Use a predictable file name within a temp folder

[schloerke]

Issue

When rendering runtime: shiny documents through shinytest, any plot figures are put into a *_files folder that is random every time a test is run.

This is problematic as the html field of the dynamic UI produced in

rmarkdown/R/shiny.R

Lines 304 to 318 in c88635f

	# For test snapshots. (The snapshotPreprocessOutput function was added
	# in shiny 1.0.4.)
	if (exists("snapshotPreprocessOutput", asNamespace("shiny"))) {
	doc_ui <- shiny::snapshotPreprocessOutput(
	doc_ui,
	function(value) {
	# Since the html data can be very large, just record a hash of it.
	value$html <- sprintf("[html data sha1: %s]",
	digest::digest(value$html, algo = "sha1", serialize = FALSE)
	)
	value
	}
	)
	}

If a plot is produced, value$html will contain something similar to

<p><img src="file847d61950236_files/figure-html/unnamed-chunk-12-1.png" width="960" data-figure-id=fig1 /></p>

The problem comes from the random name of file847d61950236_files, as it is random every time the rmarkdown document is rendered.

rmarkdown/R/shiny.R

Lines 452 to 454 in c88635f

	# It's not cacheable, and should be rendered to a session-specific temporary
	# file
	output_dest <- tempfile(fileext = ".html")

tempfile()s do not listen to the set.seed() value.

> set.seed(1234); tempfile()
#> [1] "/var/folders/0k/bxg5lhr92sq74mb1d446ql540000gp/T//RtmpTi0WqW/filee5b3219c1a8f"
> set.seed(1234); tempfile()
#> [1] "/var/folders/0k/bxg5lhr92sq74mb1d446ql540000gp/T//RtmpTi0WqW/filee5b3f93b386"

Given the random output file name, the *_files directory is created from it.

rmarkdown/R/shiny.R

Lines 240 to 241 in c88635f

	# check to see if the output already exists
	resource_folder <- knitr_files_dir(output_dest)

---

Fix

If rmarkdown rendered inside a temp folder within the R session temp folder, then names could be predictable and would not need to worry about clashing.

Ex: Looking at the same <img> tag as above when running rmarkdown::run("index.Rmd") :

<p><img src="index_files/figure-html/unnamed-chunk-12-1.png" width="960" data-figure-id=fig1></p>

index_files is a consistent name, but because there was another temp folder used, then there is no clashing.

---

Cautions:

• The temp folder is not deleted until the R session is stopped. (A slow memory leak.)

[yihui]

Thanks!

@cderv Feel free to merge if it looks good to you, too.

[cderv]

Yes it looks good to me too.

I don't know a lot about shinytest so if it fixed the issue, then it is good. Thanks @schloerke !