From f7d9b439720fed4434a532244f0eb873cf14eb91 Mon Sep 17 00:00:00 2001
From: "Felix S. Klock II" <pnkfelix@pnkfx.org>
Date: Thu, 23 Apr 2015 22:45:03 +0200
Subject: [PATCH] Latent bug in iter_structural_ty: handle `_match::Single` on
 zero-variant enum.

(This may not be the *best* fix, compared to e.g. returning
`_match::NoBranch` from `trans_switch` on a zero-variant enum. But it
is one of the *simplest* fixes available.)
---
 src/librustc_trans/trans/adt.rs  | 1 +
 src/librustc_trans/trans/base.rs | 7 +++++--
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/librustc_trans/trans/adt.rs b/src/librustc_trans/trans/adt.rs
index ffa068a2ae44..2057f502c1b6 100644
--- a/src/librustc_trans/trans/adt.rs
+++ b/src/librustc_trans/trans/adt.rs
@@ -769,6 +769,7 @@ pub fn trans_switch<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
             (_match::Switch, Some(trans_get_discr(bcx, r, scrutinee, None)))
         }
         Univariant(..) => {
+            // N.B.: Univariant means <= 1 enum variants (*not* == 1 variants).
             (_match::Single, None)
         }
     }
diff --git a/src/librustc_trans/trans/base.rs b/src/librustc_trans/trans/base.rs
index 59f3ff726026..f3d82970e4ee 100644
--- a/src/librustc_trans/trans/base.rs
+++ b/src/librustc_trans/trans/base.rs
@@ -471,8 +471,11 @@ pub fn iter_structural_ty<'blk, 'tcx, F>(cx: Block<'blk, 'tcx>,
 
           match adt::trans_switch(cx, &*repr, av) {
               (_match::Single, None) => {
-                  cx = iter_variant(cx, &*repr, av, &*(*variants)[0],
-                                    substs, &mut f);
+                  if n_variants != 0 {
+                      assert!(n_variants == 1);
+                      cx = iter_variant(cx, &*repr, av, &*(*variants)[0],
+                                        substs, &mut f);
+                  }
               }
               (_match::Switch, Some(lldiscrim_a)) => {
                   cx = f(cx, lldiscrim_a, cx.tcx().types.isize);