R devel - Sep 2022 - Time to drop globalenv() from searches in package code?

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.)

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.

Duncan Murdoch

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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> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
-- 
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
241 Schaeffer Hall                  email:   luke-tierney at uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu