In tikz externalize: how to get the filename match the Figure label automatically?

Question

I'd like to externalize my Tikz pictures and automatically give them the Name Figure1.pdf, Figure2a.pdf, Figure2b.pdf etc.

Therefore, I'd like to combine \textsetnextfilename with some thing like cleveref which gives me the reference string I like automatically.

The purpose is, that I have to submit all figures individually as a PDF for a journal and I'd like to make sure they know which figure belongs where, without me naming everything manually and keeping track of which pdf is where after I moved stuff in the document.

%MWE
\documentclass{article}
\usepackage{cleveref}
\usepackage{tikz}
\usetikzlibrary{external}
\tikzexternalize
\begin{document}
\tikzsetnextfilename{Figure1 (manually)} %%% Here should be some construct with \cref{fig:Test} that expands to Figure 1...
\begin{figure}
\centering
\begin{tikzpicture}
\draw[fill=gray](0,0)rectangle(0.3\textwidth,0.3\textwidth)node[midway, anchor=center,font=\Huge]{A};
\end{tikzpicture}
\caption{Blababal}\label{fig:Test}
\end{figure}
\Cref{fig:Test} shows a square with a uppercase letter A. 
\end{document}

So something based on \cref{fig:Test} has to be entered as an argument to \tikzsetnextfilename to result automatically in having the PDF file names 'Figure 1.pdf'. In the MWE I put it manually, but how to automatize with \cref? If there is a way without \cref that would off also be fine.

Answer 1

The following produces externalised PDFs named Figure1.pdf and Figure2.pdf. \arrastikzsetnextfilename increments the figure counter, sets the filename and then decrements the counter, which \caption will then increment so that the figure's number matches the externalised filename.

\documentclass{article}
\usepackage{tikz}
\usepackage{cleveref}
\usetikzlibrary{external}
\tikzexternalize
\newcommand*\arrastikzsetnextfilename{%
  \refstepcounter{figure}\edef\tempa{Figure\thefigure}%
  \expandafter\tikzsetnextfilename{\tempa}%
  \addtocounter{figure}{-1}%
}
\begin{document}
\arrastikzsetnextfilename
\begin{figure}
  \tikz{\node {first};}

  \caption{first}\label{fig:first}
\end{figure}
\arrastikzsetnextfilename
\begin{figure}
  \tikz{\node {second};}

  \caption{second}\label{fig:second}
\end{figure}
\end{document}

Answer 2

Using labels for file names can be done. But since \ref-like commands can't be use with \tikzexternalize and the default mode=convert with system call, it is necessary to use \tikzexternalize[mode=list and make]. This will produce a file named main.makefile for main.tex. And the figures have to be build manually in a shell with make -f main.makefile.

If that isn't to much trouble, here is a solution.

Instead of calling \tikzsetnextfilename{...} \NextFigureNameByLabel{<label>} must be called. The file names for the figures will then be e.g. Figure-1 or Figure-2b.

It will produce a warning for undefined labels. In that case there will be files named Figure-??..... This also happens on the first run, when labels are not set yet. This can be ignored.

So run LaTeX twice to get references right, execute make -f main.makefile, and then run LaTeX again.

\documentclass{article}
\usepackage{cleveref}
\usepackage{tikz}
\usetikzlibrary{external}
\usepackage{subcaption}

\makeatletter
% based on LaTeX definition of \ref, only gives out the number
\def\@setvalref#1#2#3{%
  \ifx#1\relax
    % warning will not work here, moved to \NextFigureNameByLabel
%    \protect\G@refundefinedtrue
    ??%
%    \@latex@warning{Reference ‘#3’ on page \thepage \space undefined}%
  \else
    \expandafter#2#1%
  \fi}
\def\valref#1{\expandafter\@setvalref\csname r@#1\endcsname\@firstoftwo{#1}}

\newcommand{\NextFigureNameByLabel}[1]{%
    % to get a proper warning for undefined labels
    \expandafter\ifx\csname r@#1\endcsname\relax
        \protect\G@refundefinedtrue
        \@latex@warning{Reference ‘#1’ on page \thepage \space undefined}%
    \fi    
    \edef\NFNtemp{Figure-\valref{#1}}%
    \expandafter\tikzsetnextfilename\expandafter{\NFNtemp}%
}
\makeatother

\tikzexternalize[mode=list and make]
\begin{document}
\begin{figure}
\centering
\NextFigureNameByLabel{fig:SubA}
\begin{subfigure}{0.42\textwidth}
\centering
\begin{tikzpicture}
\draw[fill=gray](0,0)rectangle(0.3\textwidth,0.3\textwidth)node[midway, anchor=center,font=\Huge]{A};
\end{tikzpicture}
\caption{Blababal}\label{fig:SubA}
\end{subfigure}
\NextFigureNameByLabel{fig:SubB}
\begin{subfigure}{0.42\textwidth}
\centering
\begin{tikzpicture}
\draw[fill=gray](0,0)rectangle(0.3\textwidth,0.3\textwidth)node[midway, anchor=center,font=\Huge]{B};
\end{tikzpicture}
\caption{Blababal}\label{fig:SubB}
\end{subfigure}
\caption{Blababal}\label{fig:Test}
\end{figure}
\Cref{fig:Test} shows two squares with a uppercase letters. (\ref{fig:Test})
\Cref{fig:SubA} shows a square with a uppercase letter A. (\ref{fig:SubA})
\Cref{fig:SubB} shows a square with a uppercase letter B. (\ref{fig:SubB})
\end{document}