Arch Linux

Description:

The microtype LaTeX package (currently at v2.6a in the texlive-core Arch package) emits a series of warnings along the lines of,
"Unknown slot number of character".
This is fixed in version v2.7 of the package (https://tex.stackexchange.com/q/373594).

Steps to reproduce:

Run lualatex or xelatex on the following:

\documentclass{article}
\usepackage{microtype}
\begin{document}
fooey
\end{document}

You should see a long list of warnings starting with:

Package microtype Warning: Unknown slot number of character
(microtype) `\`A'
(microtype) in font encoding `TU' in inheritance list
(microtype) `microtype.cfg/358(protrusion)'.

Manually updating the package (found at /usr/share/texmf-dist/tex/latex/microtype) to v2.7 fixes the problem.