create type hole to see which tests fail

src/core/tUnification.ml

@@ -39,6 +39,7 @@ type unification_context = {
 	equality_kind           : eq_kind;
 	equality_underlying     : bool;
 	strict_field_kind       : bool;
+	type_param_pairs        : (typed_type_param * typed_type_param) list ref option;
 }
 
 type unify_min_result =
@@ -64,6 +65,7 @@ let default_unification_context = {
 	equality_kind           = EqStrict;
 	equality_underlying     = false;
 	strict_field_kind       = false;
+	type_param_pairs        = None;
 }
 
 (* Unify like targets (e.g. Java) probably would. *)
@@ -75,6 +77,7 @@ let native_unification_context = {
 	equality_underlying   = false;
 	allow_arg_name_mismatch = true;
 	strict_field_kind       = false;
+	type_param_pairs        = None;
 }
 
 module Monomorph = struct
@@ -575,6 +578,14 @@ let rec type_eq uctx a b =
 	| TEnum (e1,tl1) , TEnum (e2,tl2) ->
 		if e1 != e2 && not (param = EqCoreType && e1.e_path = e2.e_path) then error [cannot_unify a b];
 		type_eq_params uctx a b tl1 tl2
+	| TInst ({cl_kind = KTypeParameter ttp1},tl1) , TInst ({cl_kind = KTypeParameter ttp2},tl2) when uctx.type_param_pairs <> None ->
+		let pairs = Option.get uctx.type_param_pairs in
+		begin try
+			let ttp3 = List.assq ttp1 !pairs in
+			if ttp2 != ttp3 then error [cannot_unify a b]
+		with Not_found ->
+			pairs := (ttp1,ttp2) :: !pairs
+		end
 	| TInst (c1,tl1) , TInst (c2,tl2) ->
 		if c1 != c2 && not (param = EqCoreType && c1.cl_path = c2.cl_path) && (match c1.cl_kind, c2.cl_kind with KExpr _, KExpr _ -> false | _ -> true) then error [cannot_unify a b];
 		type_eq_params uctx a b tl1 tl2
@@ -732,6 +743,14 @@ let rec unify (uctx : unification_context) a b =
 		unify_to {uctx with allow_transitive_cast = false} a b ab tl
 	| TAbstract (a1,tl1) , TAbstract (a2,tl2) ->
 		unify_abstracts uctx a b a1 tl1 a2 tl2
+	| TInst ({cl_kind = KTypeParameter ttp1},tl1) , TInst ({cl_kind = KTypeParameter ttp2},tl2) when uctx.type_param_pairs <> None ->
+		let pairs = Option.get uctx.type_param_pairs in
+		begin try
+			let ttp3 = List.assq ttp1 !pairs in
+			if ttp2 != ttp3 then error [cannot_unify a b]
+		with Not_found ->
+			pairs := (ttp1,ttp2) :: !pairs
+		end
 	| TInst (c1,tl1) , TInst (c2,tl2) ->
 		let rec loop c tl =
 			if c == c2 then begin

src/typing/tanon_identification.ml

@@ -69,6 +69,7 @@ object(self)
 			equality_kind = EqStricter;
 			equality_underlying = false;
 			strict_field_kind = true;
+			type_param_pairs = None;
 		} else {default_unification_context with equality_kind = EqDoNotFollowNull} in
 
 		let check () =

src/typing/typeloadCheck.ml

@@ -48,16 +48,17 @@ let is_generic_parameter ctx c =
 		false
 
 let valid_redefinition map1 map2 f1 t1 f2 t2 = (* child, parent *)
+	let uctx = {default_unification_context with type_param_pairs = Some (ref [])} in
 	let valid t1 t2 =
-		Type.unify t1 t2;
+		unify_custom uctx t1 t2;
 		if is_null t1 <> is_null t2 || ((follow t1) == t_dynamic && (follow t2) != t_dynamic) then raise (Unify_error [Cannot_unify (t1,t2)]);
 	in
 	begin match PurityState.get_purity_from_meta f2.cf_meta,PurityState.get_purity_from_meta f1.cf_meta with
 		| PurityState.Pure,PurityState.MaybePure -> f1.cf_meta <- (Meta.Pure,[EConst(Ident "expect"),f2.cf_pos],null_pos) :: f1.cf_meta
 		| PurityState.ExpectPure p,PurityState.MaybePure -> f1.cf_meta <- (Meta.Pure,[EConst(Ident "expect"),p],null_pos) :: f1.cf_meta
 		| _ -> ()
 	end;
-	let t1, t2 = (match f1.cf_params, f2.cf_params with
+	(* let t1, t2 = (match f1.cf_params, f2.cf_params with
 		| [], [] -> t1, t2
 		| l1, l2 when List.length l1 = List.length l2 ->
 			let to_check = ref [] in
@@ -89,7 +90,7 @@ let valid_redefinition map1 map2 f1 t1 f2 t2 = (* child, parent *)
 		| _  ->
 			(* ignore type params, will create other errors later *)
 			t1, t2
-	) in
+	) in *)
 	match f1.cf_kind,f2.cf_kind with
 	| Method m1, Method m2 when not (m1 = MethDynamic) && not (m2 = MethDynamic) ->
 		begin match follow t1, follow t2 with