In reply to @ultranix:matrix.org
it wont evaluate if i try to read a string from builtins.readFile /run/secrets/* since its a impure path

I just came across this method to import modules from other channels:

{ lib, config, latestModulesPath, channels, ... }:
let
  domain = "files.${config.networking.domain}";
  seafileModule = import
    "${latestModulesPath}/services/networking/seafile.nix"
    { inherit config lib; pkgs = channels.latest; };
in
{
  imports = [ seafileModule ];
  services.seafile = {

channels is a module arg I added in my flake.nix, its just self.pkgs.${system}

I'd like to add this to an overlay for element-desktop (from unstable, I added it to the inherit list in overrides.nix)

    fixupPhase = ''
      sed -i "s#exec#LD_PRELOAD=${pkgs.sqlcipher}/lib/libsqlcipher.so exec#g" "$out/bin/element-desktop"
    '';

I thought adding a overlays/element-desktop.nix file could be the solution, looking similar to this:

self: super: {
  element-desktop = super.element-desktop.overrideAttrs (old: {
      fixupPhase = ''
        sed -i "s#exec#LD_PRELOAD=${pkgs.sqlcipher}/lib/libsqlcipher.so exec#g" "$out/bin/element-desktop"
      '';
  });
}

but ofc I get: error: undefined variable 'pkgs'

You should use makeWrapper for this

wrapProgram $out/bin/element-desktop \
  --prefix LD_PRELOAD : ${prev.sqlcipher}/lib/libsqlcipher
so

Wow search in encrypted rooms really works with that change

channels: final: prev: {
  element-desktop-search-fixed = channels.latest.element-desktop-wayland.overrideAttrs (oldAttrs: {
    fixupPhase = ''
      sed -i "s#exec#LD_PRELOAD=${channels.latest.sqlcipher}/lib/libsqlcipher.so exec#g" "$out/bin/element-desktop"
    '';
  });
}