refactor a bit

src/test/compile-fail/issue-43355.rs

@@ -0,0 +1,29 @@
+// Copyright 2017 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.
+
+pub trait Trait1<X> {
+    type Output;
+}
+
+pub trait Trait2<X> {}
+
+pub struct A;
+
+impl<X, T> Trait1<X> for T where T: Trait2<X> {
+    type Output = ();
+}
+
+impl<X> Trait1<Box<X>> for A {
+//~^ ERROR conflicting implementations of trait
+//~| downstream crates may implement trait `Trait2<std::boxed::Box<_>>` for type `A`
+    type Output = i32;
+}
+
+fn main() {}