[Rd] [External] Time to drop globalenv() from searches in package code?

[iuke-tier@ey m@iii@g oii uiow@@edu]

On Thu, 15 Sep 2022, Duncan Murdoch wrote:

> The author of this Stackoverflow question 
> https://stackoverflow.com/q/73722496/2554330 got confused because a typo in 
> his code didn't trigger an error in normal circumstances, but it did when he 
> ran his code in pkgdown.
>
> The typo was to use "x" in a test, when the local variable was named ".x". 
> There was no "x" defined locally or in the package or its imports, so the 
> search got all the way to the global environment and found one.  (The very 
> confusing part for this user was that it found the right variable.)
>
> This author had suppressed the "R CMD check" check for use of global 
> variables.  Obviously he shouldn't have done that, but he's working with 
> tidyverse NSE, and that causes so many false positives that it is somewhat 
> understandable he would suppress one too many.
>
> The pkgdown simulation of code in examples doesn't do perfect mimicry of 
> running it at top level; the fake global environment never makes it onto the 
> search list.  Some might call this a bug, but I'd call it the right search 
> strategy.
>
> My suggestion is that the search for variables in package code should never 
> get to globalenv().  The chain of environments should stop after handling the 
> imports.  (Probably base package functions should also be implicitly 
> imported, but nothing else.)
>

This was considered and discussed when I added namespaces. Basically
it would mean making the parent of the base namespace environment be
the empty environment instead of the global environment. As a design
this is cleaner, and it would be a one-line change in eval.c.  But
there were technical reasons this was not a viable option at the time,
also a few political reasons. The technical reasons mostly had to do
with S3 dispatch.

Changes over the years, mostly from work Kurt has done, to S3 dispatch
for methods defined and registered in packages might make this more
viable in principle, but there would still be a lot of existing code
that would stop working. For example, 'make check' with the one-line
change fails in a base example that defines an S3 method. It might be
possible to fiddle with the dispatch to keep most of that code
working, but I suspect that would be a lot of work. Seeing what it
would take to get 'make check' to succeed would be a first step if
anyone wants to take a crack at it.

> I suspect this change would reveal errors in lots of packages, but the number 
> of legitimate uses of the current search strategy has got to be pretty small 
> nowadays, since we've been getting warnings for years about implicit imports 
> from other standard packages.

Your definition of 'legitimate' is probably quite similar to mine, but
there is likely to be a small but vocal minority with very different
views :-).

Best,

luke

> Duncan Murdoch
>
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-- 
Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
    Actuarial Science
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