[R-pkg-devel] [External] Re: Subset assignment rule changes in R-devel

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

On Sun, 14 Dec 2025, Simon Urbanek wrote:

> Konrad,
>
> I can reproduce this is current R-devel on any platform, so this should be very easy to reproduce, it is not OS-specific at all - all R-devel checks will flag it eventually. I would guess this is from:
>
> r89121 | luke | 2025-12-09 04:28:24 +1300 (Tue, 09 Dec 2025) | 3 lines
>
> Mark values returned by active binding functions as not mutable to
> prevent unintended mutation in complex assignments.
>
> So it looks like it is intentional. May need some discussion on whether this requires some re-design of your package to make it safer or if it is a valid use-cases that may need further consideration.

Looks like it is a side effect of that bug fix that it is waking up a
misfeature of the interpreted complex assignment code. The compiled
version of the complex assignment code is cleaner and does not have
this issue, so you could use

f <- function (value) {
     if (missing(value)) {
         evalq(x[1L, ], .GlobalEnv)
     } else {
         assign_expr <- substitute(x[1L, ] <- value, list(value = value))
         cmp_assign_expr <- compiler::compile(assign_expr)
         eval(cmp_assign_expr, .GlobalEnv)
     }
}

Depending on how close this is to what you are really doing Konrad,
you can also use .GlobalEnv$x and avoid eval():

f <- function (value) {
     if (missing(value))
         .GlobalEnv$x[1L, ]
     else
         .GlobalEnv$x[1L, ] <- value
}

I'll see if I can figure out what is going on in the interpreted
assignment code.

Best,

luke

>
> Cheers,
> Simon
>
>
>> On 15 Dec 2025, at 10:50, Konrad Rudolph <konrad.rudolph using gmail.com> wrote:
>>
>> Hi all,
>>
>> One of my packages is failing on CRAN in R-devel [1], and I was requested
>> to fix it. However, it is *only* failing on one specific configuration,
>> 'r-devel-linux-x86_64-debian-gcc'. All other combinations — clang on
>> Debian, both clang and GCC on Fedora, and Windows — keep running just fine.
>> As my package is not using compiled code or anything OS-specific, I am at a
>> loss to explain this highly specific failure. Before attempting to build a
>> container image with this specific configuration locally (… are these
>> configurations available as ready-made images?), I wanted to check if there
>> was an obvious change in R-devel which might explain the issue.
>>
>> There are two failures, both with the same error message: “cannot change
>> value of locked binding for '*tmp*'”. My package’s code isn’t attempting to
>> directly change `*tmp*`, but it is using eval() to perform subset
>> assignment to a complex expression inside an active binding. Here’s a
>> minimal code snippet that *should* be equivalent to one of the two
>> failures, and which should therefore also fail (in the last line):
>>
>>   x = data.frame(a = 1 : 2, b = c('a', 'b'))
>>
>>   f = function (value) {
>>     if (missing(value)) {
>>       evalq(x[1L, ], .GlobalEnv)
>>     } else {
>>       assign_expr = substitute(x[1L, ] <- value, list(value = value))
>>       eval(assign_expr, .GlobalEnv)
>>     }
>>   }
>>
>>   makeActiveBinding('ax', f, .GlobalEnv)
>>
>>   ax[1L] = 3L
>>
>> I had a look at the changes in in R-devel, but I couldn’t find anything
>> obviously relevant. In particular, the code of R_MakeActiveBinding() hasn’t
>> been touched in literally decades, and similar for the code that (as far as
>> I understand) performs subset assignment, applydefine().
>>
>> Does anybody have an idea what might be going on here, or how to debug this
>> issue?
>>
>> Cheers,
>> Konrad
>>
>> [1] https://cran.r-project.org/web/checks/check_results_aka.html
>>
>> --
>> Konrad Rudolph
>>
>> [[alternative HTML version deleted]]
>>
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>
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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
241 Schaeffer Hall                  email:   luke-tierney using uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu/