From e910d40e6a650c06edc6e43a77a823170c47b4f2 Mon Sep 17 00:00:00 2001
From: Scott Olson <scott@solson.me>
Date: Fri, 18 Mar 2016 12:11:39 -0600
Subject: [PATCH] Add error message for missing MIR.

---
 src/interpreter.rs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/interpreter.rs b/src/interpreter.rs
index 7c62f701856..80a86764c44 100644
--- a/src/interpreter.rs
+++ b/src/interpreter.rs
@@ -743,7 +743,9 @@ impl<'a, 'tcx: 'a, 'arena> Interpreter<'a, 'tcx, 'arena> {
 
                 use rustc::middle::cstore::CrateStore;
                 let cs = &self.tcx.sess.cstore;
-                let mir = cs.maybe_get_item_mir(self.tcx, def_id).unwrap();
+                let mir = cs.maybe_get_item_mir(self.tcx, def_id).unwrap_or_else(|| {
+                    panic!("no mir for {:?}", def_id);
+                });
                 let cached = Rc::new(mir);
                 mir_cache.insert(def_id, cached.clone());
                 CachedMir::Owned(cached)