Test case for issue #115.

src/test/run-pass/interface-narrowing.rs

@@ -0,0 +1,19 @@
+//xfail-stage1
+//xfail-stage2
+//xfail-stage3
+
+// Test case for issue #115.
+type base =
+  obj {
+    fn foo();
+  };
+
+obj derived() {
+  fn foo() {}
+  fn bar() {}
+}
+
+fn main() {
+  let d = derived();
+  let b:base = d as base;
+}