How to convert packageOverrides to overlays?

1

As per the manual — 2.6 Declarative Package Management — I’m currently using packageOverrides in my ~/.config/nixpkgs/config.nix.

In 3.2 Defining Overlays it says

Overlays are similar to other methods for customizing Nixpkgs, in particular the packageOverrides attribute described in Section 2.5, “Modify packages via packageOverrides ”. Indeed, packageOverrides acts as an overlay with only the super argument. It is therefore appropriate for basic use, but overlays are more powerful and easier to distribute.

So I’m looking to migrate my packageOverrides to overlays (if that’s recommended?).

The challenge I’m facing (in doing so incrementally), is that the overlays don’t seem to take effect in a buildEnv within packageOverrides.

If I try to create these overlays for example, removing their definitions from packageOverrides they either fail to be found (in the case of markdown) or aren’t applied (in the case of emacs).

Any tips welcome. Thanks!

What I thought I could do…

#~/.config/nixpkgs/overlays/markdown.nix
self: super: {
  markdown = super.emem.overrideAttrs (oldAttrs: rec {
      installPhase = oldAttrs.installPhase + ''
        ln -fs $out/bin/emem $out/bin/markdown
      '';
    });
}

and

#~/.config/nixpkgs/overlays/emacs.nix
self: super: {
  emacs = super.callPackage ./nixpkgs/emacs { };
}

#~/.config/nixpkgs/overlays/nixpkgs/emacs/default.nix
{ pkgs ? import <nixpkgs> {} }:
with pkgs;

let

  myEmacsConfig = ./default.el;

in

emacsWithPackages (...);

What currently works using packageOverrides.

{
  allowUnfree = true;
  packageOverrides = pkgs: with pkgs; rec {

    myProfile = pkgs.writeText "my-profile" ''
      export PATH=$HOME/.nix-profile/bin:/nix/var/nix/profiles/default/bin:/sbin:/bin:/usr/sbin:/usr/bin
      export MANPATH=$HOME/.nix-profile/share/man:/nix/var/nix/profiles/default/share/man:/usr/share/man
      export IDEA_VM_OPTIONS=~/Library/Preferences/IntelliJIdea2019.3/idea.vmoptions

      function idownload {
        if [ "$#" -ne 1 ] || ! [ -e $1 ]; then
          echo "Usage: idownload <file|dir>";
          return 1;
        fi
        find . -name '.*icloud' |\
        perl -pe 's|(.*)/.(.*).icloud|$1/$2|s' |\
        while read file; do brctl download "$file"; done
      }
    '';

    myPackages = buildEnv {
      name = "my-packages";
      paths = [
        (runCommand "profile" {} ''
          mkdir -p $out/etc/profile.d
          cp ${myProfile} $out/etc/profile.d/my-profile.sh
      ‘')
      ...
      emacs
      markdown
      ...
      ];
      pathsToLink = [ "/share/man" "/share/doc" "/bin" "/etc" "/Applications" ];
      extraOutputsToInstall = [ "man" "doc" ];
    };

    markdown = emem.overrideAttrs (oldAttrs: rec {
      installPhase = oldAttrs.installPhase + ''
        ln -fs $out/bin/emem $out/bin/markdown
      '';
    });

   #
   # COMMENTING OUT BELOW WITH OVERLAYS IN PLACE FAILS
   #
    myEmacsConfig = ./overlays/pkgs/emacs/default.el;

    emacs = emacsWithPackages (epkgs:
      # CONFIG setup
      [
        (runCommand "default.el" {} ''
          mkdir -p $out/share/emacs/site-lisp
          cp ${myEmacsConfig} $out/share/emacs/site-lisp/default.el
        '')
      ] ++

      # ELPA packages
      (with epkgs.elpaPackages; [
        ...
      ]) ++

      (with epkgs.melpaPackages; [
        ...
      ]) ++

      # MELPA stable packages
      (with epkgs.melpaStablePackages; [
        ...
      ]));
  };
}
2

Yes.

Just out of curiosity, why not alias emem=markdown?

What exactly are you trying to achieve?

3

I’d added markdown-mode to my emacs config, and when wanting to preview the markdown it looks for a markdown executable.