Add tests for #21410 and #24972

Closes #21410.
Closes #24972.

src/test/run-pass/issue-21410.rs

@@ -0,0 +1,15 @@
+// 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.
+
+fn g<F>(_: F) where F: FnOnce(Option<F>) {}
+
+fn main() {
+    g(|_| {  });
+}

src/test/run-pass/issue-24972.rs

@@ -0,0 +1,36 @@
+// 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.
+
+#![feature(rustc_private)]
+
+extern crate serialize;
+
+use serialize::{Encodable, Decodable};
+use std::fmt::Display;
+
+pub trait Entity : Decodable + Encodable + Sized {
+    type Key: Clone + Decodable + Encodable + ToString + Display + Eq + Ord + Sized;
+
+    fn id(&self) -> Self::Key;
+
+    fn find_by_id(id: Self::Key) -> Option<Self>;
+}
+
+pub struct DbRef<E: Entity> {
+    pub id: E::Key,
+}
+
+impl<E> DbRef<E> where E: Entity {
+    fn get(self) -> Option<E> {
+        E::find_by_id(self.id)
+    }
+}
+
+fn main() {}