Ignore first parskip inside a save box

Question

I have the following definition (MWE below) of a lrbox. If I use the normal setting parskip=off the interaction \mdf@restoreparams works as expected. Inside the lrbox I can use parskip and parindent. But if I use the option parskip=half I get an extra skip at the beginning of the save box. How can I avoid this.

Picture

MWE:

\documentclass[parskip=half]{scrreprt}
\usepackage{kantlipsum}

\catcode`\@11\relax

\def\mdf@lrbox#1{%
 \edef\mdf@restoreparams{%
   \parindent=\the\parindent \parskip=\the\parskip}%
 \setbox#1\vbox\bgroup%
   \color@begingroup%
%     \mdf@horizontalmargin@equation%
     \columnwidth=\hsize%
     \textwidth=\hsize%
     \let\if@nobreak\iffalse%
     \let\if@noskipsec\iffalse%
     \let\par\@@par%
     \let\-\@dischyph%
     \let\'\@acci\let\`\@accii\let\=\@acciii%
     \parindent\z@ \parskip\z@skip%
     \linewidth\hsize%
     \@totalleftmargin\z@%
     \leftskip\z@skip \rightskip\z@skip \@rightskip\z@skip%
     \parfillskip\@flushglue \lineskip\normallineskip%
     \baselineskip\normalbaselineskip%
%%  \sloppy%
     \let\\\@normalcr%
     \hrule \@height\z@ \@width\hsize\relax
     \mdf@restoreparams\relax
     \@afterindentfalse%
     \@afterheading%
}

\def\endmdf@lrbox{\color@endgroup\egroup}


\newbox\MyTestBox

\begin{document}


\mdf@lrbox\MyTestBox
\kant[1]

\kant[1]
\endmdf@lrbox

\fbox{\box\MyTestBox}
\end{document}

I didn't tag this question with KOMA because the same result is reached by the header with a standard class

\documentclass[]{report}
\usepackage{parskip}

or with memoir

\documentclass[]{memoir}
\setlength{\parindent}{0pt}
\nonzeroparskip

Answer 1

Well....

If you don't do

     \hrule \@height\z@ \@width\hsize\relax

Then you don't get the parskip at the top.

Then in your end code, if the width of the box is not what you expect (because no paragraph material has been added) do

\vbox{
hrule \@height\z@ \@width\hsize\relax
\unvbox the box you had
}

---

\documentclass[parskip=half]{scrreprt}
\usepackage{kantlipsum}

\catcode`\@11\relax

\def\mdf@lrbox#1{%
 \edef\mdf@restoreparams{%
   \parindent=\the\parindent \parskip=\the\parskip}%
 \def\tmp{#1}%
 \setbox#1\vbox\bgroup%
   \color@begingroup%
%     \mdf@horizontalmargin@equation%
     \columnwidth=\hsize%
     \textwidth=\hsize%
     \let\if@nobreak\iffalse%
     \let\if@noskipsec\iffalse%
     \let\par\@@par%
     \let\-\@dischyph%
     \let\'\@acci\let\`\@accii\let\=\@acciii%
     \parindent\z@ \parskip\z@skip%
     \linewidth\hsize%
     \@totalleftmargin\z@%
     \leftskip\z@skip \rightskip\z@skip \@rightskip\z@skip%
     \parfillskip\@flushglue \lineskip\normallineskip%
     \baselineskip\normalbaselineskip%
%%  \sloppy%
     \let\\\@normalcr%
%     \hrule \@height\z@ \@width\hsize\relax
     \mdf@restoreparams\relax
     \@afterindentfalse%
     \@afterheading%

}

\def\endmdf@lrbox{\color@endgroup\egroup
\ifdim\wd\tmp<\hsize
\typeout{making box fill width}
\setbox\tmp\vbox{%
\hrule \@height\z@ \@width\hsize\relax
\unvbox\tmp}%
\fi
}


\newbox\MyTestBox

\begin{document}

\mdf@lrbox\MyTestBox
\kant[1]

\kant[1]
\endmdf@lrbox




\fbox{\box\MyTestBox}



\mdf@lrbox\MyTestBox
\begin{tabbing}aaa\end{tabbing}
\endmdf@lrbox


\fbox{\box\MyTestBox}

\end{document}

Answer 2

You can add \vskip-\parskip just at the end of the definition of \mdf@lrbox, that is between \@afterheading and the closing brace.

This will cancel out the \parskip glue automatically inserted when the first paragraph is about to be started.