[typeclasses] functionalize typeclass evar handling

This avoids all the side effects associated with the manipulation of an
unresolvable flag. In the new design:

- The evar_map stores a set of evars that are candidates for typeclass
  resolution, which can be retrieved and set.

  We maintain the invariant that it always contains only undefined
  evars.

- At the creation time of an evar (new_evar), we classify it as a
  potential candidate of resolution.

  - This uses a hook to test if the conclusion ends in a typeclass
    application. (hook set in typeclasses.ml)

  - This is an approximation if the conclusion is an existential (i.e.
    not yet determined). In that case we register the evar as
    potentially a typeclass instance, and later phases must consider
    that case, dropping the evar if it is not a typeclass.

  - One can pass the ~typeclass_candidate:false flag to new_evar to
    prevent classification entirely. Typically this is for new goals
    which should not ever be considered to be typeclass resolution
    candidates.

  - One can mark a subset of evars unresolvable later if
    needed. Typically for clausenv, and marking future goals as
    unresolvable even if they are typeclass goals. For clausenv for
    example, after turing metas into evars we first (optionally) try a
    typeclass resolution on the newly created evars and only then mark
    the remaining newly created evars as subgoals. The intent of the
    code looks clearer now.

  This should prevent keeping testing if undefined evars are classes
  all the time and crawling large sets when no typeclasses are present.

- Typeclass candidate evars stay candidates through
  restriction/evar-evar solutions.

- Evd.add uses ~typeclass_candidate:false to avoid recomputing if the new
  evar is a candidate. There's a deficiency in the API, in most use
  cases of Evd.add we should rather use a:

  `Evd.update_evar_info : evar_map -> Evar.t -> (evar_info -> evar_info)
  -> evar_map`

  Usually it is only about nf_evar'ing the evar_info's contents, which
  doesn't change the evar candidate status.

- Typeclass resolution can now handle the set of candidates
  functionally: it always starts from the set of candidates (and not the
  whole undefined_map) and a filter on it, potentially splitting it in
  connected components, does proof search for each component in an
  evar_map with an empty set of typeclass evars (allowing clean
  reentrancy), then reinstates the potential remaining unsolved
  components and filtered out typeclass evars at the end of
  resolution.

  This means no more marking of resolvability/unresolvability
  everywhere, and hopefully a more efficient implementation in general.

- This is on top of the cleanup of evar_info's currently but can
  be made independent.

[typeclasses] Fix cases.ml: none of the new_evars should be typeclass candidates

Solve bug in inheritance of flags in evar-evar solutions.

Renaming unresolvable to typeclass_candidate (positive) and fix maybe_typeclass_hook

2 files changed, 41 insertions, 66 deletions

diff --git a/tactics/autorewrite.ml b/tactics/autorewrite.ml
index 8e296de617..76cbdee0d5 100644
--- a/tactics/autorewrite.ml
+++ b/tactics/autorewrite.ml
@@ -226,7 +226,7 @@ let decompose_applied_relation metas env sigma c ctype left2right =
     let eqclause = Clenv.mk_clenv_from_env env sigma None (EConstr.of_constr c,ty) in
     let eqclause =
       if metas then eqclause
-      else clenv_pose_metas_as_evars eqclause (Evd.undefined_metas eqclause.evd)
+      else fst (clenv_pose_metas_as_evars eqclause (Evd.undefined_metas eqclause.evd))
     in
     let (equiv, args) = EConstr.decompose_app sigma (Clenv.clenv_type eqclause) in
     let rec split_last_two = function
diff --git a/tactics/class_tactics.ml b/tactics/class_tactics.ml
index f075e5e44a..81cf9289d1 100644
--- a/tactics/class_tactics.ml
+++ b/tactics/class_tactics.ml
@@ -494,15 +494,15 @@ let top_sort evm undefs =
   let tosee = ref undefs in
   let rec visit ev evi =
     let evs = Evarutil.undefined_evars_of_evar_info evm evi in
-      tosee := Evar.Map.remove ev !tosee;
+      tosee := Evar.Set.remove ev !tosee;
       Evar.Set.iter (fun ev ->
-        if Evar.Map.mem ev !tosee then
-          visit ev (Evar.Map.find ev !tosee)) evs;
+        if Evar.Set.mem ev !tosee then
+          visit ev (Evd.find evm ev)) evs;
       l' := ev :: !l';
   in
-    while not (Evar.Map.is_empty !tosee) do
-      let ev, evi = Evar.Map.min_binding !tosee in
-        visit ev evi
+    while not (Evar.Set.is_empty !tosee) do
+      let ev = Evar.Set.choose !tosee in
+        visit ev (Evd.find evm ev)
     done;
     List.rev !l'
 
@@ -512,15 +512,9 @@ let top_sort evm undefs =
 *)
 
 let evars_to_goals p evm =
-  let goals = ref Evar.Map.empty in
-  let fold ev evi evm =
-    let evm, goal = p evm ev evi in
-    let () = if goal then goals := Evar.Map.add ev evi !goals in
-    evm
-  in
-  let evm = Evd.fold_undefined fold evm evm in
-  if Evar.Map.is_empty !goals then None
-  else Some (!goals, evm)
+  let goals, nongoals = Evar.Set.partition (p evm) (Evd.get_typeclass_evars evm) in
+  if Evar.Set.is_empty goals then None
+  else Some (goals, nongoals)
 
 (** Making local hints  *)
 let make_resolve_hyp env sigma st flags only_classes pri decl =
@@ -641,11 +635,6 @@ module Search = struct
       occur_existential evd concl
     else true
 
-  let mark_unresolvables sigma goals =
-    List.fold_left
-      (fun sigma gl -> Evd.set_resolvable_evar sigma gl false)
-      sigma goals
-
   (** The general hint application tactic.
       tac1 + tac2 .... The choice of OR or ORELSE is determined
       depending on the dependencies of the goal and the unique/Prop
@@ -776,7 +765,7 @@ module Search = struct
             shelve_goals shelved <*>
               (if List.is_empty goals then tclUNIT ()
                else
-	         let sigma' = mark_unresolvables sigma goals in
+                 let sigma' = make_unresolvables (fun x -> List.mem_f Evar.equal x goals) sigma in
                  with_shelf (Unsafe.tclEVARS sigma' <*> Unsafe.tclNEWGOALS (CList.map Proofview.with_empty_state goals)) >>=
                       fun s -> result s i (Some (Option.default 0 k + j)))
           end
@@ -938,14 +927,15 @@ module Search = struct
   let run_on_evars env evm p tac =
     match evars_to_goals p evm with
     | None -> None (* This happens only because there's no evar having p *)
-    | Some (goals, evm') ->
+    | Some (goals, nongoals) ->
        let goals =
          if !typeclasses_dependency_order then
-           top_sort evm' goals
-         else List.map (fun (ev, _) -> ev) (Evar.Map.bindings goals)
+           top_sort evm goals
+         else Evar.Set.elements goals
        in
+       let evm = Evd.set_typeclass_evars evm Evar.Set.empty in
        let fgoals = Evd.save_future_goals evm in
-       let _, pv = Proofview.init evm' [] in
+       let _, pv = Proofview.init evm [] in
        let pv = Proofview.unshelve goals pv in
        try
          let (), pv', (unsafe, shelved, gaveup), _ =
@@ -964,7 +954,13 @@ module Search = struct
                       acc && okev) evm' true);
            let fgoals = Evd.shelve_on_future_goals shelved fgoals in
            let evm' = Evd.restore_future_goals evm' fgoals in
+           let nongoals' =
+             Evar.Set.fold (fun ev acc -> match Evarutil.advance evm' ev with
+                 | Some ev' -> Evar.Set.add ev acc
+                 | None -> acc) nongoals (Evd.get_typeclass_evars evm')
+           in
            let evm' = evars_reset_evd ~with_conv_pbs:true ~with_univs:false evm' evm in
+           let evm' = Evd.set_typeclass_evars evm' nongoals' in
            Some evm'
          else raise Not_found
        with Logic_monad.TacticFailure _ -> raise Not_found
@@ -1016,7 +1012,7 @@ let deps_of_constraints cstrs evm p =
 let evar_dependencies pred evm p =
   Evd.fold_undefined
     (fun ev evi _ ->
-      if Evd.is_resolvable_evar evm ev && pred evm ev evi then
+      if Evd.is_typeclass_evar evm ev && pred evm ev evi then
         let evars = Evar.Set.add ev (Evarutil.undefined_evars_of_evar_info evm evi)
         in Intpart.union_set evars p
       else ())
@@ -1032,8 +1028,7 @@ let split_evars pred evm =
 
 let is_inference_forced p evd ev =
   try
-    let evi = Evd.find_undefined evd ev in
-    if Evd.is_resolvable_evar evd ev && snd (p ev evi)
+    if Evar.Set.mem ev (Evd.get_typeclass_evars evd) && p ev
     then
       let (loc, k) = evar_source ev evd in
       match k with
@@ -1065,55 +1060,32 @@ let error_unresolvable env comp evd =
   Pretype_errors.unsatisfiable_constraints env evd ev comp
 
 (** Check if an evar is concerned by the current resolution attempt,
-    (and in particular is in the current component), and also update
-    its evar_info.
-    Invariant : this should only be applied to undefined evars,
-    and return undefined evar_info *)
+    (and in particular is in the current component).
+    Invariant : this should only be applied to undefined evars. *)
 
-let select_and_update_evars p oevd in_comp evd ev evi =
-  assert (evi.evar_body == Evar_empty);
+let select_and_update_evars p oevd in_comp evd ev =
   try
-    let _ = Evd.find_undefined oevd ev in
-    if Evd.is_resolvable_evar oevd ev then
-      Evd.set_resolvable_evar evd ev false,
-      (in_comp ev && p evd ev evi)
-    else evd, false
-  with Not_found ->
-    Evd.set_resolvable_evar evd ev false, p evd ev evi
+    if Evd.is_typeclass_evar oevd ev then
+      (in_comp ev && p evd ev (Evd.find evd ev))
+    else false
+  with Not_found -> false
 
 (** Do we still have unresolved evars that should be resolved ? *)
 
 let has_undefined p oevd evd =
-  let check ev evi = snd (p oevd ev evi) in
+  let check ev evi = p oevd ev in
   Evar.Map.exists check (Evd.undefined_map evd)
 
-(** Revert the resolvability status of evars after resolution,
-    potentially unprotecting some evars that were set unresolvable
-    just for this call to resolution. *)
-
-let revert_resolvability oevd evd =
-  let fold ev _evi evd =
-    try
-      if not (Evd.is_resolvable_evar evd ev) then
-        let _evi' = Evd.find_undefined oevd ev in
-        if Evd.is_resolvable_evar oevd ev then
-          Evd.set_resolvable_evar evd ev true
-        else evd
-      else evd
-    with Not_found -> evd
-  in
-  Evd.fold_undefined fold evd evd
-
 exception Unresolved
 
 (** If [do_split] is [true], we try to separate the problem in
     several components and then solve them separately *)
 let resolve_all_evars debug depth unique env p oevd do_split fail =
-  let split = if do_split then split_evars p oevd else [Evar.Set.empty] in
-  let in_comp comp ev = if do_split then Evar.Set.mem ev comp else true
-  in
+  let tcs = Evd.get_typeclass_evars oevd in
+  let split = if do_split then split_evars p oevd else [tcs] in
+  let in_comp comp ev = if do_split then Evar.Set.mem ev comp else true in
   let rec docomp evd = function
-    | [] -> revert_resolvability oevd evd
+    | [] -> evd
     | comp :: comps ->
       let p = select_and_update_evars p oevd (in_comp comp) in
       try
@@ -1131,7 +1103,9 @@ let resolve_all_evars debug depth unique env p oevd do_split fail =
 
 let initial_select_evars filter =
   fun evd ev evi ->
-    filter ev (snd evi.Evd.evar_source) &&
+    filter ev (Lazy.from_val (snd evi.Evd.evar_source)) &&
+    (** Typeclass evars can contain evars whose conclusion is not
+        yet determined to be a class or not. *)
     Typeclasses.is_class_evar evd evi
 
 let resolve_typeclass_evars debug depth unique env evd filter split fail =
@@ -1223,5 +1197,6 @@ let autoapply c i =
     unify_e_resolve false flags gl
                                  ((c,cty,Univ.ContextSet.empty),0,ce) <*>
       Proofview.tclEVARMAP >>= (fun sigma ->
-      let sigma = Typeclasses.mark_unresolvables ~filter:Typeclasses.all_goals sigma in
+      let sigma = Typeclasses.make_unresolvables
+          (fun ev -> Typeclasses.all_goals ev (Lazy.from_val (snd (Evd.find sigma ev).evar_source))) sigma in
       Proofview.Unsafe.tclEVARS sigma) end