Auto merge of #22541 - Manishearth:rollup, r=Gankro 1.0.0-alpha.2

Continued from #22520

1 files changed, 49 insertions, 0 deletions

diff --git a/src/test/run-pass/variance-trait-matching.rs b/src/test/run-pass/variance-trait-matching.rs
new file mode 100644
index 00000000000..10441bee3cb
--- /dev/null
+++ b/src/test/run-pass/variance-trait-matching.rs
@@ -0,0 +1,49 @@
+// 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.
+
+#![allow(dead_code)]
+
+// Get<T> is covariant in T
+trait Get<T> {
+    fn get(&self) -> T;
+}
+
+struct Cloner<T:Clone> {
+    t: T
+}
+
+impl<T:Clone> Get<T> for Cloner<T> {
+    fn get(&self) -> T {
+        self.t.clone()
+    }
+}
+
+fn get<'a, G>(get: &G) -> i32
+    where G : Get<&'a i32>
+{
+    // This call only type checks if we can use `G : Get<&'a i32>` as
+    // evidence that `G : Get<&'b i32>` where `'a : 'b`.
+    pick(get, &22)
+}
+
+fn pick<'b, G>(get: &'b G, if_odd: &'b i32) -> i32
+    where G : Get<&'b i32>
+{
+    let v = *get.get();
+    if v % 2 != 0 { v } else { *if_odd }
+}
+
+fn main() {
+    let x = Cloner { t: &23 };
+    let y = get(&x);
+    assert_eq!(y, 23);
+}
+
+