Add support for recursive types

Signed-off-by: Nathan Rebours <[email protected]>

deriver/ppx_deriving_dyn.ml

@@ -327,11 +327,9 @@ module Impl = struct
 
   let generate ~ctxt (rec_flag, type_declarations) =
     let loc = Expansion_context.Deriver.derived_item_loc ctxt in
+    let rec_flag = really_recursive rec_flag type_declarations in
     match type_declarations with
     | [] -> assert false
-    | [ type_declaration ] ->
-      let value_binding = value_binding ~loc type_declaration in
-      [ Ast_builder.Default.pstr_value ~loc Nonrecursive [ value_binding ] ]
     | type_decls ->
       let value_bindings = List.map (value_binding ~loc) type_decls in
       [ Ast_builder.Default.pstr_value ~loc rec_flag value_bindings ]

test/deriver/test_to_dyn.expected.ml

@@ -66,6 +66,17 @@ include
        | `C (x0, x1) -> Dyn.variant "C" [Dyn.int x0; Dyn.string x1])
         polymorphic_variant
   end[@@ocaml.doc "@inline"][@@merlin.hide ]
+type recursive =
+  | Leaf 
+  | Node of recursive * recursive [@@deriving dyn][@@ocaml.warning "-37"]
+include
+  struct
+    let rec recursive_to_dyn =
+      function
+      | Leaf -> Dyn.variant "Leaf" []
+      | Node (x0, x1) ->
+          Dyn.variant "Node" [recursive_to_dyn x0; recursive_to_dyn x1]
+  end[@@ocaml.doc "@inline"][@@merlin.hide ]
 type mrec_1 =
   | A of int 
   | B of mrec_2 

test/deriver/test_to_dyn.ml

@@ -37,6 +37,11 @@ type polymorphic_variant =
   ]
 [@@deriving dyn]
 
+type recursive =
+  | Leaf
+  | Node of recursive * recursive
+[@@deriving dyn] [@@ocaml.warning "-37"]
+
 type mrec_1 =
   | A of int
   | B of mrec_2