don't respect beamer theme's buildin theorem/proof block

[XiangyunHuang]

here is a minimal, self-contained, and reproducible example

---
title: "beamer"
documentclass: beamer
output: 
  bookdown::pdf_book: 
    base_format: rmarkdown::beamer_presentation
    toc: no
    latex_engine: xelatex
    citation_package: natbib
    theme: Xiaoshan # https://www.ctan.org/pkg/pgfornament-han 
    template: null
link-citations: yes
colorlinks: yes
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = FALSE)
```

## some blocks from beamer theme [*Xiaoshan*](https://github.com/liantze/pgfornament-han/)

::: {.block data-latex="{Metropolis}"}
block is ok.
:::


::: {.exampleblock data-latex="{Metropolis}"}
exampleblock is also ok.
:::

::: {.theorem data-latex="{Metropolis}"}
theorem is not ok.
:::

my session info

xfun::session_info('bookdown')

R version 4.0.4 (2021-02-15)
Platform: x86_64-apple-darwin20.3.0 (64-bit)
Running under: macOS Big Sur 10.16, RStudio 1.4.1106

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   bookdown_0.21     digest_0.6.27     evaluate_0.14     glue_1.4.2       
  graphics_4.0.4    grDevices_4.0.4   highr_0.9         htmltools_0.5.1.1 jsonlite_1.7.2   
  knitr_1.32        magrittr_2.0.1    markdown_1.1      methods_4.0.4     mime_0.10        
  rlang_0.4.10      rmarkdown_2.7     stats_4.0.4       stringi_1.5.4     stringr_1.4.0    
  tinytex_0.31      tools_4.0.4       utils_4.0.4       xfun_0.22         yaml_2.2.1      

This bug also reported here

[cderv]

Oh yes I see what is the issue.

I think this message is printed in the console during R Markdown rendering:

[WARNING] data-latex attribute can't be used with one of bookdown custom environment. It has been removed.

As bookdown already use a theorem environment built-in, one can't use the custom block syntax from https://bookdown.org/yihui/rmarkdown-cookbook/custom-blocks.html with one of the supported environemnt.
We do that to prevent a double processing by rmarkdown specific Lua filter for LaTeX divs (which is used in this example).

Obviously we are not supporting beamer correctly in the Lua filter or at least in our logic.
Also, maybe there should be a way to opt-out using bookdown's environment feature and let users customize directly according to its needs.

Is theorem an environment built in beamer ? I don't know much.

[cderv]

Is theorem an environment built in beamer ? I don't know much.

It seems to be at least for Metropolis theme in beamer
https://www.tug.org/texlive//Contents/live/texmf-dist/doc/latex/beamertheme-metropolis/metropolistheme.pdf

This will conflict with our mechanism in restore_block2() where we add the definition in preamble if not already.

bookdown/R/latex.R

Lines 233 to 236 in df6786e

	# add the necessary definition in the preamble when block2 engine (\BeginKnitrBlock) or pandoc
	# fenced div (\begin) is used
	if (length(grep(sprintf('^\\\\(BeginKnitrBlock|begin)\\{(%s)\\}', paste(all_math_env, collapse = '|')), x)) &&
	length(grep('^\\s*\\\\newtheorem\\{theorem\\}', head(x, i))) == 0) {

If we support beamer the \begin{theorem} will be written in tex file which will trigger the above and add a new definition - which should not be there as beamer already defines one.

We could

• make an exception for \begin{theorem}{Metropolis} (but I don't know if there is other)
• provide a way to opt out this mechanism in bookdown::pdf_book() that one would need to use with a beamer template defining theorem
• Opt out automatically for \documentclass[]{beamer}

The more generic in the second one. 🤔

[yihui]

@XiangyunHuang By using the data-latex attribute, did you just want to provide a name to the theorem? If so, the syntax is:

::: {.theorem name="Metropolis"}
theorem is ok.
:::

But we don't support beamer yet. @cderv I don't remember why we didn't support beamer, but I feel we should:

bookdown/inst/rmarkdown/lua/custom-environment.lua

Line 134 in 6854e02

-- TODO: should we support beamer also ?

[XiangyunHuang]

@yihui When I use the way you provided, it's not ok, either. I have upgraded bookdown to latest dev version, here is new session info

xfun::session_info('bookdown')
#> R version 4.0.4 (2021-02-15)
#> Platform: x86_64-apple-darwin20.3.0 (64-bit)
#> Running under: macOS Big Sur 11.2.3
#> 
#> 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   bookdown_0.21.11  digest_0.6.27     evaluate_0.14    
#>   glue_1.4.2        graphics_4.0.4    grDevices_4.0.4   highr_0.9        
#>   htmltools_0.5.1.1 jsonlite_1.7.2    knitr_1.32        magrittr_2.0.1   
#>   markdown_1.1      methods_4.0.4     mime_0.10         rlang_0.4.10     
#>   rmarkdown_2.7     stats_4.0.4       stringi_1.5.4     stringr_1.4.0    
#>   tinytex_0.31      tools_4.0.4       utils_4.0.4       xfun_0.22        
#>   yaml_2.2.1

^{Created on 2021-04-20 by the reprex package (v2.0.0)}

[yihui]

That's expected. As I said above, the theorem Divs don't work for beamer yet. We'll probably fix it.

[cderv]

@yihui we don't support it because the previous syntax does not support either

> dir.create(tmp_dir <- tempfile())
> owd <- setwd(tmp_dir)
> xfun::write_utf8(c(
+ '---
+ title: "Minimal Working Example"
+ output: bookdown::beamer_presentation2
+ ---
+ 
+ ```{theorem}
+ test
+ ```'
+ ), "test.Rmd")
> rmarkdown::render("test.Rmd", "bookdown::beamer_presentation2", quiet = TRUE)
! LaTeX Error: Command \theorem already defined.
               Or name \end... illegal, see p.192 of the manual.

Error: LaTeX failed to compile test.tex. See https://yihui.org/tinytex/r/#debugging for debugging tips. See test.log for more info.
Run `rlang::last_error()` to see where the error occurred.
> setwd(owd)
> unlink(tmp_dir, recursive = TRUE)

^{To run the above code: Copy then use reprex::reprex_rescue() before pasting in a script}

Problem is the same here: beamer already define a theorem environment and currently our internal restore_block2 does not take that into account. I will then add in the preamble a second definition. Hence the issue

! LaTeX Error: Command \theorem already defined.

Fixing this should allow to support the new syntax too.

[cderv]

Looking more into beamer by doing small quick test, it seems that the following among bookdown Theorem and proof env are already defined when using a documentclass beamer

• theorem
• lemma
• corollary
• definition
• example
• solution

The other are not defined and their definition by bookdown in preamble does not cause error

• proposition
• conjecture
• exercise
• hypothesis
• remark

So we are in a hybrid state with beamer.

Currently what we do when we detect than one of the environment is used:

• if \newtheorem{theorem} is already define in the tex document, we don't add any definition
• if not, bookdown will add definition for all this environment in the preamble before compiling to PDF.

So we could either do if we detect it is beamer used:

1. we don't add any new definition. This would mean that missing environment should be defined by the user in a preamble.tex as bookdown won't add any. Also internationalization won't work for those environment.
2. we only add add the missing environment defintion. internationalization won't work for env define in beamer though.

1 is the simpler and we let the user handle the rest. 2 is the better to support all env documented as supported in bookdown. I wonder if we could modify the already define one 🤔

[cderv]

Ok I found the source: https://github.com/josephwright/beamer/blob/56b5d77a5b1ad886f452f23148b0e2e36094c689/base/beamerbasetheorems.sty#L114

This where the \newtheorem happens and translation is done in a better way than in bookdown using \translate command from the translator CTAN package.

So I tend to think that with beamer we do nothing special to let user customize as they need.

[cderv]

Oh and also @XiangyunHuang, I hope you notice that you don't need bookdown for this example to work.

---
title: "beamer"
output: 
  rmarkdown::beamer_presentation:
    toc: no
    latex_engine: xelatex
    citation_package: natbib
    theme: Xiaoshan # https://www.ctan.org/pkg/pgfornament-han 
    template: null
link-citations: yes
colorlinks: yes
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = FALSE)
```

## some blocks from beamer theme [*Xiaoshan*](https://github.com/liantze/pgfornament-han/)

::: {.block data-latex="{Metropolis}"}
block is ok.
:::


::: {.exampleblock data-latex="{Metropolis}"}
exampleblock is also ok.
:::

::: {.theorem data-latex="{Metropolis}"}
theorem is not ok.
:::

But you may need to use bookdown for its other features. (Cross referencies I believe ?)

[cderv]

we don't support it because the previous syntax does not support either

#1145 will fix this for now.

[XiangyunHuang]

But you may need to use bookdown for its other features. (Cross referencies I believe ?)

Yes.