Wrong kerning in math between w and subscript-j

[nagmat84]

Describe the bug

In mathematics, a base symbol w followed by a subscript j have too much space while at the same time the j and the following letter nearly collide. The overall visual appearance looks as if the subscript j actually belonged to the following letter but not to its true base symbol.

To Reproduce

Compile this MWE with LuaLaTeX or XeLaTeX

\documentclass{article}
\usepackage{libertinus}
\begin{document}
\(w_j q^j\) 
\end{document}

Expected behavior

The spacing between the w and the j should be smaller, the spacing between the j and the q should be bigger.

Screenshots

Additional context

Also, see here: https://tex.stackexchange.com/q/530675/47156

[khaledhosny]

I improved it a bit for XeTeX already, but for LuaTeX it is still broken because LuaTeX does not apply italic correction by default (for reasons beyond me).

[nagmat84]

OK. Then, who is the correct addressee to whom I should post a bug report?

[khaledhosny]

XeTeX output:

[khaledhosny]

LuaTeX developers.

[nagmat84]

Sure thing. I hoped, you had an URL or mail address of the project. I was apparently unable to find it. Of course, there is http://www.luatex.org, but I hoped there would be something like a bug tracker or similar. It does not seem to be right, to post a bug to the legal contact of that website.

[waldyrious]

Looking at the description of the mirror repository https://github.com/TeX-Live/luatex, it says:

for issues please contact the luatex mailing list

And in the support page at luatex.org/support.html there are two mailing lists mentioned (luatex and dev-luatex), whose archives are public and show recent activity. So I guess that's where bugs can be reported.