Fallback font ignores font weight about kitty HOT 4 CLOSED

Not something I care about, patches welcome. Relevant code is
fallback_font in fontconfig.c and in core_text.m

For fontconfig you will need to create a function that gets the weight
from the base face in freetype.c and use that in your fontconfig query,
being careful to do a fallback query if there are no matches with the
specified weight.

from kitty.

Seems I need to modify create_fallback_face, not fallback_face, to change the fallback font.

1. So what's fallback_face for?
2. I don't find any function in freetype2 to get the weight from a face. So should I manually match style strings in font_family like "Light", "Thin" to FC_WEIGHT_LIGHT, FC_WEIGHT_THIN?

from kitty.

If freetype doesnt have a function for it, then use the fonts psname,
and find the weight property via fontconfig instead for that psname.

from kitty.

Or better store the weight from fontconfig in the face object when creating the face from the fontconfig descriptor, so you can refer to it in the matching code later.

from kitty.