Build profile for nopcre2 build in Ubuntu

[Jonathan Nieder]

Jonathan Nieder wrote:
> (please cc me on replies, since I am not subscribed)
> Hi,
>
> Context: https://bugs.ubuntu.com/1729075

This was meant to be a link to
https://bugs.launchpad.net/ubuntu/+source/sbuild/+bug/1734339
Sorry for the confusion.

> In Debian, occasionally a package needs different build-time
> dependencies per target environment, due to missing packages, behavior
> differences, or other reasons.  Most of the time, developers don't run
> into such issues, but when they do, they're able to resolve them using
> arch-qualified build-depends.  sbuild respects arch-qualifications so
> this results in a working build on all relevant arches.
>
> In [1] I ran into a similar issue: Ubuntu is not able to use the git
> package from Debian because
>
> - in Debian, the package uses Build-Depends to allow builds against
>   pcre2 and older pcre.  The first alternative is pcre2, so that is
>   what Debian uses (good).  In backports, pcre2 is not available so
>   it falls back to the older pcre (also good).
>
> - Ubuntu has pcre2 but it is not part of main[2].
>
> So Ubuntu patches the package to build against the old version of
> pcre.  That alone would be fine, but it results in the package in
> Ubuntu falling out of date.  I would like to update the package in
> Debian to be usable in Ubuntu as-is to prevent that happening.
>
> If I could use
>
>         Build-Depends: libpcre2-dev <!ubuntu> | ...fallback...
>
> then I'd do that and be done.
>
> https://wiki.debian.org/BuildProfileSpec#Derivative_specific_profiles
> discourages this application of build profiles and says to prefer
> something distribution-agnostic like "nosystemd".  Fair enough: if
> I could use
>
>         Build-Depends: libpcre2-dev <!nopcre2> | ...fallback...
>
> then I'd do that and be done.
>
> Sensible?  Any downsides I'm missing?

Thanks,
Jonathan

> [1] https://bugs.launchpad.net/ubuntu/+source/git/+bug/1729075
> [2] https://bugs.launchpad.net/ubuntu/+source/pcre2/+bug/1636666