Extra horizontal space with forest and standalone pacakage

Question

I created some style files for standalone pictures. However, I get unwanted horizontal space.

Here is my first MWE1:

\documentclass[convert={true,convertexe={magick.exe},
   command=\unexpanded{{\convertexe\space -density \density\space \infile\space \ifx\size\empty\else -resize \size\fi\space \outfile}}}]{standalone}

\RequirePackage{forest}

\begin{document}

\begin{forest}
[ 2 [1] [3]]
\end{forest}

\end{document}

The result is:

However, I want to change my transparent background. Here is MWE2:

\documentclass[convert={true,convertexe={magick.exe},
   command=\unexpanded{{\convertexe\space -density \density\space \infile\space \ifx\size\empty\else -resize \size\fi\space -transparent white'rgb(100,200,100)' \outfile}}}]{standalone}

\RequirePackage{forest}
\RequirePackage{xcolor}

\begin{document}

\definecolor{tr}{RGB}{100,200,100}
\pagecolor{tr}

\begin{forest}
[ 2 [1] [3]]
\end{forest}

\end{document}

The result is:

Notice the extra horizontal space before the tree. This is just a MWE, so it is not a lot. However, with bigger trees, the space gets bigger:

Does anyone have an idea to get rid of this?

Answer 1

You just have to place the settings before \begin{document}

\documentclass{standalone}

\usepackage{forest}
\usepackage{xcolor}

\definecolor{tr}{RGB}{100,200,100}
\pagecolor{tr}

\begin{document}

\begin{forest}
[ 2 [1] [3]]
\end{forest}

\end{document}

However, forest has the tendency to add space; an easy workaround is to call standalone with the varwidth option.

\documentclass[varwidth]{standalone}

\usepackage{forest}
\usepackage{xcolor}

\definecolor{tr}{RGB}{100,200,100}
\pagecolor{tr}

\begin{document}

\begin{forest}
  [A[B[D][E]][C[F][G]]]
\end{forest}

\end{document}

Compare with the output one gets without varwidth:

General solution

The spaces are added because of an unprotected end of line in the definition of \pgfutilsolvetwotwoleqfloat in pgfutil-common.tex, precisely at the end of line 712

712                 \edef\pgf@marshal{
713                     \noexpand\pgfmathfloatdivide@
714                         {\csname r\Pb\endcsname}
715                         {\csname m\Pb b\endcsname}%
716                 }%

Indeed, if I do

\documentclass{standalone}

\usepackage{forest}
\usepackage{etoolbox}

\makeatletter
% remove the stray space
\patchcmd{\pgfutilsolvetwotwoleqfloat}
  { \noexpand\pgfmathfloatdivide@}
  {\noexpand\pgfmathfloatdivide@}
  {}{}
\makeatother

\begin{document}

\begin{forest}
  [A[B[D][E]][C[F][G]]]
\end{forest}

\end{document}

the result is correct as expected

Thanks to cfr who was able to circumscribe the problem. See the issue report at https://github.com/pgf-tikz/pgf/issues/764

Answer 2

This isn't an answer, but an attempt to point towards the problem. forest is adding space, as the following example shows:

\documentclass[border=12pt]{standalone}
\usepackage[]{forest}
\forestset{
  pack stage/.style={TeX=a,for root'=pack,TeX=b}
}
\begin{document}
\fbox{\begin{forest}
  [A[B[D][E]][C[F][G]]]
\end{forest}}
\end{document}

The problem can be traced to the following lines in forest.sty:

  \pgfintersectionofpaths{\pgfsetpath\forest@all@edges}{\pgfsetpath\forest@node@edge}%
  \def\forest@edgenode@intersections{}%

Adding markers as follows

  X\pgfintersectionofpaths{\pgfsetpath\forest@all@edges}{\pgfsetpath\forest@node@edge}%
  Y\def\forest@edgenode@intersections{}%

shows the culprit is somewhere here

However, I'm not sure how to debug this further, so posting this in the hope somebody else may be able to follow the trail from here.

Answer 3

I want to add an answer for anyone with a recent TeXlive (in my case 2022) who comes across this question and still gets horizontal space. Use case is for defining commands for that standalone file that are not needed in the main document that the standalone is being \includestandalone{}'ed into to. Comments are required at the end of every line after \begin{document} regardless of whether it is necessary in normal LaTeX. For example:

\documentclass{standalone}

\usepackage{forest}
\usepackage{xcolor}

\begin{document}
\definecolor{tr}{RGB}{100,200,100}
\pagecolor{tr}
\tikzset{%
    dotted_block/.style={draw=red!70!white, line width=0.5pt, dash pattern=on 2pt off 2pt,
            inner ysep=0pt,inner xsep=-2pt, rectangle, rounded corners}%
}
\begin{forest}
[ 2 [1] [3]]
\end{forest}
\end{document}

produces:

whereas with comments at the end of every line after \begin{document}:

\documentclass{standalone}

\usepackage{forest}
\usepackage{xcolor}

\begin{document}
\definecolor{tr}{RGB}{100,200,100}%
\pagecolor{tr}%
\tikzset{%
    dotted_block/.style={draw=red!70!white, line width=0.5pt, dash pattern=on 2pt off 2pt,%
            inner ysep=0pt,inner xsep=-2pt, rectangle, rounded corners}%
}%
\begin{forest}
[ 2 [1] [3]]
\end{forest}
\end{document}

produces:

I could not find a reference to this and searching within the forest documentation on CTAN for "space" and "comment" didn't turn up this advice so maybe it will be helpful to others.