dh_installsystemd and Also= directive

[Daniele Nicolodi]

Hello,

please keep me in Cc, I'm not subscribed to the list.

I'm implementing user units support in dh_installsystemd. For doing so
the code needs a bit of refactoring and thus I'm trying to understand
how the tool is supposed to operate and adding some tests to check that
nothing will break in the process.

dh_installsystemd needs to resolve Also= directives in service files to
emit postrm blocks to disable all unit enabled at installation time. The
code seems to try to support unit files that have Also= directives
pointing to units defined in other packages, however, if one of those is
encountered dh_installsystemd fails a bit later when it tries to read
the unit file specified in the Also= directive and does not find it.

Because of this failure, I believe that no one relays on this
functionality. I also don't think it is a good practice to have an unit
have an Also= directive pointing to a unit defined in another package,
it seems a recipe for unexpected results.

Should this use case be supported?  Or should the half baked support be
removed and error handling in dh_installsystemd improved a bit?

Thanks. Cheers,
Dan