Help with opium framework(OCaml) version

[OnofreTZK]

Issue description

Some of my personal projects use versions 0.19.0 and 0.20.0 of opium and the one available at ocamlPackages is 0.18.0. This is breaking everything due to a change in http client(cohttp to httpaf) and other refactorations.

I've tried some configs in order to customize my nix-shell but I didn't manage make it work.

I came here to ask for help

Steps to reproduce

my opium-overlay.nix:

self: super: {
  opium_kernel = super.ocaml-ng.ocamlPackages_4_12.opium_kernel.overrideAttrs (old: rec {
    pname = "opium";
    version = "0.20.0";

    useDune2 = true;

    minimalOCamlVersion = "4.12.1";

    src = super.fetchurl {
      url = "https://github.com/rgrinberg/opium/releases/download/${version}/opium-${version}.tbz";
      sha256 = "09ygcxxd5warkdzz17rgpidrd0pg14cy2svvnvy1hna080lzg7vp";
    };
    
    meta = with super.lib; {
      homepage = "https://github.com/rgrinberg/opium";
      description = "Sinatra like web toolkit for OCaml";
      license = licenses.mit;
      maintainers = [ maintainers ];
    };
  });
  
}

my shell.nix:

let
  pkgs = import <nixpkgs> {
    overlays = [
      (import ./opium-overlay.nix)
    ];
  };
  ocamlPackages = pkgs.ocaml-ng.ocamlPackages_4_12;
  #updated_opium = pkgs.callPackage ./opium-overlay.nix { };
in
pkgs.mkShell {
  # build tools
  nativeBuildInputs = with ocamlPackages; [ 
    ocaml 
    findlib 
    dune_2 
    ocaml-lsp 
  ];
  
  # dependencies
  buildInputs = with ocamlPackages; [ 
    caqti
    caqti-lwt
    caqti-driver-postgresql 
    uuidm
    ppx_deriving_yojson
    lwt_ppx
    cohttp-lwt-unix
    mirage-crypto-rng
    sha
    cmdliner
    httpaf
    fmt
    mtime
    ptime
    magic-mime
    mirage-crypto
    re
    uri
    result
    astring
    base64
    alcotest
    qcheck-alcotest
    opium
  ];
}

Technical details

The shell is launching without problems but the version of opium still 0.18.0.

[vbgl]

opium has been updated to 0.20.0: #206977