Re: Support for optional substvars

[Niels Thykier <niels@thykier.net>]

Guillem Jover:
> Hi Niels!
> 
> Several months ago you asked on IRC about extending the substvars file
> format to be able to mark substvars as optional (so that they would not
> warn in case they end up not being used, like how several of the built-in
> ones are handled). At the time I mentioned that I'd need to ponder about
> it but had no energy (or motivation) do work on stuff.
> 
> I've not forgotten about it, and it has been on the back of my head,
> and I've been converging on using «?=» as operator. Then rechecked the
> IRC logs, and noticed that was exactly one of the formats you proposed
> at the time (so either it stuck in the background and subconsciously
> surfaced, or I came to the same conclusion :). In any case, I've prepared
> the attached patch, which I'd be happy to include for 1.21.8, in case
> something like this works for you?
> 
> Thanks,
> Guillem

Possibly related.  I had a look at deb-substvars(5).  While it lists the
debian/substvars file in the synopsis, the manpage does not actually
cover the contents/syntax of that file at all.  Instead it details how
and when substitutions are applied in the build artefacts (which is
valuable knowledge, but does not match the synopsis at all as far as I
can tell).

Thanks,
~Niels