Auto merge of #28938 - GlenDC:master, r=Manishearth

Here is my attempt to resolve issue #28822, @Manishearth.
Please let me know if it's fine. And if not, what should I do instead?

This issue felt like quite a good start for some rust contributions. It allows me to get used to the workflow  and codebase of rust in an easy-to-swallow manner. Are there any other issues you would recommend me to look at? :) Would love to do some more stuff!

src/librustc/middle/check_const.rs

@@ -177,6 +177,7 @@ impl<'a, 'tcx> CheckCrateVisitor<'a, 'tcx> {
             for arg in &fd.inputs {
                 match arg.pat.node {
                     hir::PatIdent(hir::BindByValue(hir::MutImmutable), _, None) => {}
+                    hir::PatWild(_) => {}
                     _ => {
                         span_err!(self.tcx.sess, arg.pat.span, E0022,
                                   "arguments of constant functions can only \

src/test/run-pass/issue-28822.rs

@@ -0,0 +1,16 @@
+// Copyright 2014 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(const_fn)]
+
+fn main() {}
+
+const fn size_ofs(_: usize) {}
+const fn size_ofs2(_foo: usize) {}