\DisableLigatures no longer working with microtype 3.2 and unicode-math

[njbart]

Description

Using \DisableLigatures[?,!]{} no longer seems to work with microtype 2024/12/12 v3.2 in the presence of \usepackage{unicode-math}.

Error message processing the MWE below (engine: This is LuaHBTeX, Version 1.18.0 (TeX Live 2024) (format=lualatex 2024.12.4) 17 DEC 2024 13:34:

! Undefined control sequence.
<argument> MT@feat 

Commenting out either \usepackage{unicode-math} or \DisableLigatures[?,!]{} results in a successful run of lualatex.

On a different machine which still has microtype 2024/03/29 3.1b, the unmodified MWE below continues to work well.

Background

This is to avoid unwanted ligatures: when the following is intended:
if a latex file contains character combinations such as !`.

pandoc (and quarto) unfortunately emit latex code containing !`` and ?``, even when unicode !“ or ?“ is used in the markdown source, and \usepackage{unicode-math} is included by pandoc (and quarto) by default and cannot easily be removed. In pandoc, latex ligatures can only be completely disabled, and in quarto, they cannot be disabled at all so far. In particular when using quarto, the only workaround I’ve found has been to use lualatex and the \DisableLigatures command.

Minimal example demonstrating the issue

\documentclass{article}
\usepackage{microtype}
\usepackage{unicode-math}
\usepackage{fontspec}
\setmainfont[Renderer=Basic]{Arial}
\DisableLigatures[?,!]{}
\begin{document}
„Hi!``

„What?``
\end{document}

[schlcht]

thanks for the report, that's just one definition missing:

\def\MT@noligatures{%
  \MT@dotrue
  \let\@tempa\MT@nl@setname
  \def\MT@feat{nl}% <-- THIS LINE
  \MT@map@clist@n{font,encoding,family,series,shape,size}{%
    \MT@ifdefined@n@TF{MT@checklist@##1}%
      {\csname MT@checklist@##1\endcsname}%
      {\MT@checklist@{##1}}%
    {nl}%
  }%
  \ifMT@do
    \MT@noligatures@\MT@font\MT@nl@ligatures
  \fi
}