Auto merge of #24144 - richo:ptr-formatter, r=alexcrichton

~~I believe this should fix the issue. Opening a PR to ensure noone duplicates effort, I'm running check now.~~

Closes #24091

src/test/run-pass/fmt-pointer-trait.rs

@@ -0,0 +1,28 @@
+// 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(libc)]
+extern crate libc;
+use std::ptr;
+use std::rc::Rc;
+use std::sync::Arc;
+
+fn main() {
+    let p: *const libc::c_void = ptr::null();
+    let rc = Rc::new(1usize);
+    let arc = Arc::new(1usize);
+    let b = Box::new("hi");
+
+    let _ = format!("{:p}{:p}{:p}",
+                    rc, arc, b);
+
+    assert_eq!(format!("{:p}", p),
+               "0x0");
+}