Functions are not properly GC'd

[wch]

Here's a normal case of a function being GC'd. (I'm creating it in a local environment so that I can register a finalizer.)

f <- local({
  e <- environment()
  reg.finalizer(e, function(e) message(format(e), " finalized\n"))
  function() {
    message("Environment is ", format(e), "\n")
  }
})

f()
#> Environment is <environment: 0x7fad6689cdb0>

rm(f); invisible(gc())
#> <environment: 0x7fad6689cdb0> finalized

With cpp11, if I pass f to a C++ function as a cpp11::function object, it does NOT get GC'd:

library(cpp11)
cpp_function('void invoke(function fn) {
  fn();
}')

f <- local({
  e <- environment()
  reg.finalizer(e, function(e) message(format(e), " finalized\n"))
  function() {
    message("Environment is ", format(e), "\n")
  }
})

invoke(f)
#> Environment is <environment: 0x7fad67438b20>

rm(f); invisible(gc())
# (No output)
invisible(gc())
# (No output)

However, if I call invoke() on another function, it seems to free up the reference to the previous function that was passed to invoke(), and allows it to be GC'd:

invoke(function() 1)
invisible(gc())
#> <environment: 0x7fad67438b20> finalized

[wch]

I've also found that if the invoke function is modified to not actually invoke fn, but just takes it as an argument, the object does get GC'd.

library(cpp11)
cpp_function('void invoke2(function fn) {
  fn;
}')

f <- local({
  e <- environment()
  reg.finalizer(e, function(e) message(format(e), " finalized\n"))
  message("Environment is ", format(e), "\n")
  function() {
    message("Environment is ", format(e), "\n")
  }
})
#> Environment is <environment: 0x7fbef15b7878>

invoke2(f)

rm(f); invisible(gc())
#> <environment: 0x7fbef15b7878> finalized