Support unit reloading

[eclairevoyant]

Followup to #50

• restart all services that changed in the manifest
• support restartTriggers/reloadTriggers
• remove *IfChanged
• docs

[bwolf]

I am just curious about what is missing about systemd service restarts, as we already have restartTriggers. I am using it like this in my service definition and it does not work:

restartTriggers = [
  (builtins.hashString "sha256" "${cfg.a}:${cfg.b}")
];

Doing a nixos-rebuild switch followed by systemctl --user daemon-reload and systemctl --user restart my.service and changing cfg.a followed by sudo nixos-rebuild switch does nothing. Am I doing something wrong, is the implementation incomplete, or what else is missing?

[eclairevoyant]

restartTriggers is currently a no-op, that's why this ticket exists. NixOS does not handle (re)starting/stopping user services after activation, which is why we have to write our own activation-time program to do so.

[bwolf]

Thank you. Now I understand it.

[NotAShelf]

With #114 reload and restart triggers should work properly. The VM tests pass, but I'd appreciate more hands-on testing as well :)