Packaging existing opam repositories

[eureka-cpu]

Hello, I'm trying to package this repo https://github.com/semgrep/ocaml-tree-sitter-core using opam-nix since I cannot seem to do it with buildDunePackage from nixpkgs. I've made a fork and done the following, but I get this error:

{
  description = "Packages ocaml-tree-sitter-core using opam-nix.";

  inputs.nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
  inputs.opam-nix.url = "github:tweag/opam-nix";

  outputs = { self, nixpkgs, opam-nix }:
    let
      inherit (nixpkgs.lib) genAttrs;
      inherit (nixpkgs.lib.systems) flakeExposed;
      eachSystem = f: genAttrs flakeExposed (system: f system);
    in
    {
      packages = eachSystem (system:
        let
          inherit (opam-nix.lib.${system}) buildOpamProject';
          tree-sitter = (buildOpamProject' { } ./. {
            ocaml-system = "*";
          }).tree-sitter;
        in
        tree-sitter);
    };
}

error:
       … while checking flake output 'packages'
         at /nix/store/p2zwmnyjs0f0wcmzn17r4dh2aavla66y-source/flake.nix:14:7:
           13|     {
           14|       packages = eachSystem (system:
             |       ^
           15|         let

       … while checking the derivation 'packages.x86_64-linux.outPath'
         at /nix/store/i5zbq5by44gz4w1v0kwdcv2d8vacqhd1-source/lib/customisation.nix:421:7:
          420|         drv.drvPath;
          421|       outPath =
             |       ^
          422|         assert condition;

       error: flake attribute 'packages.x86_64-linux.outPath' is not a derivation

EDIT: It builds now but the result is basically empty. I see lib, nix-support and share. lib has only empty directories, nix-support has some files which have nix-store paths, and share has man pages but that's it.

[eureka-cpu]

Agh, somehow this was just a syntax error...

[eureka-cpu]

{
  description = "Packages ocaml-tree-sitter-core using opam-nix.";

  inputs.nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
  inputs.opam-nix.url = "github:tweag/opam-nix";

  outputs = { self, nixpkgs, opam-nix }:
    let
      inherit (nixpkgs.lib) genAttrs;
      inherit (nixpkgs.lib.systems) flakeExposed;
      eachSystem = f: genAttrs flakeExposed (system: f system);
    in
    {
      packages = eachSystem (system:
        let
          inherit (opam-nix.lib.${system}) buildOpamProject';
          tree-sitter = (buildOpamProject' { } ./. {
            ocaml-system = "*";
          }).tree-sitter;
        in
        { default = tree-sitter; }); # this fixed it
    };
}