Hello,

On my system I have a variable weight .ttf font[1] installed somewhere.
When I build with --enable-check-lisp-object-type, the line

    int candidate = XFIXNUM (AREF (entity, prop)) >> 8;

in font_delete_unmatched and the expression

   EMACS_INT diff = ((XFIXNUM (AREF (entity, i)) >> 8)
                     - (XFIXNUM (spec_prop[i]) >> 8));

in font_score have failed assertions because the FONT_WEIGHT_INDEX for
this .ttf file is nil:

    #<font-entity ftcrhb CYRE Inconsolata nil iso10646-1 nil normal nil
     0 nil 100 0 ((:font-entity
     "/usr/share/fonts/inconsolata/Inconsolata-VariableFont_wdth,wght.ttf"
     . 0))>

I don't believe Emacs really knows how to handle these multi-weight .ttf
files?  Thus I propose the attached patch, to handle the value.

[1]  https://github.com/googlefonts/Inconsolata/tree/main/fonts/variable

-- 
Sean Whitton