[Rd] codetools wrongly complains about lazy evaluation in S4 methods

[Gabriel Becker]

The API supported workaround is to call globalVariables, which,
essentially, declares the variables without defining them (a distinction R
does not usually make).

The issue with this approach, of course, is that its a very blunt
instrument. It will cause false negatives if you accidentally use the same
symbol in a standard evaluation context elsewhere in your code.
Nonetheless, that's the intended approach as far as i know.

Best,
~G



On Wed, Jun 7, 2023 at 1:07 AM Serguei Sokol via R-devel <
r-devel using r-project.org> wrote:

> Le 03/06/2023 à 17:50, Mikael Jagan a écrit :
> > In a package, I define a method for not-yet-generic function 'qr.X'
> > like so:
> >
> >     > setOldClass("qr")
> >     > setMethod("qr.X", signature(qr = "qr"), function(qr, complete,
> > ncol) NULL)
> >
> > The formals of the newly generic 'qr.X' are inherited from the
> > non-generic
> > function in the base namespace.  Notably, the inherited default value of
> > formal argument 'ncol' relies on lazy evaluation:
> >
> >     > formals(qr.X)[["ncol"]]
> >     if (complete) nrow(R) else min(dim(R))
> >
> > where 'R' must be defined in the body of any method that might
> > evaluate 'ncol'.
> > To my surprise, tools:::.check_code_usage_in_package() complains about
> > the
> > undefined symbol:
> >
> >     qr.X: no visible binding for global variable 'R'
> >     qr.X,qr: no visible binding for global variable 'R'
> >     Undefined global functions or variables:
> >       R
> I think this issue is similar to the complaints about non defined
> variables in expressions involving non standard evaluation, e.g. column
> names in a data frame which are used as unquoted symbols. One of
> workarounds is simply to declare them somewhere in your code. In your
> case, it could be something as simple as:
>
>    R=NULL
>
> Best,
> Serguei.
>
> >
> > I claim that it should _not_ complain, given that lazy evaluation is a
> > really
> > a feature of the language _and_ given that it already does not
> > complain about
> > the formals of functions that are not S4 methods.
> >
> > Having said that, it is not obvious to me what in codetools would need
> > to change
> > here.  Any ideas?
> >
> > I've attached a script that creates and installs a test package and
> > reproduces
> > the check output by calling tools:::.check_code_usage_in_package().
> > Hope it
> > gets through.
> >
> > Mikael
> >
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>
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