Cannot decorate an empty path

Question

I want to save a path, draw it cropped and put an arrow on it

\documentclass[10pt,convert={convertexe=magick,density=1000,outext=.png}]{standalone}
\usepackage{tikz}
\usetikzlibrary{decorations.markings}
\begin{document}
\begin{tikzpicture}
\path[save path=\test] (0,0) -- (5,5);
\node at (0,0) {origin};
\begin{scope}
\clip (1,1) rectangle (4,4);
\draw[decorate,decoration={markings,mark=at position 0.5 with {\arrow{stealth}}}][use path=\test];
\end{scope}
\end{tikzpicture}
\end{document}

Well, putting arrow does not work, because I get the message

! Package pgf Error: I cannot decorate an empty path.

What is a workaround for this problem?

Answer 1

The use path facility provided by TikZ is not quite as sophisticated as it needs to be. In particular, it doesn't make the path work with actions and decorations.

My spath3 library (development version on github) handles this correctly, as in the following version of your code.

Note that if you want your line drawn and decorated then you should put the decoration in a pre or post action.

\documentclass[10pt,convert={convertexe=magick,density=1000,outext=.png}]{standalone}
%\url{https://tex.stackexchange.com/q/650655/86}
\usepackage{tikz}
\usetikzlibrary{decorations.markings,spath3}
\begin{document}
\begin{tikzpicture}
\path[spath/save=test] (0,0) -- (5,5);
\node at (0,0) {origin};
\begin{scope}
\clip (1,1) rectangle (4,4);
\draw[postaction={decorate},decoration={markings,mark=at position 0.5 with {\arrow{stealth}}}][spath/use=test];
\end{scope}
\end{tikzpicture}
\end{document}