flake.nix

{
  inputs = {
    opam-nix.url = "github:tweag/opam-nix";
    flake-utils.url = "github:numtide/flake-utils";
    nixpkgs.follows = "opam-nix/nixpkgs";
    opam-repository = {
      url = "github:ocaml/opam-repository";
      flake = false;
    };
  };
  outputs =
    {
      self,
      flake-utils,
      opam-nix,
      nixpkgs,
      opam-repository,
    }@inputs:
    flake-utils.lib.eachDefaultSystem (
      system:
      let
        pkgs = nixpkgs.legacyPackages.${system};
        on = opam-nix.lib.${system};
        localPackagesQuery = builtins.mapAttrs (_: pkgs.lib.last) (on.listRepo (on.makeOpamRepo ./.));
        devPackagesQuery = {
          ocaml-lsp-server = "*";
          ocamlformat = "*";
        };
        query = devPackagesQuery // {
          ocaml-base-compiler = "*";
        };
        scope = on.buildOpamProject' { repos = [ "${opam-repository}" ]; } ./. query;
        overlay = final: prev: {
          # You can add overrides here
        };
        scope' = scope.overrideScope overlay;
        # Packages from devPackagesQuery
        devPackages = builtins.attrValues (pkgs.lib.getAttrs (builtins.attrNames devPackagesQuery) scope');
        # Packages in this workspace
        packages = pkgs.lib.getAttrs (builtins.attrNames localPackagesQuery) scope';
      in
      {
        legacyPackages = scope';

        inherit packages;

        ## If you want to have a "default" package which will be built with just `nix build`, do this instead of `inherit packages;`:
        # packages = packages // { default = packages.<your default package>; };

        devShells.default = pkgs.mkShell {
          inputsFrom = builtins.attrValues packages;
          buildInputs = devPackages ++ [
            pkgs.rust-analyzer
          ];
        };
      }
    );
}