Ignore empty non-mapped aesthetics (#6011)

* drop empty aesthetics with warning

* add test

* add news bullet

Author: teunbrand

NEWS.md

@@ -1,5 +1,7 @@
 # ggplot2 (development version)
 
+* Passing empty unmapped aesthetics to layers raises a warning instead of
+  throwing an error (@teunbrand, #6009).
 * Moved {mgcv} from Imports to Suggests (@teunbrand, #5986)
 * New `reset_geom_defaults()` and `reset_stat_defaults()` to restore all geom or
   stat default aesthetics at once (@teunbrand, #5975).

R/layer.R

@@ -146,6 +146,15 @@ layer <- function(geom = NULL, stat = NULL,
   if (any(pattern)) {
     aes_params[pattern] <- lapply(aes_params[pattern], list)
   }
+  # Drop empty aesthetics
+  empty_aes <- names(aes_params)[lengths(aes_params) == 0]
+  if (length(empty_aes) > 0) {
+    cli::cli_warn(
+      "Ignoring empty aesthetic{?s}: {.arg {empty_aes}}.",
+      call = call_env
+    )
+    aes_params <- aes_params[setdiff(names(aes_params), empty_aes)]
+  }
 
   # Warn about extra params and aesthetics
   extra_param <- setdiff(names(params), all)

tests/testthat/test-layer.R

@@ -25,6 +25,13 @@ test_that("unknown aesthetics create warning", {
   expect_warning(geom_point(aes(blah = "red")), "unknown aesthetics")
 })
 
+test_that("empty aesthetics create warning", {
+  expect_warning(
+    geom_point(fill = NULL, shape = character()),
+    "Ignoring empty aesthetics"
+  )
+})
+
 test_that("invalid aesthetics throws errors", {
   # We want to test error and ignore the scale search message
   suppressMessages({