Issue with shorthands using KOMA-Script

[fsl-digital]

There is a problem with spanish when using a KOMA-Script class like scrbook instead of the standard classes. However, changing the language also resolves the problem. Therefore I report the problem here as well (cf. https://sourceforge.net/p/koma-script/tickets/102/).

\documentclass{scrbook}
\usepackage[spanish]{babel}

\begin{document}
   Test
\end{document}

results in the error: LaTeX hooks Error: Generic hooks cannot be added to '\@startsection'.

[sieversMartin]

This was meant to be reported from my personal account @sieversMartin

[u-fischer]

You can avoid the error with \usepackage[spanish,es-noquoting]{babel}.

Basically this is a variant of latex3/latex2e#1099: The \@startsection command contains a <, and as spanish makes that active the command hook patching fails.

[jbezos]

@sieversMartin The problem seems to be a combination of the hooking mechanism and an unprotected use in KOMA of a babel shorthand. This issue should be fixed in KOMA. As a workaround, follow the advice by Ulrike.

[u-fischer]

@jbezos No, it is not an "unprotected use" from KOMA. The problem is that you can not patch \@startsection if babel makes the < active. (It would probably work, if the shorthand is created later in the document).

\documentclass{article}
\usepackage[spanish]{babel}
\AddToHook{cmd/@startsection/before}{blub}
\begin{document}
   Test
\end{document}

[jbezos]

@u-fischer Point taken.

[smetaon]

The same problem is with czech and slovak, but not russian. Babel 25.17, koma 3.49, babel-czech 3.1a, babel-slovak 3.1a, babel-russian 1.3m.

[jbezos]

@smetaon The problem can affect many languages, in fact:

\documentclass{article}
\def\test#1{!}
\usepackage[french]{babel}
\AddToHook{cmd/test/after}{xx}
\begin{document}
\test{X}
\end{document}

I’m investigating how to deal with shorthands and hooks, although it doesn’t seem trivial.

[u-fischer]

@jbezos can you try to move the shorthand activation from the begindocument hook into the begindocument/end hook? Then you would be after the patching code.

[jbezos]

@u-fischer It’s problematic if there is some \AtBeginDocument after loading babel dealing somehow with catcodes (or expecting some particular values). It can break existing documents and packages.