add ~variant_as_array

README.md

@@ -74,7 +74,7 @@ Tuples are converted to `{ "type": "array", "items": [...] }`.
 
 #### Variants and polymorphic variants
 
-Variants are converted to `{ "type": "string", "enum": [...] }`.
+Variants are converted to `{ "type": "string", "enum": [...] }` by default.
 
 if the JSON variant names differ from OCaml conventions, users can specify the corresponding JSON string explicitly using `[@name "constr"]`, for example:
 
@@ -85,6 +85,15 @@ type t =
 [@@deriving jsonschema]
 ```
 
+If you want to use the same encoding as [ppx_deriving_json] and [ppx_yojson_conv], you can use the `~variant_as_array` flag:
+
+```ocaml
+type t =
+| Typ   [@name "type"]
+| Class [@name "class"]
+[@@deriving jsonschema ~variant_as_array]
+```
+
 #### Records
 
 Records are converted to `{ "type": "object", "properties": {...}, "required": [...] }`.

src/ppx_deriving_jsonschema.ml

@@ -1,6 +1,13 @@
 open Ppxlib
 open Ast_builder.Default
 
+type config = {
+  variant_as_array : bool;
+    (** Encode variants as arrays of string enum instead of a string enum.
+      Provides compatibility with the encoding used by the [ppx_deriving_json]
+      and [ppx_yojson_conv] extensions. *)
+}
+
 let deriver_name = "jsonschema"
 
 let jsonschema_key =
@@ -31,8 +38,8 @@ let attributes =
     Attribute.T jsonschema_polymorphic_variant_name;
   ]
 
-let args () = Deriving.Args.(empty)
-(* let args () = Deriving.Args.(empty +> arg "option1" (eint __) +> flag "flag") *)
+(* let args () = Deriving.Args.(empty) *)
+let args () = Deriving.Args.(empty +> flag "variant_as_array")
 
 let deps = []
 
@@ -49,9 +56,21 @@ let null ~loc = [%expr `Assoc [ "type", `String "null" ]]
 
 let char ~loc = [%expr `Assoc [ "type", `String "string"; "minLength", `Int 1; "maxLength", `Int 1 ]]
 
-let enum ~loc values =
-  let values = List.map (fun name -> [%expr `String [%e estring ~loc name]]) values in
-  [%expr `Assoc [ "type", `String "string"; "enum", `List [%e elist ~loc values] ]]
+let enum ~loc ~config values =
+  match config.variant_as_array with
+  | true ->
+    let values = List.map (fun name -> [%expr `String [%e estring ~loc name]]) values in
+    [%expr
+      `Assoc
+        [
+          "type", `String "array";
+          "items", `Assoc [ "type", `String "string"; "enum", `List [%e elist ~loc values] ];
+          "minContains", `Int 1;
+          "maxContains", `Int 1;
+        ]]
+  | false ->
+    let values = List.map (fun name -> [%expr `String [%e estring ~loc name]]) values in
+    [%expr `Assoc [ "type", `String "string"; "enum", `List [%e elist ~loc values] ]]
 
 let array_ ~loc element_type = [%expr `Assoc [ "type", `String "array"; "items", [%e element_type] ]]
 
@@ -67,26 +86,26 @@ let is_optional_type core_type =
   | [%type: [%t? _] option] -> true
   | _ -> false
 
-let rec type_of_core ~loc core_type =
+let rec type_of_core ~loc ~config core_type =
   match core_type with
   | [%type: int] | [%type: int32] | [%type: int64] | [%type: nativeint] -> type_def ~loc "integer"
   | [%type: float] -> type_def ~loc "number"
   | [%type: string] | [%type: bytes] -> type_def ~loc "string"
   | [%type: bool] -> type_def ~loc "boolean"
   | [%type: char] -> char ~loc
   | [%type: unit] -> null ~loc
-  | [%type: [%t? t] option] -> type_of_core ~loc t
-  | [%type: [%t? t] ref] -> type_of_core ~loc t
+  | [%type: [%t? t] option] -> type_of_core ~loc ~config t
+  | [%type: [%t? t] ref] -> type_of_core ~loc ~config t
   | [%type: [%t? t] list] | [%type: [%t? t] array] ->
-    let t = type_of_core ~loc t in
+    let t = type_of_core ~loc ~config t in
     array_ ~loc t
   | _ ->
   match core_type.ptyp_desc with
   | Ptyp_constr (id, []) ->
     (* todo: support using references with [type_ref ~loc type_name] instead of inlining everything *)
     type_constr_conv ~loc id ~f:(fun s -> s ^ "_jsonschema") []
   | Ptyp_tuple types ->
-    let ts = List.map (type_of_core ~loc) types in
+    let ts = List.map (type_of_core ~loc ~config) types in
     tuple ~loc ts
   | Ptyp_variant (row_fields, _, _) ->
     let constr_names =
@@ -102,7 +121,7 @@ let rec type_of_core ~loc core_type =
             Format.asprintf "unsupported polymorphic variant type: %a" Astlib.Pprintast.core_type core_type (* todo: *))
         row_fields
     in
-    enum ~loc constr_names
+    enum ~loc ~config constr_names
   | _ ->
     (* Format.printf "unsuported core type: %a\n------\n" Astlib.Pprintast.core_type core_type; *)
     [%expr
@@ -113,7 +132,7 @@ let rec type_of_core ~loc core_type =
         ]]
 
 (* todo: add option to inline types instead of using definitions references *)
-let object_ ~loc fields =
+let object_ ~loc ~config fields =
   let fields, required =
     List.fold_left
       (fun (fields, required) ({ pld_name = { txt = name; _ }; pld_type; _ } as field) ->
@@ -125,7 +144,7 @@ let object_ ~loc fields =
         let type_def =
           match Attribute.get jsonschema_ref field with
           | Some def -> type_ref ~loc def
-          | None -> type_of_core ~loc pld_type
+          | None -> type_of_core ~loc ~config pld_type
         in
         ( [%expr [%e estring ~loc name], [%e type_def]] :: fields,
           if is_optional_type pld_type then required else name :: required ))
@@ -140,8 +159,9 @@ let object_ ~loc fields =
         "required", `List [%e elist ~loc required];
       ]]
 
-let derive_jsonschema ~ctxt ast =
+let derive_jsonschema ~ctxt ast variant_as_array =
   let loc = Expansion_context.Deriver.derived_item_loc ctxt in
+  let config = { variant_as_array } in
   match ast with
   | _, [ { ptype_name = { txt = type_name; _ }; ptype_kind = Ptype_variant variants; _ } ] ->
     let variants =
@@ -161,13 +181,13 @@ let derive_jsonschema ~ctxt ast =
         variants
     in
     (* let names = List.map (fun { pcd_name = { txt = value; _ }; _ } -> value) variants in *)
-    let jsonschema_expr = create_value ~loc type_name (enum ~loc variants) in
+    let jsonschema_expr = create_value ~loc type_name (enum ~loc ~config variants) in
     [ jsonschema_expr ]
   | _, [ { ptype_name = { txt = type_name; _ }; ptype_kind = Ptype_record label_declarations; _ } ] ->
-    let jsonschema_expr = create_value ~loc type_name (object_ ~loc label_declarations) in
+    let jsonschema_expr = create_value ~loc type_name (object_ ~loc ~config label_declarations) in
     [ jsonschema_expr ]
   | _, [ { ptype_name = { txt = type_name; _ }; ptype_kind = Ptype_abstract; ptype_manifest = Some core_type; _ } ] ->
-    let jsonschema_expr = create_value ~loc type_name (type_of_core ~loc core_type) in
+    let jsonschema_expr = create_value ~loc type_name (type_of_core ~loc ~config core_type) in
     [ jsonschema_expr ]
   | _, _ast ->
     (* Format.printf "unsuported type: %a\n======\n" Format.(pp_print_list Astlib.Pprintast.type_declaration) ast; *)

test/test.expected.ml

@@ -60,6 +60,24 @@ include
       [@@warning "-32-39"]
   end[@@ocaml.doc "@inline"][@@merlin.hide ]
 let () = print_schema kind_jsonschema
+type kind_as_array =
+  | Success 
+  | Error 
+  | Skipped [@name "skipped"][@@deriving jsonschema ~variant_as_array]
+include
+  struct
+    let kind_as_array_jsonschema =
+      `Assoc
+        [("type", (`String "array"));
+        ("items",
+          (`Assoc
+             [("type", (`String "string"));
+             ("enum",
+               (`List [`String "Success"; `String "Error"; `String "skipped"]))]));
+        ("minContains", (`Int 1));
+        ("maxContains", (`Int 1))][@@warning "-32-39"]
+  end[@@ocaml.doc "@inline"][@@merlin.hide ]
+let () = print_schema kind_as_array_jsonschema
 type poly_kind = [ `Aaa  | `Bbb  | `Ccc [@name "ccc"]][@@deriving jsonschema]
 include
   struct
@@ -70,6 +88,22 @@ include
       [@@warning "-32-39"]
   end[@@ocaml.doc "@inline"][@@merlin.hide ]
 let () = print_schema poly_kind_jsonschema
+type poly_kind_as_array = [ `Aaa  | `Bbb  | `Ccc [@name "ccc"]][@@deriving
+                                                                 jsonschema
+                                                                   ~variant_as_array]
+include
+  struct
+    let poly_kind_as_array_jsonschema =
+      `Assoc
+        [("type", (`String "array"));
+        ("items",
+          (`Assoc
+             [("type", (`String "string"));
+             ("enum", (`List [`String "Aaa"; `String "Bbb"; `String "ccc"]))]));
+        ("minContains", (`Int 1));
+        ("maxContains", (`Int 1))][@@warning "-32-39"]
+  end[@@ocaml.doc "@inline"][@@merlin.hide ]
+let () = print_schema poly_kind_as_array_jsonschema
 type poly_inherit = [ `New_one  | poly_kind][@@deriving jsonschema]
 include
   struct

test/test.ml

@@ -35,6 +35,14 @@ type kind =
 
 let () = print_schema kind_jsonschema
 
+type kind_as_array =
+  | Success
+  | Error
+  | Skipped [@name "skipped"]
+[@@deriving jsonschema ~variant_as_array]
+
+let () = print_schema kind_as_array_jsonschema
+
 type poly_kind =
   [ `Aaa
   | `Bbb
@@ -44,6 +52,15 @@ type poly_kind =
 
 let () = print_schema poly_kind_jsonschema
 
+type poly_kind_as_array =
+  [ `Aaa
+  | `Bbb
+  | `Ccc [@name "ccc"]
+  ]
+[@@deriving jsonschema ~variant_as_array]
+
+let () = print_schema poly_kind_as_array_jsonschema
+
 type poly_inherit =
   [ `New_one
   | poly_kind

test/test_schemas.expected.json

@@ -12,11 +12,25 @@
   "type": "string",
   "enum": [ "Success", "Error", "skipped" ]
 }
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "type": "array",
+  "items": { "type": "string", "enum": [ "Success", "Error", "skipped" ] },
+  "minContains": 1,
+  "maxContains": 1
+}
 {
   "$schema": "https://json-schema.org/draft/2020-12/schema",
   "type": "string",
   "enum": [ "Aaa", "Bbb", "ccc" ]
 }
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "type": "array",
+  "items": { "type": "string", "enum": [ "Aaa", "Bbb", "ccc" ] },
+  "minContains": 1,
+  "maxContains": 1
+}
 {
   "$schema": "https://json-schema.org/draft/2020-12/schema",
   "type": "string",