Make object types not implement associated trait. Fixes #5087.

src/test/compile-fail/object-does-not-impl-trait.rs

@@ -0,0 +1,17 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Test that an object type `@Foo` is not considered to implement the
+// trait `Foo`. Issue #5087.
+
+trait Foo {}
+fn take_foo<F:Foo>(f: F) {}
+fn take_object(f: @Foo) { take_foo(f); } //~ ERROR failed to find an implementation of trait
+fn main() {}