Merge pull request #20 from benbellick/better-errors

fully improve errors and add test for open variant cstr

src/decoders_deriver.ml

@@ -337,12 +337,19 @@ let implementation_generator ~(loc : location) ~rec_flag ~substitutions
   let imple_expr =
     match (type_decl.ptype_kind, type_decl.ptype_manifest) with
     | Ptype_abstract, Some manifest -> expr_of_typ ~substitutions manifest
-    | Ptype_variant cstrs, None -> expr_of_variant ~loc ~substitutions cstrs
+    | Ptype_abstract, None ->
+        Location.raise_errorf ~loc
+          "Cannot construct decoder for %s: cannot decode abstract type"
+          type_decl.ptype_name.txt
+    | Ptype_variant cstrs, _ -> expr_of_variant ~loc ~substitutions cstrs
     | Ptype_record label_decs, _ ->
         expr_of_record ~substitutions ~loc label_decs
-    | Ptype_open, _ -> Location.raise_errorf ~loc "Unhandled open"
-    | _ -> Location.raise_errorf ~loc "Unhandled mystery"
+    | Ptype_open, _ ->
+        Location.raise_errorf ~loc
+          "Cannot construct decoder for %s: cannot decode extensible type"
+          type_decl.ptype_name.txt
   in
+
   match rec_flag with
   | Nonrecursive -> imple_expr
   | Recursive -> wrap_as_aux ~loc ~name ~expr:imple_expr

src/encoders_deriver.ml

@@ -205,7 +205,6 @@ and expr_of_variant ~loc cstrs =
   pexp_function ~loc cases
 
 let implementation_generator ~(loc : location) type_decl : expression =
-  let _name = to_encoder_name type_decl.ptype_name.txt in
   let imple_expr =
     match (type_decl.ptype_kind, type_decl.ptype_manifest) with
     | Ptype_abstract, Some manifest -> (
@@ -223,7 +222,11 @@ let implementation_generator ~(loc : location) type_decl : expression =
             in
             [%expr fun [%p args] -> [%e expr]]
         | _ -> expr)
-    | Ptype_variant cstrs, None -> expr_of_variant ~loc cstrs
+    | Ptype_abstract, None ->
+        Location.raise_errorf ~loc
+          "Cannot construct encoder for %s: cannot encode abstract type"
+          type_decl.ptype_name.txt
+    | Ptype_variant cstrs, _ -> expr_of_variant ~loc cstrs
     | Ptype_record label_decs, _ ->
         (* And in the case of a top-level record, we also need to explicitly wrap in a lambda with args *)
         let arg_fields =
@@ -237,8 +240,10 @@ let implementation_generator ~(loc : location) type_decl : expression =
         let args = Ast_builder.Default.ppat_record ~loc arg_fields Closed in
         let expr = expr_of_record ~loc label_decs in
         [%expr fun [%p args] -> [%e expr]]
-    | Ptype_open, _ -> Location.raise_errorf ~loc "Unhandled open"
-    | _ -> Location.raise_errorf ~loc "Unhandled mystery"
+    | Ptype_open, _ ->
+        Location.raise_errorf ~loc
+          "Cannot construct encoder for %s: cannot encode extensible type"
+          type_decl.ptype_name.txt
   in
   imple_expr
 

test/test_decoders.ml

@@ -319,3 +319,11 @@ let%test "char" =
   (* We expect an error here because the string must have length 1 *)
   | Error _ -> true
   | _ -> false
+
+type var = A | B
+type open_var = var = A | B [@@deriving decoders]
+
+let%test "type alias opened cstrs" =
+  match D.decode_string open_var_decoder {|{"B":null}|} with
+  | Ok B -> true
+  | _ -> false

test/test_encoders.ml

@@ -140,3 +140,11 @@ type my_char = char [@@deriving encoders]
 
 let%test "char" =
   match E.encode_string my_char_encoder 'c' with {|"c"|} -> true | _ -> false
+
+type var = A | B
+type open_var = var = A | B [@@deriving encoders]
+
+let%test "type alias opened cstrs" =
+  match E.encode_string open_var_encoder A with
+  | {|{"A":null}|} -> true
+  | _ -> false