Paul Taylor's diagrams.sty NEVER HAPPEN error

Question

I am a tikz-cd user trying to render a document that uses diagrams.sty. I am getting the error "THIS (S) SHOULD NEVER HAPPEN" when running the minimal example below in Overleaf (and locally too). I should note that I am using the latest (v3.96) release of the package. Any ideas on how to get rid of the error?

\documentclass{standalone}
\usepackage{diagrams}

\begin{document}
    \begin{diagram}
        A & \rTo & B
    \end{diagram}
\end{document}

Answer 1

It should be reported to the package author (also the version on ctan does not run at all as it fails a date self-check).

It is missing an \unskip for current latex, this patches it to run without warning.

\documentclass{standalone}
\usepackage{diagrams}

\makeatletter
\def\foo#1\endgraf\unskip#2\foo{\def\row@to@buffer{#1\endgraf\unskip\unskip#2}}
\expandafter\foo\row@to@buffer\foo
\makeatother
\begin{document}
    \begin{diagram}
        A & \rTo & B
    \end{diagram}
\end{document}