From 140ab5ac87ae4ea00165e1e34547a3445f22b298 Mon Sep 17 00:00:00 2001
From: Jeffrey Seyfried <jeffrey.seyfried@gmail.com>
Date: Mon, 25 Jan 2016 03:43:40 +0000
Subject: [PATCH] Allow access to unit and tuple variants of an enum through a
 type alias of the enum

---
 src/librustc_typeck/check/_match.rs           | 12 +++----
 src/librustc_typeck/check/method/mod.rs       |  9 ++++++
 .../run-pass/enum-alias-access-variant.rs     | 32 +++++++++++++++++++
 3 files changed, 47 insertions(+), 6 deletions(-)
 create mode 100644 src/test/run-pass/enum-alias-access-variant.rs

diff --git a/src/librustc_typeck/check/_match.rs b/src/librustc_typeck/check/_match.rs
index c43349f88104d..27c0ecca73818 100644
--- a/src/librustc_typeck/check/_match.rs
+++ b/src/librustc_typeck/check/_match.rs
@@ -640,8 +640,9 @@ pub fn check_pat_enum<'a, 'tcx>(pcx: &pat_ctxt<'a, 'tcx>,
     };
 
     // Items that were partially resolved before should have been resolved to
-    // associated constants (i.e. not methods).
-    if path_res.depth != 0 && !check_assoc_item_is_const(pcx, def, pat.span) {
+    // variants or associated constants (i.e. not methods).
+    if let Def::Variant(..) = def {
+    } else if path_res.depth != 0 && !check_assoc_item_is_const(pcx, def, pat.span) {
         fcx.write_error(pat.id);
         return;
     }
@@ -675,10 +676,9 @@ pub fn check_pat_enum<'a, 'tcx>(pcx: &pat_ctxt<'a, 'tcx>,
         }
     };
 
-    // If we didn't have a fully resolved path to start with, we had an
-    // associated const, and we should quit now, since the rest of this
-    // function uses checks specific to structs and enums.
-    if path_res.depth != 0 {
+    // If we have an associated const, and we should quit now, since
+    // the rest of this function uses checks specific to structs and enums.
+    if let Def::AssociatedConst(..) = def {
         if is_tuple_struct_pat {
             report_bad_struct_kind(false);
         } else {
diff --git a/src/librustc_typeck/check/method/mod.rs b/src/librustc_typeck/check/method/mod.rs
index fc2dd4475e3ff..5d55e236451f8 100644
--- a/src/librustc_typeck/check/method/mod.rs
+++ b/src/librustc_typeck/check/method/mod.rs
@@ -336,6 +336,15 @@ pub fn resolve_ufcs<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
                               expr_id: ast::NodeId)
                               -> Result<(Def, LastPrivate), MethodError<'tcx>>
 {
+    // First check if method_name is a variant of self_ty
+    if let &ty::TyS { sty: ty::TyEnum(adt_def, _), .. } = self_ty {
+        for variant in adt_def.variants.iter() {
+            if variant.name == method_name {
+                return Ok((Def::Variant(adt_def.did, variant.did), LastMod(AllPublic)))
+            }
+        }
+    }
+
     let mode = probe::Mode::Path;
     let pick = try!(probe::probe(fcx, span, mode, method_name, self_ty, expr_id));
     let def_id = pick.item.def_id();
diff --git a/src/test/run-pass/enum-alias-access-variant.rs b/src/test/run-pass/enum-alias-access-variant.rs
new file mode 100644
index 0000000000000..93f167dc4ddb2
--- /dev/null
+++ b/src/test/run-pass/enum-alias-access-variant.rs
@@ -0,0 +1,32 @@
+// Copyright 2016 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.
+
+// Checks that unit and tuple enum variants can be accessed through a type alias of the enum
+
+enum Foo {
+    Unit,
+    Bar(i32),
+}
+
+type Alias = Foo;
+
+impl Default for Foo {
+    fn default() -> Self {
+        Self::Unit
+    }
+}
+
+fn main() {
+    let t = Alias::Bar(0);
+    match t {
+        Alias::Unit => {}
+        Alias::Bar(_i) => {}
+    }
+}