Validate compatibility with Pandoc 2.0

[jmcphers]

Pandoc 2.0 contains a large number of changes, some of which change behavior in important ways. While we don't bundle 2.0 yet, we do use the system version of Pandoc over our own in some configurations, so need to ensure compatibility with the new version.

@jjallaire pointed out that we may need to adjust our self-contained HTML generation function here so that it works with both Pandoc 1 and Pandoc 2:

rstudio/src/cpp/session/modules/ModuleTools.R

Line 297 in b84eed5

.rs.addFunction("pandocSelfContainedHtml", function(input, output) {

See also the comments on this issue:

ramnathv/htmlwidgets#289

and this this PR from @jcheng5 which addresses it:

ramnathv/htmlwidgets#292

[jmcphers]

Since Pandoc 2 already exists in the wild, we should actually make this change for 1.1 patch (changed milestone). The work that should happen in 1.2 is updating the internal copy of Pandoc to Pandoc 2, which is now tracked in #1807.

[jmcphers]

pandocSelfContainedHtml always uses RSTUDIO_PANDOC to determine the version of Pandoc to use.

rstudio/src/cpp/session/modules/ModuleTools.R

Lines 325 to 327 in 560aeb2

	# build the conversion command
	pandoc <- file.path(Sys.getenv("RSTUDIO_PANDOC"), "pandoc")
	command <- paste(shQuote(c(pandoc, args)), collapse = " ")

It is possible to set RSTUDIO_PANDOC to Pandoc 2, even in RStudio 1.1, but it's probably not common. Compare with find_pandoc in the rmarkdown package, which will use a new pandoc in preference to RSTUDIO_PANDOC if it finds one.

https://github.com/rstudio/rmarkdown/blob/2b418a242af8a4eca1d3156614d25816d39e721a/R/pandoc.R#L513-L549

[jmcphers]

backported to 1.1 in 80e1cb9.

[ronblum]

Knit to HTML fails with RStudio 1.1.412 (both open source and Pro) on OpenSUSE 12.3 with Pandoc 2.0.6, with the error message:

/usr/bin/pandoc2.0.6/pandoc +RTS -K512m -RTS bobo.utf8.md --to html --from markdown+autolink_bare_uris+ascii_identifiers+tex_math_single_backslash --output bobo.html --smart --email-obfuscation none --self-contained --standalone --section-divs --template /home/rstudio/R/x86_64-suse-linux-gnu-library/3.4/rmarkdown/rmd/h/default.html --no-highlight --variable highlightjs=1 --variable 'theme:bootstrap' --include-in-header /tmp/RtmpYTAMGV/rmarkdown-str17687c71322e.html --mathjax --variable 'mathjax-url:https://mathjax.rstudio.com/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML'
--smart/-S has been removed. Use +smart or -smart extension instead.
For example: pandoc -f markdown+smart -t markdown-smart.
Try pandoc --help for more information.
Error: pandoc document conversion failed with error 2
Execution halted

Publishing is succeeds, though with the console message:

--smart/-S has been removed. Use +smart or -smart extension instead.
For example: pandoc -f markdown+smart -t markdown-smart.
Try pandoc --help for more information.

Knit to HTML works fine with RStudio 1.1.383 on OpenSUSE, and 1.1.412 works fine on other environments (Ubuntu 16.0.4, MacOS 10.12.6).

[jmcphers]

What version of the rmarkdown package are you using?

[ronblum]

1.6. It works fine with 1.8. Sorry about that. All good.