nixpkgs.nix

let
  version = {
    name = "nixpkgs-21.05-darwin-20210827";
    url = "https://github.com/nixos/nixpkgs.git";
    rev = "9d6766c0f0b3b03bd63ffc08b2e23e476145719d";
    ref = "nixpkgs-21.05-darwin";
  };
  jvmOverlay = self: super:                                   
    let
      scala = super.scala.override { jre = self.jre_headless; };
    in { inherit scala; };
in import (builtins.fetchGit version) {
  overlays = [ jvmOverlay ];
  config.allowUnfree = true;
}                                                             

shell.nix

{ nixpkgs ? import ./nixpkgs.nix
}:
let
  inherit (nixpkgs) pkgs;
  inherit (pkgs) mkShell;
  
in mkShell {
  buildInputs = with pkgs; [
    scala                                   
    sbt
    sbt-extras
    metals                                  
    entr
  ];
}