Use our own prefix to look up systemd user services dir

[ncfavier]

Fixes the build on NixOS.

See https://www.bassi.io/articles/2018/03/15/pkg-config-and-paths/ and the discussion at NixOS/nixpkgs#164105 (comment).

[ncfavier]

@fujiwarat is there any problem with this change?

[fujiwarat]

LGTM.

Could you please add the prefix "configure: " to your patch subject and rebase your patch if you wish to import your signature?

[ncfavier]

Done

[fujiwarat]

Sorry, thinking about this patch again, I think this patch has a problem.
If system's prefix is /usr and ibus's prefix is /opt, the service files will be installed in /opt/lib/systemd/user

Why don't you fix systemduserunitdir in systemd.pc?
https://github.com/systemd/systemd/blob/main/src/core/systemd.pc.in

Seems you wish to install the service files in /lib/systemd/user so I think ${libdir} is better than ${prefix}/lib in systemd.pc ?
/lib is symlink of /usr/lib in Fedora.

[ncfavier]

If system's prefix is /usr and ibus's prefix is /opt, the service files will be installed in /opt/lib/systemd/user

I don't think that's a real life problem. It seems to be the way /opt is intended to be used ("Generally, all data required to support a package on a system must be present within /opt/<package>"). If the user wants systemd to use those unit files, they'd have to copy/link them to a location systemd knows about.

In NixOS we want to install the unit files in $ibus/lib/systemd/user, where ibus=/nix/store/...-ibus. By default they would go in $systemd/lib/systemd/user, where systemd=/nix/store/...-systemd, so the proposed solution is to replace systemd's prefix $systemd with ibus' prefix $ibus.

I'm not sure how $libdir would solve that?

[fujiwarat]

I mean the systemd.pc.in would be:

libdir=@libdir@
systemduserunitdir=${libdir}/systemd/user

And the systemd.pc could be built with the configure file.

[fujiwarat]

E.g. ibus/engine/Makefile.am indicates $(XKBCONFIG_BASE) to find the directory from xkeyboard-config.pc
And ibus/autogen.sh can run without --prefix=/usr option against /usr/local

[jtojnar]

If ibus is installed to /usr/local, I would expect the systemd unit to be installed under /usr/local too, so that is another argument in favour of this. And systemd supports that.

[fujiwarat]

OK, thank you for the explanation.
Now the patch sounds good with me.
I will integrate the patch tomorrow.

[fujiwarat]

Thank you for the patch.
I forgot to ask to add BUG= lines.