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: https://github.com/yihui/knitr/blob/50e28dab843109d5292e26695d1b486b36eec0e2/R/spin.R#L119-L121

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 https://github.com/yihui/knitr/blob/50e28dab843109d5292e26695d1b486b36eec0e2/R/spin.R#L44-L47

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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