catch Nondep_cannot_erase exception

testsuite/tests/typing-fstclassmod/nondep_instance.ml

@@ -42,6 +42,10 @@ module Primitive(Linear_map : Linear_map) = struct
     Linear_map.scale s x
 end;;
 [%%expect{|
-Uncaught exception: Ctype.Nondep_cannot_erase(_)
-
+Line 3, characters 21-22:
+3 |     Linear_map.scale s x
+                         ^
+Error: This expression has type (module Scalar with type t = s)
+       but an expression was expected of type
+         (module Vector_space with type scalar = 'a and type t = 'b)
 |}];;

typing/ctype.ml

@@ -2473,6 +2473,8 @@ let eq_package_path env p1 p2 =
 let nondep_type' = ref (fun _ _ _ -> assert false)
 let package_subtype = ref (fun _ _ _ _ _ _ _ -> assert false)
 
+exception Nondep_cannot_erase of Ident.t
+
 let rec concat_longident lid1 =
   let open Longident in
   function
@@ -2514,7 +2516,10 @@ let complete_type_list ?(allow_absent=false) env nl1 lv2 mty2 nl2 tl2 =
         match Env.find_type_by_name lid env' with
         | (_, {type_arity = 0; type_kind = Type_abstract;
                type_private = Public; type_manifest = Some t2}) ->
-            (n, nondep_instance env' lv2 id2 t2) :: complete nl ntl2
+            begin match nondep_instance env' lv2 id2 t2 with
+            | exception Nondep_cannot_erase _ -> raise Exit
+            | t -> (n, t) :: complete nl ntl2
+            end
         | (_, {type_arity = 0; type_kind = Type_abstract;
                type_private = Public; type_manifest = None})
           when allow_absent ->
@@ -4607,8 +4612,6 @@ let nondep_variants = TypeHash.create 17
 let clear_hash ()   =
   TypeHash.clear nondep_hash; TypeHash.clear nondep_variants
 
-exception Nondep_cannot_erase of Ident.t
-
 let rec nondep_type_rec ?(expand_private=false) env ids ty =
   let expand_abbrev env t =
     if expand_private then expand_abbrev_opt env t else expand_abbrev env t