refresh metas in rewrite hints loaded from .vo files (fix bug #3815)

Meta variables in rewrite rules are named by integers that are allocated
sequentially at runtime (fresh_meta in tactics/term_dnet.ml).  This causes
a problem when some rewrite rules (with meta variables) are generated by
coqc, saved in a .vo file, and then imported into another coqc/coqtop
process.  The new process will allocate its own meta variable numbers
starting from 0, colliding with existing imported meta variable numbers.
One manifestation of this issue was various failures of [rewrite_strat];
see bug #3815 for examples.

This change fixes the problem, by replacing all meta variable numbers
in imported rewrite rules at import time.  This seems to fix the various
failures reported in bug #3815.

Thanks to Jason Gross for tracking down the commit that introduced this
bug in the first place (71a9b7f2).

5 files changed, 27 insertions, 0 deletions

diff --git a/tactics/autorewrite.ml b/tactics/autorewrite.ml
index ee8e1855d..4eb8a7925 100644
--- a/tactics/autorewrite.ml
+++ b/tactics/autorewrite.ml
@@ -211,6 +211,7 @@ let cache_hintrewrite (_,(rbase,lrl)) =
   let base = try raw_find_base rbase with Not_found -> HintDN.empty in
   let max = try fst (Util.List.last (HintDN.find_all base)) with Failure _ -> 0
   in
+  let lrl = HintDN.refresh_metas lrl in
   let lrl = HintDN.map (fun (i,h) -> (i + max, h)) lrl in
     rewtab:=String.Map.add rbase (HintDN.union lrl base) !rewtab
 
diff --git a/tactics/dnet.ml b/tactics/dnet.ml
index bb71620c0..93334db73 100644
--- a/tactics/dnet.ml
+++ b/tactics/dnet.ml
@@ -39,6 +39,7 @@ sig
   val inter : t -> t -> t
   val union : t -> t -> t
   val map : (ident -> ident) -> (unit structure -> unit structure) -> t -> t
+  val map_metas : (meta -> meta) -> t -> t
 end
 
 module Make =
@@ -288,4 +289,13 @@ struct
       | Node e -> Node (T.map (map sidset sterm) e) in
     Nodes (tmap_map sterm snode t, Mmap.map (idset_map sidset) m)
 
+  let rec map_metas f (Nodes (t, m)) : t =
+    let f_node = function
+      | Terminal (e, is) -> Terminal (T.map (map_metas f) e, is)
+      | Node e -> Node (T.map (map_metas f) e)
+    in
+    let m' = Mmap.fold (fun m s acc -> Mmap.add (f m) s acc) m Mmap.empty in
+    let t' = Tmap.fold (fun k n acc -> Tmap.add k (f_node n) acc) t Tmap.empty in
+    Nodes (t', m')
+
 end
diff --git a/tactics/dnet.mli b/tactics/dnet.mli
index 4bfa7263e..52853d702 100644
--- a/tactics/dnet.mli
+++ b/tactics/dnet.mli
@@ -113,6 +113,8 @@ sig
 
   (** apply a function on each identifier and node of terms in a dnet *)
   val map : (ident -> ident) -> (unit structure -> unit structure) -> t -> t
+
+  val map_metas : (meta -> meta) -> t -> t
 end
 
 module Make :
diff --git a/tactics/term_dnet.ml b/tactics/term_dnet.ml
index e637b2e36..e79fc6dc9 100644
--- a/tactics/term_dnet.ml
+++ b/tactics/term_dnet.ml
@@ -371,6 +371,17 @@ struct
   let find_all dn = Idset.elements (TDnet.find_all dn)
 
   let map f dn = TDnet.map f (fun x -> x) dn
+
+  let refresh_metas dn =
+    let new_metas = ref Int.Map.empty in
+    let refresh_one_meta i =
+      try Int.Map.find i !new_metas
+      with Not_found ->
+        let new_meta = fresh_meta () in
+        let () = new_metas := Int.Map.add i new_meta !new_metas in
+        new_meta
+    in
+    TDnet.map_metas refresh_one_meta dn
 end
 
 module type S =
@@ -385,4 +396,5 @@ sig
   val search_pattern : t -> constr -> ident list
   val find_all : t -> ident list
   val map : (ident -> ident) -> t -> t
+  val refresh_metas : t -> t
 end
diff --git a/tactics/term_dnet.mli b/tactics/term_dnet.mli
index a5c80cc00..58f95ac6c 100644
--- a/tactics/term_dnet.mli
+++ b/tactics/term_dnet.mli
@@ -80,6 +80,8 @@ sig
   val find_all : t -> ident list
 
   val map : (ident -> ident) -> t -> t
+
+  val refresh_metas : t -> t
 end
 
 module Make :