WISH: Clarify the 'Work dir does not exist' error message

[HenrikBengtsson]

With future.batchtools and other wrappers, it become a bit tricky to track down where errors are coming from when running in batch mode. For instance, I got some:

Error : BatchtoolsError in BatchtoolsFuture ('future_lapply-1'): 'Work dir does not exist'

I wasn't sure if that was from the scheduler or batchtools, but it turns out it's from here:

batchtools/R/doJobCollection.R

Lines 84 to 86 in 1001440

	# set work dir
	if (!fs::dir_exists(jc$work.dir))
	return(error("Work dir does not exist"))

Would you mind updating to something like:

error("Working directory (%s) for the batchtools registry does not exist", jc$work.dir)

[HenrikBengtsson]

Forgot to say, including what the working directory is also helpful in cases where it is set to, say, a local temp folder that is not available on the compute node processing the job.

[HenrikBengtsson]

Actually, even more informative would be:

error("Working directory (%s) for the batchtools registry does not exist on host %s",
      sQuote(jc$work.dir), sQuote(Sys.info()[["nodename"]]))

Annotating other errors that occur when trying to launch a job in a similar fashion would help troubleshoot failed jobs; it's not always clear when, where, and on which R process these errors take place.