afterpage can lose a complete page

[davidcarlisle]

Brief outline of the bug

If \afterpage is followed by more than a page worth of material before the output routine is called it can lose
the entire page and insert its material before the contributions held over.

Originally reported at

https://tex.stackexchange.com/questions/738483/afterpage-command-making-a-full-page-disappear

But this version is from @u-fischer and works with pdflatex, the problem shows on old releases so doesn't seem related to recent changes for marks or para hooks.

Minimal example showing the bug

\RequirePackage{latexbug}
\documentclass[]{book}%
\usepackage{afterpage}

\begin{document}
abc

\vspace{26\baselineskip}

abc

\afterpage{\clearpage Whatever \clearpage}

ups-A where is the rule?\\\rule{4pt}{\textheight}\\ups-B
%\\here is comes

abc

\end{document}

Log file (required) and possibly PDF file

afterpage-x.log

[FrankMittelbach]

The problem is this part of \AP@savetop

  \begingroup
  \nointerlineskip\null
    \output{%
      \global\setbox\AP@partial\vbox{%
        \unvbox\@cclv
        \global\setbox\@ne\lastbox}%
       \global\setbox\AP@footins\box\footins}%
  \eject
  \endgroup}

If the galley has more material than a page than the \lastbox will not take out the \null box but something else (in this case the rule. So what you need is something like

  \nointerlineskip\null
  \output{%
     \ifnum\outputpenalty=-100013
      \typeout{---> special penalty reached}%
      \global\setbox\AP@partial\vbox{%
        \unvbox\@cclv
        \global\setbox\@ne\lastbox}%
      \global\setbox\AP@footins\box\footins
      \else
       \typeout{---> special penalty NOT reached}%
       \the\AP@output 
     \fi
  }%
  \penalty-100013

We don't have a registry for special penaltiers but I think 100013 is ok,

[davidcarlisle]

@FrankMittelbach

If the galley has more material than a page than the \lastbox will not take out the \null box but something else

ah thanks, I got that far, but then got lost:-) Penalty looks good thanks, I'll do some testing and arrange an update