Add test for issue rust-lang#17594

Author: nikomatsakis

src/test/run-pass/multidispatch-conditional-impl-not-considered.rs

@@ -0,0 +1,33 @@
+// 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 correctly ignore the blanket impl
+// because (in this case) `T` does not impl `Clone`.
+//
+// Issue #17594.
+
+use std::cell::RefCell;
+
+trait Foo {
+    fn foo(&self) {}
+}
+
+impl<T> Foo for T where T: Clone {}
+
+struct Bar;
+
+impl Bar {
+    fn foo(&self) {}
+}
+
+fn main() {
+    let b = RefCell::new(Bar);
+    b.borrow().foo()
+}