generator: add support of $defs for json schema

lib/generator.ml

@@ -221,7 +221,12 @@ let make_atd_of_schemas schemas =
 let make_atd_of_jsonschema input =
   let schema = Json_schema_j.schema_of_string input in
   let root_type_name = Option.value ~default:"root" schema.title in
-  make_atd_of_schemas [ root_type_name, Obj schema ]
+  let defs =
+    match schema.defs with
+    | None -> []
+    | Some defs -> List.map (fun (name, schema) -> name, Obj schema) defs
+  in
+  make_atd_of_schemas ([ root_type_name, Obj schema ] @ defs)
 
 let make_atd_of_openapi input =
   let root = Openapi_j.root_of_string input in

tests/smoke.t

@@ -50,6 +50,8 @@ Generate ATD out of JSON Schema that contains defs
   type json <ocaml module="Yojson.Basic" t="t"> = abstract
   type int64 = int <ocaml repr="int64">
 
+  type name = string
+
   type root = {
     first_name: name;
     last_name: name;