From e8bde450d05908f70ab2c82d9d24f0807c56a94a Mon Sep 17 00:00:00 2001
From: Emilio Jesus Gallego Arias
Date: Wed, 4 Mar 2020 21:39:42 -0500
Subject: [exn] [tactics] improve backtraces on monadic errors

Current backtraces for tactics leave a bit to desire, for example
given the program:

```coq
Lemma u n : n + 0 = n.
rewrite plus_O_n.
```

the backtrace stops at:

```
Found no subterm matching "0 + ?M160" in the current goal.
Called from file "proofs/proof.ml", line 381, characters 4-42
Called from file "tactics/pfedit.ml", line 102, characters 31-58
Called from file "plugins/ltac/g_ltac.mlg", line 378, characters 8-84
```

Backtrace information `?info` is as of today optional in some tactics,
such as `tclZERO`, it doesn't cost a lot  however to reify backtrace
information indeed in `tclZERO` and provide backtraces for all tactic
errors. The cost should be small if we are not in debug mode.

The backtrace for the failed rewrite is now:

```
Found no subterm matching "0 + ?M160" in the current goal.
Raised at file "pretyping/unification.ml", line 1827, characters 14-73
Called from file "pretyping/unification.ml", line 1929, characters 17-53
Called from file "pretyping/unification.ml", line 1948, characters 22-72
Called from file "pretyping/unification.ml", line 2020, characters 14-56
Re-raised at file "pretyping/unification.ml", line 2021, characters 66-73
Called from file "proofs/clenv.ml", line 254, characters 12-58
Called from file "proofs/clenvtac.ml", line 95, characters 16-53
Called from file "engine/proofview.ml", line 1110, characters 40-46
Called from file "engine/proofview.ml", line 1115, characters 10-34
Re-raised at file "clib/exninfo.ml", line 82, characters 4-38
Called from file "proofs/proof.ml", line 381, characters 4-42
Called from file "tactics/pfedit.ml", line 102, characters 31-58
Called from file "plugins/ltac/g_ltac.mlg", line 378, characters 8-84
```

which IMO is much better.
---
 plugins/omega/coq_omega.ml | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

(limited to 'plugins/omega')

diff --git a/plugins/omega/coq_omega.ml b/plugins/omega/coq_omega.ml
index 79d6c05e1d..3ba6365783 100644
--- a/plugins/omega/coq_omega.ml
+++ b/plugins/omega/coq_omega.ml
@@ -1475,7 +1475,9 @@ let coq_omega =
       let path = simplify_strong (new_id,new_var_num,display_var) system in
       if !display_action_flag then display_action display_var path;
       tclTHEN prelude (replay_history tactic_normalisation path)
-    with NO_CONTRADICTION -> tclZEROMSG (Pp.str"Omega can't solve this system")
+    with NO_CONTRADICTION as e ->
+      let _, info = Exninfo.capture e in
+      tclZEROMSG ~info (Pp.str"Omega can't solve this system")
   end
   end
 
@@ -1890,7 +1892,9 @@ let destructure_goal =
                                          end)
                 intro
             with Undecidable -> Tactics.elim_type (Lazy.force coq_False)
-            | e when Proofview.V82.catchable_exception e -> Proofview.tclZERO e
+            | e when Proofview.V82.catchable_exception e ->
+              let e, info = Exninfo.capture e in
+              Proofview.tclZERO ~info e
           in
           tclTHEN goal_tac destructure_hyps
     in
-- 
cgit v1.2.3