unwanted en-dash ligature with lualatex but not with xelatex

Question

I am trying to generate PDF documentation out of Pandoc Markdown README document. Here is MWE:

\documentclass[english,]{article}
\usepackage[T1]{fontenc}
\usepackage{ifxetex,ifluatex}

\ifnum 0\ifxetex 1\fi\ifluatex 1\fi=0 % if pdftex
  \usepackage[utf8]{inputenc}
\else % if luatex or xelatex
  \ifxetex
    \usepackage{mathspec}
    \usepackage{xltxtra,xunicode}
  \else
    \usepackage{fontspec}
  \fi
\fi

\defaultfontfeatures{Ligatures=TeX}
\setmonofont[Scale=MatchLowercase]{DejaVu Sans Mono}

\begin{document}
\texttt{-{}-enable-debugging}
\end{document}

When I generate a PDF using lualatex (beta-0.76.0-2013070111 (TeX Live 2013/Debian) (rev 4627)) it creates a en-dash instead of typesetting --:

The en-dash is unwanted. XeLaTeX does not do that. I want two dashes.

UPDATE

In the end, I have created a patch that makes Pandoc use -\/- instead of -{}- to avoid the ligature.

Answer 1

The error is in declaring

\defaultfontfeatures{Ligatures=TeX}

before loading the mono font. This will add the common TeX ligatures to the normal set, in particular turns -- into an en-dash.

---

By the way, you shouldn't load either xltxtra or xunicode; xltxtra has some features, but it's quite improbable you really need them. It used to be recommended when fontspec was in its older versions. Now it does the main things xltxtra was used for and also loads xunicode. Since mathspec loads fontspec just that package is sufficient.

Also avoid fontenc for XeLaTeX and LuaLaTeX. Put it in the pdflatex specific part.