Provide a way to start context for extention packages

[yutannihilation]

I'm implementing r-lib/vdiffr#88 to let vdiffr get rid of explicit context(). At the time of starting it, I thought I just can use testthat::context() inside start_test(). But, now context() is deprecated, and ProgressReporter uses an unexported function start_context(). So, now I don't know what to do.

testthat/R/reporter-progress.R

Lines 74 to 81 in d07d805

	start_file = function(file) {
	self$file_name <- file
	self$ctxt_issues <- Stack$new()
	self$ctxt_start_time <- proc.time()
	name <- context_name(self$file_name)
	context_start(name)
	},

Are there any way for external packages to do the same thing as ProgressReporter does? Or, more broadly, what is the supposed way of implementing a custom reporter at the moment...?

[hadley]

Hmmm maybe the right thing to do is export something like start_file_context() for use by external reporters.

But we should also talk about what you’re doing in vdiffr because I’ve been thinking that the new snapshot functions (not implemented yet) should be designed to be extensible so vdiffr could become much simpler.

[yutannihilation]

Honestly, I don't know well about the internals of vdiffr. I just wanted to remove all context() in ggplot2, and expected it was an easy job to tweak vdiffr's reporter. If vdiffr needs some major refactoring, I think I'm not the right person to do it...

[hadley]

Ok, I just wanted to make sure you weren't doing a bunch of work on vdiffr that I was about to make obsolete 😄

[yutannihilation]

Thanks!