header-includes in beamer_presentation() is not working as with pdf_document()

[samcarter]

If beamer_presentation is specified as output, macros with an optional argument at the end get incorrectly parsed to tex. Take for example the following example with \setbeamertemplate{footline}[frame number] in the header-includes:

---
title: "**TITLE**"
subtitle: "Subtitle"
author: "Name"
institute: ""
date: January 25, 2022
output:
  beamer_presentation:
    keep_tex: true
header-includes:
  - \setbeamertemplate{footline}[frame number]
---

test

The resulting .tex file will have

\setbeamertemplate{footline}{[}frame number{]}

instead of

\setbeamertemplate{footline}[frame number]

If I change the output to something else, the macro will be parsed correctly:

---
title: "**TITLE**"
subtitle: "Subtitle"
author: "Name"
institute: ""
date: January 25, 2022
output:
  pdf_document:
    keep_tex: true
header-includes:
  - \usepackage{beamerarticle}
  - \setbeamertemplate{footline}[frame number]
---

test

I tested this with the following environment:

R version 4.1.1 (2021-08-10)
Platform: aarch64-apple-darwin20 (64-bit)
Running under: macOS Big Sur 11.6.1, RStudio 2021.9.0.351

Locale: en_US.UTF-8 / en_US.UTF-8 / en_US.UTF-8 / C / en_US.UTF-8 / en_US.UTF-8

Package version:
  base64enc_0.1.3   bslib_0.3.1       digest_0.6.29     evaluate_0.14     fastmap_1.1.0     fs_1.5.2          glue_1.6.1        graphics_4.1.1   
  grDevices_4.1.1   highr_0.9         htmltools_0.5.2   jquerylib_0.1.4   jsonlite_1.7.3    knitr_1.37        magrittr_2.0.1    methods_4.1.1    
  R6_2.5.1          rappdirs_0.3.3    rlang_0.4.12      rmarkdown_2.11.12 sass_0.4.0        stats_4.1.1       stringi_1.7.6     stringr_1.4.0    
  tinytex_0.36      tools_4.1.1       utils_4.1.1       xfun_0.29         yaml_2.2.2       

Pandoc version: 2.17.0.1

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[cderv]

I think this is an issue with Pandoc. I need to check with earlier version than 2.17.0.1

However, there should be not issue if you insert in the header by using raw attributes to tell pandoc to not Parse you content

header-includes:
  - | 
    ```{=latex}
    \setbeamertemplate{footline}[frame number]
    ```

An example is show in the Pandoc doc: https://pandoc.org/MANUAL.html#extension-yaml_metadata_block

It is best to write raw latex with this syntax when you can
https://bookdown.org/yihui/rmarkdown-cookbook/raw-latex.html

I'll look for the potential issue in pandoc though 🤔

[samcarter]

@cderv Thanks for the tip with the raw code!

(it also failed with pandoc 2.14, but the checklist in the issue templated required updating to the current version, so I moved to 2.17)

[cderv]

It seems Pandoc will parse this

\setbeamertemplate{footline}[frame number]

as

\setbeamertemplate{footline}{[}frame number{]}

since as long as I can try (pandoc 2.0.3).

I don't think this i really an issue, as one should definitely use raw attribute to prevent any transformation

However, maybe an issue should be open in Pandoc ?

The reprex would be

❯ echo "\setbeamertemplate{footline}[frame number]" | pandoc -t native
[ Para
    [ RawInline (Format "tex") "\\setbeamertemplate{footline}"
    , Str "[frame"
    , Space
    , Str "number]"
    ]
]`

we see that the part in bracket is not parsed as a rawInline. Hence the result.

Using raw attribute makes sure it is

❯ pandoc -t native
`\setbeamertemplate{footline}[frame number]`{=latex}
^Z
[ Para
    [ RawInline
        (Format "latex")
        "\\setbeamertemplate{footline}[frame number]"
    ]
]

If that is ok with you I'll close the issue here, and one could be opened on Pandoc's side if this is really an issue.

[samcarter]

@cderv Sure, you can close this issue. Thanks for your time in investigating this!

[samcarter]

I asked this question over at pandoc and the different behaviour seems to be specific to rmarkdown as with pandoc, the macro will always be parsed incorrectly

No idea. With straight pandoc, you'll get the same result for this whether you do -t beamer or -t latex. So it shouldn't make a difference.

(jgm/pandoc#7867 (comment))

[cderv]

Good catch. I did not pay attention to that in your question.

I have answered there: jgm/pandoc#7867 (comment)

In fact we are doing a different processing

rmarkdown/R/pdf_document.R

Lines 165 to 168 in b53a7ce

	# make sure --include-in-header from command line will not completely
	# override header-includes in metadata but give the latter lower precedence:
	# https://github.com/rstudio/rmarkdown/issues/1359
	args <- append_in_header(process_header_includes(metadata))

This was to fix an issue and I think we did not do the same for Beamer. I think we should.

See my comment on the other repo for why this causes the difference you see.

Thanks for getting to the bottom of this !

[samcarter]

@cderv Thanks for your response! Would be really awesome if you could do the same for beamer.

[cderv]

This should work the same on both format now. Thanks !

[samcarter]

@cderv Thanks a lot!!!

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