Cfrgtkky

LuaLaTeX is not inserting em dashes unless there is space around the triple dash.
It works fine when using a unicode em dash, or explicitly using the textemdash macro.

Here is a MWE:

documentclass{article}



begin{document}



begin{enumerate}

  item en--dash

  item em---dash

  item em --- dash space

end{enumerate}

begin{enumerate}

  item en–dash unicode

  item em—dash unicode

  item em — dash space unicode

end{enumerate}

begin{enumerate}

  item entextendash{}dash macro

  item emtextemdash{}dash macro

  item em textemdash{} dash space macro

end{enumerate}



end{document}

Which produces:

Compiled using LuaTeX, Version 1.07.0 (TeX Live 2018)

The question is:

I would like to know why em dash ligatures without surrounding spaces are not rendered as em dashes in the PDF output. It seems like a bug to me. how can I fix it?

You can add automatichyphenmode=1 to your preamble:

documentclass{article}

automatichyphenmode=1

begin{document}



begin{enumerate}

  item en--dash

  item em---dash

  item em --- dash space

end{enumerate}

begin{enumerate}

  item en–dash unicode

  item em—dash unicode

  item em — dash space unicode

end{enumerate}

begin{enumerate}

  item entextendash{}dash macro

  item emtextemdash{}dash macro

  item em textemdash{} dash space macro

end{enumerate}



end{document}

To expand a bit on Alan's answer:

It is imho clearly a bug in the fontloader imported from context (you see the same in context if you set automatichyphenmode=0). It only happens if the fonts are rendered with the mode=node:

documentclass{article}



begin{document}

fonttest={file:lmroman10-regular.otf:mode=node;+tlig}

test



A---B



fonttest={file:lmroman10-regular.otf:mode=base;+tlig}

test



A---B

end{document}

The source of the problem is imho that with automatichyphenmode=0, luatex has at first to convert the last hyphen to a discretionary to allow a linebreak:

A---B  ---> A--discretionary{-}{}{-}B

and after the line has been set this has to be converted back again to ---, and this step seems to fail.

The problem has been reported, but it is unclear if it will be fixed.

automatichyphenmode=1 avoids the problem by not converting the hyphen to a discretionary in a number of cases. So you should be aware of the fact that this suppress line breaking in a number of cases:

documentclass[parskip=half-]{scrartcl}

begin{document}





parbox[t]{1pt}{%

textbf{0}



automatichyphenmode=0

A-B



A--B



A---B



-begin



A!-B}

hspace{2cm}

parbox[t]{1pt}{automatichyphenmode=1

textbf{1}



A-B



A--B



A---B



-begin



A!-B}



end{document}