Improve knitr::spin rendering with .Rmd files

[kylebutts]

I recently discovered knitr::spin which I agree is knitr's best hidden gem!

The current version uses knit2html which (1) raises warning that rmarkdown::render should be used and (2) ignores the output yaml option:

knitr/R/spin.R

Lines 119 to 121 in 50e28da

	if (format == 'Rmd') {
	knit2html(outsrc, text = txt, envir = envir)
	} else if (!is.null(outsrc) && (format %in% c('Rnw', 'Rtex'))) {

A proposed solution that works with both text and hair options

if (format == 'Rmd') {
  if (is.null(outsrc)) {
    knit2html(outsrc, text = txt, envir = envir) 
  } else {
    rmarkdown::render(outsrc, envir = envir)
  }
} else if (!is.null(outsrc) && (format %in% c('Rnw', 'Rtex'))) { 

Would you welcome a PR adding this change?

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[cderv]

Documentation of the function says

knitr/R/spin.R

Lines 44 to 47 in 50e28da

	#' When the output format is Rmd, it is compiled to HTML via
	#' \code{\link{knit2html}()}, which uses R Markdown v1 instead of v2. If you
	#' want to use the latter, you should call
	#' \code{rmarkdown::\link[rmarkdown]{render}()} instead.

Try using rmarkdown::render() on the .R file directly. See documentation at https://rmarkdown.rstudio.com/docs/reference/compile_notebook.html

[kylebutts]

Thanks @cderv. I hadn't seen that in the documentation but pieced it together. Why not have the default be to use render which seems more robust (using v2) and lets you specify output format?

[cderv]

I'll let @yihui answer to that.

[kylebutts]

I originally found about this function from the R Markdown Cookbook: https://bookdown.org/yihui/rmarkdown-cookbook/spin.html

This example would suggest you get a pdf document out, but you get an html

[cderv]

Thanks for the context, this is indeed confusing...

@yihui as anything changed since we wrote the R Markdown cookbook ?

rmarkdown::render() on R file seems the way to spin and create the report with Rmd format. Should knitr::spin() offer to do rmarkdown::render() if a Rmd file with R Markdown V2 is detected ?

Otherwise, the cookbook should be updated 🤔

[yihui]

Why not have the default be to use render which seems more robust (using v2) and lets you specify output format?

@kylebutts knitr::spin() was introduced before the rmarkdown package was born, so it uses knitr::knit2html() instead of rmarkdown::render() mainly for historical reasons.

This example would suggest you get a pdf document out, but you get an html

We need to clarify in the book that the R script is supposed to be rendered via rmarkdown::render() instead of knitr::spin() (spin() is only an intermediate step). Thanks!

Should knitr::spin() offer to do rmarkdown::render() if a Rmd file with R Markdown V2 is detected ?

@cderv That's probably a good idea. Anyway, the cookbook definitely needs a bit more clarification.

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