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).

1 files changed, 10 insertions, 0 deletions

diff --git a/tactics/dnet.ml b/tactics/dnet.ml
index bb71620c09..93334db73c 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