Where should character globals be looked up?

[DavisVaughan]

I have this issue in furrr as well, but wanted to start discussion here so we can both do the same thing.

In the following example, I understand why wrapper2() always finds y, but I would imagine that wrapper("y") should also find y. This is something that I've hit while writing tests for furrr.

I think the issue is that the environment used to find these globals is just the execution environment of future_lapply(). It is created here:

future.apply/R/future_lapply.R

Line 159 in 1d19bbf

future.envir <- environment() ## Not used; just to clarify the above.

And passed through and eventually used here:

future.apply/R/globals.R

Line 33 in 1d19bbf

globals <- globalsByName(globals, envir = envir, mustExist = FALSE)

The parent environment of this env is the future.apply namespace environment, so there is no way for it to find y. I'm wondering if instead we should be calling envir <- parent.frame() from future_lapply() and friends to find globals. That would contain y, and I think it would have a correct chain of environments for finding other globals further up. Thoughts?

library(future.apply)
#> Loading required package: future
plan(multisession, workers = 2)

fn <- function(x) {
  exists("y")
}

wrapper <- function(future.globals = TRUE) {
  y <- 1
  future_lapply(1, fn, future.globals = future.globals)
}

wrapper2 <- function(future.globals = TRUE) {
  y <- 1
  
  # finds `y` from enclosing env of `fn`
  fn <- function(x) {
    exists("y")
  }
  
  future_lapply(1, fn, future.globals = future.globals)
}

wrapper()
#> [[1]]
#> [1] FALSE
wrapper("y")
#> [[1]]
#> [1] FALSE

wrapper2()
#> [[1]]
#> [1] TRUE
wrapper2("y")
#> [[1]]
#> [1] TRUE

^{Created on 2020-07-29 by the reprex package (v0.3.0)}