dh_installsystemd and Also= directive

[Niels Thykier]

Daniele Nicolodi:
> On 11/06/2018 00:26, Niels Thykier wrote:
>> Daniele Nicolodi:
>>> 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.
>>
>> Ack, note that the "late failure" is deliberate to present as many
>> issues to the user as possible (to keep the amount of "rinse and
>> repeat"-testing to a minimum).
> 
> A bit later is a few lines of code below, in the same iteration. I don't
> see how that may be helpful.
> 

Sorry, I was thinking of a different check then.

>>> 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.
>>
>> I do not think it was ever intended to support units from other
>> packages.  And I agree, it looks like a recipe for disaster.
> 
> The emitted warning seems to suggest that Also= pointing to units in
> other packages was considered a possibility. I'm happy to read otherwise.
> 

I suspect it was intended for units in a different binary built from the
same source, but honestly, I do not know.

>>> Should this use case be supported?  Or should the half baked support be
>>> removed and error handling in dh_installsystemd improved a bit?
>>
>> I think this is mostly a question of documentation changes and possible
>> a tweak of the error message?
> 
> Which error message?  Right now dh_installsystemd fails complaining it
> cannot open a file for reading.
> 
> Cheers,
> Dan
> 

My assumption for that remark was wrong (per above).

Thanks,
~Niels