Use new LaTeX templates from Pandoc

[adunning]

This is following on the discussion from #1509. The default-1.17.0.2.tex template is based is on the version at https://github.com/jgm/pandoc-templates/blob/fea830fcd27b4df2a337ac774daa7d4bbca00866/default.latex, which shows that the differences boil down to the following sections:

• rmarkdown/inst/rmd/latex/default-1.17.0.2.tex

  Line 108 in c0b5945

  \newcommand{\passthrough}[1]{#1}

  : added in bc2a49e for Pandoc 2.x compatibility, already in newer upstream templates

• rmarkdown/inst/rmd/latex/default-1.17.0.2.tex

  Line 190 in c0b5945

  %%% Use protect on footnotes to avoid problems with footnotes in titles

  : I'm having trouble finding the reason for this, but if memory serves, this was a very old Pandoc bug in which it wasn't using \thanks for footnotes for \maketitle

• rmarkdown/inst/rmd/latex/default-1.17.0.2.tex

  Line 195 in c0b5945

  %%% Change title format to be more compact

The last bit is the only significant difference in the repository's template. I think the intent of this was to fix the problem that Pandoc doesn't render \subtitle by default. This could be done more efficiently by adding the following via header-includes:

% Render \subtitle in \maketitle
\usepackage{titling}
\providecommand{\subtitle}[1]{%
  \posttitle{%
    \par\end{center}
    \begin{center}\large#1\end{center}
  }%
}

This should be fixed upstream; I'll take care of it.

[adunning]

Simpler code, submitted in jgm/pandoc#5213:

\usepackage{etoolbox}
\makeatletter
\providecommand{\subtitle}[1]{% add subtitle to \maketitle
  \apptocmd{\@title}{\par {\large #1 \par}}{}{}
}
\makeatother

[adunning]

The subtitle fix is now in the upstream template. I still don't entirely understand what the footnote protection is intended to achieve, but I think we can assume it's unnecessary, because this certainly works:

pandoc -o test.pdf << EOT

---
title: "Test^[test]"
---

test

EOT

[adunning]

The subtitle fix (and other improvements) will be in the Pandoc 2.6, which will be out soon. For earlier versions, you could simply add my etoolbox solution above through header-includes without having to maintain separate templates.

If you also want to retain the compression of \maketitle (I don't think its appearance is desirable, but putting that aside), I could come up with something that could also be inserted this way.

[yihui]

Yes, as I said in #1509 (comment), I'm all for dropping our homemade LaTeX template if there is a more elegant way through header-includes. Thank you!

BTW, RStudio 1.2.x (not officially released yet) has bundled Pandoc 2.6 on Windows only. For *nix platforms, the Pandoc version is still 2.3.1. For RStudio 1.1.x, it is still Pandoc 1.9.x. When you patch the default template, you'll need to consider these information.

[adunning]

That's excellent. Allowing each version of Pandoc to use its built-in template will fix the problems that the custom templates were attempting to solve.

If you're concerned about the subtitle not appearing for users of Pandoc 1.16 (when the problem first appeared) through 2.5, you could add the etoolbox code from above through header-includes if the version of Pandoc is less than 2.6. That will avoid potential conflicts with the titling package while changing the appearance minimally. This is completely backwards-compatible; adding the code through header-includes in versions before Pandoc 1.16 won't do any harm.

[yihui]

Sounds great! I guess I won't have time for this in the next few months, but I'd welcome a pull request!

[jemus42]

Quick question as I found this issue through searching before I submit a different issue:

Am I understanding correctly that this is related to my surprise given that subtitle: my subtitle in the YAML header of document to be rendered through pdf_document actually gives be a subtitle even though as of now that is not a documented argument in pdf_document() (which also does not have ...)?

I compared this to html_document() which at least has ... and says it passes those to html_document_base() – I'm since trying to figure out how pdf_document knows about the subtitle: YAML option and doesn't throw an error due to an unknown argument.

(For completeness: I'm on pandoc ‘2.7.1’)

[adunning]

Right – the subtitle variable is covered through the LaTeX template. There are a number of similar things not in the Rmarkdown documentation; see the Pandoc manual.

[yihui]

I have finished tweaking the PR #1563 and merged it. Thanks a lot for your contribution! I'm really happy about the outcome!

[adunning]

Thank you for the revisions and all your work on this!

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