# Problems with mathtools package

The following code produces an error. If the mathtools package is removed, it works. Why?

\documentclass{report}

\usepackage{mathtools}
\usepackage{etoolbox}

\newbool{shorttoc}

\makeatletter
\patchcmd{\@startshorttoc}{\bgroup}{\bgroup\booltrue{shorttoc}}{}{}
\makeatother

\begin{document}

\tableofcontents

\chapter{Test Appendix}

\end{document}


This question is related to an earlier question of mine.

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mathtools loads the calc package, which change the \setcounter command. You now have to protect it too:
\addtocontents{toc}{\protect\ifbool{shorttoc}{\protect\setcounter{tocdepth}{0}}{}}