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

[Mikael Jagan]

Thanks both.  Yes, I was aware of globalVariables, etc.  I guess I was hoping
to be pointed to the right place in the source code, in case the issue could
be addressed properly, notably as it seems to have already been addressed for
functions that are not S4 methods, i.e., codetools is apparently not bothered
by

     def <- function(x = y) { y <- 0; x }

but still complains about

     setMethod("someGeneric", "someClass", def)

...

Mikael

On 2023-06-07 5:13 am, Gabriel Becker wrote:
> 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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