[Rd] package vignettes build in the same R process?

Duncan Murdoch murdoch.duncan at gmail.com
Sat Nov 8 14:00:11 CET 2014

On 08/11/2014, 3:29 AM, Wolfgang Huber wrote:
> 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.

What are you talking about?  I didn't object to Martin making this
change, I was just pointing out that it is only a good idea, not a
perfect one.

Duncan Murdoch

> 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
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