Another babel-french incompatibility with crossreftools

Question

With the indicated line commented-out, the following course using both babel-french and crossreftools gives the expected output from the two crossreftools commands near its end:

\documentclass{article}
\usepackage{amsthm}
\usepackage{thmtools}

%\usepackage[french,main=english]{babel}

\makeatletter
\declaretheoremstyle[
  headformat=\NAME\NUMBER\let\thmt@space\@empty\NOTE,
]{thmstyle}
\makeatother
\theoremstyle{thmstyle}
\declaretheorem[name=Theorem]{theorem}

\usepackage[pdftex,colorlinks]{hyperref}
\usepackage[nameinlink,noabbrev,capitalize]{cleveref}

\usepackage{crossreftools}

\begin{document}

\begin{theorem}[theorem of Pythagoras]
  \label{thm:prelim}

  The square of the hypotenuse of a right triangle equals the sum of the squares of the other two sides.

\end{theorem}

\crtrefanchor{thm:prelim} --- \verb!\crtrefanchor{thm:prelim}!

\crtrefname{thm:prelim} --- \verb!\crtrefanchor{thm:prelim}!

\end{document}

However, when that line is uncommented, this error occurs:

./clash.tex:23: Missing \endcsname inserted.
<to be read again> 
               :
l.23       \label{thm:prelim}

Undoubtedly the error has the same cause as noted in https://tex.stackexchange.com/a/510593/13492: the french option to babel makes : active, which interferes with the colon's use in the label.

A fix for another such class between babel-french and crossreftools was given in https://tex.stackexchange.com/a/510641/13492.

Question: How can this incompatibility be fixed for these two crossreftools commands?

Note: Why colons in labels?

In the book-length document from which the preceding MWE arises, I've been using colons in labels because they nearly all already have hyphens embedded in the phrase following the colon, e.g.,\label{thm:law-large-numbers}. Such a label makes the type of theorem (or definition, etc.) visually separate from the terse description of that particular theorem (etc.).

I tried semicolon instead, but find that also no good, since babel-french makes it active, too.

Character | might do (hope it doesn't lead to other problems), but it's rather obtrusive compared with : in a label. (Still, it will take some work to replace the colons in some 1500-1600 labels without inadvertently replacing needed colons punctuation body text.)

Answer 1

This may help. I don't know if it is robust enough, but in simple cases it should work:

\edef\myoldcatcode{\the\catcode`\:}
\let\myoriglabel\label
\def\label{\catcode`\:=11 \mynewlabel}
\def\mynewlabel#1{\myoriglabel{#1}\catcode`\:=\myoldcatcode}

Answer 2

You just need to make : safe when constructing csnames, something like

\documentclass{article}
\usepackage{amsthm}
\usepackage{thmtools}

\usepackage[french,main=english]{babel}

\makeatletter
\declaretheoremstyle[
  headformat=\NAME\NUMBER\let\thmt@space\@empty\NOTE,
]{thmstyle}

\let\zzz\active@prefix
\def\active@prefix{\ifincsname\expandafter\string\else\expandafter\zzz\fi}
\makeatother
\theoremstyle{thmstyle}
\declaretheorem[name=Theorem]{theorem}

\usepackage[pdftex,colorlinks]{hyperref}
\usepackage[nameinlink,noabbrev,capitalize]{cleveref}

\usepackage{crossreftools}

\begin{document}

\begin{theorem}[theorem of Pythagoras]
  \label{thm:prelim}

  The square of the hypotenuse of a right triangle equals the sum of the squares of the other two sides.

\end{theorem}

\crtrefanchor{thm:prelim} --- \verb!\crtrefanchor{thm:prelim}!

\crtrefname{thm:prelim} --- \verb!\crtrefanchor{thm:prelim}!

\end{document}