From a52a2d2110fcf20d532a2005c1957cba0d2c4043 Mon Sep 17 00:00:00 2001
From: Gaëtan Gilbert <gaetan.gilbert@skyskimmer.net>
Date: Fri, 11 May 2018 14:43:44 +0200
Subject: Fix restrict_universe_context

---
 engine/univops.ml  | 85 +++++++-----------------------------------------------
 engine/univops.mli |  5 +++-
 2 files changed, 14 insertions(+), 76 deletions(-)

(limited to 'engine')

diff --git a/engine/univops.ml b/engine/univops.ml
index 76dbaa250..3fd518490 100644
--- a/engine/univops.ml
+++ b/engine/univops.ml
@@ -35,79 +35,14 @@ let universes_of_constr env c =
     | _ -> Constr.fold aux s c
   in aux LSet.empty c
 
-type graphnode = {
-  mutable up : constraint_type LMap.t;
-  mutable visited : bool
-}
-
-let merge_types d d0 =
-  match d, d0 with
-  | _, Lt | Lt, _ -> Lt
-  | Le, _ | _, Le -> Le
-  | Eq, Eq -> Eq
-
-let merge_up d b up =
-  let find = try Some (LMap.find b up) with Not_found -> None in
-  match find with
-  | Some d0 ->
-    let d = merge_types d d0 in
-    if d == d0 then up else LMap.add b d up
-  | None -> LMap.add b d up
-
-let add_up a d b graph =
-  let node, graph =
-    try LMap.find a graph, graph
-    with Not_found ->
-      let node = { up = LMap.empty; visited = false } in
-      node, LMap.add a node graph
-  in
-  node.up <- merge_up d b node.up;
-  graph
-
-(* for each node transitive close until you find a non removable, discard the rest *)
-let transitive_close removable graph =
-  let rec do_node a node =
-    if not node.visited
-    then
-      let keepup =
-        LMap.fold (fun b d keepup ->
-            if not (LSet.mem b removable)
-            then merge_up d b keepup
-            else
-              begin
-                match LMap.find b graph with
-                | bnode ->
-                  do_node b bnode;
-                  LMap.fold (fun k d' keepup ->
-                    merge_up (merge_types d d') k keepup)
-                    bnode.up keepup
-                | exception Not_found -> keepup
-              end
-          )
-          node.up LMap.empty
-      in
-      node.up <- keepup;
-      node.visited <- true
-  in
-  LMap.iter do_node graph
-
-let restrict_universe_context (univs,csts) keep =
-  let removable = LSet.diff univs keep in
-  let (csts, rem) =
-    Constraint.fold (fun (a,d,b as cst) (csts, rem) ->
-        if LSet.mem a removable || LSet.mem b removable
-        then (csts, add_up a d b rem)
-        else (Constraint.add cst csts, rem))
-      csts (Constraint.empty, LMap.empty)
-  in
-  transitive_close removable rem;
-  let csts =
-    LMap.fold (fun a node csts ->
-        if LSet.mem a removable
-        then csts
-        else
-          LMap.fold (fun b d csts -> Constraint.add (a,d,b) csts)
-            node.up csts)
-      rem csts
-  in
+let restrict_universe_context (univs, csts) keep =
+  let removed = LSet.diff univs keep in
+  if LSet.is_empty removed then univs, csts
+  else
+  let allunivs = Constraint.fold (fun (u,_,v) all -> LSet.add u (LSet.add v all)) csts univs in
+  let g = UGraph.empty_universes in
+  let g = LSet.fold UGraph.add_universe_unconstrained allunivs g in
+  let g = UGraph.merge_constraints csts g in
+  let allkept = LSet.diff allunivs removed in
+  let csts = UGraph.constraints_for ~kept:allkept g in
   (LSet.inter univs keep, csts)
diff --git a/engine/univops.mli b/engine/univops.mli
index d1585414c..0b37ab975 100644
--- a/engine/univops.mli
+++ b/engine/univops.mli
@@ -14,5 +14,8 @@ open Univ
 (** The universes of monomorphic constants appear. *)
 val universes_of_constr : Environ.env -> constr -> LSet.t
 
-(** Shrink a universe context to a restricted set of variables *)
+(** [restrict_universe_context (univs,csts) keep] restricts [univs] to
+   the universes in [keep]. The constraints [csts] are adjusted so
+   that transitive constraints between remaining universes (those in
+   [keep] and those not in [univs]) are preserved. *)
 val restrict_universe_context : ContextSet.t -> LSet.t -> ContextSet.t
-- 
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