revert c4eb88fc07e35c95456f160ab4364cca8c7286b4, reopen #5785

src/typing/type.ml

@@ -1785,17 +1785,6 @@ let rec unify a b =
 		(match !t with
 		| None -> if not (link t b a) then error [cannot_unify a b]
 		| Some t -> unify a t)
-	| TType (t1,tl1), TType (t2,tl2) when t1 == t2 ->
-		if not (List.exists (fun (a2,b2) -> fast_eq a a2 && fast_eq b b2) (!unify_stack)) then begin
-			try
-				unify_stack := (a,b) :: !unify_stack;
-				List.iter2 unify tl1 tl2;
-				unify_stack := List.tl !unify_stack;
-			with
-				Unify_error l ->
-					unify_stack := List.tl !unify_stack;
-					error (cannot_unify a b :: l)
-		end
 	| TType (t,tl) , _ ->
 		if not (List.exists (fun (a2,b2) -> fast_eq a a2 && fast_eq b b2) (!unify_stack)) then begin
 			try