Nested lists without hyphenation using sloppypar

Question

I use XeTeX, Version 3.1415926-2.4-0.9998 (TeX Live 2012/W32TeX).

I want to create a nested list without hyphenation. I am using the sloppypar environment with hyphenation command to turn off hyphenation. This creates issues when used with a nested numbered list created using enumerate. In the MWE below, the second item in the outer list is not numbered, while the first item in the second inner list has the combined number 2(a). The nested list works fine without sloppypar as the second section below shows.

\documentclass{article}
\usepackage{ragged2e}
\usepackage{polyglossia}
\begin{document}
\section{Nested list with sloppypar}
\begin{enumerate}
\item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah blah blah.\end{sloppypar}
\begin{enumerate}
    \item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah blah blah.\end{sloppypar}
    \item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah blah blah.\end{sloppypar}
\end{enumerate}
\item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah blah blah.\end{sloppypar}
\begin{enumerate}
    \item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah blah blah.\end{sloppypar}
    \item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah blah blah.\end{sloppypar}
\end{enumerate}
\end{enumerate}

\section{Nested list without sloppypar}
\begin{enumerate}
\item Blah blah blah.
\begin{enumerate}
    \item Blah blah blah.
    \item Blah blah blah.
\end{enumerate}
\item Blah blah blah.
\begin{enumerate}
    \item Blah blah blah.
    \item Blah blah blah.
\end{enumerate}
\end{enumerate}
\end{document}

Answer 1

Just add a \par or blank line leaving the nested enumerate environment.

\documentclass{article}
\usepackage{ragged2e}
\usepackage{polyglossia}
\begin{document}
\section{Nested list with sloppypar}
\begin{enumerate}
\item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah blah blah.\end{sloppypar}
\begin{enumerate}
    \item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah blah blah.\end{sloppypar}
    \item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah blah blah.\end{sloppypar}
\end{enumerate}\par % <----- ADDED PAR IS HERE
\item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah blah blah.\end{sloppypar}
\begin{enumerate}
    \item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah blah blah.\end{sloppypar}
    \item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah blah blah.\end{sloppypar}
\end{enumerate}
\end{enumerate}

\section{Nested list without sloppypar}
\begin{enumerate}
\item Blah blah blah.
\begin{enumerate}
    \item Blah blah blah.
    \item Blah blah blah.
\end{enumerate}
\item Blah blah blah.
\begin{enumerate}
    \item Blah blah blah.
    \item Blah blah blah.
\end{enumerate}
\end{enumerate}
\end{document}

As I tell the OP in the comments below, I cannot give a definitive answer as to why the \par is needed. But the symptom of the original MWE gave the appearance of a misinterpreted paragraph/group issue. So it was a natural first guess, and in this case, it proved sufficient.

Alternately, the nested enumerate could be enclosed in its own group, as follows:

\documentclass{article}
\usepackage{ragged2e}
\usepackage{polyglossia}
\begin{document}
\section{Nested list with sloppypar}
\begin{enumerate}
\item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah blah blah.\end{sloppypar}
{\begin{enumerate}
    \item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah blah blah.\end{sloppypar}
    \item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah blah blah.\end{sloppypar}
\end{enumerate}}
\item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah blah blah.\end{sloppypar}
\begin{enumerate}
    \item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah blah blah.\end{sloppypar}
    \item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah blah blah.\end{sloppypar}
\end{enumerate}
\end{enumerate}
\end{document}

Answer 2

In a list environment, the action of \item is deferred when a paragraph is started. And \begin{sloppypar} starts with \par, which confuses this mechanism.

Here's a minimal example that emulates what sloppypar does: \par at the beginning, some other actions that don't concern the issue, and \par at the end.

\documentclass{article}

\newenvironment{foo}{\par}{\par}

\begin{document}

\begin{enumerate}
  \item \begin{foo}x\end{foo}
  \begin{enumerate}
    \item \begin{foo}x\end{foo}
  \end{enumerate}
  \item \begin{foo}x\end{foo}
  \begin{enumerate}
    \item \begin{foo}x\end{foo}
  \end{enumerate}
\end{enumerate}

\end{document}

As you see, the problem is exactly the same.

I'm not sure about the need of \justifying in your document, but in my opinion you should define a wrapper environment:

\documentclass{article}

\usepackage{polyglossia}

\usepackage{kantlipsum} % for mock text

\newenvironment{sloppyenumerate}
 {\begin{enumerate}\sloppy\hyphenrules{nohyphenation}}
 {\end{enumerate}}

\begin{document}

\begin{sloppyenumerate}
\item \kant[2]
\begin{enumerate}
    \item \kant[3]
\end{enumerate}
\item \kant[4]
\begin{enumerate}
    \item \kant[5]
\end{enumerate}
\end{sloppyenumerate}

\end{document}

If you need to selectively use \sloppy for some of the items, don't use sloppypar:

\newenvironment{sloppyitem}
 {\sloppy\hyphenrules{nohyphenation}}
 {\par}% <--- the \par here is fundamental

and use

\item \begin{sloppyitem}text\end{sloppyitem}

Answer 3

While Steven's answer certainly solves your problem, the way you are marking up your document is not ideal. You can simplify everything a lot with the following:

\usepackage{etoolbox}
\AtBeginEnvironment{enumerate}{\sloppy\hyphenrules{nohyphenation}}

Compare (and comment out the \AtBeginEnvironment line to see the difference):

\documentclass{article}
\usepackage[vmargin=1cm]{geometry}
\usepackage{ragged2e}
\usepackage{polyglossia}
\def\bb{I want to create a nested list withouthyphenation. Iamusingthesloppyparenvironmentwithhyphenationcommandtoturnoffhyphenation. This creates issues when used with a nested numbered list created using enumerate. In the MWE below, the second item in the outer list is not numbered, while the first item in the second inner list has the combined number 2(a). The nested list works fine without sloppypar as the second section below shows.}

\usepackage{etoolbox}


\begin{document}

\bb

\section{Nested list with sloppypar}
\begin{enumerate}
\item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}\bb \end{sloppypar}
  \begin{enumerate}
  \item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}\bb
      blah blah.\end{sloppypar}
  \item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah
      blah blah.\end{sloppypar}
  \end{enumerate}\par
\item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah blah
    blah.\end{sloppypar}
  \begin{enumerate}
  \item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}Blah
      blah blah.\end{sloppypar}
  \item \begin{sloppypar}\justifying\hyphenrules{nohyphenation}\bb \end{sloppypar}
  \end{enumerate}
\end{enumerate}

\section{Nested list without sloppypar}

\AtBeginEnvironment{enumerate}{\sloppy\hyphenrules{nohyphenation}}
\begin{enumerate}
\item \bb
  \begin{enumerate}
  \item \bb
  \item Blah blah blah.
  \end{enumerate}
\item Blah blah blah.
  \begin{enumerate}
  \item Blah blah blah.
  \item \bb
  \end{enumerate}
\end{enumerate}

\bb

\end{document}

The .tex file is much easier to read in the second case.