On Thu, Jul 29, 2021 at 09:54:20AM +0200, luigi scarso wrote:
> On Mon, Jun 21, 2021 at 5:03 PM Marcel Krüger <tex@2krueger.de> wrote:
>
> > Hi,
> >
> > consider the following plain LuaTeX document:
> >
> > \textdir TRT
> > \noindent\par
> > \bye
> >
> > without the `\textdir TRT` line or with `\textdir TLT`, this would lead
> > to "warning  (pdf backend): no pages of output.", but with the non
> > default "\textdir", it creates an empty (except for the page number) page
> > instead.
> >
> > This can be avoided by setting \pardir too:
> >
> > \textdir TRT\pardir TRT
> > \noindent\par
> > \bye
> >
> > again produces no output, but adding a group around it reintroduces the
> > issue:
> >
> > \begingroup
> > \textdir TRT\pardir TRT
> > \noindent\par
> > \endgroup
> > \bye
> >
> > leads to an empty page.
> >
> > Of course similar things happen not only for otherwise empty documents:
> > Instead of empty paragraphs disappearing, they add empty lines.
> >
> > Together, this is not only inconsistent with other engines which always
> > discard empty paragraphs, but also leads to hard to predict behavior
> > (especially for users who are not familiar with the implementation of
> > LuaTeX's directional system), so I think it would be great if LuaTeX
> > could always remove such empty paragraphs.
> >
> >
> (sorry for the delay)
> Do you have  a patch to propose  ?

I attached a patch which adds a \emptyparmode parameter with three
possible states:

  - 0: Never ignore empty paragraphs. Not sure if this is useful, but it
    seemed like an obvious thing to add.
  - 1: The default: A paragraph is empty is it contains at most one
    node. This is the old behavior.
  - 2: A paragraph is empty if it only contains local_par and dir nodes.
    This is what I would consider the expected behavior.

Best regards,
Marcel