\documentclass{article}
\usepackage{listings}
\lstavoidwhitepre
\lstset{language=Caml}
\lstset{keywordstyle=\textbf,commentstyle=\emph}
\begin{document}
\section*{Code that should copy-paste properly}
\begin{lstlisting}
  let x = 1 in
  x+x (* Two lines *)
\end{lstlisting}
There should be indentation above!

\end{document}
