Restore old guides in guides() (#6167)

* Early exit earlier

* fix `is.guide()` -> `inherits()`

* explicitly test `guides()` adds old S3 guides properly

Author: teunbrand

R/guides-.R

@@ -68,11 +68,14 @@ NULL
 #' }
 guides <- function(...) {
   args <- list2(...)
-  if (length(args) > 0) {
-    if (is.list(args[[1]]) && !is.guide(args[[1]])) args <- args[[1]]
-    args <- rename_aes(args)
+  # If there are no guides do nothing
+  if (length(args) == 0) {
+    return(NULL)
   }
 
+  if (is.list(args[[1]]) && !inherits(args[[1]], "guide")) args <- args[[1]]
+  args <- rename_aes(args)
+
   idx_false <- vapply(args, isFALSE, FUN.VALUE = logical(1L))
   if (isTRUE(any(idx_false))) {
     deprecate_warn0("3.3.4", "guides(`<scale>` = 'cannot be `FALSE`. Use \"none\" instead')")
@@ -84,11 +87,6 @@ guides <- function(...) {
     return(guides_list(guides = args))
   }
 
-  # If there are no guides, do nothing
-  if (length(args) == 0) {
-    return(NULL)
-  }
-
   # Raise warning about unnamed guides
   nms <- names(args)
   if (is.null(nms)) {

tests/testthat/test-guides.R

@@ -577,12 +577,16 @@ test_that("old S3 guides can be implemented", {
 
   withr::local_environment(my_env)
 
+  my_guides <- guides(x = guide_circle())
+  expect_length(my_guides$guides, 1)
+  expect_s3_class(my_guides$guides[[1]], "guide")
+
   expect_snapshot_warning(
     expect_doppelganger(
       "old S3 guide drawing a circle",
       ggplot(mtcars, aes(disp, mpg)) +
         geom_point() +
-        guides(x = "circle")
+        my_guides
     )
   )
 })