From ffaedd3c3ff5cada49f8da07ed97ff1029a48c85 Mon Sep 17 00:00:00 2001
From: Thomas Lin Pedersen <thomasp85@gmail.com>
Date: Fri, 12 Nov 2021 10:35:31 +0100
Subject: [PATCH 1/2] follow tidyverse recycling rules

---
 NEWS.md   | 3 +++
 R/geom-.r | 2 +-
 R/layer.r | 3 ++-
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/NEWS.md b/NEWS.md
index 5163888679..b92410a8d4 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,8 @@
 # ggplot2 (development version)
 
+* Aesthetics of length 1 are now recycled to 0 if the length of the data is 0 
+  (@thomasp85, #4588)
+
 * Setting `stroke` to `NA` in `geom_point()` will no longer impair the sizing of
   the points (@thomasp85, #4624)
 
diff --git a/R/geom-.r b/R/geom-.r
index e513769c03..8265d6cd4c 100644
--- a/R/geom-.r
+++ b/R/geom-.r
@@ -208,7 +208,7 @@ NULL
 .stroke <- 96 / 25.4
 
 check_aesthetics <- function(x, n) {
-  ns <- vapply(x, length, numeric(1))
+  ns <- vapply(x, length, integer(1))
   good <- ns == 1L | ns == n
 
   if (all(good)) {
diff --git a/R/layer.r b/R/layer.r
index 197d32549d..dcb66f92bf 100644
--- a/R/layer.r
+++ b/R/layer.r
@@ -264,7 +264,8 @@ Layer <- ggproto("Layer", NULL,
       if (length(evaled) == 0) {
         n <- 0
       } else {
-        n <- max(vapply(evaled, length, integer(1)))
+        aes_n <- vapply(evaled, length, integer(1))
+        n <- if (min(aes_n) == 0) 0L else max(aes_n)
       }
     }
     check_aesthetics(evaled, n)

From ecb0ae027e5191c723cfdc729c35c1b7dddf9dc7 Mon Sep 17 00:00:00 2001
From: Thomas Lin Pedersen <thomasp85@gmail.com>
Date: Tue, 16 Nov 2021 15:27:30 +0100
Subject: [PATCH 2/2] add tests for recycling to 0

---
 tests/testthat/test-aes-setting.r | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tests/testthat/test-aes-setting.r b/tests/testthat/test-aes-setting.r
index baa6a12077..4c3e055ea8 100644
--- a/tests/testthat/test-aes-setting.r
+++ b/tests/testthat/test-aes-setting.r
@@ -13,6 +13,17 @@ test_that("aesthetic parameters match length of data", {
   set_colours(rep("red", 5))
 })
 
+test_that("Length 1 aesthetics are recycled to 0", {
+  p <- ggplot(data.frame(x = numeric(), y = numeric())) +
+    geom_point(aes(x, y, colour = "red"))
+
+  expect_silent(plot(p))
+
+  data <- layer_data(p)
+
+  expect_equal(nrow(data), 0)
+})
+
 test_that("legend filters out aesthetics not of length 1", {
   df <- data_frame(x = 1:5, y = 1:5)
   p <- ggplot(df, aes(x, y, colour = factor(x))) +