Add regression tests for #20763. Fixes #20763.

src/test/run-pass/issue-20763-1.rs

@@ -0,0 +1,32 @@
+// 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.
+
+trait T0 { type O; }
+
+struct S<A>(A);
+impl<A> T0 for S<A> { type O = A; }
+
+trait T1: T0 {
+    // this looks okay but as we see below, `f` is unusable
+    fn m0<F: Fn(<Self as T0>::O) -> bool>(self, f: F) -> bool;
+}
+
+// complains about the bounds on F here not being required by the trait
+impl<A> T1 for S<A> {
+    fn m0<F: Fn(A) -> bool>(self, f: F) -> bool { f(self.0) }
+}
+
+// // complains about mismatched types: <S<A> as T0>::O vs. A
+// impl<A> T1 for S<A>
+// {
+//     fn m0<F: Fn(<Self as T0>::O) -> bool>(self, f: F) -> bool { f(self.0) }
+// }
+
+fn main() { }

src/test/run-pass/issue-20763-2.rs

@@ -0,0 +1,27 @@
+// 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.
+
+trait T0 { type O; }
+
+struct S<A>(A);
+impl<A> T0 for S<A> { type O = A; }
+
+trait T1: T0 {
+    // this looks okay but as we see below, `f` is unusable
+    fn m0<F: Fn(<Self as T0>::O) -> bool>(self, f: F) -> bool;
+}
+
+// complains about mismatched types: <S<A> as T0>::O vs. A
+impl<A> T1 for S<A>
+{
+    fn m0<F: Fn(<Self as T0>::O) -> bool>(self, f: F) -> bool { f(self.0) }
+}
+
+fn main() { }