Make upload.fun configurable via option

[wlandau]

As much as I love automatic image embedding in reprex, it does present a challenge for those of us collaborating on confidential projects in a locked-down industry setting. My own company's proxies do not block the uploads, and the URLs are public. We would still like to share rendered reprexes in our internal private repos.

[jennybc]

This example shows how to override upload.fun, in this case forcing the fig to stay local:

reprex/R/reprex.R

Lines 176 to 188 in de45a37

	#' # write reprex to file AND keep figure local too, i.e. don't post to imgur
	#' tmp <- file.path(tempdir(), "foofy")
	#' reprex({
	#' #+ setup, include = FALSE
	#' knitr::opts_knit$set(upload.fun = identity)
	#'
	#' #+ actual-reprex-code
	#' #' Some prose
	#' ## regular comment
	#' (x <- 1:4)
	#' median(x)
	#' plot(x)
	#' }, outfile = tmp)

With that in mind, what are you thinking?

[jennybc]

If specifying upload.fun in the reprex code is unattractive (which I can imagine), the options would seem to be ... putting this under the control of an option (meh) or allowing a custom reprex template (?). I used to expose the knitr options more, but got no sense that anyone ever used it and removed that.

[wlandau]

That example definitely helps, and I personally think calling knitr::opts_knit$set(upload.fun = identity) is not too much to ask. But maybe some guidance on the usage of upload.fun and other knitr options would be nice, with cross-references alongside mentions of Imgur.

[jennybc]

I'm highjacking your issue @wlandau.

Note to self: wrap upload.fun and put the logic about doing different things for different venues inside it. Then make that something that is configurable via option. Default behaviour for general population stays the same but people like @wlandau can re-configure and we could share a recipe that helps people in China and can't use imgur.com (see the ending of the #220 saga).

[wlandau]

Thanks, @jennybc!

[jennybc]

Also related to #259 re: making the options better documented.

[jennybc]

I should announce here that, now that the big transition to a proper Rmd document format + reprex_render() is done ... there is no remaining technical blocker here. It's a matter of me (or someone else) figuring out how to execute this.