siunitx abbreviations don't work inside glossaries entries

Question

Here, siunitx abbreviations throw an error if used inside a glossary entry key, however, if the unit is given without abbreviations, no error shows up.

\documentclass{article}

\usepackage{lipsum}
\usepackage{booktabs}
\usepackage{calc,siunitx}
\sisetup{load-configurations = abbreviations}
\usepackage{glossaries}

\makenoidxglossaries

\newlength\glsnamewidth
\newlength\glsunitwidth

\settowidth{\glsnamewidth}{\textbf{sign}}
\settowidth{\glsunitwidth}{\textbf{unit}}

\newglossarystyle{namedescunit}{%
  \setlength{\glsdescwidth}{\linewidth-\glsnamewidth-\glsunitwidth-6\tabcolsep}%
  \renewenvironment{theglossary}%
    {\begin{supertabular}{p{\glsnamewidth}p{\glsunitwidth}p{\glsdescwidth}}}%
    {\end{supertabular}}%
 \renewcommand*{\glossaryheader}{}%
  \renewcommand*{\glsgroupheading}[1]{}%
  \renewcommand{\glossentry}[2]{%
    \raggedright\glstarget{##1}{\glossentryname{##1}} & 
    \centering\glossentrysymbol{##1} &
    \glossentrydesc{##1}\tabularnewline
  }%
  \renewcommand{\subglossentry}[3]{\glossentry{##2}{##3}}%
  \renewcommand*{\glsgroupskip}{}%
}

\setglossarystyle{namedescunit}

%%%%%%%%% this code block causes the crash %%%%%%%%%%%
    \makeatletter
    \appto\@newglossaryentryposthook{%
        \settowidth{\dimen@}{\glsentryname{\@glo@label}}%
        \ifdim\dimen@>\glsnamewidth
        \setlength{\glsnamewidth}{\dimen@}%
        \fi
        \settowidth{\dimen@}{\glsentrysymbol{\@glo@label}}%
        \ifdim\dimen@>\glsunitwidth
        \setlength{\glsunitwidth}{\dimen@}%
        \fi
    }%
    \makeatother
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\glssetnoexpandfield{symbol}
\newglossaryentry{L}{name={L},description={Buchstabe},symbol={---}}
\newglossaryentry{P}{name={Cp},description={specific heat},symbol={[\si{\J\per\kg\per\K}]}}

\begin{document}

\lipsum[1]
\glsaddall

\printnoidxglossaries

\end{document}

Answer 1

It seems that \si the \si abbreviation commands like \J (see Ulrike's answer) can't be processed in the preamble. This can be demonstrated with:

\documentclass{article}

\usepackage{siunitx}

\settowidth{\dimen0}{[\si{\J\per\kg\per\K}]}

\begin{document}
\end{document}

This causes the error:

! Undefined control sequence.
<argument> \J 
              \per \kg \per \K 

Moving \settowidth to the document environment gets rid of the error.

This means that the unit width can't be calculated in the preamble for your MWE, but \makenoidxglossaries won't permit \newglossaryentry in the document environment (and it's not recommended with \makeglossaries). Instead you can make use of the \glsFindWidestUsedAnyNameSymbol command provided with glossaries-extra-stylemods:

\documentclass{article}

\usepackage{lipsum}
\usepackage{booktabs}
\usepackage{calc,siunitx}
\sisetup{load-configurations = abbreviations}
\usepackage[stylemods]{glossaries-extra}

\makenoidxglossaries

\newlength\glsnamewidth
\newlength\glsunitwidth

\settowidth{\glsnamewidth}{\textbf{sign}}
\settowidth{\glsunitwidth}{\textbf{unit}}

\newglossarystyle{namedescunit}{%
  \setlength{\glsdescwidth}{\linewidth-\glsnamewidth-\glsunitwidth-6\tabcolsep}%
  \renewenvironment{theglossary}%
    {\begin{supertabular}{p{\glsnamewidth}p{\glsunitwidth}p{\glsdescwidth}}}%
    {\end{supertabular}}%
 \renewcommand*{\glossaryheader}{}%
  \renewcommand*{\glsgroupheading}[1]{}%
  \renewcommand{\glossentry}[2]{%
    \raggedright\glstarget{##1}{\glossentryname{##1}} & 
    \centering\glossentrysymbol{##1} &
    \glossentrydesc{##1}\tabularnewline
  }%
  \renewcommand{\subglossentry}[3]{\glossentry{##2}{##3}}%
  \renewcommand*{\glsgroupskip}{}%
}

\setglossarystyle{namedescunit}

\newglossaryentry{L}{name={L},description={Buchstabe},symbol={---}}
\newglossaryentry{P}{name={Cp},description={specific heat},symbol={[\si{\J\per\kg\per\K}]}}

\begin{document}
\lipsum[1]
\gls{L}, \gls{P}.


\glsFindWidestUsedAnyNameSymbol{\glsunitwidth}
\settowidth{\dimen0}{\glsgetwidestname}
\ifdim\dimen0>\glsnamewidth
 \glsnamewidth=\dimen0
\fi

\printnoidxglossaries

\end{document}

\glsFindWidestUsedAnyNameSymbol only checks entries that have been marked as used (through commands like \gls) so needs to be used just before the glossary (provided it's at the end of the document). If you use \glsaddall instead, use \glsFindWidestAnyNameSymbol which can be placed at the start of the document:

\begin{document}
\glsFindWidestAnyNameSymbol{\glsunitwidth}
\settowidth{\dimen0}{\glsgetwidestname}
\ifdim\dimen0>\glsnamewidth
 \glsnamewidth=\dimen0
\fi

\lipsum[1]
\glsaddall

\printnoidxglossaries

\end{document}

Answer 2

The definitions for the abbreviations are loaded only at begin document. So you should either move your glossary definition behind \begin{document}, not use abbreviations in the glossary definitions or load the abbreviations earlier:

\documentclass{article}

\usepackage{lipsum}
\usepackage{booktabs}
\usepackage{calc,siunitx}

%load abbreviations:
\ExplSyntaxOn
\__siunitx_load_abbreviations:
\ExplSyntaxOff

\usepackage{glossaries}

\makenoidxglossaries

\newlength\glsnamewidth
\newlength\glsunitwidth

\settowidth{\glsnamewidth}{\textbf{sign}}
\settowidth{\glsunitwidth}{\textbf{unit}}

\newglossarystyle{namedescunit}{%
  \setlength{\glsdescwidth}{\linewidth-\glsnamewidth-\glsunitwidth-6\tabcolsep}%
  \renewenvironment{theglossary}%
    {\begin{supertabular}{p{\glsnamewidth}p{\glsunitwidth}p{\glsdescwidth}}}%
    {\end{supertabular}}%
 \renewcommand*{\glossaryheader}{}%
  \renewcommand*{\glsgroupheading}[1]{}%
  \renewcommand{\glossentry}[2]{%
    \raggedright\glstarget{##1}{\glossentryname{##1}} &
    \centering\glossentrysymbol{##1} &
    \glossentrydesc{##1}\tabularnewline
  }%
  \renewcommand{\subglossentry}[3]{\glossentry{##2}{##3}}%
  \renewcommand*{\glsgroupskip}{}%
}

\setglossarystyle{namedescunit}

%%%%%%%%% this code block causes the crash %%%%%%%%%%%
    \makeatletter
    \appto\@newglossaryentryposthook{%
        \settowidth{\dimen@}{\glsentryname{\@glo@label}}%
        \ifdim\dimen@>\glsnamewidth
        \setlength{\glsnamewidth}{\dimen@}%
        \fi
        \settowidth{\dimen@}{\glsentrysymbol{\@glo@label}}%
        \ifdim\dimen@>\glsunitwidth
        \setlength{\glsunitwidth}{\dimen@}%
        \fi
    }%
    \makeatother
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\glssetnoexpandfield{symbol}
\newglossaryentry{L}{name={L},description={Buchstabe},symbol={---}}
\newglossaryentry{P}{name={Cp},description={specific heat},symbol={[\si{\J\per\kg\per\K}]}}

\begin{document}

\lipsum[1]
\glsaddall

\printnoidxglossaries

\end{document}

You could make a feature request for siunitx that it adds a option to load them directly.

Answer 3

I found a similiar question here. @tomriddle suggested a quite simple solution in comparison to the already provided answers by using \unexpanded{} in the entry. I am no expert if this can cause some problems down the line but the solution worked well in my document.

Here is an example:

\newacronym{MC}{\unexpanded{\si{\micro}C}}{Mikrocontroller}