Account for repeated requests for a LinkingTo dependency

Closes #1648, closes #1329

Author: jennybc

R/helpers.R

@@ -34,7 +34,11 @@ use_dependency <- function(package, type, min_version = NULL) {
 
   changed <- FALSE
 
-  # No existing dependency, so can simply add
+  # One of:
+  # * No existing dependency
+  # * Adding existing non-LinkingTo dependency to LinkingTo
+  # * New use of a LinkingTo package as a non-LinkingTo dependency
+  # In all cases, we can can simply make the change.
   if (!any(existing_dep) || any(is_linking_to)) {
     ui_done("Adding {ui_value(package)} to {ui_field(type)} field in DESCRIPTION")
     desc$set_dep(package, type, version = version)
@@ -43,6 +47,16 @@ use_dependency <- function(package, type, min_version = NULL) {
     return(invisible(changed))
   }
 
+  # Request to add a dependency that is already in LinkingTo and only in
+  # LinkingTo as a LinkingTo dependency --> no need to do anything.
+  if (identical(existing_type, "LinkingTo") && type == "LinkingTo") {
+     ui_done(
+       "Package {ui_value(package)} is already listed in \\
+        {ui_value('LinkingTo')} in DESCRIPTION, no change made."
+      )
+    return(invisible(changed))
+  }
+
   existing_type <- setdiff(existing_type, "LinkingTo")
   delta <- sign(match(existing_type, types) - match(type, types))
   if (delta < 0) {

tests/testthat/_snaps/package.md

@@ -60,3 +60,10 @@
       * In your package code, use `rlang::is_installed("purrr")` or `rlang::check_installed("purrr")` to test if purrr is installed
       * Then directly refer to functions with `purrr::fun()`
 
+# use_package() does not fall over on 2nd LinkingTo request
+
+    Code
+      use_dependency("rlang", "LinkingTo")
+    Message
+      v Package 'rlang' is already listed in 'LinkingTo' in DESCRIPTION, no change made.
+

tests/testthat/test-package.R

@@ -40,6 +40,18 @@ test_that("use_package(type = 'Suggests') guidance w/o and w/ rlang", {
   expect_snapshot(use_package("purrr", "Suggests"))
 })
 
+test_that("use_package() does not fall over on 2nd LinkingTo request", {
+  local_edition(3)
+  create_local_package()
+  local_interactive(FALSE)
+
+  use_dependency("rlang", "LinkingTo")
+
+  withr::local_options(list(usethis.quiet = FALSE))
+
+  expect_snapshot(use_dependency("rlang", "LinkingTo"))
+})
+
 # use_dev_package() -----------------------------------------------------------
 
 test_that("use_dev_package() writes a remote", {