1 files changed, 38 insertions, 0 deletions
diff --git a/tests/ui/variance/variance-trait-matching.rs b/tests/ui/variance/variance-trait-matching.rs
new file mode 100644
index 00000000000..b4efee7d604
--- /dev/null
+++ b/tests/ui/variance/variance-trait-matching.rs
@@ -0,0 +1,38 @@
+#![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 fails to type-check because, without variance, we can't
+    // use `G : Get<&'a i32>` as evidence that `G : Get<&'b i32>`,
+    // even if `'a : 'b`.
+    pick(get, &22) //~ ERROR explicit lifetime required in the type of `get` [E0621]
+}
+
+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);
+}