Allow to build for non-systemd systems

[hasufell]

This will disable systemd integration for all cabal users,
but fixes #1200.

There are two other ways to fix this:

• provide a hackage overlay, which contains lobemo-scribe-systemd
  only or all 3rdparty packages and then add that overlay to
  cabal.project (downside: stack doesn't seem to be able to use
  hackage overlays)
• provide 2 cabal.project files and let user choose via e.g.:
  --project-file=cabal.project.nosystemd
  (downside: maintaining yet another file)

---

Edit: third option could be to document for non-systemd users how to edit cabal.project, but I guess that's a bit awkward?

[erikd]

This solution is not acceptable because it disables systemd for all cabal users. IOHK"s devops currently rely on this and they run the current core nodes, so they are pretty important.

Unfortunatley, the other options are also rather sub optimal.

What about supplying a simple shell script that reads in the current cabal.project file and spits out cabal.project.nosystemd . This script would live in the scripts/ directory and with a little extra documentation would have a very high probability to avoid bit rot and should just DoTheRightThing (tm).

[hasufell]

That's certainly an option. What about providing a hackage overlay? I find that an interesting idea in general and would be eager to look into it. But it will add more steps to release cycle.

[rvl]

@hasufell Why do you need to disable systemd anyway?
You can just install the systemd development package for your Linux distribution and then the cabal build will succeed.
If you have religious objections to systemd, there is always cabal.project.local.

[hasufell]

You can just install the systemd development package for your Linux distribution and then the cabal build will succeed.

1. not all distros have systemd: https://pkgs.alpinelinux.org/packages?name=systemd&branch=edge
2. on some distros you cannot have eudev and systemd installed at the same time, because they are both udev providers: https://gitlab.exherbo.org/exherbo/arbor/-/blob/aec8e96ed61483f92995680ad0e3b414934fee0a/packages/sys-apps/eudev/eudev.exlib#L34
3. disabling systemd is already explicitly supported, this PR just deals with a cabal bug

If you have religious objections to systemd, there is always cabal.project.local.

That doesn't work, as discussed in this PR, because of #1200 and haskell/cabal#5444

[disassembler]

That doesn't work, as discussed in this PR, because of #1200 and haskell/cabal#5444

This seems to me like an issue that should be fixed upstream.

[hasufell]

This seems to me like an issue that should be fixed upstream.

Yes, there already is an issue open, but there is no clear timeline, so it needs a workaround.

[disassembler]

I don't see a reason to address this. The work-around is you modify the cabal.proejct file (as this patch does, and ideally when cabal is fixed, just add to cabal.project.local), but this patch would break our nix builds and cabal builds for anyone that wants systemd (which there are a number of pool operators I've been helping this weekend trying to get systemd services setup on non-nixos).

[hasufell]

@disassembler as @erikd pointed out, this could be done by a shell script. I don't believe users will figure this out on their own. Is there any reason to not accept a patch for that?