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

[Serguei Sokol]

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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