From 59dc42e51d4b8505e087be2a7860d1c110f89192 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Wed, 2 Apr 2025 10:08:03 +0200
Subject: [PATCH 1/5] cleanup branch

---
 man/stat_connect.Rd                                    | 10 +++++-----
 .../{scale-colour-continuous.md => scale-colour.md}    |  0
 2 files changed, 5 insertions(+), 5 deletions(-)
 rename tests/testthat/_snaps/{scale-colour-continuous.md => scale-colour.md} (100%)

diff --git a/man/stat_connect.Rd b/man/stat_connect.Rd
index d62ba610a5..24166744d8 100644
--- a/man/stat_connect.Rd
+++ b/man/stat_connect.Rd
@@ -128,11 +128,11 @@ Connect successive points with lines of different shapes.
 }
 \section{Aesthetics}{
 
-\code{stat_connect()} understands the following aesthetics (required aesthetics are in bold):
-\itemize{
-\item \strong{\code{\link[=aes_position]{x}} \emph{or} \code{\link[=aes_position]{xmin}} \emph{or} \code{\link[=aes_position]{xmax}}}
-\item \strong{\code{\link[=aes_position]{y}} \emph{or} \code{\link[=aes_position]{ymin}} \emph{or} \code{\link[=aes_position]{ymax}}}
-\item \code{\link[=aes_group_order]{group}}
+\code{stat_connect()} understands the following aesthetics. Required aesthetics are displayed in bold and defaults are displayed for optional aesthetics:
+\tabular{rll}{
+• \tab \strong{\code{\link[=aes_position]{x}} \emph{or} \code{\link[=aes_position]{xmin}} \emph{or} \code{\link[=aes_position]{xmax}}} \tab   \cr\cr
+• \tab \strong{\code{\link[=aes_position]{y}} \emph{or} \code{\link[=aes_position]{ymin}} \emph{or} \code{\link[=aes_position]{ymax}}} \tab   \cr\cr
+• \tab \code{\link[=aes_group_order]{group}} \tab → inferred \cr\cr
 }
 Learn more about setting these aesthetics in \code{vignette("ggplot2-specs")}.
 }
diff --git a/tests/testthat/_snaps/scale-colour-continuous.md b/tests/testthat/_snaps/scale-colour.md
similarity index 100%
rename from tests/testthat/_snaps/scale-colour-continuous.md
rename to tests/testthat/_snaps/scale-colour.md

From 3fcfbe374617cf04b93c3d8d6880ce1f1dae8c8d Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Wed, 2 Apr 2025 10:13:26 +0200
Subject: [PATCH 2/5] For backward compatibility, `zeroGrob()` returns a
 `nullGrob()` subclass

---
 NAMESPACE     |  5 -----
 R/grob-null.R | 20 ++------------------
 R/utilities.R |  9 +++++++++
 3 files changed, 11 insertions(+), 23 deletions(-)

diff --git a/NAMESPACE b/NAMESPACE
index 088da2ba6c..b0d3fc0713 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -19,7 +19,6 @@ S3method(as.list,ggproto)
 S3method(autolayer,default)
 S3method(autoplot,default)
 S3method(c,mapped_discrete)
-S3method(drawDetails,zeroGrob)
 S3method(element_grob,element_blank)
 S3method(element_grob,element_line)
 S3method(element_grob,element_point)
@@ -76,9 +75,7 @@ S3method(ggplot_gtable,ggplot_built)
 S3method(grid.draw,absoluteGrob)
 S3method(grid.draw,ggplot)
 S3method(grobHeight,absoluteGrob)
-S3method(grobHeight,zeroGrob)
 S3method(grobWidth,absoluteGrob)
-S3method(grobWidth,zeroGrob)
 S3method(grobX,absoluteGrob)
 S3method(grobY,absoluteGrob)
 S3method(guide_gengrob,default)
@@ -87,7 +84,6 @@ S3method(guide_merge,default)
 S3method(guide_train,default)
 S3method(guide_transform,default)
 S3method(heightDetails,titleGrob)
-S3method(heightDetails,zeroGrob)
 S3method(limits,Date)
 S3method(limits,POSIXct)
 S3method(limits,POSIXlt)
@@ -149,7 +145,6 @@ S3method(vec_ptype2,mapped_discrete.factor)
 S3method(vec_ptype2,mapped_discrete.integer)
 S3method(vec_ptype2,mapped_discrete.mapped_discrete)
 S3method(widthDetails,titleGrob)
-S3method(widthDetails,zeroGrob)
 export("%+%")
 export("%+replace%")
 export(.data)
diff --git a/R/grob-null.R b/R/grob-null.R
index 217c5a7560..193255a824 100644
--- a/R/grob-null.R
+++ b/R/grob-null.R
@@ -5,22 +5,6 @@
 zeroGrob <- function() .zeroGrob
 
 .zeroGrob <- NULL
-on_load(.zeroGrob <- grob(cl = "zeroGrob", name = "NULL"))
+on_load(.zeroGrob <- add_class(nullGrob(), "zeroGrob"))
 
-#' @export
-#' @method widthDetails zeroGrob
-widthDetails.zeroGrob <- function(x) unit(0, "cm")
-#' @export
-#' @method heightDetails zeroGrob
-heightDetails.zeroGrob <- function(x) unit(0, "cm")
-#' @export
-#' @method grobWidth zeroGrob
-grobWidth.zeroGrob <- function(x) unit(0, "cm")
-#' @export
-#' @method grobHeight zeroGrob
-grobHeight.zeroGrob <- function(x) unit(0, "cm")
-#' @export
-#' @method drawDetails zeroGrob
-drawDetails.zeroGrob <- function(x, recording) {}
-
-is.zero <- function(x) is.null(x) || inherits(x, "zeroGrob")
+is.zero <- function(x) is.null(x) || inherits(x, "null")
diff --git a/R/utilities.R b/R/utilities.R
index 8f0672c142..96ebd1e59c 100644
--- a/R/utilities.R
+++ b/R/utilities.R
@@ -959,3 +959,12 @@ compute_data_size <- function(data, size, default = 0.9,
   data[[target]] <- res * (default %||% 0.9)
   data
 }
+
+add_class <- function(x, new_class) {
+  new_class <- setdiff(new_class, class(x))
+  if (length(new_class) < 1) {
+    return(x)
+  }
+  class(x) <- union(new_class, class(x))
+  x
+}

From 5d55ae88b14d1c091ad5120832a08956961eb5a7 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Wed, 2 Apr 2025 10:14:29 +0200
Subject: [PATCH 3/5] adjust tests

---
 tests/testthat/test-facet-strips.R   | 2 +-
 tests/testthat/test-stat-density2d.R | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tests/testthat/test-facet-strips.R b/tests/testthat/test-facet-strips.R
index d13f8d500c..8bc684dbe7 100644
--- a/tests/testthat/test-facet-strips.R
+++ b/tests/testthat/test-facet-strips.R
@@ -132,7 +132,7 @@ test_that("strips can be removed", {
     theme(strip.background = element_blank(), strip.text = element_blank())
   g_grobs <- ggplotGrob(g)
   strip_grobs <- g_grobs$grobs[grepl('strip-', g_grobs$layout$name)]
-  expect_true(all(sapply(strip_grobs, inherits, 'zeroGrob')))
+  expect_true(all(sapply(strip_grobs, inherits, 'null')))
 })
 
 test_that("padding is only added if axis is present", {
diff --git a/tests/testthat/test-stat-density2d.R b/tests/testthat/test-stat-density2d.R
index 43a99e9513..2e2896cc47 100644
--- a/tests/testthat/test-stat-density2d.R
+++ b/tests/testthat/test-stat-density2d.R
@@ -100,5 +100,5 @@ test_that("stat_density_2d handles faulty bandwidth", {
   p <- ggplot(faithful, aes(eruptions, waiting)) +
     stat_density_2d(h = c(0, NA))
   expect_snapshot_warning(b <- ggplot_build(p))
-  expect_s3_class(layer_grob(b)[[1]], "zeroGrob")
+  expect_s3_class(layer_grob(b)[[1]], "null")
 })

From a8306d36ca109d50a6909a9abd8d94954dd63bd5 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Wed, 2 Apr 2025 11:05:57 +0200
Subject: [PATCH 4/5] add news bullet

---
 NEWS.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/NEWS.md b/NEWS.md
index 363a20cc28..a33dc3a529 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,6 @@
 # ggplot2 (development version)
 
+* (internal) `zeroGrob()` now returns a `grid::nullGrob()` (#6390).
 * `position_fill()` avoids stacking observations of zero (@teunbrand, #6338)
 * New `layer(layout)` argument to interact with facets (@teunbrand, #3062)
 * New `stat_connect()` to connect points via steps or other shapes 

From 674b6d0bd79453fcd7d1d775e51cbaac25b4067e Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Wed, 2 Apr 2025 11:08:02 +0200
Subject: [PATCH 5/5] migrate to grob utilities

---
 DESCRIPTION        |  1 -
 R/grob-null.R      | 10 ----------
 R/utilities-grid.R | 11 +++++++++++
 man/zeroGrob.Rd    |  2 +-
 4 files changed, 12 insertions(+), 12 deletions(-)
 delete mode 100644 R/grob-null.R

diff --git a/DESCRIPTION b/DESCRIPTION
index 82266c740f..83ca78ce8e 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -173,7 +173,6 @@ Collate:
     'ggplot2-package.R'
     'grob-absolute.R'
     'grob-dotstack.R'
-    'grob-null.R'
     'grouping.R'
     'theme-elements.R'
     'guide-.R'
diff --git a/R/grob-null.R b/R/grob-null.R
deleted file mode 100644
index 193255a824..0000000000
--- a/R/grob-null.R
+++ /dev/null
@@ -1,10 +0,0 @@
-#' The zero grob draws nothing and has zero size.
-#'
-#' @keywords internal
-#' @export
-zeroGrob <- function() .zeroGrob
-
-.zeroGrob <- NULL
-on_load(.zeroGrob <- add_class(nullGrob(), "zeroGrob"))
-
-is.zero <- function(x) is.null(x) || inherits(x, "null")
diff --git a/R/utilities-grid.R b/R/utilities-grid.R
index a935d5b38f..3bd29e9ceb 100644
--- a/R/utilities-grid.R
+++ b/R/utilities-grid.R
@@ -48,6 +48,17 @@ gg_par <- function(..., stroke = NULL, pointsize = NULL) {
   inject(gpar(!!!args))
 }
 
+#' The zero grob draws nothing and has zero size.
+#'
+#' @keywords internal
+#' @export
+zeroGrob <- function() .zeroGrob
+
+.zeroGrob <- NULL
+on_load(.zeroGrob <- add_class(nullGrob(), "zeroGrob"))
+
+is.zero <- function(x) is.null(x) || inherits(x, "null")
+
 width_cm <- function(x) {
   if (is.grob(x)) {
     convertWidth(grobWidth(x), "cm", TRUE)
diff --git a/man/zeroGrob.Rd b/man/zeroGrob.Rd
index e4aac88eb0..6fcfe56218 100644
--- a/man/zeroGrob.Rd
+++ b/man/zeroGrob.Rd
@@ -1,5 +1,5 @@
 % Generated by roxygen2: do not edit by hand
-% Please edit documentation in R/grob-null.R
+% Please edit documentation in R/utilities-grid.R
 \name{zeroGrob}
 \alias{zeroGrob}
 \title{The zero grob draws nothing and has zero size.}