Remove the forward class hint feature.

It was not documented, not properly tested and thus likely buggy. Judging
from the code alone I spotted already one potential bug. Further more it was
prominently making use of the infamous "arbitrary term as hint" feature.

Since the only user in our CI seems to be a math-classes file that introduced
the feature under a claim of "cleanup", I believe we can safely remove it
without anyone noticing.

6 files changed, 9 insertions, 20 deletions

diff --git a/vernac/classes.ml b/vernac/classes.ml
index b38a249b73..3485d17951 100644
--- a/vernac/classes.ml
+++ b/vernac/classes.ml
@@ -58,13 +58,7 @@ let is_local_for_hint i =
 let add_instance_base inst =
   let locality = if is_local_for_hint inst then Goptions.OptLocal else Goptions.OptGlobal in
   add_instance_hint (Hints.IsGlobRef inst.is_impl) [inst.is_impl] ~locality
-    inst.is_info;
-  List.iter (fun (path, pri, c) ->
-    let h = Hints.IsConstr (EConstr.of_constr c, None) [@ocaml.warning "-3"] in
-    add_instance_hint h path
-                ~locality pri)
-    (build_subclasses ~check:(not (isVarRef inst.is_impl))
-       (Global.env ()) (Evd.from_env (Global.env ())) inst.is_impl inst.is_info)
+    inst.is_info
 
 let mk_instance cl info glob impl =
   let global =
diff --git a/vernac/g_vernac.mlg b/vernac/g_vernac.mlg
index e0550fd744..5b039e76f3 100644
--- a/vernac/g_vernac.mlg
+++ b/vernac/g_vernac.mlg
@@ -469,11 +469,8 @@ GRAMMAR EXTEND Gram
     [ [ id = identref; c=constructor_type -> { c id } ] ]
   ;
   of_type_with_opt_coercion:
-    [ [ ":>>" -> { Some false }
-        | ":>"; ">" -> { Some false }
-        | ":>" -> { Some true }
-        | ":"; ">"; ">" -> { Some false }
-        | ":"; ">" -> { Some true }
+    [ [   ":>" -> { Some () }
+        | ":"; ">" -> { Some () }
         | ":" -> { None } ] ]
   ;
 END
diff --git a/vernac/ppvernac.ml b/vernac/ppvernac.ml
index b73e7c7515..8a98a43ba0 100644
--- a/vernac/ppvernac.ml
+++ b/vernac/ppvernac.ml
@@ -504,8 +504,7 @@ let pr_intarg n = spc () ++ int n
 
 let pr_oc = function
   | None -> str" :"
-  | Some true -> str" :>"
-  | Some false -> str" :>>"
+  | Some () -> str" :>"
 
 let pr_record_field (x, { rf_subclass = oc ; rf_priority = pri ; rf_notation = ntn }) =
   let prx = match x with
diff --git a/vernac/record.ml b/vernac/record.ml
index bd5b71cd6b..79abf94726 100644
--- a/vernac/record.ml
+++ b/vernac/record.ml
@@ -557,7 +557,7 @@ let declare_class def cumulative ubinders univs id idbuild paramimpls params uni
       Impargs.declare_manual_implicits false (GlobRef.ConstRef proj_cst) (List.hd fieldimpls);
       Classes.set_typeclass_transparency (EvalConstRef cst) false false;
       let sub = match List.hd coers with
-        | Some b -> Some ((if b then Backward else Forward), List.hd priorities)
+        | Some () -> Some (Backward, List.hd priorities)
         | None -> None
       in
       [cref, [Name proj_name, sub, Some proj_cst]]
@@ -568,8 +568,7 @@ let declare_class def cumulative ubinders univs id idbuild paramimpls params uni
         params template ~kind:Decls.Method ~name:[|binder_name|] record_data
       in
        let coers = List.map2 (fun coe pri ->
-                              Option.map (fun b ->
-                              if b then Backward, pri else Forward, pri) coe)
+                              Option.map (fun () -> Backward, pri) coe)
           coers priorities
        in
       let map ind =
diff --git a/vernac/vernacentries.ml b/vernac/vernacentries.ml
index fba6800729..60c6d2ec0b 100644
--- a/vernac/vernacentries.ml
+++ b/vernac/vernacentries.ml
@@ -776,7 +776,7 @@ let vernac_inductive ~atts kind indl =
       | _ -> CErrors.user_err Pp.(str "Definitional classes do not support the \"|\" syntax.")
     in
     let (coe, (lid, ce)) = l in
-    let coe' = if coe then Some true else None in
+    let coe' = if coe then Some () else None in
     let f = AssumExpr ((make ?loc:lid.loc @@ Name lid.v), ce),
             { rf_subclass = coe' ; rf_priority = None ; rf_notation = [] ; rf_canonical = true } in
     vernac_record ~template udecl ~cumulative (Class true) ~poly finite [id, bl, c, None, [f]]
diff --git a/vernac/vernacexpr.ml b/vernac/vernacexpr.ml
index d8e17d00e3..721e710e1d 100644
--- a/vernac/vernacexpr.ml
+++ b/vernac/vernacexpr.ml
@@ -106,8 +106,8 @@ type search_restriction =
 
 type verbose_flag   = bool (* true = Verbose;       false = Silent         *)
 type coercion_flag  = bool (* true = AddCoercion    false = NoCoercion     *)
-type instance_flag  = bool option
-  (* Some true = Backward instance; Some false = Forward instance, None = NoInstance *)
+type instance_flag  = unit option
+  (* Some () = Backward instance, None = NoInstance *)
 
 type export_flag    = bool (* true = Export;        false = Import         *)