Markdown generation fails with recursive type definition

[edwintorok]

If I have a type the refers to itself then generating the markdown fails with a stackoverflow:

open Idl
let err = DefaultError.err
module Test(R:RPC) = struct
  type t = | A of t list | B [@@deriving rpcty]
  let t_p = Param.mk ~name:"test" t

  let description = Interface.{
    name = "Test";
    namespace = None;
    description=[];
    version =(0,0,0);
  }
  open R
  let implementation = implement description
  let foo = declare "foo" [] (t_p @-> returning t_p err)
end
module M = Test(Codegen.Gen())
let () =
  let impl = M.implementation () in
  let interfaces = Codegen.Interfaces.create ~name:"Foo" ~title:""
    ~description:[""] ~interfaces:[impl] in
  Markdowngen.to_string interfaces |> print_endline

$ ocamlfind ocamlopt x.ml -package rpclib.markdown,ppx_deriving_rpc -linkpkg && OCAMLRUNPARAM=b ./a.out
Fatal error: exception Stack overflow
Raised by primitive operation at file "lib/rpc_genfake.ml", line 67, characters 28-58
Called from file "lib/rpc_genfake.ml", line 99, characters 23-61
Called from file "list.ml", line 59, characters 20-23
Called from file "lib/rpc_genfake.ml", line 98, characters 4-182
Called from file "lib/rpc_genfake.ml", line 67, characters 28-58
Called from file "lib/rpc_genfake.ml", line 99, characters 23-61
Called from file "list.ml", line 59, characters 20-23
Called from file "lib/rpc_genfake.ml", line 98, characters 4-182
Called from file "lib/rpc_genfake.ml", line 67, characters 28-58
Called from file "lib/rpc_genfake.ml", line 99, characters 23-61
Called from file "list.ml", line 59, characters 20-23
Called from file "lib/rpc_genfake.ml", line 98, characters 4-182
Called from file "lib/rpc_genfake.ml", line 67, characters 28-58
Called from file "lib/rpc_genfake.ml", line 99, characters 23-61
...

[gaborigloi]

I've reproed this issue again:

/t/test $ cat jbuild 
(jbuild_version 1)

(executable
 ((name main)
  (libraries (rpclib rpclib.markdown))
  (preprocess (pps (ppx_deriving_rpc)))))
/t/test $ cat main.ml 
open Idl
let err = DefaultError.err
module Test(R:RPC) = struct
  type t = | A of t list | B [@@deriving rpcty]
  let t_p = Param.mk ~name:"test" t

  let description = Interface.{
    name = "Test";
    namespace = None;
    description=[];
    version =(0,0,0);
  }
  open R
  let implementation = implement description
  let foo = declare "foo" [] (t_p @-> returning t_p err)
end
module M = Test(Codegen.Gen())
let () =
  let impl = M.implementation () in
  let interfaces = Codegen.Interfaces.create ~name:"Foo" ~title:""
    ~description:[""] ~interfaces:[impl] in
  Markdowngen.to_string interfaces |> print_endline
/t/test $
/t/test $ env OCAMLRUNPARAM=b  _build/default/main.exe         
Fatal error: exception Stack overflow
Raised by primitive operation at file "camlinternalFormat.ml", line 1416, characters 26-62
Called from file "camlinternalFormat.ml", line 1656, characters 16-29
Called from file "src/lib/rpc_genfake.ml" (inlined), line 108, characters 15-44
Called from file "src/lib/rpc_genfake.ml", line 121, characters 53-61
Called from file "src/lib/rpc_genfake.ml", line 139, characters 22-50
Called from file "src/lib/rpc_genfake.ml", line 121, characters 40-61
Called from file "src/lib/rpc_genfake.ml", line 139, characters 22-50

[gaborigloi]

Looks like it loops in gen_nice between the List and Variant cases. We may also have another infinite loop in the markdown generator where we recursively expand the types.

[gaborigloi]

I have confirmed that these recursive values are correctly marshaled and unmarshaled by the library, so markdown generation should also work, and this is indeed a bug:

utop # let v = Rpcmarshal.marshal typ_of (A [B;A[B;B]]);;
val v : Rpc.t =
  Rpc.Enum
   [Rpc.String "A";
    Rpc.Enum
     [Rpc.String "B";
      Rpc.Enum [Rpc.String "A"; Rpc.Enum [Rpc.String "B"; Rpc.String "B"]]]]
─( 10:40:23 )─< command 6 >──────────────────────────────────────{ counter: 0 }─
utop # Rpcmarshal.unmarshal typ_of v;;
- : (t, Rpcmarshal.err) result = Result.Ok (A [B; A [B; B]])
─( 10:40:39 )─< command 7 >──────────────────────────────────────────────{ counter: 0 }─
utop #