LaTeX: Add math_numsep support to latex builder

[thfanning]

Subject: math_numsep support in LaTeX builder

Feature or Bugfix

• Feature

Purpose

• Add math_numsep support to latex builder.

Detail

• math_numsep defines the text separator to use between section numbers and equation numbers.
• This works for HTML, but is not easy for users to integrate into LaTeX.
• When not using Sphinx, an author might use a solution like \renewcommand{\theequation}{\thesection-\arabic{equation}}, but this is not viable due to the complexity in Sphinx's numbering.
• Sphinx number definitions are in ./sphinx/texinputs/sphinxlatexnumfig.sty
• This patch exports the configuration option to the latex numbering definition for parity with HTML.

Relates

• Allow configuring the separator used in numbering equations #12523

[jfbu]

I checked separate chunks now I need to revisit the whole LaTeX file to make sure this does not break some at-this-time not seen constraints.

[jfbu]

LGTM with nits.

With

latex_theme = 'howto'
# latex_toplevel_sectioning = 'part'

numfig = True
math_numfig = True
numfig_secnum_depth = 1
math_numsep = "-"

there is a problem in the output with prefixed dots. This problem goes away if the suggested change above is merged. But even with the suggested change, then if we uncomment the latex_toplevel_sectioning line a new problem arises that the separator is used but there is nothing before it.

(I had a bit forgotten the numfig and numfig_secnum_depth things which are bit complex in sphinx.writers.latex.)

I see how to address the issue I raised via somewhat scary hack to get rid of an extra prefixed dot. (We would then use it also for chapter) Maybe you will come out with simpler way to address raised difficulty which would be better for long term maintenance.

[jfbu]

LGTM with nits.

I have pushed some own code which fixes the issues I had. Ideally some test should be modified so what we can check that for example using math_numsep = "-" is obeyed via the mathnumsep=- in LaTeX. Actually it would be safer if mathnumsep={%s} syntax (here the {..} are real braces to end in LaTeX) was used --- for example if separator is set to a comma. I will push an additional commit and will check in passing if test can be updated as I requested.

edit: both done in later commit.

[jfbu]

Ready to go. I don't think it is worthwile to add a versionchanged in doc/usage/configuration.rst only to say LaTeX support was added at 8.0 as the 7.4.x series is so recent?

(but maybe some CHANGES update when it gets merged after 8.0.0)

Edit: On further thoughts I will add a latex doc as it seems necessary to explain what to do if string for html is not suitable for latex.

[jfbu]

@thfanning I have merged master, removed the disabling in preamble, and prepared CHANGES.rst for 8.1.0 release. Are you ok with current state of this PR? We could add a .. versionchanged:: 8.1.0 entry to doc/usage/configuration.rst to say it applies to latex builder as well but other entries in Options for Maths say nothing specific, so maybe it is actually better not to worry.

[jfbu]

Thanks for contribution!