#10 Infinite loop

[Rolf]

The following example cannot be compiled (infinite loop). About a quarter of a year ago, such a construct still worked. I don't know what the problem is (my code ?, KOMA-Script?, LaTeX?). For my minimal example see attachment.

[Markus Kohm]

Seems to be a bug in KOMA-Script.

Nevertheless I would recommend to use \LoadClassWithOptions, because it doesn't make sense to explicitly pass all the global options to the class, which surely does not know all of them.

[Markus Kohm]

I was wrong. It is not a bug in KOMA-Script but either a bug or feature of LaTeX. Your

\DeclareOption*{\PassOptionsToClass{\CurrentOption}{scrlttr2}}

does not add the option to the raw option list \@raw@opt@foo.cls but the unexpanded \CurrentOption. AFAIK the KOMA-Script classes currently are the only classes, that process the raw option list. So the problem does currently only affects the KOMA-Script classes.

However, you can test the problem without KOMA-Script:

\begin{filecontents*}[force]{testclass.cls}
\ProvidesClass{testclass}[2021/06/05 v0.0 test class]
\DeclareOption*{\PassOptionsToClass{\CurrentOption}{testclassi}}
\ProcessOptions\relax
\LoadClass{testclassi}
\endinput
\end{filecontents*}
\begin{filecontents*}[force]{testclassi.cls}
\ProvidesClass{testclassi}[2021/06/05 v0.0 internal test class]
\expandafter\show\csname @raw@opt@testclassi.cls\endcsname
\expandafter\show\csname opt@testclassi.cls\endcsname
\ProcessOptions\relax
\LoadClass{minimal}
\endinput
\end{filecontents*}
%------------------------------------------------------------
\documentclass[draft]{testclass}
\begin{document}
\end{document}

results in

> \@raw@opt@testclassi.cls=macro:
->\CurrentOption ,.
<recently read> \@raw@opt@testclassi.cls 

l.2 ...ow\csname @raw@opt@testclassi.cls\endcsname

> \opt@testclassi.cls=macro:
->draft,.
<recently read> \opt@testclassi.cls 

l.3 ...er\show\csname opt@testclassi.cls\endcsname

So the raw option list and the classic options list differs here. The classic options list contains the expanded \CurrentOption → draft, but the raw option list contains \CurrentOption itself.

I don't know whether this is a bug in LaTeX or a mistake in your code. But you can fix your code, be forcing a one step expansion:

\begin{filecontents*}{foo.cls}
\ProvidesClass{foo}[2021/06/04 v0.1a foo-Klasse (RN)]
\DeclareOption*{\expandafter\PassOptionsToClass\expandafter{\CurrentOption}{scrlttr2}}
\ProcessOptions\relax
\LoadClass{scrlttr2}
\endinput
\end{filecontents*}
%------------------------------------------------------------
\documentclass[twoside]{foo}
\usepackage[ngerman]{babel}
\begin{document}
\begin{letter}{Petra Mustermann\\
Vor dem Berg 1\\
12345 Musterhausen}
XXXXXXXXXXXXXXXXXXXXXXXXXXXX
\newpage
YYYYYYYYYYYYYYYYYYYYYYYYYYYY
\end{letter}
\end{document}

Please ask The LaTeX Team, whether this is intended or not.

[Markus Kohm]

[r3604] adds a very simple detection and proper error message for this case.

[Markus Kohm]

Delegated to The LaTeX Team → https://github.com/latex3/latex2e/issues/580

[David Carlisle]

sorry about that, we'll arrange a patch level 1 latex update.