bug#59347: 29.0.50; `:family` face setting ignored

[Gregory Heytings]

> I'd prefer to delay the discussion of this until after Stefan has time 
> to see why DejaVu Sans is rejected in his cases and describe his 
> findings.
>
> If you already did that, please describe your findings.

It's described in the commit message.  DejaVu Sans is rejected because the 
font of the default face has a 'medium' weight, and DejaVu Sans (like many 
other fonts) does not explicitly support that weight.  For many fonts (and 
for Emacs until recently), normal, regular and medium are the same weight.

> AFAIU, Stefan discovered that the problematic attribute was foundry, and 
> and your patch does nothing about foundry.

I don't know how he reached that conclusion, but it's most likely not the 
cause of the problem.

> It sounds like your patch is for another problem altogether.

I don't think so, at least my intention was to fix this bug (and also at 
least bug#57555, which is the same one).

> > +  /* If weight is "medium" in SPEC, also try "normal".  Fonts with an
> > +     explicit "medium" weight are much less common than fonts with an
> > +     explicit "normal" weight, and for a long time "medium" and
> > +     "normal" (a.k.a. "regular" a.k.a. "book") were synonymous in
> > +     Emacs.  See e.g. bug#59347 and bug#57555.  */
> > +  weight[0] = AREF (spec, FONT_WEIGHT_INDEX);
> > +  if (EQ (weight[0], Qmedium))
> > +    weight[1] = Qnormal, weight[2] = zero_vector;
> > +  else
> > +    weight[1] = zero_vector;
>
> This is not enough, IMO: you need to make sure the scoring of candidates 
> is still correct.  For example, if the weights of two candidates differ 
> (normal vs medium), but sizes are the same or close, how will that 
> compare with candidates whose weights are identical, but sizes differ? 
> IOW, we need to reconsider how font_score scores the candidates.

I don't understand your question.  The patch essentially adds an inner 
loop in the loop of fond_find_for_lface, to make sure that when weight == 
medium, we call font_list_entities two times, first with

(family, foundry, registry, adstyle, weight == medium)

and then (if the previous call did not succeed to find a matching font, 
IOW, if it did not return nil) with

(family, foundry, registry, adstyle, weight == normal)

There is no scoring involved at that point, AFAIU.