[Rd] [External] Re: Repeated library() of one package with different include.only= entries

[Martin Maechler]

I think we should try to advance and hopefully finalize this
thread before we forget about it ..

>>>>> Michael Chirico  n Thu, 11 Apr 2024 09:10:11 -0700 writes:

    >> I would assume that

    >> library(Matrix, include.only="isDiagonal")

    >> implies that only `isDiagonal` ends up on the search path

    > This could also be a reasonable behavior, but neither does that happen
    > today.

Indeed; I think we should signal a warning at least in the case
it does not happen --- namely when "parts of Matrix" are already
in the search path.

    >> I think a far better approach to solve Michael's problem is simply to use

    >> fac2sparse <- Matrix::fac2sparse

    > This does not fully simulate attachment, e.g. running package hooks &
    > resolving Depends.

(indeed; as library() is really about search() patch attchment)

    >> ?library could also mention using detach() followed by library() or
    >> attachNamespace() with a new include.only specification.

    > This is the "quite hard to accomplish" I alluded to, admittedly I hadn't
    > forced myself to write it all out -- maybe it's not as bad as all that.
    > After some iterations, today I think we'd want to do...

    > modify_attach <- function(pkg, new_names) {
    >   if (!startsWith(pkg, "package:")) pkg <- paste0("package:", pkg)
    >   old <- tryCatch(ls(pkg, all.names=TRUE), error=\(c) character())
    >   if (length(old)) detach(pkg)
    >   attachNamespace(.rmpkg(pkg), include.only=c(new_names, old))
    > }

    > Perhaps detach() could invisibly return the exported names to make this a
    > tiny bit easier (today it returns NULL):

I agree that such changed detach() behavior would be "nice" here;
but I wouldn't like to change its default behavior, notably as
in 99.5% of its use, the names would not be used.
I'd agree to add a new option for detach() to return the names
(visibly in that case).

    > modify_attach <- function(pkg, new_names) {
    >   if (!startsWith(pkg, "package:")) pkg <- paste0("package:", pkg)
    >   old <- tryCatch(detach(pkg), error=\(c) character())
    >   attachNamespace(.rmpkg(pkg), include.only=c(new_names, old))
    > }

    > Regardless, I think your suggestion to just point to
    > detach()+attachNamespace() is reasonable enough, the rare users that care
    > about this are likely to be able to figure out the rest from there.

So I think we agree here;  mentioning such a modify_attach()
... I'd use an example *without* tryCatch() as I think the user
    should choose their own line of action in such cases
...
on the help page would then be appropriate. 

Martin

    > On Thu, Apr 11, 2024 at 7:37 AM <luke-tierney using uiowa.edu> wrote:

    >> On Thu, 11 Apr 2024, Duncan Murdoch wrote:
    >> 
    >> > On 11/04/2024 7:04 a.m., Martin Maechler wrote:
    >> >>>>>>> Michael Chirico
    >> >>>>>>>      on Mon, 8 Apr 2024 10:19:29 -0700 writes:
    >> >>
    >> >>      > Right now, attaching the same package with different
    >> include.only= has no effect:
    >> >>
    >> >>      > library(Matrix, include.only="fac2sparse")
    >> >>      > library(Matrix)
    >> >>      > ls("package:Matrix")
    >> >>      > # [1] "fac2sparse"
    >> >>
    >> >>      > ?library does not cover this case -- what is covered is the _loading_
    >> >>      > behavior of repeated calls:
    >> >>
    >> >>      >> [library and require] check and update the list of currently attached
    >> >>      > packages and do not reload a namespace which is already loaded
    >> >>
    >> >>      > But here we're looking at the _attach_ behavior of repeated calls.
    >> >>
    >> >>      > I am particularly interested in allowing the exports of a
    >> package to be
    >> >>      > built up gradually:
    >> >>
    >> >>      > library(Matrix, include.only="fac2sparse")
    >> >>      > library(Matrix, include.only="isDiagonal") # want:ls("package:Matrix") -->
    >> >>      > c("fac2sparse", "isDiagonal")
    >> >>      > ...
    >> >>
    >> >>      > It seems quite hard to accomplish this at the moment. Is the behavior to
    >> >>      > ignore new inclusions intentional? Could there be an argument to get
    >> >>      > different behavior?
    >> >>
    >> >> As you did not get an answer yet, ..., some remarks by an
    >> >> R-corer who has tweaked library() behavior in the past :
    >> >>
    >> >> - The `include.only = *` argument to library() has been a
    >> >>    *relatively* recent addition {given the 25+ years of R history}:
    >> >>
    >> >>    It was part of the extensive new features by Luke Tierney for
    >> >>    R 3.6.0  [r76248 | luke | 2019-03-18 17:29:35 +0100], with NEWS entry
    >> >>
    >> >>      • library() and require() now allow more control over handling
    >> >>        search path conflicts when packages are attached. The policy is
    >> >>        controlled by the new conflicts.policy option.
    >> >>
    >> >> - I haven't seen these (then) new features been used much, unfortunately,
    >> >>    also not from R-core members, but I'd be happy to
    >> >>    be told a different story.
    >> >>
    >> >> For the above reasons, it could well be that the current
    >> >> implementation {of these features} has not been exercised a lot
    >> >> yet, and limitations as you found them haven't been noticed yet,
    >> >> or at least not noticed on the public R mailing lists, nor
    >> >> otherwise by R-core (?).
    >> >>
    >> >> Your implicitly proposed new feature (or even *changed*
    >> >> default behavior) seems to make sense to me -- but as alluded
    >> >> to, above, I haven't been a conscious user of any
    >> >> 'library(.., include.only = *)' till now.
    >> >
    >> > I don't think it makes sense.  I would assume that
    >> >
    >> >  library(Matrix, include.only="isDiagonal")
    >> >
    >> > implies that only `isDiagonal` ends up on the search path, i.e.
    >> > "include.only" means "include only", not "include in addition to whatever
    >> > else has already been attached".
    >> >
    >> > I think a far better approach to solve Michael's problem is simply to use
    >> >
    >> >  fac2sparse <- Matrix::fac2sparse
    >> >  isDiagonal <- Matrix::isDiagonal
    >> >
    >> > instead of messing around with the user's search list, which may have been
    >> > intentionally set to include only one of those.
    >> >
    >> > So I'd suggest changing the docs to say
    >> >
    >> > "[library and require] check and update the list of currently attached
    >> > packages and do not reload a namespace which is already loaded. 
    >> >  If a package is already attached, no change will be made."
    >> 
    >> ?library could also mention using detach() followed by library() or
    >> attachNamespace() with a new include.only specification.
    >> 
    >> Best,
    >> 
    >> luke
    >> 
    >> >
    >> > Duncan Murdoch