Scoping issue with tar_make_future(): variables declared in _targets.r can conflict with functions from imported packages

[mkoohafkan]

In this example, variables defined in _targets.r conflict with identically-named functions imported by packages specified via tar_option_set(). The following example reproduces the error with plan(callr) and tar_make_future(). The issue does not occur when calling tar_make() or using plan(sequential). In this example, a variable year conflicts with the function lubridate::year().

_targets.r

library(targets)
library(tarchetypes)
library(future)
library(future.callr)

source("R/test.r")

plan(callr)

tar_option_set(packages = c("lubridate"))

year = 2022
categories = data.frame(category = LETTERS[1:5])


tar_map(
  values = categories,
  names = "category",
  tar_target("test", test_fun(category, year),
    iteration = "list")
)

R/test.r

test_fun = function(category, year) {
  data.frame(
    chosen_category = rep(category, 4),
    chosen_year = rep(year, 4),
    value = rnorm(4)
  )
}

console

targets::tar_make_future(workers = 2)
## start target test_A
## start target test_B
## error target test_A
## end pipeline
## Error in tar_throw_run(target$metrics$error) :
##   attempt to replicate an object of type 'closure'
## Error in `tar_throw_run()`:
## ! callr subprocess failed: attempt to replicate an object of type 'closure'
## Visit https://books.ropensci.org/targets/debugging.html for debugging advice.
## Run `rlang::last_error()` to see where the error occurred.

[wlandau]

I can reproduce this with just future.callr (see below) so targets is not the source of the bug. Would you submit an issue to https://github.com/HenrikBengtsson/future.callr?

library(future)
library(future.callr)

# with a callr future
plan(callr)
f <- future({
  suppressPackageStartupMessages(library(lubridate))
  fun(year)
},
globals = list(fun = function(year) year, year = 2022)
)
value(f)
#> function (x) 
#> UseMethod("year")
#> <bytecode: 0x7fda22231148>
#> <environment: namespace:lubridate>

# with a multisession future
plan(multisession)
f <- future({
  suppressPackageStartupMessages(library(lubridate))
  fun(year)
},
globals = list(fun = function(year) year, year = 2022)
)
value(f)
#> [1] 2022

^{Created on 2022-02-03 by the reprex package (v2.0.1)}