A fix for #5097 (status of evars refined by "clear" in ltac: closed wrt evars).

If an existing evar was cleared in pretyping (typically while
processing "ltac:"), it created an evar considered as new. Updating
them instead along the "cleared" flag.

If correct, I suspect similar treatment should be done for refining
along "change", "rename" and "move".

5 files changed, 59 insertions, 43 deletions

diff --git a/pretyping/evarutil.ml b/pretyping/evarutil.ml
index 759e0e4d6..9a9c946ae 100644
--- a/pretyping/evarutil.ml
+++ b/pretyping/evarutil.ml
@@ -600,6 +600,28 @@ let gather_dependent_evars evm l =
 
 (* /spiwack *)
 
+(** [advance sigma g] returns [Some g'] if [g'] is undefined and is
+    the current avatar of [g] (for instance [g] was changed by [clear]
+    into [g']). It returns [None] if [g] has been (partially)
+    solved. *)
+(* spiwack: [advance] is probably performance critical, and the good
+   behaviour of its definition may depend sensitively to the actual
+   definition of [Evd.find]. Currently, [Evd.find] starts looking for
+   a value in the heap of undefined variable, which is small. Hence in
+   the most common case, where [advance] is applied to an unsolved
+   goal ([advance] is used to figure if a side effect has modified the
+   goal) it terminates quickly. *)
+let rec advance sigma evk =
+  let evi = Evd.find sigma evk in
+  match evi.evar_body with
+  | Evar_empty -> Some evk
+  | Evar_defined v ->
+      if Option.default false (Store.get evi.evar_extra cleared) then
+        let (evk,_) = Term.destEvar v in
+        advance sigma evk
+      else
+        None
+
 (** The following functions return the set of undefined evars
     contained in the object, the defined evars being traversed.
     This is roughly a combination of the previous functions and
diff --git a/pretyping/evarutil.mli b/pretyping/evarutil.mli
index f68651a74..b60daae6d 100644
--- a/pretyping/evarutil.mli
+++ b/pretyping/evarutil.mli
@@ -123,6 +123,12 @@ val evar_absorb_arguments : env -> evar_map -> existential -> constr list ->
     its (partial) definition. *)
 val gather_dependent_evars : evar_map -> evar list -> (Evar.Set.t option) Evar.Map.t
 
+(** [advance sigma g] returns [Some g'] if [g'] is undefined and is
+    the current avatar of [g] (for instance [g] was changed by [clear]
+    into [g']). It returns [None] if [g] has been (partially)
+    solved. *)
+val advance : evar_map -> evar -> evar option
+
 (** The following functions return the set of undefined evars
     contained in the object, the defined evars being traversed.
     This is roughly a combination of the previous functions and
diff --git a/pretyping/pretyping.ml b/pretyping/pretyping.ml
index 2e164e540..c4ea79f95 100644
--- a/pretyping/pretyping.ml
+++ b/pretyping/pretyping.ml
@@ -183,17 +183,24 @@ type inference_flags = {
   expand_evars : bool
 }
 
-let frozen_holes (sigma, sigma') =
-  (); fun ev -> Evar.Map.mem ev (Evd.undefined_map sigma)
-
-let pending_holes (sigma, sigma') =
-  let fold evk _ accu =
-    if not (Evd.mem sigma evk) then Evar.Set.add evk accu else accu
-  in
-  Evd.fold_undefined fold sigma' Evar.Set.empty
+(* Compute the set of still-undefined initial evars up to restriction
+   (e.g. clearing) and the set of yet-unsolved evars freshly created
+   in the extension [sigma'] of [sigma] (excluding the restrictions of
+   the undefined evars of [sigma] to be freshly created evars of
+   [sigma']). Otherwise said, we partition the undefined evars of
+   [sigma'] into those already in [sigma] or deriving from an evar in
+   [sigma] by restriction, and the evars properly created in [sigma'] *)
+
+let frozen_and_pending_holes (sigma, sigma') =
+  let add_derivative_of evk evi acc =
+    match advance sigma' evk with None -> acc | Some evk' -> Evar.Set.add evk' acc in
+  let frozen = Evd.fold_undefined add_derivative_of sigma Evar.Set.empty in
+  let fold evk _ accu = if not (Evar.Set.mem evk frozen) then Evar.Set.add evk accu else accu in
+  let pending = Evd.fold_undefined fold sigma' Evar.Set.empty in
+  (frozen,pending)
 
 let apply_typeclasses env evdref frozen fail_evar =
-  let filter_frozen = frozen in
+  let filter_frozen evk = Evar.Set.mem evk frozen in
   evdref := Typeclasses.resolve_typeclasses
      ~filter:(if Flags.is_program_mode () 
 	      then (fun evk evi -> Typeclasses.no_goals_or_obligations evk evi && not (filter_frozen evk))
@@ -244,8 +251,7 @@ let check_evars_are_solved env current_sigma frozen pending =
 (* Try typeclasses, hooks, unification heuristics ... *)
 
 let solve_remaining_evars flags env current_sigma pending =
-  let frozen = frozen_holes pending in
-  let pending = pending_holes pending in
+  let frozen,pending = frozen_and_pending_holes pending in
   let evdref = ref current_sigma in
   if flags.use_typeclasses then apply_typeclasses env evdref frozen false;
   if Option.has_some flags.use_hook then
@@ -255,8 +261,7 @@ let solve_remaining_evars flags env current_sigma pending =
   !evdref
 
 let check_evars_are_solved env current_sigma pending =
-  let frozen = frozen_holes pending in
-  let pending = pending_holes pending in
+  let frozen,pending = frozen_and_pending_holes pending in
   check_evars_are_solved env current_sigma frozen pending
 
 let process_inference_flags flags env initial_sigma (sigma,c) =
diff --git a/proofs/proofview.ml b/proofs/proofview.ml
index 2fc404235..46a370d53 100644
--- a/proofs/proofview.ml
+++ b/proofs/proofview.ml
@@ -146,33 +146,9 @@ let focus i j sp =
   let (new_comb, context) = focus_sublist i j sp.comb in
   ( { sp with comb = new_comb } , context )
 
-
-(** [advance sigma g] returns [Some g'] if [g'] is undefined and is
-    the current avatar of [g] (for instance [g] was changed by [clear]
-    into [g']). It returns [None] if [g] has been (partially)
-    solved. *)
-(* spiwack: [advance] is probably performance critical, and the good
-   behaviour of its definition may depend sensitively to the actual
-   definition of [Evd.find]. Currently, [Evd.find] starts looking for
-   a value in the heap of undefined variable, which is small. Hence in
-   the most common case, where [advance] is applied to an unsolved
-   goal ([advance] is used to figure if a side effect has modified the
-   goal) it terminates quickly. *)
-let rec advance sigma g =
-  let open Evd in
-  let evi = Evd.find sigma g in
-  match evi.evar_body with
-  | Evar_empty -> Some g
-  | Evar_defined v ->
-      if Option.default false (Store.get evi.evar_extra Evarutil.cleared) then
-        let (e,_) = Term.destEvar v in
-        advance sigma e
-      else
-        None
-
 (** [undefined defs l] is the list of goals in [l] which are still
     unsolved (after advancing cleared goals). *)
-let undefined defs l = CList.map_filter (advance defs) l
+let undefined defs l = CList.map_filter (Evarutil.advance defs) l
 
 (** Unfocuses a proofview with respect to a context. *)
 let unfocus c sp =
@@ -429,7 +405,7 @@ let iter_goal i =
   Comb.get >>= fun initial ->
   Proof.List.fold_left begin fun (subgoals as cur) goal ->
     Solution.get >>= fun step ->
-    match advance step goal with
+    match Evarutil.advance step goal with
     | None -> return cur
     | Some goal ->
         Comb.set [goal] >>
@@ -453,7 +429,7 @@ let fold_left2_goal i s l =
   in 
   Proof.List.fold_left2 err begin fun ((r,subgoals) as cur) goal a ->
     Solution.get >>= fun step ->
-    match advance step goal with
+    match Evarutil.advance step goal with
     | None -> return cur
     | Some goal ->
         Comb.set [goal] >>
@@ -497,7 +473,7 @@ let tclDISPATCHGEN0 join tacs =
         let open Proof in
         Pv.get >>= function
         | { comb=[goal] ; solution } ->
-            begin match advance solution goal with
+            begin match Evarutil.advance solution goal with
             | None -> tclUNIT (join [])
             | Some _ -> Proof.map (fun res -> join [res]) tac
             end
@@ -1012,7 +988,7 @@ module Goal = struct
     Pv.get >>= fun step ->
     let sigma = step.solution in
     let map goal =
-      match advance sigma goal with
+      match Evarutil.advance sigma goal with
       | None -> None (** ppedrot: Is this check really necessary? *)
       | Some goal ->
         let gl =
@@ -1026,7 +1002,7 @@ module Goal = struct
 
   let unsolved { self=self } =
     tclEVARMAP >>= fun sigma ->
-    tclUNIT (not (Option.is_empty (advance sigma self)))
+    tclUNIT (not (Option.is_empty (Evarutil.advance sigma self)))
 
   (* compatibility *)
   let goal { self=self } = self
diff --git a/test-suite/bugs/closed/5097.v b/test-suite/bugs/closed/5097.v
new file mode 100644
index 000000000..37b239cf6
--- /dev/null
+++ b/test-suite/bugs/closed/5097.v
@@ -0,0 +1,7 @@
+(* Tracing existing evars along the weakening rule ("clear") *)
+Goal forall y, exists x, x=0->x=y.
+intros.
+eexists ?[x].
+intros.
+let x:=constr:(ltac:(clear y; exact 0)) in idtac x.
+Abort.