From dcbb27aa60f5105a49d5e416490d6549385c325d Mon Sep 17 00:00:00 2001
From: Michael Hewson <michael@michaelhewson.ca>
Date: Thu, 9 Nov 2017 08:39:02 -0500
Subject: [PATCH] fix the bug in region_inference where constraint origins were
 being overwritten

---
 src/librustc/infer/region_inference/mod.rs | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/librustc/infer/region_inference/mod.rs b/src/librustc/infer/region_inference/mod.rs
index 8351be49076..0bc388a0089 100644
--- a/src/librustc/infer/region_inference/mod.rs
+++ b/src/librustc/infer/region_inference/mod.rs
@@ -633,11 +633,12 @@ impl<'a, 'gcx, 'tcx> RegionVarBindings<'a, 'gcx, 'tcx> {
 
         debug!("RegionVarBindings: add_constraint({:?})", constraint);
 
-        if self.constraints.borrow_mut().insert(constraint, origin).is_none() {
+        self.constraints.borrow_mut().entry(constraint).or_insert_with(|| {
             if self.in_snapshot() {
                 self.undo_log.borrow_mut().push(AddConstraint(constraint));
             }
-        }
+            origin
+        });
     }
 
     fn add_verify(&self, verify: Verify<'tcx>) {