Moves `terra` to Suggests

[Aariq]

Closes #10. Moves terra to Suggests and moves check for terra to top of tar_*() functions.

Also moves validation of filetype to tar_*() functions. I think this might make error traces more readable to users, but haven't really tested thoroughly

[njtierney]

I think to fully close #10 we should implement this using rlang::check_installed().

[Aariq]

I think we should take advantage of rlang::check_installed("pkg") here to provide a neater user experience

I tried using this instead, but the error message from a targets pipeline was not as nice. The code in tar_terra_*() will never be run in an interactive session, which means the user will never see the benefits of rlang::check_installed() (prompting to install missing package) anyway.

> foo <- function() {
+     if (!requireNamespace("asdf")) {
+         stop("package 'asdf' is required", call. = FALSE)
+     }
+ }
> callr::r(foo)
Error: 
! in callr subprocess.
Caused by error: 
! package 'asdf' is required
ℹ See `$stderr` for standard error.
Type .Last.error to see the more details.

> foo2 <- function() {
+     rlang::check_installed("asdf")
+ }
> callr::r(foo2)
Error: 
! in callr subprocess.
Caused by error in `(function () …`:
! The package "asdf" is required.
Type .Last.error to see the more details.

[njtierney]

Great reprex! I'd be tempted to submit that as a bug to rlang - seems like unexpected behaviour, it doesn't even pass the "reason" argument through when specifying. Good catch.

I was thinking that it might be worthwhile passing through a function to manage this (see foo3 that I wrote) - just wrapping the code you wrote. What do you think? It's a small thing, but we use it a couple of times and I think it will also make testing that component of the package easier. Let me know your thoughts :)

foo <- function() {
       if (!requireNamespace("asdf")) {
           stop("package 'asdf' is required", call. = FALSE)
       }
  }
callr::r(foo)
#> Error: ! in callr subprocess.
#> Caused by error: 
#> ! package 'asdf' is required

foo2 <- function() {
     rlang::check_installed("asdf",
                            reason = "Please install asdf")
 }
callr::r(foo2)
#> Error: ! in callr subprocess.
#> Caused by error in `(function () …`:
#> ! The package "asdf" is required Please install asdf

foo3 <- function() {
  .check_pkg_installed <- function(pkg){
    if (!requireNamespace(pkg)) {
      cli::cli_abort("package {.pkg {pkg}} is required",
                     call = rlang::caller_env())
    }
  }

  .check_pkg_installed("asdf")
}

callr::r(foo3)
#> Error: ! in callr subprocess.
#> Caused by error in `(function () …`:
#> ! package asdf is required
callr::r(foo)
#> Error: ! in callr subprocess.
#> Caused by error: 
#> ! package 'asdf' is required

^{Created on 2024-03-20 with reprex v2.1.0}

Session info

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[Aariq]

I was thinking that it might be worthwhile passing through a function to manage this

Yeah! Saves the trouble of remembering to change the package name in two places. Do you want to implement this in this PR?

[njtierney]

Yup, I'll make a couple of changes now.