make latex-div lua filter apply only on latex output and no need for data-latex=""

[cderv]

Design about this lua filters by @RLesur has been discussed in yihui/bookdown-crc#1 and added in rmarkdown in cecd812

Currently, the lua filter is only activated and useful for latex output if data-latex= has been added. If not useful, it must be set to ""

I think this is not obvious from what you expect from pandoc and it does not serve well "multi-format" output, because you need to add data-latex="" if you want it to work in pdf and in html. Currently, it seems that example in ongoing bookdown-cookbook is not working : rstudio/rmarkdown-cookbook#188

How about improving the filter my thought:

• we could make the Div function only apply for latex output format in the lua filter. No return nil required, and no risk to conflict with fenced_divs for other format ?
• That way if no data-latex= is provided, we could generate a verbatim environment, and otherwise data-latex should be provided to set options.

I don't think this will break anything, just change the way the lua filter is activated, to make this type of example works
https://bookdown.org/yihui/rmarkdown-cookbook/multi-column-layout.html

I have something like this in mind

Div = function (div)
  local options = div.attributes['data-latex']

  -- if the output format is not latex, the object is left unchanged
  if FORMAT ~= 'latex' and FORMAT ~= 'beamer' then
    -- if options has been set for latex, unset for other output
    if options then
      div.attributes['data-latex'] = nil
    end
    return div
  end

  local env = div.classes[1]
  -- if the div has no class, the object is left unchanged
  if not env then return nil end

  -- insert raw latex before content
  table.insert(
    div.content, 1,
    pandoc.RawBlock('tex', '\\begin' .. '{' .. env .. '}' .. (options or ""))
  )
  -- insert raw latex after content
  table.insert(
    div.content,
    pandoc.RawBlock('tex', '\\end{' .. env .. '}')
  )
  return div
end

[yihui]

The new Div filter you proposed looks good to me. I just applied the code. Thank you very much!

[yihui]

Continuing from rstudio/bookdown#883 (comment).

Requiring the data-latex attribute will also solve #1815 elegantly (I know you probably can't read Chinese). I couldn't apply the Lua filter to beamer_presentation because Pandoc reserved some special fenced Divs for beamer and we must not convert them to LaTeX environments in our way. If we require the data-latex attribute, these reserved Divs won't be affected because they don't have the data-latex attribute.

[github-actions]

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