#1 scrbase breaks option handling of LaTeX 2020-05-01

[Markus Kohm]

The new option handling of LaTeX 2021-05-01 allows:

\documentclass[foo=bar,bar={foo}]{article}
\begin{document}

\end{document}

without error. There is only a message:

LaTeX Warning: Unused global option(s):
    [foo,bar].

Former LaTeX versions reported an error:

LaTeX Error: Missing \begin{document}.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              

l.113 \input
            {size1\@ptsize.clo}

But scrbase breaks the new option handling of LaTeX 2020-05-02:

\documentclass[foo=bar,bar={foo}]{article}
\usepackage{scrbase}
\begin{document}

\end{document}

results in:

! LaTeX Error: Missing \begin{document}.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              

l.502 \FamilyProcessOptions{KOMA}
                               \relax

[Markus Kohm]

The reason of the issue is the usage of \in@. \in@ explicitly does not support braces. A poor man's loop like

\in@false
\@for \reserved@a:=\@declaredoptions\do{%
   \ifx\CurrentOption\reserved@a\in@true\fi
}%

instead of

\in@{,\CurrentOption,}{,\@declaredoptions,}

could solve this. Maybe \CurrentOption should be

Maybe rewriting the whole code using the LaTeX 3 layer of LaTeX 2021/05/01 would be an alternative approach. In this case we could use \clist_map_inline:Nn and \clist_map_break: to increase speed. On the other hand, classes and packages, that use \FamilyProcessOptions shouldn't have several dozens of options declared using \DeclareOption (instead of \DefineFamilyKey etc.). So the poor man's loop should be fast enough.

BTW: \FamilyProcessOptions is based on LaTeX's \ProcessOptions*. LaTeX2e <2021-05-01> pre-release-2 (develop 2021-3-2 branch) has the same issue with \ProcessOptions*. So maybe I should wait with the final implementation until this will be fixed. Then I could (again) use the fixed \ProcessOptions* code as a template for my own changes.

I've commited a kind of early fix (as shown above). This could be fixed again, after \ProcessOptions* will have been fixed in the LaTeX kernel.

[Markus Kohm]

The LaTeX kernel now uses the fast check I've suggested in https://github.com/latex3/latex2e/issues/513#issuecomment-789082387 and so do I.