Savetrees and extra space when changing to monospace font

Question

I recently noticed a subtle issue while working on a paper: with savetrees enabled, when you use \tt inside running text, LaTeX switches to the monospace font before inserting the interword space, but then when it returns to the prevailing font it uses that font's interword space. If you use \texttt instead, the space both before and after the monospace text are set in the monospace font.

Here's a minimal example:

\documentclass{article}

\usepackage[subtle]{savetrees}

\begin{document}

You should use the {\tt mkdir} command to create directories.

You should use the \texttt{mkdir} command to create directories.

\end{document}

This produces:

The spacing difference after "mkdir" is obvious. If you look more carefully, you'll note that on both lines the space before "mkdir" is also wider than the space between other words (e.g. in "use the").

Commenting out savetrees makes the problem go away; the spacing around "mkdir" becomes the same as the spacing between other words regardless of which typesetting approach is used.

I experimented and found that I could use \hspace{0pt} in front of the {\tt mkdir} to cause savetrees to use the prevailing font's whitespace settings. (Actually I'm using \hspace{0pt}\nolinebreak because it's all inside a macro.) But that seems like an ugly hack. I tried {} as a cleaner option but it had no effect.

So: (1) is this a savetrees bug? and (2) is there a better way to work around it? I want the prevailing font's whitespace on both sides of "mkdir", since to my eyes it looks better and anyway the spaces aren't inside the changed font.

Answer 1

This is not a solution, but an explanation with one not-very-satisfactory workaround and a second hideous one.

The basic problem is not in savetrees but microtype. Initially, I assumed it must have to do with word spacing, but drew a blank. The problem is actually triggered by tracking. So one workaround is to use savetrees but disable this particular option.

To see the problem, you can trace tracking through savetrees's quite simple code in the documentation. The option is implemented using microtype, but only if we're producing PDF and LuaTeX is not the engine.

The following is equivalent to loading savetrees with subtle and only tracking enabled.

\documentclass{article}

\usepackage[letterspace=-25]{microtype}
\newcommand \sttest{%
  You should use the {\tt mkdir} command to create directories and not use {\tt\textbackslash tt}!\par
  You should use the {\ttfamily mkdir} command to create directories and not use {\ttfamily\textbackslash tt}!\par
  You should use the \texttt{mkdir} command to create directories and not use \texttt{\textbackslash tt}!\par
  You should use the \texttt{mkdir}{} command to create directories and not use \texttt{\textbackslash tt}!\par
}

\begin{document}
\sttest


{\lsstyle
  \sttest}
\SetTracking[
  spacing={-25*,,},
  outer spacing={-25*,,},
  outer kerning={0,0},
]{encoding=*}{-25}
{\lsstyle
  \sttest}

\end{document}

Workaround 1

Use savetrees with all options except tracking.

\documentclass{article}

\usepackage[subtle,tracking=normal]{savetrees}%,tracking=tight
\usepackage{microtype}
\newcommand \sttest{%
  You should use the {\tt mkdir} command to create directories and not use {\tt\textbackslash tt}!\par
  You should use the {\ttfamily mkdir} command to create directories and not use {\ttfamily\textbackslash tt}!\par
  You should use the \texttt{mkdir} command to create directories and not use \texttt{\textbackslash tt}!\par
  You should use the \texttt{mkdir}{} command to create directories and not use \texttt{\textbackslash tt}!\par
}

\begin{document}
\parindent=0pt
\sttest


{\lsstyle
  \sttest}
\end{document}

Obviously, if you then use letterspacing, you'll get a bizarre result, but presumably you could omit \lsstyle in your real document. (It is not recommended for general usage, but only for caps/small-caps and in specialist cases.) This will use a little more paper (but be typographically superior, of course).

Workaround 2

If you are really committed to reducing paper, you could enable savetrees's tracking locally. I absolutely wouldn't do this (but I don't use savetrees either). If you nonetheless wish to do so, you can set microtype up so that letter-spacing emulates savetrees's tracking option and use \lsstyle to enable it locally.

\documentclass{article}

\usepackage[subtle,tracking=normal]{savetrees}
\makeatletter
\usepackage[letterspace=\st@cspace@shrink]{microtype}
\makeatother
\newcommand \sttest{%
  You should use the {\tt mkdir} command to create directories and not use {\tt\textbackslash tt}!\par
  You should use the {\ttfamily mkdir} command to create directories and not use {\ttfamily\textbackslash tt}!\par
  You should use the \texttt{mkdir} command to create directories and not use \texttt{\textbackslash tt}!\par
  You should use the \texttt{mkdir}{} command to create directories and not use \texttt{\textbackslash tt}!\par
}

\begin{document}
\parindent=0pt
\sttest

{\lsstyle
  \sttest}
\end{document}

But if you're OK with that, I doubt you'd have asked the original question .... So workaround 1 is likely preferable.