Do not give a name to anonymous evars anymore. See bug #4547.

The current solution may not be totally ideal though. We generate names for
anonymous evars on the fly at printing time, based on the Evar_kind data they
are wearing. This means in particular that the printed name of an anonymous
evar may change in the future because some unrelate evar has been solved or
introduced.

interp/constrextern.ml

@@ -988,7 +988,10 @@ let rec glob_of_pat env sigma = function
   | PEvar (evk,l) ->
       let test (id,_,_) = function PVar id' -> Id.equal id id' | _ -> false in
       let l = Evd.evar_instance_array test (Evd.find sigma evk) l in
-      let id = Evd.evar_ident evk sigma in
+      let id = match Evd.evar_ident evk sigma with
+      | None -> Id.of_string "__"
+      | Some id -> id
+      in
       GEvar (loc,id,List.map (on_snd (glob_of_pat env sigma)) l)
   | PRel n ->
       let id = try match lookup_name_of_rel n env with

pretyping/detyping.ml

@@ -518,7 +518,10 @@ let rec detype flags avoid env sigma t =
 	  with Not_found -> isVarId id c in
       let id,l =
         try
-          let id = Evd.evar_ident evk sigma in
+          let id = match Evd.evar_ident evk sigma with
+          | None -> Evd.pr_evar_suggested_name evk sigma
+          | Some id -> id
+          in
           let l = Evd.evar_instance_array bound_to_itself_or_letin (Evd.find sigma evk) cl in
           let fvs,rels = List.fold_left (fun (fvs,rels) (_,c) -> match kind_of_term c with Rel n -> (fvs,Int.Set.add n rels) | Var id -> (Id.Set.add id fvs,rels) | _ -> (fvs,rels)) (Id.Set.empty,Int.Set.empty) l in
           let l = Evd.evar_instance_array (fun d c -> not !print_evar_arguments && (bound_to_itself_or_letin d c && not (isRel c && Int.Set.mem (destRel c) rels || isVar c && (Id.Set.mem (destVar c) fvs)))) (Evd.find sigma evk) cl in

pretyping/evarutil.ml

@@ -365,14 +365,7 @@ let new_pure_evar_full evd evi =
   (evd, evk)
 
 let new_pure_evar sign evd ?(src=default_source) ?filter ?candidates ?store ?naming ?(principal=false) typ =
-  let default_naming =
-    if principal then
-        (* waiting for a more principled approach
-           (unnamed evars, private names?) *)
-        Misctypes.IntroFresh (Names.Id.of_string "tmp_goal")
-      else
-        Misctypes.IntroAnonymous
-  in
+  let default_naming = Misctypes.IntroAnonymous in
   let naming = Option.default default_naming naming in
   let newevk = new_untyped_evar() in
   let evd = evar_declare sign newevk typ ~src ?filter ?candidates ?store ~naming evd in

pretyping/evd.ml

@@ -208,15 +208,6 @@ let map_evar_info f evi =
     evar_concl = f evi.evar_concl;
     evar_candidates = Option.map (List.map f) evi.evar_candidates }
 
-let evar_ident_info evi =
-  match evi.evar_source with
-  | _,Evar_kinds.ImplicitArg (c,(n,Some id),b) -> id
-  | _,Evar_kinds.VarInstance id -> id
-  | _,Evar_kinds.GoalEvar -> Id.of_string "Goal"
-  | _ ->
-      let env = reset_with_named_context evi.evar_hyps (Global.env()) in
-      Namegen.id_of_name_using_hdchar env evi.evar_concl Anonymous
-
 (* This exception is raised by *.existential_value *)
 exception NotInstantiatedEvar
 
@@ -588,7 +579,7 @@ val add_name_undefined : intro_pattern_naming_expr -> Evar.t -> evar_info -> t -
 val remove_name_defined : Evar.t -> t -> t
 val rename : Evar.t -> Id.t -> t -> t
 val reassign_name_defined : Evar.t -> Evar.t -> t -> t
-val ident : Evar.t -> t -> Id.t
+val ident : Evar.t -> t -> Id.t option
 val key : Id.t -> t -> Evar.t
 
 end =
@@ -598,47 +589,52 @@ type t = Id.t EvMap.t * existential_key Idmap.t
 
 let empty = (EvMap.empty, Idmap.empty)
 
-let add_name_newly_undefined naming evk evi (evtoid,idtoev) =
+let add_name_newly_undefined naming evk evi (evtoid, idtoev as names) =
   let id = match naming with
-  | Misctypes.IntroAnonymous ->
-      let id = evar_ident_info evi in
-      Namegen.next_ident_away_from id (fun id -> Idmap.mem id idtoev)
+  | Misctypes.IntroAnonymous -> None
   | Misctypes.IntroIdentifier id ->
-      let id' =
-        Namegen.next_ident_away_from id (fun id -> Idmap.mem id idtoev) in
-      if not (Names.Id.equal id id') then
-        user_err_loc
-          (Loc.ghost,"",str "Already an existential evar of name " ++ pr_id id);
-      id'
+    if Idmap.mem id idtoev then
+    user_err_loc
+      (Loc.ghost,"",str "Already an existential evar of name " ++ pr_id id);
+    Some id
   | Misctypes.IntroFresh id ->
-      Namegen.next_ident_away_from id (fun id -> Idmap.mem id idtoev) in
-  (EvMap.add evk id evtoid, Idmap.add id evk idtoev)
+    let id = Namegen.next_ident_away_from id (fun id -> Idmap.mem id idtoev) in
+    Some id
+  in
+  match id with
+  | None -> names
+  | Some id -> (EvMap.add evk id evtoid, Idmap.add id evk idtoev)
 
 let add_name_undefined naming evk evi (evtoid,idtoev as evar_names) =
   if EvMap.mem evk evtoid then
     evar_names
   else
     add_name_newly_undefined naming evk evi evar_names
 
-let remove_name_defined evk (evtoid,idtoev) =
-  let id = EvMap.find evk evtoid in
-  (EvMap.remove evk evtoid, Idmap.remove id idtoev)
+let remove_name_defined evk (evtoid, idtoev as names) =
+  let id = try Some (EvMap.find evk evtoid) with Not_found -> None in
+  match id with
+  | None -> names
+  | Some id -> (EvMap.remove evk evtoid, Idmap.remove id idtoev)
 
 let rename evk id (evtoid, idtoev) =
-  let id' = EvMap.find evk evtoid in
-  if Idmap.mem id idtoev then anomaly (str "Evar name already in use");
-  (EvMap.add evk id evtoid (* overwrite old name *), Idmap.add id evk (Idmap.remove id' idtoev))
-
-let reassign_name_defined evk evk' (evtoid,idtoev) =
-  let id = EvMap.find evk evtoid in
-  (EvMap.add evk' id (EvMap.remove evk evtoid),
-   Idmap.add id evk' (Idmap.remove id idtoev))
+  let id' = try Some (EvMap.find evk evtoid) with Not_found -> None in
+  match id' with
+  | None -> (EvMap.add evk id evtoid, Idmap.add id evk idtoev)
+  | Some id' ->
+    if Idmap.mem id idtoev then anomaly (str "Evar name already in use");
+    (EvMap.update evk id evtoid (* overwrite old name *), Idmap.add id evk (Idmap.remove id' idtoev))
+
+let reassign_name_defined evk evk' (evtoid, idtoev as names) =
+  let id = try Some (EvMap.find evk evtoid) with Not_found -> None in
+  match id with
+  | None -> names (** evk' must not be defined *)
+  | Some id ->
+    (EvMap.add evk' id (EvMap.remove evk evtoid),
+    Idmap.add id evk' (Idmap.remove id idtoev))
 
 let ident evk (evtoid, _) =
-  try EvMap.find evk evtoid
-  with Not_found ->
-    (* Unnamed (non-dependent) evar *)
-    add_suffix (Id.of_string "X") (string_of_int (Evar.repr evk))
+  try Some (EvMap.find evk evtoid) with Not_found -> None
 
 let key id (_, idtoev) =
   Idmap.find id idtoev
@@ -682,7 +678,7 @@ let add d e i = match i.evar_body with
   let evar_names = EvNames.add_name_undefined Misctypes.IntroAnonymous e i d.evar_names in
   { d with undf_evars = EvMap.add e i d.undf_evars; evar_names }
 | Evar_defined _ ->
-  let evar_names = try EvNames.remove_name_defined e d.evar_names with Not_found -> d.evar_names in
+  let evar_names = EvNames.remove_name_defined e d.evar_names in
   { d with defn_evars = EvMap.add e i d.defn_evars; evar_names }
 
 let remove d e =
@@ -1706,7 +1702,34 @@ type unsolvability_explanation = SeveralInstancesFound of int
 (**********************************************************)
 (* Pretty-printing *)
 
-let pr_existential_key sigma evk = str "?" ++ pr_id (evar_ident evk sigma)
+let pr_evar_suggested_name evk sigma =
+  let base_id evk' evi =
+  match evar_ident evk' sigma with
+  | Some id -> id
+  | None -> match evi.evar_source with
+  | _,Evar_kinds.ImplicitArg (c,(n,Some id),b) -> id
+  | _,Evar_kinds.VarInstance id -> id
+  | _,Evar_kinds.GoalEvar -> Id.of_string "Goal"
+  | _ ->
+      let env = reset_with_named_context evi.evar_hyps (Global.env()) in
+      Namegen.id_of_name_using_hdchar env evi.evar_concl Anonymous
+  in
+  let names = EvMap.mapi base_id sigma.undf_evars in
+  let id = EvMap.find evk names in
+  let fold evk' id' (seen, n) =
+    if seen then (seen, n)
+    else if Evar.equal evk evk' then (true, n)
+    else if Id.equal id id' then (seen, succ n)
+    else (seen, n)
+  in
+  let (_, n) = EvMap.fold fold names (false, 0) in
+  if n = 0 then id else Nameops.add_suffix id (string_of_int (pred n))
+
+let pr_existential_key sigma evk = match evar_ident evk sigma with
+| None ->
+  str "?" ++ pr_id (pr_evar_suggested_name evk sigma)
+| Some id ->
+  str "?" ++ pr_id id
 
 let pr_instance_status (sc,typ) =
   begin match sc with
@@ -1895,7 +1918,7 @@ let pr_evar_list sigma l =
     h 0 (str (string_of_existential ev) ++
       str "==" ++ pr_evar_info evi ++
       (if evi.evar_body == Evar_empty
-       then str " {" ++ pr_id (evar_ident ev sigma) ++ str "}"
+       then str " {" ++  pr_existential_key sigma ev ++ str "}"
        else mt ()))
   in
   h 0 (prlist_with_sep fnl pr l)

pretyping/evd.mli

@@ -249,7 +249,7 @@ val evar_source : existential_key -> evar_map -> Evar_kinds.t located
 (** Convenience function. Wrapper around {!find} to recover the source of an
     evar in a given evar map. *)
 
-val evar_ident : existential_key -> evar_map -> Id.t
+val evar_ident : existential_key -> evar_map -> Id.t option
 
 val rename : existential_key -> Id.t -> evar_map -> evar_map
 
@@ -603,6 +603,8 @@ type unsolvability_explanation = SeveralInstancesFound of int
 
 val pr_existential_key : evar_map -> evar -> Pp.std_ppcmds
 
+val pr_evar_suggested_name : existential_key -> evar_map -> Id.t
+
 (** {5 Debug pretty-printers} *)
 
 val pr_evar_info : evar_info -> Pp.std_ppcmds

printing/printer.ml

@@ -400,7 +400,7 @@ let display_name = false
 
 (* display a goal name *)
 let pr_goal_name sigma g =
-  if display_name then str " " ++ Pp.surround (pr_id (Evd.evar_ident g sigma))
+  if display_name then str " " ++ Pp.surround (pr_existential_key sigma g)
   else mt ()
 
 (* display the conclusion of a goal *)

proofs/goal.ml

@@ -89,7 +89,10 @@ module V82 = struct
   (* Instantiates a goal with an open term, using name of goal for evk' *)
   let partial_solution_to sigma evk evk' c =
     let id = Evd.evar_ident evk sigma in
-    Evd.rename evk' id (partial_solution sigma evk c)
+    let sigma = partial_solution sigma evk c in
+    match id with
+    | None -> sigma
+    | Some id -> Evd.rename evk' id sigma
 
   (* Parts of the progress tactical *)
   let same_goal evars1 gl1 evars2 gl2 =

proofs/proofview.ml

@@ -1093,7 +1093,10 @@ struct
       | None -> Evd.define gl.Goal.self c sigma
       | Some evk ->
           let id = Evd.evar_ident gl.Goal.self sigma in
-          Evd.rename evk id (Evd.define gl.Goal.self c sigma)
+          let sigma = Evd.define gl.Goal.self c sigma in
+          match id with
+          | None -> sigma
+          | Some id -> Evd.rename evk id sigma
     in
     (** Restore the [future goals] state. *)
     let sigma = Evd.restore_future_goals sigma prev_future_goals prev_principal_goal in

test-suite/bugs/closed/3068.v

@@ -56,7 +56,7 @@ Section Finite_nat_set.
       subst fs1.
       apply iff_refl.
     intros H.
-    eapply counted_list_equal_nth_char.
+    eapply (counted_list_equal_nth_char _ _ _ _ ?[def]).
     intros i.
     destruct (counted_def_nth fs1 i _ ) eqn:H0.
     (* This was not part of the initial bug report; this is to check that

test-suite/output/Existentials.out

@@ -1,5 +1,4 @@
-Existential 1 =
-?Goal1 : [p : nat  q := S p : nat  n : nat  m : nat |- ?y = m] 
+Existential 1 = ?Goal : [p : nat  q := S p : nat  n : nat  m : nat |- ?y = m] 
 Existential 2 =
 ?y : [p : nat  q := S p : nat  n : nat  m : nat |- nat] (p, q cannot be used)
 Existential 3 = ?Goal0 : [q : nat  n : nat  m : nat |- n = ?y] 

test-suite/output/Notations.out

@@ -111,14 +111,14 @@ fun x : option Z => match x with
                     | NONE2 => 0
                     end
      : option Z -> Z
-fun x : list ?T1 => match x with
-                    | NIL => NONE2
-                    | (_ :') t => SOME2 t
-                    end
-     : list ?T1 -> option (list ?T1)
+fun x : list ?T => match x with
+                   | NIL => NONE2
+                   | (_ :') t => SOME2 t
+                   end
+     : list ?T -> option (list ?T)
 where
-?T1 : [x : list ?T1  x1 : list ?T1  x0 := x1 : list ?T1 |- Type] (x, x1,
-      x0 cannot be used)
+?T : [x : list ?T  x1 : list ?T  x0 := x1 : list ?T |- Type] (x, x1,
+     x0 cannot be used)
 s
      : s
 10

test-suite/output/inference.out

@@ -9,10 +9,10 @@ fun (m n p : nat) (H : S m <= S n + p) => le_S_n m (n + p) H
 fun n : nat => let x := A n in ?y ?y0 : T n
      : forall n : nat, T n
 where
-?y : [n : nat  x := A n : T n |- ?T0 -> T n] 
-?y0 : [n : nat  x := A n : T n |- ?T0] 
+?y : [n : nat  x := A n : T n |- ?T -> T n] 
+?y0 : [n : nat  x := A n : T n |- ?T] 
 fun n : nat => ?y ?y0 : T n
      : forall n : nat, T n
 where
-?y : [n : nat |- ?T0 -> T n] 
-?y0 : [n : nat |- ?T0] 
+?y : [n : nat |- ?T -> T n] 
+?y0 : [n : nat |- ?T] 

test-suite/success/apply.v

@@ -543,7 +543,7 @@ Qed.
 Lemma bar (X: nat -> nat -> Prop) (foo:forall x, X x x) (a: unit) (H: tt = a):
   exists x, exists y, X x y.
 Proof.
-intros; eexists; eexists; case H.
+intros; eexists; eexists ?[y]; case H.
 apply (foo ?y).
 Grab Existential Variables.
 exact 0.

test-suite/success/destruct.v

@@ -96,21 +96,21 @@ Abort.
 (* Check that subterm selection does not solve existing evars *)
 
 Goal exists x, S x = S 0.
-eexists.
+eexists ?[x].
 Show x.  (* Incidentally test Show on a named goal *)
 destruct (S _). (* Incompatible occurrences but takes the first one since Oct 2014 *)
 change (0 = S 0).
 Abort.
 
 Goal exists x, S 0 = S x.
-eexists.
+eexists ?[x].
 destruct (S _). (* Incompatible occurrences but takes the first one since Oct 2014 *)
 change (0 = S ?x).
 [x]: exact 0. (* Incidentally test applying a tactic to a goal on the shelve *)
 Abort.
 
 Goal exists n p:nat, (S n,S n) = (S p,S p) /\ p = n.
-do 2 eexists.
+eexists ?[n]; eexists ?[p].
 destruct (_, S _). (* Was unifying at some time in trunk, now takes the first occurrence *)
 change ((n, n0) = (S ?p, S ?p) /\ ?p = ?n).
 Abort.
@@ -426,7 +426,7 @@ destruct b eqn:H.
 (* Check natural instantiation behavior when the goal has already an evar *)
 
 Goal exists x, S x = x.
-eexists.
+eexists ?[x].
 destruct (S _).
 change (0 = ?x).
 Abort.