\robustify doesn't undefine \foo[space]

[josephwright]

With the example

\RequirePackage{etoolbox}
\DeclareRobustCommand\foo[2][]{}
\expandafter\show\csname foo \endcsname
\robustify\foo
\expandafter\show\csname foo \endcsname

the robustify procedure makes \foo a \protected version of the LaTeX kernel \foo[space]. The code in etoolbox has

        \if@tempswa
          \ifcsdef{\string#1 }
            {}
            {\csundef{\expandafter\@gobble\string#1 }}%

but the logic here seems odd/wrong.

Need to check exactly what the LaTeX kernel does in all cases and make sure we leave only the 'required' parts about.

[lstonys]

It does undefine. Just \show\csname it makes as a \relax

\let \fee\etb@undefined

\show\fee
> \fee=undefined.
l.22 \show\fee

\expandafter\show \csname fee\endcsname
> \fee=\relax.
<recently read> \fee