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> How do I create a nix package that clones eMacs from GitHub and builds it from source?

{ pkgs ? import <nixpkgs> {}, fetchFromGitHub }:

let

  emacsSrc = fetchFromGitHub {

    owner = "emacs-mirror";

    repo = "emacs";

    rev = "master";

    sha256 = "0xabcd1234";

  };

in pkgs.stdenv.mkDerivation {

  name = "emacs";

  version = "27.1";

  src = emacsSrc;

  buildInputs = [ pkgs.autoconf pkgs.make ];

  configurePhase = ''

    autoconf

    ./configure --prefix=$out

  '';

  buildPhase = "make";

  installPhase = "make install";

}