Auto merge of #33694 - arielb1:fuzzy-on-unimplemented, r=nikomatsakis

implement fuzzy matching in on_unimplemented

Fixes #31062

r? @nikomatsakis

src/test/compile-fail/on-unimplemented/multiple-impls.rs

@@ -0,0 +1,55 @@
+// Copyright 2016 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 if the on_unimplemented message override works
+
+#![feature(on_unimplemented)]
+#![feature(rustc_attrs)]
+
+struct Foo<T>(T);
+struct Bar<T>(T);
+
+#[rustc_on_unimplemented = "trait message"]
+trait Index<Idx: ?Sized> {
+    type Output: ?Sized;
+    fn index(&self, index: Idx) -> &Self::Output;
+}
+
+#[rustc_on_unimplemented = "on impl for Foo"]
+impl Index<Foo<usize>> for [i32] {
+    type Output = i32;
+    fn index(&self, _index: Foo<usize>) -> &i32 {
+        loop {}
+    }
+}
+
+#[rustc_on_unimplemented = "on impl for Bar"]
+impl Index<Bar<usize>> for [i32] {
+    type Output = i32;
+    fn index(&self, _index: Bar<usize>) -> &i32 {
+        loop {}
+    }
+}
+
+#[rustc_error]
+fn main() {
+    Index::index(&[] as &[i32], 2u32);
+    //~^ ERROR E0277
+    //~| NOTE trait message
+    //~| NOTE required by
+    Index::index(&[] as &[i32], Foo(2u32));
+    //~^ ERROR E0277
+    //~| NOTE on impl for Foo
+    //~| NOTE required by
+    Index::index(&[] as &[i32], Bar(2u32));
+    //~^ ERROR E0277
+    //~| NOTE on impl for Bar
+    //~| NOTE required by
+}

src/test/compile-fail/on-unimplemented/slice-index.rs

@@ -18,5 +18,7 @@ use std::ops::Index;
 fn main() {
     let x = &[1, 2, 3] as &[i32];
     x[1i32]; //~ ERROR E0277
-             //~| NOTE a usize is required
+             //~| NOTE slice indices are of type `usize`
+    x[..1i32]; //~ ERROR E0277
+               //~| NOTE slice indices are of type `usize`
 }