From 8ef1be1aead0dbcc2d3cc46a7e5eaa02f9ad6069 Mon Sep 17 00:00:00 2001
From: Hugo Herbelin
Date: Thu, 26 Apr 2018 15:51:03 +0200
Subject: Unification failure: don't give preference to a "beyond capabilities"
 error.

This is actually a bit ad hoc at this stage in the sense that this is
specifically to prefer an informative first-order unification failure
over the currently always uninformative failure coming from
second-order unification.

When second-order unification shall be able to give more information,
one may consider alternative strategies, even maybe reporting not just
one but the list of failures in all (interesting) branches.
---
 pretyping/evarconv.ml | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

(limited to 'pretyping')

diff --git a/pretyping/evarconv.ml b/pretyping/evarconv.ml
index 13676b674c..e978adf761 100644
--- a/pretyping/evarconv.ml
+++ b/pretyping/evarconv.ml
@@ -227,7 +227,10 @@ let check_conv_record env sigma (t1,sk1) (t2,sk2) =
 (* Precondition: one of the terms of the pb is an uninstantiated evar,
  * possibly applied to arguments. *)
 
-let join_failures evd1 evd2 e1 e2 = (evd2,e2)
+let join_failures evd1 evd2 e1 e2 =
+  match e1, e2 with
+  | _, CannotSolveConstraint (_,ProblemBeyondCapabilities) -> (evd1,e1)
+  | _ -> (evd2,e2)
 
 let rec ise_try evd = function
     [] -> assert false
-- 
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