[R-pkg-devel] Handling Not-Always-Needed Dependencies?

[Duncan Murdoch]

On 03/08/2016 5:32 AM, Mark van der Loo wrote:
>
> After reading the link in Dirk's initial reply, how about adding fields
> 'Recommends' and 'Build-Depends' to DESCRIPTION as in Debian?
>
> Recommends: only gets installed, can be used via if(requireNamespace())
> from the package and in pkg tests[1]. [Debian: The Recommends field
> should list packages that would be found together with this one in all
> but unusual installations.]
> Build-Depends: gets installed before build, removed after.
> Suggests: only installed when requested at install.packages() and only
> used in examples/vignettes.

I think the distinction between Recommends and Suggests is too subtle 
here.  I already think it's a bad thing that we are using these words in 
ways that don't really correspond to English usage.  I'd much rather 
have a way of declaring explicitly the different aspects of dependence 
on a package rather than bundling them up into cute labels, but it's too 
late for that now.  However, we don't need to make things worse.

>
> If 'tons of packages' are using if(requireNamespace) in their package
> code there seems to be a need for something like this. Compliance to the
> above can be checked automatically and  a gradual implementation via
> NOTE->WARNING->ERROR in R CMD check seems possible.

I don't follow the argument here.  What problem are you solving?

> Perhaps more controversially a 'Breaks' field could be considered. There
> are a few packages out there that have many, many, dependencies.
> Implementing breaking updates currently depends on the willingness of
> many authors to update their package or convincing the CRAN maintainers
> to allow for (temporary) breakage.

This isn't controversial, it's just a bad idea.  Don't encourage people 
to break things.

> The suggestion to have functions auto-install things is very
> inconvenient for the good reasons pointed out by Thomas. Additionally,
> it is often based on the wrong assumptions. Example: the RGtk2 package
> has this habit of trying to install when libgtk2 is not on the path. But
> in my case that is often exactly the case: it is just not on the path
> (libgtk2 is on the network, the VM just doesn't know yet). So I'd rather
> have a proper and accurate error message (which is good practice anyway).
>
>
> Best,
> Mark
>
> [1] actually, once we know a pkg is Recommended, the
> 'if(requireNamespace)' could even be absorbed in the :: operator.

I don't see how :: would be any different than it is now.  If you don't 
have foo available, and you try to use foo::bar(), what would happen 
other than an error?

Duncan Murdoch

>
>
>
>
> Op wo 3 aug. 2016 om 01:46 schreef Duncan Murdoch
> <murdoch.duncan at gmail.com <mailto:murdoch.duncan at gmail.com>>:
>
>     On 02/08/2016 6:34 PM, Dirk Eddelbuettel wrote:
>     >
>     > On 2 August 2016 at 18:13, Duncan Murdoch wrote:
>     > | Okay, now I think I understand, but I agree with CRAN.  It is not
>     > | feasible to tell if the test happened somewhere in the code
>     unless we
>     > | enforce a particular way of writing the test.
>     >
>     > Debian has well over 20k packages, and they are tested this way.
>     You just
>     > need to show the will of testing in an _empty_ environment to ensure
>     > _everything_ that is needed is loaded.
>     >
>     > | I would object if I had to write if (requireNamespace("foo"))
>     multiple
>     > | times just to satisfy CRAN's test, when any sane human could
>     tell that
>     > | the first test was sufficient.
>     > |
>     > | For example, if my package Suggests: foo, I should be able to write
>     > |
>     > | if (!requireNamespace("foo"))
>     > |    stop("Package foo is needed for this example")
>     > |
>     > | and then merrily call foo::bar() as many times as I like.
>     > |
>     > | Or am I still misunderstanding you?  What particular thing
>     should CRAN
>     > | change?
>     >
>     > You seem to misunderstand that both you and I want
>     >
>     >   if (!requireNamespace("foo"))
>     >      stop("Package foo is needed for this example")
>     >
>     > (or alternative per-call tests) and that CRAN does not enforce either.
>     >
>     > CRAN, like Hadley, just closes its eyes, swallows hard, and then
>     simply loads
>     > everything treating Suggests as if it were Depends.
>     >
>     > But it ain't. Suggests != Depends.
>     >
>     > Now clearer?
>
>
>     So really what you're suggesting is that CRAN should run tests with the
>     suggested packages absent.  Presumably tests should also be run with
>     them present.
>
>     But if they did that, the code that I want to write would call stop()
>     and fail.  So we'd need some way to say "Let the user know they need
>     'foo' to run this, but don't fail."  And we'd need to phase this in
>     really gradually, because tons of packages are using code like my
>     example.
>
>     You volunteered to help CRAN package checking.  Why not put together
>     code to implement your idea, and see how big the problem would be to
>     phase it in, by seeing how many packages fail under it?
>
>     Duncan Murdoch
>
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