nixos: handle Systemd unit reload and restart triggers

[NotAShelf]

This is a port of my personal reload/restart trigger system, detached from the manifest parser that I ended up writing. Mostly streamlined, but the logic might not be as robust as we desire. Partially addresses #63

tl;dr: Introduces a new mechanism for automatically reloading or restarting systemd user units when their configuration changes. I've added test cases to make sure they actually work right, but there might be edge cases that I'm not actually seeing here.

[GetPsyched]

Not sure about the tests, but the systemd service looks decent.

Thanks for working on this :)

[NotAShelf]

Turns out the tests were failing because the strict checks were failing. Fixed.

[fxzzi]

maybe i've set this up wrong but it seems to just reload the service every time. Here's an example service that seems to just restart even without changes

    hj = {
      xdg.data.files."walls".source = "${pins.walls}/images"; # wallpapers

      packages = [pkgs.hyprpaper];
      xdg.config.files."hypr/hyprpaper.conf" = {
        generator = self.lib.generators.toHyprlang {};
        value = {
          splash = 0;
          "wallpaper[]".path = "~/.local/state/wallpaper";
        };
      };

      systemd.services.hyprpaper = {
        description = "Hyprpaper wallpaper manager";
        after = ["graphical-session.target"];
        wantedBy = ["graphical-session.target"];
        partOf = ["graphical-session.target"];
        unitConfig = {
          ConditionEnvironment = "WAYLAND_DISPLAY";
        };
        serviceConfig = {
          Type = "simple";
          Restart = "always";
          ExecStart = "${getExe pkgs.hyprpaper}";
        };
        restartTriggers = [config.hj.xdg.config.files."hypr/hyprpaper.conf".source];
      };
    };

is that even how the restarTrigger should work? Do I need to write the actual path i.e. ~/.config/hypr/hyprpaper.conf? And should I add pkgs.hyprpaper in there also to make the systemd service restart on hyprpaper update or is that automatic?

[eclairevoyant]

restartTriggers if written correctly should only fire if one of the paths listed has changed. I'll have to test more thoroughly this weekend.

[fxzzi]

then something is definitely off on my end.

[fxzzi]

latest changes got it working, seems to work perfectly for me :) adding the files i source, plus the package itself to the list, and the service will reload on changes to any of them.

thx :)

edit: also tested on my friends system. works perfectly

[NotAShelf]

Thank you mr fazbear

Could be merged with @eclairevoyant's approval