From 0a00445b113d61a82613f1ba641454b76bd6387c Mon Sep 17 00:00:00 2001
From: Pierre-Marie Pédrot
Date: Mon, 16 Jul 2018 14:07:01 +0200
Subject: Fix #7291: unify tactic should have more descriptive error messages.

We simply reuse the same exception as the pretyper instead of raising the
generic failure exception in Tactics.unify.
---
 tactics/tactics.ml | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tactics/tactics.ml b/tactics/tactics.ml
index 928530744a..3a09a0e00e 100644
--- a/tactics/tactics.ml
+++ b/tactics/tactics.ml
@@ -5062,6 +5062,7 @@ let constr_eq ~strict x y =
 
 let unify ?(state=full_transparent_state) x y =
   Proofview.Goal.enter begin fun gl ->
+  let env = Proofview.Goal.env gl in
   let sigma = Proofview.Goal.sigma gl in
   try
     let core_flags =
@@ -5077,7 +5078,7 @@ let unify ?(state=full_transparent_state) x y =
     let sigma = w_unify (Tacmach.New.pf_env gl) sigma Reduction.CONV ~flags x y in
     Proofview.Unsafe.tclEVARS sigma
   with e when CErrors.noncritical e ->
-    Tacticals.New.tclFAIL 0 (str"Not unifiable")
+    Proofview.tclZERO (PretypeError (env, sigma, CannotUnify (x, y, None)))
   end
 
 module Simple = struct
-- 
cgit v1.2.3


From ec0e4eb918fc6d95abd5f92b9bea0464662e7245 Mon Sep 17 00:00:00 2001
From: Pierre-Marie Pédrot
Date: Tue, 24 Jul 2018 11:07:04 +0200
Subject: Update the documentation w.r.t. the new error raised by unify.

---
 doc/sphinx/proof-engine/tactics.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/sphinx/proof-engine/tactics.rst b/doc/sphinx/proof-engine/tactics.rst
index ec085a71e5..89668a2d7e 100644
--- a/doc/sphinx/proof-engine/tactics.rst
+++ b/doc/sphinx/proof-engine/tactics.rst
@@ -3976,7 +3976,7 @@ succeeds, and results in an error otherwise.
    This tactic checks whether its arguments are unifiable, potentially
    instantiating existential variables.
 
-.. exn:: Not unifiable.
+.. exn:: Unable to unify @term with @term.
 
 .. tacv:: unify @term @term with @ident
 
-- 
cgit v1.2.3