caption for listings in margin

Question

The floatrow package enables one to put in the margin captions for figures and tables, but it seems there is missing the possibility of doing the same for the lstlisting environment from listings package.

A workaround is to put the lstlisting in a figure (see sample). But this doesn't allow us to keep the page breaking for long code listings. Is there a way to put lstlisting captions in the margin? I've looked inside the floatrow package to see if I can extend it, but I don't know how.

\documentclass{memoir}
\usepackage{listings}
\usepackage{floatrow}
\floatsetup[figure]{margins=hangright,capposition=beside,capbesideposition={top,left},floatwidth=\textwidth}

\begin{document}
\begin{figure}
  \begin{lstlisting}

    This is a test
  \end{lstlisting}
  \caption{This is a test.}
\end{figure}
\end{document}

The caption package has a way to put Fig X: inside the margin (see below), but putting the third argument within llap doesn't seem to work.

\DeclareCaptionFormat{llap}{\llap{#1#2}#3\par}
\captionsetup{lstlisting}{format=llap,labelsep=quad,singlelinecheck=no}

Answer 1

memoir and floatrow don't cooperate well. If you want side captions for table and figure, you can use memoir's \sidecap command (See section 10.10 SIDE CAPTIONS of the manual). In the case of listings produced with lstlisting, one has to do some additional work.

The following code (that admits improvements) shows one approach; the caption is stored in a box of width \sidecapwidth and then placed in the margin using \sidepar:

\documentclass{memoir}
\usepackage{listings}
\usepackage{graphicx}
\usepackage{caption}
\usepackage{marginnote}
\usepackage{lipsum}

\newsavebox\mycap
\newlength\mycapHt

\setlength\sidecapwidth{77pt}

\DeclareCaptionFormat{llap}{%
  \begin{lrbox}{\mycap}
  \begin{minipage}{\sidecapwidth}
  \raggedright#1:#2#3
  \end{minipage}%
  \end{lrbox}%
  \settoheight\mycapHt{\usebox\mycap}%
  \addtolength\mycapHt{.85\baselineskip}%
  \setlength\sideparvshift{\mycapHt}%
  \sidepar{\usebox\mycap}}
\captionsetup[lstlisting]{format=llap,labelsep=space,singlelinecheck=no}

\begin{document}

\begin{figure}
\begin{sidecaption}{An illustration}[fig:ill]
\centering
\includegraphics[height=4cm]{example-image-a}
\end{sidecaption}
\end{figure}
\lipsum[4]
\begin{lstlisting}[caption={test caption for a listing}]
This is a test
This is a test
This is a test
This is a test
This is a test
\end{lstlisting}
\lipsum[4]
\begin{lstlisting}[caption={test caption for a listing that will span several lines}]
This is a test
This is a test
This is a test
This is a test
This is a test
This is a test
This is a test
This is a test
This is a test
This is a test
This is a test
This is a test
This is a test
This is a test
This is a test
\end{lstlisting}
\lipsum[4]

\end{document}