Generate a PDF with Chrome using the Knit button of RStudio IDE

[RLesur]

Here's a proposal to create a custom render function for the RStudio IDE.
My main problem is to give a name for this new function 😃 (that's why I open a PR).

In short, by adding knit: pagedown::knit_pdf_chrome in the YAML header, a PDF is also generated by clicking on the "Knit" button of RStudio.
I don't like very much the current name knit_pdf_chrome but I have no better idea. I'd appreciate any proposal.

This PR also enhances the documentation about printing to PDF.

[yihui]

Instead of introducing a new function, I'd like make chrome_print work for the Knit button. We need to add the encoding argument to it (and ignore it). Then the only tricky thing is determine whether chrome_print is called by RStudio when the user clicks the Knit button. I think this should be sufficient:

is_rstudio_knit = !interactive() && !is.na(Sys.getenv('RSTUDIO', NA)) && !missing(encoding)

If you want to be more strict, you can add another condition length(match.call()) == 3 (to make sure only two arguments are passed to the function).

Then we call rmarkdown::render(..., quiet = is_rstudio_knit) to suppress the message, and emit the message('\nOutput create: ...') by ourselves.

Does this proposal sound good?

[RLesur]

Does this proposal sound good?

Of course... because I had already thought about that 😄
I like this idea very much. I will try.

[RLesur]

Then we call rmarkdown::render(..., quiet = is_rstudio_knit)

I already tried quiet = TRUE. In this case, this also removes the knitr progress messages because the quiet argument is passed to knitr::knit() by rmarkdown::render().
This leads to a different user experience. That's why I used suppressMessages() and not quiet.

[yihui]

I wonder what happens if you don't change the quiet argument, but just add another message() in the end. When there are two messages, RStudio might be open the file in the last message. You can test it.

[RLesur]

You can test it.

I've already tested it 😉 and RStudio IDE opens the file in the first message.

[yihui]

Perfect! Thank you!