[metapost] Change 2.25.0 breaks existing code

[Toby Thurston]

I've raised an issue for this, but I thought I should mention it here too.

https://github.com/lualatex/luamplib/issues/117

I've recently updated my mactex 2023 install with tlmgr and I find that your change 2.25.0 breaks some of my existing code.

For example, this document

\documentclass[border=5mm]{standalone}
\usepackage{luamplib}
\begin{document}
\begin{mplibcode}
beginfig(1);
label(TEX("\large A"), origin);
endfig;
\end{mplibcode}
\end{document}

used to compile OK, but now it gives a "TeX Capacity Exceeded" error as it expands some of the internal macros.

This is apparently because you are doing something special to the <string> argument to the TEX() macro.  

To avoid this error I have to add "\mplibtextextlabel{enable}" to the preamble.

But then the TEX() macro is redundant!  

I can see (some) reason for allowing this to cause an error:

\documentclass[border=5mm]{standalone}
\usepackage{luamplib}
\begin{document}
\begin{mplibcode}
beginfig(1);
label("\large A", origin);
endfig;
\end{mplibcode}
\end{document}

And in most circumstances I am very happy to do this:

\documentclass[border=5mm]{standalone}
\usepackage{luamplib}
\mplibtextextlabel{enable}
\begin{document}
\begin{mplibcode}
beginfig(1);
label("\large A", origin);
endfig;
\end{mplibcode}
\end{document}

But this form was occasionally useful, and removing it is annoying and confusing (at least).

\documentclass[border=5mm]{standalone}
\usepackage{luamplib}
\begin{document}
\begin{mplibcode}
beginfig(1);
label(TEX("\large A"), origin);
endfig;
\end{mplibcode}
\end{document}

Any thoughts or comments??

Toby
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