Forbid associated items in inherent impls

Closes #20359

Author: nrc

src/librustc_typeck/collect.rs

@@ -607,6 +607,11 @@ fn convert(ccx: &CollectCtxt, it: &ast::Item) {
                         methods.push(&**method);
                     }
                     ast::TypeImplItem(ref typedef) => {
+                        if opt_trait_ref.is_none() {
+                            tcx.sess.span_err(typedef.span,
+                                              "associated items are not allowed in inherent impls");
+                        }
+
                         let typ = ccx.to_ty(&ExplicitRscope, &*typedef.typ);
                         tcx.tcache
                            .borrow_mut()

src/test/compile-fail/assoc-inherent.rs

@@ -0,0 +1,19 @@
+// Copyright 2015 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 associated types are forbidden in inherant impls.
+
+struct Foo;
+
+impl Foo {
+    type Bar = int; //~ERROR associated items are not allowed in inherent impls
+}
+
+fn main() {}