   }
-  if (!field_value.IsNull()) {
-    return &field_value;
+  ASSERT(result.IsInstance());

[siva, 2012/01/31 00:52:34]

Why is this assert needed here doesn't the ^= assignment below have the same
assertion?

[turnidge, 2012/01/31 21:56:31]

 Removed.

+  Instance& value = Instance::ZoneHandle();

[siva, 2012/01/31 00:52:34]

why not call it field_value instead of value to retain the old code

[turnidge, 2012/01/31 21:56:31]

Done.

+  value ^= result.raw();
+  if (!value.IsNull()) {

[siva, 2012/01/31 00:52:34]

The NULL check can be done before we create an Instance handle that way we save
on a handle creation.

[turnidge, 2012/01/31 21:56:31]

Done.

+    return &value;
   }
   return NULL;
 }