Do not ICE when projecting out of a value with type ty::ty_err

src/test/compile-fail/associated-types-ICE-when-projecting-out-of-err.rs

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+// Copyright 2014 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 we do not ICE when the self type is `ty::err`, but rather
+// just propagate the error.
+
+#![crate_type = "lib"]
+#![feature(associated_types, default_type_params, lang_items)]
+#![no_std]
+
+#[lang="sized"]
+pub trait Sized for Sized? {
+    // Empty.
+}
+
+#[lang = "add"]
+trait Add<RHS=Self> {
+    type Output;
+
+    fn add(self, RHS) -> Self::Output;
+}
+
+fn ice<A>(a: A) {
+    let r = loop {};
+    r = r + a; // here the type `r` is not yet inferred, hence `r+a` generates an error.
+    //~^ ERROR type of this value must be known
+}