Polyglossia error on setting a language

Question

This simple file

\documentclass{standalone}

\usepackage{polyglossia}
   \setdefaultlanguage{portuguese}

\begin{document}
O modelo bond-plus.
\end{document}

generates the error:

! Illegal unit of measure (pt inserted).
<to be read again> 
                   \unskip 
l.8 \end{document}

under xelatex which seems to be a bit cryptic. It works apparently fine with lualatex. Encapsulatig the term "bond-plus" inside \emph{bond-plus} generates an even further cryptic error:

! Missing number, treated as zero.
<to be read again> 
                   \aftergroup 
l.7 O modelo \emph{bond-plus}

Is this something to be expected? I am running TL'22.

Answer 1

polyglossia doesn't correctly terminate an \hskip, and so it takes the plus as a continuation and then complains that a dimension is missing.

\documentclass{article}

\usepackage{polyglossia}
\setmainlanguage{portuguese}
\makeatletter
\def\portuguese@@@splhyphen#1{%
  \ifnum\hyphenchar \font>0%
    \kern\z@\discretionary{-}{\char\hyphenchar\the\font}{#1}%
    \nobreak\hskip\z@\relax%added relax
  \else%
    #1%
  \fi%
}
\makeatother
\begin{document}

 O modelo bond-plus. 
\end{document}

Side-remark: an example using the standalone class is not a simple file, the class is quite complicated and should only be used if really needed to demonstrate an error.