package vignettes build in the same R process?

Il giorno Nov 2, 2014, alle ore 16:10 GMT+1, Duncan Murdoch <murdoch.duncan at gmail.com> ha scritto:

On 01/11/2014, 8:44 PM, Martin Morgan wrote:

If I understand correctly, all vignettes in a package are built in the same R 
process. Global options, loaded packages, etc., in an earlier vignette persist 
in later vignettes. This can introduce user confusion (e.g., when a later 
vignette builds successfully because a package is require()'ed in an earlier 
vignette, but not the current one), difficult-to-identify bugs (e.g., when
a setting in an earlier vignette influences calculation in a latter vignette), 
and misleading information about reproducibility (e.g., when the sessionInfo() 
of a later vignette reflects packages used in earlier vignettes).

I believe the relevant code is at

src/library/tools/R/Vignettes.R:505

        output <- tryCatch({
            ## FIXME: run this in a separate process
            engine$weave(file, quiet = quiet)
            setwd(startdir)
            find_vignette_product(name, by = "weave", engine = engine)
        }, error = function(e) {
            stop(gettextf("processing vignette '%s' failed with diagnostics:\n%s",
                 file, conditionMessage(e)), domain = NA, call. = FALSE)
        })

Is building of each vignette in separate processes a reasonable feature request?

I'm not sure.  It's not perfect:  users may still see different output
than the package contains, because when they run the vignette it will
see their system state, but at least it gives them a way to get the
identical output.  On the other hand, they already have a way to do
that:  just build the whole package.  Overall I'd say it's probably a
good idea.

Let the perfect be the enemy of the good?
Martin?s proposed improvement would eliminate unnecessary complexity and a lot of potential (and actual) confusion.

Wolfgang Huber

I would prefer a way to detect and warn when vignette output depends on
the state outside the vignette, but that looks hard to do.

Duncan Murdoch