[patch] ox-latex.el: fix blank lines behavior in verse block

[Juan Manuel Macías]

Rationale for this patch: the treatment of blank lines in
`org-latex-verse-block' is inconsistent with the syntax of the `verse'
environment, both the one that includes LaTeX and the one provided by
the `verse' package as a replacement for the former.

Currently, each blank line is exported to LaTeX as an explicit vertical
space: \vspace*{1em}. This can return unexpected results. For example,
this:

┌────
│ #+begin_verse
│
│ lorem
│ ipsum
│ dolor
| 
│ #+end_verse
└────

is exported to LaTeX as:

┌────
│ \begin{verse}
│ \vspace*{1em}
│ lorem\\[0pt]
│ ipsum\\[0pt]
│ dolor\\[0pt]
│ \vspace*{1em}
│ \end{verse}
└────

In the LaTeX `verse' environment, spaces before and after the content
are not taken into account.

As for the separation between stanzas, this is marked with at least one
blank line between the stanzas, as in normal paragraphs (not with an
explicit vertical space). Also it is not necessar y that the last verse
of each stanza ends with the linebreak mark `\\'.

So, after this patch:

• Any blank line before and/or after the content is removed;

• One or more blank lines between stanzas are exported as a single blank
  line, leaving the previous final verse without the linebreak mark
  `\\';

• When verse numbering is enabled via the `:lines' attribute (for the
  `verse' package), the last verses of each stanza are marked with
  `\\!', according to the verse package syntax (this was not necessary
  with the previous behavior).


This way, the `verse' block is exported to LaTeX with the correct
syntax. This also brings the advantage of being able to globally control
the spacing between stanzas via the verse package’s \stanzaskip command.

Example:

┌────
│ #+begin_verse
│ Lorem ipsum dolor
│ lorem ipsum dolor
│ lorem ipsum dolor
│
│ Lorem ipsum dolor
│ lorem ipsum dolor
│ lorem ipsum dolor
│
│ Lorem ipsum dolor
│ lorem ipsum dolor
│ lorem ipsum dolor
│ #+end_verse
└────

LaTeX:

┌────
│ \begin{verse}
│ Lorem ipsum dolor\\[0pt]
│ lorem ipsum dolor\\[0pt]
│ lorem ipsum dolor
│
│ Lorem ipsum dolor\\[0pt]
│ lorem ipsum dolor\\[0pt]
│ lorem ipsum dolor
│
│ Lorem ipsum dolor\\[0pt]
│ lorem ipsum dolor\\[0pt]
│ lorem ipsum dolor\\[0pt]
│ \end{verse}
└────

And with verse numbers:

┌────
│ #+ATTR_LaTeX: :lines 5
│ #+begin_verse
│ Lorem ipsum dolor
│ lorem ipsum dolor
│ lorem ipsum dolor
│
│ Lorem ipsum dolor
│ lorem ipsum dolor
│ lorem ipsum dolor
│
│ Lorem ipsum dolor
│ lorem ipsum dolor
│ lorem ipsum dolor
│ #+end_verse
└────

LaTeX:

┌────
│ \begin{verse}
│ \poemlines{5}
│ Lorem ipsum dolor\\[0pt]
│ lorem ipsum dolor\\[0pt]
│ lorem ipsum dolor\\!
│
│ Lorem ipsum dolor\\[0pt]
│ lorem ipsum dolor\\[0pt]
│ lorem ipsum dolor\\!
│
│ Lorem ipsum dolor\\[0pt]
│ lorem ipsum dolor\\[0pt]
│ lorem ipsum dolor\\[0pt]
│ \end{verse}
│ \poemlines{0}
└────

N.B.: the `\\[0pt]' mark of the last verse does not affect the final result.

Best regards,

Juan Manuel

--
Juan Manuel Macías

https://juanmanuelmacias.com

https://lunotipia.juanmanuelmacias.com

https://gnutas.juanmanuelmacias.com

0001-lisp-ox-latex.el-fix-blank-lines-behavior-in-verse-b.patch
Description: Text Data