Update guidance on using suggested packages, vis-a-vis rlang

Closes #1542

Author: jennybc

R/package.R

@@ -133,17 +133,30 @@ how_to_use <- function(package, type) {
       "Are you sure you want {ui_field('Depends')}? \\
       {ui_field('Imports')} is almost always the better choice."
     ),
-    suggests = {
-      code <- glue("requireNamespace(\"{package}\", quietly = TRUE)")
-      ui_todo("Use {ui_code(code)} to test if package is installed")
-      code <- glue("{package}::fun()")
-      ui_todo("Then directly refer to functions with {ui_code(code)}")
-    },
+    suggests = suggests_usage_hint(package),
     enhances = "",
     linkingto = show_includes(package)
   )
 }
 
+suggests_usage_hint <- function(package) {
+  imports_rlang <- desc::desc_has_dep("rlang", type = "Imports", proj_get())
+  if (imports_rlang) {
+    code1 <- glue('rlang::is_installed("{package}")')
+    code2 <- glue('rlang::check_installed("{package}")')
+    ui_todo("
+      In your package code, use {ui_code(code1)} or {ui_code(code2)} to test \\
+      if {package} is installed")
+    code <- glue("{package}::fun()")
+    ui_todo("Then directly refer to functions with {ui_code(code)}")
+  } else {
+    code <- glue("requireNamespace(\"{package}\", quietly = TRUE)")
+    ui_todo("Use {ui_code(code)} to test if package is installed")
+    code <- glue("{package}::fun()")
+    ui_todo("Then directly refer to functions with {ui_code(code)}")
+  }
+}
+
 show_includes <- function(package) {
   incl <- path_package("include", package = package)
   h <- dir_ls(incl, regexp = "[.](h|hpp)$")

tests/testthat/_snaps/package.md

@@ -15,3 +15,21 @@
       Warning:
       Package 'withr' is already listed in 'Imports' in DESCRIPTION, no change made.
 
+# use_package(type = 'Suggests') guidance w/o and w/ rlang
+
+    Code
+      use_package("withr", "Suggests")
+    Message
+      v Adding 'withr' to Suggests field in DESCRIPTION
+      * Use `requireNamespace("withr", quietly = TRUE)` to test if package is installed
+      * Then directly refer to functions with `withr::fun()`
+
+---
+
+    Code
+      use_package("purrr", "Suggests")
+    Message
+      v Adding 'purrr' to Suggests field in DESCRIPTION
+      * 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()`
+

tests/testthat/test-package.R

@@ -14,6 +14,14 @@ test_that("use_package() guides new packages but not pre-existing ones", {
   })
 })
 
+test_that("use_package(type = 'Suggests') guidance w/o and w/ rlang", {
+  create_local_package()
+  withr::local_options(usethis.quiet = FALSE)
+
+  expect_snapshot(use_package("withr", "Suggests"))
+  ui_silence(use_package("rlang"))
+  expect_snapshot(use_package("purrr", "Suggests"))
+})
 
 # use_dev_package() -----------------------------------------------------------