Crated function triggers exception in non-interactive non-parallel context

[robchallen]

Using a crated function in purrr in a non-interactive session when mirai is not installed or not at a high enough version results in a unexpected failure, as purrr assumes because we have crated a function we want to run it in parallel, and in a non-interactive session where mirai is not installed it cannot consult the user to install mirai.

In my case I crated a function to support a parallel option but wanted to leave it in control of the user (and run not in parallel on CRAN checks). I was intending to use furrr for parallel rather than purrr+mirai at the moment.

testthat::test_that("crated purrr function does not throw error", {
  fn = carrier::crate(function(x) return(paste0("test", x)))
  try(pak::pkg_remove("mirai"), silent = TRUE)
  purrr::map_chr(1:10, fn)
})
#> ── Error: crated purrr function does not throw error ───────────────────────────
#> <rlib_error_package_not_found/rlang_error/error/condition>
#> Error in `parallel_pkgs_installed()`: The package "mirai" (>= 2.5.1) is required for parallel map.
#> Backtrace:
#>     ▆
#>  1. └─purrr::map_chr(1:10, fn)
#>  2.   └─purrr:::map_("character", .x, .f, ..., .progress = .progress)
#>  3.     └─purrr:::running_in_parallel(.f)
#>  4.       └─purrr:::parallel_pkgs_installed()
#>  5.         └─rlang::check_installed(...)
#> Error:
#> ! Test failed

^{Created on 2025-11-06 with reprex v2.1.1}

N.b.
packageVersion("purrr")
[1] ‘1.2.0’

[shikokuchuo]

The behaviour of in_parallel() if you don't set mirai daemons is to fall back to sequential processing, so it's fine to leave it in for CRAN checks.

The error you encountered above is a bit unfortunate, in that we need to call mirai::daemons_set() to find out if daemons have been set, and hence need to ensure that mirai is installed first.

In reality, all parallel functionality requires both mirai and carrier, so those should be listed as imports if you're using within a package. The only reason they're currently optional at purrr is considering that some people may not use parallel at all.

[robchallen]

I am trying to use in regular non-parallel mode but with a crated function, on a system that does not have mirai installed. Unfortunately using a crated function is enough to make purrr think you want to use parallel, at which point it checks to see if mirai is installed and fails if non interactive.

Its an edge case but all that needs to change to fix it is:

running_in_parallel <- function(x) {
  inherits(x, "crate") && 
    isTRUE(try(parallel_pkgs_installed(),silent=TRUE)) && 
       mirai::daemons_set()
}