use_standalone() beyond packages

- Closes #2087

Thanks @jennybc for help in person during the tidy dev day 2025

Also, claude code helped with a few things:

- Fix pluralization error with `cli::qty()`
- See examples of messages in this repo
- Use `usethis.quiet = TRUE`

Author: maurolepore

R/use_standalone.R

@@ -79,6 +79,15 @@ use_standalone <- function(repo_spec, file = NULL, ref = NULL, host = NULL) {
 
   dependencies <- standalone_dependencies(lines, path)
 
+  if (!is_package()) {
+    imports <- dependencies$imports
+    n <- cli::qty(length(imports$pkg))
+    ui_bullets(c(
+      "!" = "You'll need the following {n} package{?s}: {.pkg {imports$pkg}}."
+    ))
+    return(invisible())
+  }
+
   for (dependency in dependencies$deps) {
     use_standalone(repo_spec, dependency, ref = ref, host = host)
   }

tests/testthat/_snaps/use_standalone.md

@@ -64,6 +64,14 @@
       [4] "# ----------------------------------------------------------------------"                                            
       [5] "#"                                                                                                                   
 
+# from a non-package project throws an informative message
+
+    Code
+      use_standalone("r-lib/rlang", "types-check", ref = "73182fe94")
+    Message
+      v Writing 'R/import-standalone-types-check.R'.
+      ! You'll need the following package: rlang.
+
 # can offer choices
 
     Code

tests/testthat/test-use_standalone.R

@@ -54,6 +54,17 @@ test_that("can import standalone file with dependencies", {
   expect_match(imports, "rlang")
 })
 
+test_that("from a non-package project throws an informative message", {
+  skip_if_offline("github.com")
+  create_local_project()
+  withr::local_options(list(usethis.quiet = FALSE))
+
+  # NOTE: Check ref after r-lib/rlang@standalone-dep has been merged
+  expect_snapshot(
+    use_standalone("r-lib/rlang", "types-check", ref = "73182fe94")
+  )
+})
+
 test_that("can use full github url", {
   skip_if_offline("github.com")
   create_local_package()