nixpkgs/overriding

[giscus[bot]]

nixpkgs/overriding

An unofficial and opinionated book for beginners

https://nixos-and-flakes.thiscute.world/nixpkgs/overriding

[RobotDisco]

It's not clear to me why we start with talking about the override function and then talk about the overrideAttrs function. Do we need to explicitly check to know which function is needed for a given package?

[poopsicles]

the way i see it, override is used for the attributes passed into the function (the bits at the very top), while overrideAttrs is for the bits in the actual definition...you can read more here.

so, in the example above, pkgs.hello is defined as:

{ callPackage
, lib
, stdenv
, fetchurl
, nixos
, testers
, hello
}:

stdenv.mkDerivation (finalAttrs: {
  pname = "hello";
  version = "2.12.1";

  src = fetchurl {
    url = "mirror://gnu/hello/hello-${finalAttrs.version}.tar.gz";
    sha256 = "sha256-jZkUKv2SV28wsM18tCqNxoCZmLxdYH2Idh9RLibH2yA=";
  };

  doCheck = true;

  # ...
})

now if you wanted to change the src, you'd use overrideAttrs, but if you wanted to change, say the tester arg, you'd use override.

a useful use of this is with the sudo package:

{
  lib,
  stdenv,
  fetchurl,
  buildPackages,
  coreutils,
  pam,
  groff,
  sssd,
  nixosTests,
  sendmailPath ? "/run/wrappers/bin/sendmail",
  withInsults ? false,
  withSssd ? false,
}:

stdenv.mkDerivation (finalAttrs: {
  pname = "sudo";
  # be sure to check if nixos/modules/security/sudo.nix needs updating when bumping
  # e.g. links to man pages, value constraints etc.
  version = "1.9.16p2";

  __structuredAttrs = true;

  src = fetchurl {
    url = "https://www.sudo.ws/dist/sudo-${finalAttrs.version}.tar.gz";
    hash = "sha256-l2qlbT47KnVZMweGQoit23SMnBNuJdlanMaZqvp3I5w=";
  };
  ...
}

...the withInsults arg (which defaults to false) can be overridden like so:

security.sudo.package = pkgs.sudo.override { withInsults = true; };