Compiling old latex with latexrelease

One more latex trick, which could be helpful to you too.

It has happended to me a few times that I’m recompiling some oldish beamer, and a file that would compile perfectly a few years back, now has weird error messages. For example:

! Extra \endgroup.
\document ->\beamer@firstminutepatches \endgroup
\par \AtBeginDocument {\@if...
l.58 \begin{document}
Things are pretty mixed up, but I think the worst is over.

Last time, I found a workaround, which is to compile with the latex compiler from a few years back. This can be done easily with the latexrelease package.

For example, in my case, having the document start by

\RequirePackage[2020-02-02]{latexrelease}
\documentclass{beamer}

solved the issue.