From 9e181ca8f446d238ba279bc22fef9d166d4f38b0 Mon Sep 17 00:00:00 2001
From: Jacques Garrigue <garrigue@math.nagoya-u.ac.jp>
Date: Thu, 5 Nov 2020 11:12:01 +0900
Subject: [PATCH] must use set_state rather than backtrack in
 Typecore.type_cases

---
 typing/typecore.ml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/typing/typecore.ml b/typing/typecore.ml
index 5cd7fa168..d6f7004a8 100644
--- a/typing/typecore.ml
+++ b/typing/typecore.ml
@@ -4739,7 +4739,7 @@ and type_cases
   let cases =
     let may_backtrack = does_contain_gadt && not !Clflags.principal in
     if not may_backtrack then mk_cases false else
-    let snap = Btype.snapshot () in
+    let state = save_state (ref env) in
     let has_equation_escape err =
       match trace_of_error err with
         Some tr ->
@@ -4749,7 +4749,7 @@ and type_cases
     in
     try mk_cases false
     with Error(_,_,err) when has_equation_escape err ->
-      Btype.backtrack snap;
+      set_state state (ref env);
       let cases = mk_cases true in
       let msg =
         Format.asprintf