In Regular Subst Tactic mode, ensure that the order of hypotheses is

preserved, which is a source of incompatibilities w.r.t. released 8.5
but which looks to me to be the only possible canonical behavior.

This is I believe a better behavior than the Regular Subst Tactic
behavior in the released 8.5 and 8.5pl1. There, the order of
hypotheses in which substitutions happened was respected, but their
interleaving with other hypotheses was not respected.

So, I consider this to be a fix to the "Regular Subst Tactic" mode.

Also added a more detailed "specification" of the "Regular" behavior
of "subst" in the reference manual.

1 files changed, 18 insertions, 17 deletions

diff --git a/tactics/equality.ml b/tactics/equality.ml
index f72a72f46d..819a995db1 100644
--- a/tactics/equality.ml
+++ b/tactics/equality.ml
@@ -1595,6 +1595,17 @@ user = raise user error specific to rewrite
 (**********************************************************************)
 (* Substitutions tactics (JCF) *)
 
+let regular_subst_tactic = ref false
+
+let _ =
+  declare_bool_option
+    { optsync  = true;
+      optdepr  = false;
+      optname  = "more regular behavior of tactic subst";
+      optkey   = ["Regular";"Subst";"Tactic"];
+      optread  = (fun () -> !regular_subst_tactic);
+      optwrite = (:=) regular_subst_tactic }
+
 let unfold_body x =
   Proofview.Goal.enter begin fun gl ->
   (** We normalize the given hypothesis immediately. *)
@@ -1642,23 +1653,24 @@ let subst_one dep_proof_ok x (hyp,rhs,dir) =
   let concl = Proofview.Goal.concl (Proofview.Goal.assume gl) in
   (* The set of hypotheses using x *)
   let dephyps =
-    List.rev (snd (List.fold_right (fun (id,b,_ as dcl) (deps,allhyps) ->
+    List.rev (pi3 (List.fold_right (fun (id,b,_ as dcl) (dest,deps,allhyps) ->
       if not (Id.equal id hyp)
          && List.exists (fun y -> occur_var_in_decl env y dcl) deps
       then
-        ((if b = None then deps else id::deps), id::allhyps)
+        let id_dest = if !regular_subst_tactic then dest else MoveLast in
+        (dest,(if b = None then deps else id::deps), (id_dest,id)::allhyps)
       else
-        (deps,allhyps))
+        (MoveBefore id,deps,allhyps))
       hyps
-      ([x],[]))) in
+      (MoveBefore x,[x],[]))) in (* In practice, no dep hyps before x, so MoveBefore x is good enough *)
   (* Decides if x appears in conclusion *)
   let depconcl = occur_var env x concl in
   let need_rewrite = not (List.is_empty dephyps) || depconcl in
   tclTHENLIST
     ((if need_rewrite then
-      [revert dephyps;
+      [revert (List.map snd dephyps);
        general_rewrite dir AllOccurrences true dep_proof_ok (mkVar hyp);
-       (tclMAP intro_using dephyps)]
+       (tclMAP (fun (dest,id) -> intro_move (Some id) dest) dephyps)]
       else
        [Proofview.tclUNIT ()]) @
      [tclTRY (clear [x; hyp])])
@@ -1709,17 +1721,6 @@ let default_subst_tactic_flags () =
   else
     { only_leibniz = true; rewrite_dependent_proof = false }
 
-let regular_subst_tactic = ref false
-
-let _ =
-  declare_bool_option
-    { optsync  = true;
-      optdepr  = false;
-      optname  = "more regular behavior of tactic subst";
-      optkey   = ["Regular";"Subst";"Tactic"];
-      optread  = (fun () -> !regular_subst_tactic);
-      optwrite = (:=) regular_subst_tactic }
-
 let subst_all ?(flags=default_subst_tactic_flags ()) () =
 
   if !regular_subst_tactic then