\Romannum breaks with recent latex core

[tomh-overleaf]

Hi! It seems that a recent change to textcasing in LaTeX broke \Romannum from the romannum package.

MnWE:

\listfiles
\documentclass{article}
\usepackage{romannum}
\begin{document}
Hello! \Romannum{6}
\end{document}

Listfiles:

 *File List*
 article.cls    2021/10/04 v1.4n Standard LaTeX document class
  size10.clo    2021/10/04 v1.4n Standard LaTeX file (size option)
romannum.sty    2009/09/03 v1.0b roman numerals
stdclsdv.sty    2009/09/04 v1.1a Sectional divisions
l3backend-pdftex.def    2022-07-01 L3 backend support: PDF output (pdfTeX)
 ***********

Investigation

Unterminated \romannumeral in \romannum.

Solution

Add a space after \romannumeral #1 and \romannumeral -#1:

\newcommand{\romannum}[1]{%
  \ifnum#1<1
    \ifnum#1=0
      o%
    \else
      -\romannumeral -#1 %
    \fi
  \else
    \romannumeral #1 %
  \fi}

[FrankMittelbach]

or one could say it exhibited an existing bug in the package: try \romannum{6}15 which gave you dcxv instead of v15

[tomh-overleaf]

Gotcha! (btw it's vi15 but I get your point!)

[FrankMittelbach]

yep ... can't do roman numerals in my head :-)