Auto merge of #21278 - thchittenden:issue-21033-struct-var-pattern-fix, r=alexcrichton

Closes #21033. The new strategy for parsing a field pattern is to look 1 token ahead and if it's a colon, parse as "fieldname: pat", otherwise parse the shorthand form "(box) (ref) (mut) fieldname)". The previous strategy was to parse "(ref) (mut) fieldname" then if we encounter a colon, throw an error if either "ref" or "mut" were encountered.

src/test/compile-fail/bind-struct-early-modifiers.rs

@@ -11,7 +11,7 @@
 fn main() {
     struct Foo { x: isize }
     match (Foo { x: 10 }) {
-        Foo { ref x: ref x } => {}, //~ ERROR unexpected `:`
+        Foo { ref x: ref x } => {}, //~ ERROR expected `,`, found `:`
         _ => {}
     }
 }

src/test/run-pass/issue-21033.rs

@@ -0,0 +1,52 @@
+// 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(box_syntax)]
+
+enum E {
+    StructVar { boxed: Box<i32> }
+}
+
+fn main() {
+
+    // Test matching each shorthand notation for field patterns.
+    let mut a = E::StructVar { boxed: box 3 };
+    match a {
+        E::StructVar { box boxed } => { }
+    }
+    match a {
+        E::StructVar { box ref boxed } => { }
+    }
+    match a {
+        E::StructVar { box mut boxed } => { }
+    }
+    match a {
+        E::StructVar { box ref mut boxed } => { }
+    }
+    match a {
+        E::StructVar { ref boxed } => { }
+    }
+    match a {
+        E::StructVar { ref mut boxed } => { }
+    }
+    match a {
+        E::StructVar { mut boxed } => { }
+    }
+
+    // Test matching non shorthand notation. Recreate a since last test
+    // moved `boxed`
+    let mut a = E::StructVar { boxed: box 3 };
+    match a {
+        E::StructVar { boxed: box ref mut num } => { }
+    }
+    match a {
+        E::StructVar { boxed: ref mut num } => { }
+    }
+
+}