bug#52888: 29.0.50; font_{delete_unmatched,score} do not handle nil FONT_WEIGHT_INDEX

[Eli Zaretskii <eliz@gnu.org>]

> From: Sean Whitton <spwhitton@spwhitton.name>
> Cc: 52888@debbugs.gnu.org
> Date: Wed, 05 Jan 2022 22:41:55 -0700
> 
> > According to what I see in the documentation, FcPatternGetRange exists
> > only since version 2.11.91 of Fontconfig, whereas we support 2.2.0 and
> > up.
> 
> Ah, right.  Is this version bound written down anywhere other than the
> conditionals in configure.ac?  Sorry I didn't think to look there.

No, I don't think we document the minimum versions of prerequisites
anywhere.

> > So we cannot unconditionally use that API, and some part of the
> > temporary solution will have to be left in the source.  I'd need to
> > see the final patch with that in mind, before I can decide whether it
> > is simple/safe enough for the release branch.
> 
> My patch requires FC_VARIABLE which was not added until 2.12.91, so in
> the attached revision I've set up preprocessor conditionals based on
> FC_VARIABLE.  Checking that FC_VARIABLE is true is how we know it's one
> of the virtual entries.

OK, but (a) we need a comment there explaining why FC_VARIABLE is used
as the condition, and (b) we'd also need to merge the temporary fix in
font.c to master.

Thanks.