# TOC out of order in two-column documents

I was playing with \@outputdblcol and I came up with this:

\documentclass[twocolumn]{article}

\makeatletter
\def\@outputdblcol{%
\if@firstcolumn
\global \@firstcolumnfalse
\global \setbox\@leftcolumn \box\@outputbox
\else
\global \@firstcolumntrue
\setbox\@outputbox \vbox {%
\hb@xt@\textwidth {%
\hskip\columnwidth
\hfil
{\normalcolor\vrule \@width\columnseprule}%
\hfil
\hb@xt@\columnwidth {%
\box\@outputbox \hss}%
\hskip-\textwidth
\hb@xt@\columnwidth {%
\box\@leftcolumn \hss}%
\hskip\columnwidth \hskip\columnsep
}%
}%
\@combinedblfloats
\@outputpage
\begingroup
\@dblfloatplacement
\@startdblcolumn
{\@outputpage
\@startdblcolumn}%
\endgroup
\fi
}
\makeatother

\begin{document}
\tableofcontents
Some useless text that we are provingin Some useless text that we are provingin Some useless text that we are provingin Some useless text that we are provingin
\section{Part}
Some useless text that we are provingin
\newpage
Some useless text that we are provingin
\section{Another Part}
Some useless text that we are provingin
\section{LAst Part}
Some useless text that we are provingin
\end{document}


But interestingly even though columns are in the right order but TOC is out of order. Why is this happening? and how one should fix it? (of course without changing the definition of \@outputdblcol to its original form)?

Using David Carlisle's suggestion, I get exactly the same problem:

\documentclass[twocolumn]{article}
\TeXXeTstate=1
\makeatletter
\def\@outputdblcol{%
\if@firstcolumn
\global \@firstcolumnfalse
\global \setbox\@leftcolumn \box\@outputbox
\else
\global \@firstcolumntrue
\setbox\@outputbox \vbox {%
\hb@xt@\textwidth {\beginR%
\hb@xt@\columnwidth {%
\box\@leftcolumn \hss}%
\hfil
{\normalcolor\vrule \@width\columnseprule}%
\hfil
\hb@xt@\columnwidth {%
\box\@outputbox \hss}%
\endR}%
}%
\@combinedblfloats
\@outputpage
\begingroup
\@dblfloatplacement
\@startdblcolumn
{\@outputpage
\@startdblcolumn}%
\endgroup
\fi
}
\makeatother

\begin{document}
\tableofcontents
Some useless text that we are provingin Some useless text that we are provingin Some useless text that we are provingin Some useless text that we are provingin
\section{Part}
Some useless text that we are provingin
\newpage
Some useless text that we are provingin
\section{Another Part}
Some useless text that we are provingin
\section{LAst Part}
Some useless text that we are provingin
\end{document}


but this one works fine:

\documentclass[twocolumn]{article}
\TeXXeTstate=1
\makeatletter
\def\@outputdblcol{%
\if@firstcolumn
\global \@firstcolumnfalse
\global \setbox\@leftcolumn \box\@outputbox
\else
\global \@firstcolumntrue
\setbox\@outputbox \vbox {%
\hb@xt@\textwidth {%
\hskip\columnwidth
\hfil
{\normalcolor\vrule \@width\columnseprule}%
\hfil
\hb@xt@\columnwidth {%
\box\@leftcolumn \hss}%
\hskip-\textwidth
\hb@xt@\columnwidth {%
\box\@outputbox \hss}%
\hskip\columnwidth\hskip\columnsep   }%
}%
\@combinedblfloats
\@outputpage
\begingroup
\@dblfloatplacement
\@startdblcolumn
{\@outputpage
\@startdblcolumn}%
\endgroup
\fi
}
\makeatother

\begin{document}
\tableofcontents
Some useless text that we are provingin Some useless text that we are provingin Some useless text that we are provingin Some useless text that we are provingin
\section{Part}
Some useless text that we are provingin
\newpage
Some useless text that we are provingin
\section{Another Part}
Some useless text that we are provingin
\section{LAst Part}
Some useless text that we are provingin
\end{document}


I am only interested to how fix TOC in the first two examples.

-

\shipout makes the \write in the order that write nodes appear in the vertical list, not in the visual order, so while you have swapped the columns visually with \hskip-\textwidth this does not change the write order. Instead of doing that can you not output the columns in natural order but with directives to xetex (or luatex equivalent) to use RTL setting?

\hb@xt@\textwidth {\beginR%
..


I think \beginR is the right way to do this (but it doesn't work) so back to shuffling boxes by hand. This seems to work:

\documentclass[twocolumn]{article}

\setlength\columnseprule{1pt}

\makeatletter
\TeXXeTstate=1
\makeatletter
\def\@outputdblcol{%
\if@firstcolumn
\global \@firstcolumnfalse
\global \setbox\@leftcolumn \box\@outputbox
\else
\global \@firstcolumntrue
\setbox\@outputbox \vbox {%
\hb@xt@\textwidth {%
\kern\textwidth\llap{\hb@xt@\columnwidth {%
\box\@leftcolumn \hss}}%
\kern-\textwidth
\rlap{\hb@xt@\columnwidth {%
\box\@outputbox \hss}}%
\hfil
{\normalcolor\vrule \@width\columnseprule}%
\hfil
}%
}%
\@combinedblfloats
\@outputpage
\begingroup
\@dblfloatplacement
\@startdblcolumn
{\@outputpage
\@startdblcolumn}%
\endgroup
\fi
}

\makeatother

\begin{document}
\tableofcontents
Some useless text that we are provingin Some useless text that we are provingin Some useless text that we are provingin Some useless text that we are provingin
\section{Part}
Some useless text that we are provingin
\newpage