test: Add a test for regions, traits, and variance.

Closes #12470.

src/test/compile-fail/regions-trait-variance.rs

@@ -0,0 +1,52 @@
+// Copyright 2012 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.
+
+// Issue #12470.
+
+trait X {
+    fn get_i(&self) -> int;
+}
+
+struct B {
+    i: int
+}
+
+impl X for B {
+    fn get_i(&self) -> int {
+        self.i
+    }
+}
+
+impl Drop for B {
+    fn drop(&mut self) {
+        println!("drop");
+    }
+}
+
+struct A<'r> {
+    p: &'r X
+}
+
+fn make_a<'r>(p:&'r X) -> A<'r> {
+    A{p:p}
+}
+
+fn make_make_a() -> A {
+    let b: Box<B> = box B {
+        i: 1,
+    };
+    let bb: &B = b; //~ ERROR `*b` does not live long enough
+    make_a(bb)
+}
+
+fn main() {
+    let a = make_make_a();
+    println!("{}", a.p.get_i());
+}