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, 12 insertions, 0 deletions

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