Tweak showlabels/showkeys - wrap the label

Question

Can showlabels wrap the label in the margin? A very similar question is showlabels: wrap labels in marginpar, but the solution of @DavidCarlisle does not solve the more general case. Consider the following MWE:

\documentclass{article}
\begin{document}
\begin{figure}[ht]
  \centering
  \rule{1cm}{1cm}
  \caption{default}
  \label{fig:a very very very long and detailed label}
\end{figure}
\end{document}

When adding the package showkeys the output is:

Similar problem occurs with the showlabels package (whether the hack of @DavidCarlisle is used or not):

So, is there a way to fix it?

Answer 1

In order to split a long label without spaces, you can use the \seqsplit command from the seqsplit package. The following is an adaption of David's answer and also shows the necessity of wrapping long labels:

\documentclass{article}
\usepackage[%showframe, % show helper lines
            paperwidth=10cm, paperheight=7cm,
            hmargin=24mm,vmargin=4mm, marginparwidth=17mm,
           ]{geometry}
\usepackage{seqsplit}
\usepackage{showkeys}
\usepackage{xstring}

\renewcommand*\showkeyslabelformat[1]{%
\noexpandarg%
% instead of \textvisiblespace you can also put in ~
% if you want to keep a plain space at space characters
\StrSubstitute{\(\{\)#1\(\}\)}{ }{\textvisiblespace}[\TEMP]%
\parbox[t]{\marginparwidth}{\raggedright\normalfont\small\ttfamily\expandafter\seqsplit\expandafter{\TEMP}}}

\begin{document}
\begin{equation}
    (a\cdot b ) \cdot c = a\cdot (b\cdot c)
    \label{eq:groupassociativity}
\end{equation}
\begin{figure}[ht]
  \centering
  \rule{1cm}{1cm}
  \caption{default}
  \label{fig:a very very very long and detailed label}
\end{figure}
\end{document}

For the spaces, one needs to replace the spaces within the seqsplit, either by ~ for keeping a space or by something else like \textvisiblespace to visualize it better.

Answer 2

Having labels like this is really a misuse of the label system, labels are intended to be short symbolic names, but anyway

\documentclass{article}
\usepackage{showkeys}
\renewcommand*\showkeyslabelformat[1]{%
  \fbox{\parbox[t]{\marginparwidth}{\raggedright\normalfont\small\ttfamily#1}}}

\begin{document}
\begin{figure}[ht]
  \centering
  \rule{1cm}{1cm}
  \caption{default}
  \label{fig:a very very very long and detailed label}
\end{figure}
\end{document}