Lyluatex: Font selection

[Lukas-Fabian Moser]

Folks,

that's probably more of a Lyluatex issue, but since LilyPond's font 
handling is involved (and it's being changed right now and it's 
something I know nothing about, and we have proper font experts among 
us), maybe it's a good idea to discuss this also on the LilyPond side.

When reviving and old Lyluatex project of mine I stumbled over the 
following: When using "EB Garamond" from 
https://github.com/octaviopardo/EBGaramond12/tree/master/fonts/otf as 
main document font as in

\documentclass{article}

\usepackage[program=/home/lukas/lilypond-versions/lilypond-2.24.0/bin/lilypond,debug=true]{lyluatex}
\usepackage{fontspec}
\setmainfont{EB Garamond}
\setluaoption{ly}{pass-fonts}{true}

\begin{document}
Test

\lily{
\fixed c'{c\mark "Hallo" d e f^"Test"}
\addlyrics{c d e f}
}
Noch ein Test

\end{document}

then Lyluatex's commit e55a3832e30cd364c4 ("Fix compatibility with 
polyglossia") makes the temporary .ly file contain the following font 
selection code:

  #(define fonts
    (make-pango-font-tree "EB Garamond Regular"
                          "LMSans10"
                          "LMMono10"
                          (/ staff-height pt 20)))

while without that commit it is:

    #(define fonts
    (make-pango-font-tree "EB Garamond"
                          "Latin Modern Sans"
                          "Latin Modern Mono"
                          (/ staff-height pt 20)))

Only the second one works (LilyPond doesn't find the font with the added 
"Regular"). So for now I've reverted that commit in my local copy of 
Lyluatex.

So, my questions basically are:

- Is it the font's fault for not registering itself as "Regular" by name?
- Is it LilyPond's fault for not finding the font if "Regular" is added?
- Is any of this touched by Jean's ongoing work on restructuring 
LilyPond's font selection mechanism? (I don't think so, at least 
fonts.roman = "EB Garamond Regular" fails with 2.25.4)
- Or is this simply a bug in Lyluatex introduced with e55a3832e?

As an additional data point, both "LMSans10" and "LMMono10" _are_ being 
accepted and work the same as do "Latin Modern Sans" and "Latin Modern 
Mono".

Lukas