Microtype package produces warning when using LuaTex

Question

I am receiving the following warning message whenever I include microtype:

Module microtype Warning: overwriting function `keepligature' on input line 59

Here is a minimum working example:

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

I do not get the error when I use XeLaTex.

Does anyone know why microtype is giving this warning?

If it is harmless, is there any way to suppress it?

Answer 1

You get the warning as the newest luaotfload version changed the handling of ligatures in letterspaced fonts and for this predefines the keepligature function (see the luaotfload documentation for details).

microtype has its own keepligature definition and when installing it now warns that it overwrites luaotfload definition.

The microtype definition is compatible with the luaotfload definition -- at least the tests didn't reveal any problem --, so the warning can be ignored (but it can't be silenced).