IDEA: Signal amount=0 when receiving updates from nested progressors

[HenrikBengtsson]

When there are nested progressors, only the first one is listened to. Any progress conditions signaled by nested progressors are ignored. Here's an example of nested progressors:

library(progressr)
handlers(handler_progress(format=":spin :message [:bar] :percent"))

foo <- function(n) {
  p <- progressor(n)
  lapply(seq_len(n), FUN = function(ii) {
    p(sprintf("foo(%d)", ii))
    Sys.sleep(0.5)
  })
}

bar <- function(n) {
  p <- progressor(n)
  lapply(seq_len(n), FUN = function(ii) {
    foo(n = 5)
    p(sprintf("bar(%d)", ii))
  })
}

Calling

y <- bar(10)

will only report on bar() updates.

However, we could make use of those conditions by doing an amount=0 update, i.e. to communicate "still alive", which may for instance update a "spinner".

The code that drops/ignore nested progressors is in:

progressr/R/make_progression_handler.R

Lines 318 to 323 in a2cb9af

	## Ignore stray progressions coming from other sources, e.g.
	## a function of a package that started to report on progression.
	if (!is_owner(p)) {
	if (debug) message("- not owner of this progression. Skipping")
	return(invisible(finished))
	}