How to handle babel active characters when writing a package?

Question

In the bodeplot package, I defined new environments using (defined like this to avoid issues with externalization of tikz graphics)

\documentclass{standalone}
\usepackage{pgfplots,xparse}
\pgfplotsset{compat=1.18}
\NewDocumentEnvironment{MyEnv}{O{}mm+b}{
  \begin{tikzpicture}
    \begin{semilogxaxis}[xmin={#2},xmax={#3},ymin=0,ymax=1]
      #4
    \end{semilogxaxis}
  \end{tikzpicture}
}{}

I want users to be able to use the new environment to do things like this

\begin{document}
  \begin{MyEnv}[]{1e-1}{1e4}
    \draw[thick,blue,dashed] (axis cs:1,0) -- (axis cs:100,1);
    \addplot[variable=t,domain=1e-1:1e4] gnuplot {(t>100)?0.2:0.5};
  \end{MyEnv}
\end{document}

All of this works out for English language documents. However, if a user uses babel with any language that makes some characters in #4 active, the document cannot be compiled. For example, if I add

\usepackage[french]{babel}
\usetikzlibrary{babel}

to the preamble, I get compilation errors.

I managed to make it work for the French language work by checking for frenchbsetup and using

\AddToHook{env/MyEnv/begin}{\shorthandoff{;:!?}}

if it is detected. However, doing something like this for every active character in every language seems like the wrong approach to solve this issue.

Is there a better way detect and manage active characters in macros like this that will work with all languages supported by babel?

Answer 1

I’m not sure how tikz deals with catcodes, but I presume they must be changed somehow to their default values, usually 12 (‘other’). And the only way is with \shorthandoff (or with the low level \catcode).

However, perhaps the following idea works for you: there is a macro named \dospecials storing ‘special’ characters, and babel adds shorthands to it. Since they are stored as macros (ie, ; is stored as \;), we need some trick to get the actual character. Then we can use \ifbabelshorthand:

\documentclass{article}
\usepackage[french]{babel}
\makeatletter
\let\shorthandlist@empty
\def\do#1{%
  \begingroup
    \lccode\~=#1\relax
    \lowercase{\ifbabelshorthand~{\g@addto@macro\shorthandlist{~}}{}}
  \endgroup}
\dospecials
\makeatother
\show\shorthandlist

This will show ->~:;!?., which, if we remove the characters added by \show, is ~:;!?. It may not work for you, but at least I tried .

EDIT: Once the shorthand list is assembled, it can be used to turn shorthands off in MyEnv using \AddToHook{env/MyEnv/begin}{\expandafter\shorthandoff\expandafter{\shorthandlist}}. Complete MWE:

\documentclass{standalone}
\usepackage{pgfplots,xparse}
\pgfplotsset{compat=1.18}
\usepackage[french]{babel}
\usetikzlibrary{babel}
\NewDocumentEnvironment{MyEnv}{O{}mm+b}{
    \begin{tikzpicture}
        \begin{semilogxaxis}[xmin={#2},xmax={#3},ymin=0,ymax=1]
            #4
        \end{semilogxaxis}
    \end{tikzpicture}
}{}
\makeatletter
\let\shorthandlist@empty
\def\do#1{%
    \begingroup
    \lccode\~=#1\relax
    \lowercase{\ifbabelshorthand~{\g@addto@macro\shorthandlist{~}}{}}
    \endgroup}
\dospecials
\makeatother
\AddToHook{env/MyEnv/begin}{\expandafter\shorthandoff\expandafter{\shorthandlist}}
\begin{document}
    \begin{MyEnv}[]{1e-1}{1e4}
        \draw[thick,blue,dashed] (axis cs:1,0) -- (axis cs:100,1);
        \addplot[variable=t,domain=1e-1:1e4] gnuplot {(t>100)?0.2:0.5};
    \end{MyEnv}
\end{document}