rollup merge of #18868: nikomatsakis/issue-17388-unbound-path-assoc-type

This fixes #17388.

Note that we don't check type parameters in trait-references and so on, so we accept some nonsense (I opened https://github.com/rust-lang/rust/issues/18865). (It may be easier to just add support for `T::Foo` and deprecate the qpath code until we can implement it more robustly using the trait lookup infrastructure, not sure.)

src/test/compile-fail/associated-types-in-ambiguous-context.rs

@@ -20,12 +20,12 @@ fn get<T:Get,U:Get>(x: T, y: U) -> Get::Value {}
 
 trait Other {
     fn uhoh<U:Get>(&self, foo: U, bar: <Self as Get>::Value) {}
-    //~^ ERROR this associated type is not allowed in this context
+    //~^ ERROR no suitable bound on `Self`
 }
 
 impl<T:Get> Other for T {
     fn uhoh<U:Get>(&self, foo: U, bar: <(T, U) as Get>::Value) {}
-    //~^ ERROR this associated type is not allowed in this context
+    //~^ ERROR currently unsupported
 }
 
 trait Grab {

src/test/compile-fail/associated-types-in-wrong-context.rs

@@ -16,7 +16,7 @@ trait Get {
 }
 
 fn get(x: int) -> <int as Get>::Value {}
-//~^ ERROR this associated type is not allowed in this context
+//~^ ERROR unsupported
 
 struct Struct {
     x: int,
@@ -24,7 +24,7 @@ struct Struct {
 
 impl Struct {
     fn uhoh<T>(foo: <T as Get>::Value) {}
-    //~^ ERROR this associated type is not allowed in this context
+    //~^ ERROR no suitable bound on `T`
 }
 
 fn main() {

src/test/run-pass/associated-types-qualified-path-with-trait-with-type-parameters.rs

@@ -0,0 +1,18 @@
+// 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.
+
+#![feature(associated_types)]
+
+trait Foo<T> {
+    type Bar;
+    fn get_bar() -> <Self as Foo<T>>::Bar;
+}
+
+fn main() { }