From 21af89d773cc76eaf7240e4a16f30d4cd29139e1 Mon Sep 17 00:00:00 2001
From: Nadrieril <nadrieril+git@gmail.com>
Date: Wed, 27 Nov 2019 16:50:42 +0000
Subject: [PATCH] `UsefulWithWitness` always carries some witnesses

---
 src/librustc_mir/hair/pattern/check_match.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/librustc_mir/hair/pattern/check_match.rs b/src/librustc_mir/hair/pattern/check_match.rs
index 4463fb43583aa..56f0ace489180 100644
--- a/src/librustc_mir/hair/pattern/check_match.rs
+++ b/src/librustc_mir/hair/pattern/check_match.rs
@@ -492,7 +492,7 @@ fn check_not_useful(
     match is_useful(cx, matrix, &PatStack::from_pattern(&wild_pattern), ConstructWitness, hir_id) {
         NotUseful => Ok(()), // This is good, wildcard pattern isn't reachable.
         UsefulWithWitness(pats) => Err(if pats.is_empty() {
-            vec![wild_pattern]
+            bug!("Exhaustiveness check returned no witnesses")
         } else {
             pats.into_iter().map(|w| w.single_pattern()).collect()
         }),