Fix #8838 by forcing horizontal mode before inserting the penalty

[jfbu]

Relates

• LaTeX: table spacing sometimes broken on 3.x branch from \sphinxAtStartPar mark-up #8838, Revert "Add \nobreak inside \sphinxAtStartPar" #8840

This is better fix of #8838 than #8840. I have understood the underlying LaTeX problem.

With this input:

.. tabularcolumns:: |*{4}{p{2cm}|}

.. table:: tabular not ok

   +------------------------+------------+----------+------------------+
   | Header row, column 1   | Header 2   | Header 3 | Header 4         |
   +========================+============+==========+==================+
   | body row               | ...        | ...      | aaaaaaaaaaaaaaaa |
   +------------------------+------------+----------+------------------+
   | body row, merged columns            | column 3 | column 4         |
   +------------------------+------------+----------+------------------+

one gets

with #8840 but the better

with this one. (it is deliberate here that I use a string that TeX does not hyphenate; else there would be no overflow)

My other tests give results ok.

For example

.. table:: tabulary

   +------------------------+------------+----------+----------+
   | Header row, column 1   | Header 2   | Header 3 | Header 4 |
   +========================+============+==========+==========+
   | body row               | ...        | ...      |          |
   +------------------------+------------+----------+----------+
   | body row, merged columns            | column 3 | column 4 |
   +------------------------+------------+----------+----------+
   | body row, merged columns and rows   |          |          |
   |                                     |          |          |
   | let's make this 2 paragraphs        | column 3 | column 4 |
   +-------------------------------------+----------+----------+

@tk0miya I know merging at such late date into 3.x is a bit annoying because we have refactored a lot latex on master then merging 3.x in master may be complicated but I think this one will be ok, so I am proposing to merge into 3.x.

[jfbu]

Merging now so as to reduce your workload on release day.. I checked I could merge 3.x into master with no help so I will do it afterwards to get latex merge done.

[tk0miya]

@tk0miya I know merging at such late date into 3.x is a bit annoying because we have refactored a lot latex on master then merging 3.x in master may be complicated but I think this one will be ok, so I am proposing to merge into 3.x.

No problem. Are there any tasks before the release? I think releasing this weekend is not important. So we can postpone it if needed.

[jfbu]

@tk0miya No task left in my scope before release, go ahead!

[tk0miya]

Okay, I'm going to package it now.