Cfrgtkky

I'm using the libertinus font family with the latest version coming from github. However, the font is also installed on my system, but I stopped using this version since there was a problem with the math font, which I must say I forgot about (there is a question about that on this site).
Until now I had no problems with that, but I noticed that some ligatures are missing in the github version (for example T_h). I looked into the font files with FontForge and it seems to me that the font is actually missing this ligature as well as others (only the basic ones are present, such as f_i).
Why is this? I would assume that the more recent font version would have, if anything, more ligatures. What happened to them?

Here is an example (I'm compiling with lualatex main.tex)

documentclass{scrartcl}



usepackage{fontspec}

definstallpath{/path/to/local/fonts}

setmainfont{LibertinusSerif}[

    UprightFont    = *-Regular,

    BoldFont       = *-Bold,

    ItalicFont     = *-Italic,

    BoldItalicFont = *-BoldItalic,

    Ligatures      = TeX,

    Extension      = .otf,

    Path           = installpath/

]

%setmainfont{Libertinus Serif}



begin{document}

    Ligatures: ff fi fl ffi fft fb fh fj fk ft Qu Th

end{document}

According to the documentation at https://github.com/libertinus-fonts/libertinus/blob/master/documentation/Opentype-Features.pdf, the Th ligature is now in the Discretionary ligature set, which is off by default. Note that this also enables (at least) a tz ligature. If you don't want the other ligatures, like tz, then it is also possible to get the Th ligature by putting a Zero Width Joiner (ZWJ) in between. i.e., T<U200D>h → T_h.

The Qu ligature has been moved to Contextual Alternates, which is supposed to be on by default. The fact that this doesn't work by default with lualatex, but does with xelatex suggests that something is wrong with how lualatex or fontspec with lualatex handles the font.

This should work with the latest files in github (post release 6.6):

documentclass{article}

usepackage{fontspec}

setmainfont{Libertinus Serif}

begin{document}

Common Ligatures: ff fi fl ffi fft fb fh fj fk ft Qu Th tt tz ck ch



With verb|ZWJ|: T‍h



addfontfeatures{Contextuals=Alternate}

With verb|Contextuals=Alternate|: Qu



addfontfeatures{Ligatures=Rare}

With verb|Ligatures=Rare|: Th tt tz ck ch

end{document}