Ticket #9107: test-deep-itemize-nesting.tex

\documentclass[12pt]{article}

\usepackage{enumitem}
%\setlistdepth{9}

\makeatletter
\newcommand{\py@itemnewline}[1]{%
  \@tempdima\linewidth%
  \advance\@tempdima \leftmargin\makebox[\@tempdima][l]{#1}%
}

\newenvironment{fulllineitems}{
  \begin{list}{}{\labelwidth \leftmargin \labelsep 0pt
                 \rightmargin 0pt \topsep -\parskip \partopsep \parskip
                 \itemsep -\parsep
                 \let\makelabel=\py@itemnewline}
}{\end{list}}
\makeatother

\begin{document}

\begin{itemize}
\item 
\begin{itemize}
\item 
\begin{itemize}
\item 
\begin{itemize}
\item 
\begin{itemize}
\item 
\begin{itemize}
\item 
\end{itemize}
\end{itemize}
\end{itemize}
\end{itemize}
\end{itemize}
\end{itemize}


\end{document}