From e69687a407addd2c29510153de52a128bde4701e Mon Sep 17 00:00:00 2001
From: Teun van den Brand <49372158+teunbrand@users.noreply.github.com>
Date: Mon, 26 Aug 2024 16:10:19 +0200
Subject: [PATCH] Ignore empty non-mapped aesthetics (#6011)

* drop empty aesthetics with warning

* add test

* add news bullet
---
 NEWS.md                     | 2 ++
 R/layer.R                   | 9 +++++++++
 tests/testthat/test-layer.R | 7 +++++++
 3 files changed, 18 insertions(+)

diff --git a/NEWS.md b/NEWS.md
index b4636c5166..4cab4f4c79 100644
--- a/NEWS.md
+++ b/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).
diff --git a/R/layer.R b/R/layer.R
index 59a9dba096..eba8666de4 100644
--- a/R/layer.R
+++ b/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)
diff --git a/tests/testthat/test-layer.R b/tests/testthat/test-layer.R
index 8be6c8555f..51f0cd9eee 100644
--- a/tests/testthat/test-layer.R
+++ b/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({