ruby.nix

{
  description = "An old Ruby application";

  nixConfig = {
    extra-substituters = "https://nixpkgs-ruby.cachix.org";
    extra-trusted-public-keys =
      "nixpkgs-ruby.cachix.org-1:vrcdi50fTolOxWCZZkw0jakOnUI1T19oYJ+PRYdK4SM=";
  };

  inputs = {
    nixpkgs.url = "nixpkgs";
    ruby-nix = {
      url = "github:inscapist/ruby-nix";
      inputs.nixpkgs.follows = "nixpkgs";
    };
    fu.url = "github:numtide/flake-utils";
    bob-ruby = {
      url = "github:bobvanderlinden/nixpkgs-ruby";
      inputs.nixpkgs.follows = "nixpkgs";
    };
  };

  outputs = { self, nixpkgs, fu, ruby-nix, bob-ruby }:
    with fu.lib;
    eachDefaultSystem (system:
      let
        pkgs = import nixpkgs {
          inherit system;
          overlays = [ bob-ruby.overlays.default ];
        };
        rubyNix = ruby-nix.lib pkgs;
        ruby = pkgs."ruby-2.7.8";
      in rec {
        inherit (rubyNix {
          inherit ruby;
          name = "old-ruby-app";
        })
          env;

        devShells = rec {
          default = dev;
          dev = pkgs.mkShell {
            buildInputs = [ env ];
          };
        };
      });
}

t.c

maxfd = fdlim_get(1);
if (maxfd < 0)
	fatal("%s: fdlim_get: bad value", __progname);

/* Maximum number of file descriptors available */
#ifdef HAVE_SYSCONF
# define SSH_SYSFDMAX sysconf(_SC_OPEN_MAX)
#else
# define SSH_SYSFDMAX 10000
#endif

test.toml

[dependencies]
redis = "0.11.0"