Detect footnotes with beamer

[moewew]

Via https://tex.stackexchange.com/q/369266/35864.

Currently patching \@footnotetext does not work because -- macro cannot be retokenized clean.

I suspect this is because of the category code regime in beamer.

MWE

\documentclass{beamer}
\usepackage{lmodern}
\usepackage[style=authoryear-comp,backend=biber]{biblatex}
\addbibresource{biblatex-examples.bib}

\AtEveryCitekey{\iffootnote{y}{n}}

\begin{document}
\begin{frame}
  Lorem\footcite{sigfridsson} \cite{sigfridsson} \footnote{\cite{sigfridsson}}
\end{frame}
\end{document}

Footnote 2 is expected to show 'y' if footnote detection works.

[moewew]

biblatex 3.10 has been released. biblatex can now detect footnotes in beamer documents.