\lstlisting in \enumerate environment

Question

I simply would like to have an enumerated list that contains code, but the result is glitchy:

I would ideally have the code-block indented and starting at the same horizontal level as the item label. Here is my code:

\documentclass[10pt]{article}
\usepackage[a4paper, total={18cm, 25cm}]{geometry}
\usepackage[utf8]{inputenc}
\usepackage{fontspec}
\usepackage{enumitem}
\usepackage{xcolor}
\usepackage{listings}
\usepackage{multicol}
\usepackage{xpatch}
\usepackage{realboxes}

\definecolor{mygray}{rgb}{0.9,0.9,0.9}

\lstset{
  language=c,
  breaklines=true,
  keepspaces=true,
  backgroundcolor=\color{mygray},
  frame=single,
  framerule=0pt,  
  framextopmargin=3ex,
  framexbottommargin=3ex,
  framexleftmargin=1em,
  xleftmargin={\dimexpr 1em+3pt},
  linewidth={\dimexpr \linewidth-3pt}
}

\begin{document}
\begin{multicols}{2}
\begin{enumerate}[label=(\roman*)]
\item\begin{lstlisting}
#include <stdio.h>

int main() {
   printf("Hello World!");
}
\end{lstlisting}

\item\begin{lstlisting}[language=lisp]
(defun make-hanoi (from-tower aux-tower to-tower)
(list from-tower aux-tower to-tower))

;; Select I'th tower of HANOI
(defun hanoi-tower (hanoi i)
(nth (1- i) hanoi))
\end{lstlisting}

\end{enumerate}
\end{multicols}
\end{document}

Answer 1

You need a few adjustments:

1. issue something that makes \item to do its job, for instance \mbox{};
2. add a negative vertical space to cover your tracks;
3. fix the xleftmargin;
4. fix the linewidth.

\documentclass[10pt]{article}
\usepackage[a4paper, total={18cm, 25cm}]{geometry}
\usepackage[utf8]{inputenc}
\usepackage{fontspec}
\usepackage{enumitem}
\usepackage{xcolor}
\usepackage{listings}
\usepackage{multicol}
\usepackage{xpatch}
\usepackage{realboxes}

\definecolor{mygray}{rgb}{0.9,0.9,0.9}

\lstnewenvironment{itemlisting}[1][]
 {%
  \mbox{}
  \vspace*{-\baselineskip}
  \lstset{
    xleftmargin=\leftmargin,
    linewidth=\linewidth,
    #1
  }%
 }
 {}

\lstset{
  language=c,
  breaklines=true,
  keepspaces=true,
  backgroundcolor=\color{mygray},
  frame=single,
  framerule=0pt,  
  framextopmargin=3ex,
  framexbottommargin=3ex,
  framexleftmargin=1em,
  xleftmargin=\dimexpr 1em+3pt\relax,
  linewidth=\dimexpr \linewidth-3pt\relax
}

\begin{document}

\begin{multicols}{2}
\begin{enumerate}[label=(\roman*)]
\item \begin{itemlisting}
#include <stdio.h>

int main() {
   printf("Hello World!");
}
\end{itemlisting}

\item\begin{itemlisting}[language=lisp]
(defun make-hanoi (from-tower aux-tower to-tower)
(list from-tower aux-tower to-tower))

;; Select I'th tower of HANOI
(defun hanoi-tower (hanoi i)
(nth (1- i) hanoi))
\end{itemlisting}

\end{enumerate}
\end{multicols}
\end{document}

I left the bad column break to show what can be the remaining issues: apparently, listings considers the space above the listing in the frame as a good page break point; I'm afraid you'll have to manually adjust the bad breaks.