From 122df1d061745f9d1caef2956e294ed17183cc6b Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Tue, 12 Mar 2024 15:39:48 +0100
Subject: [PATCH 1/9] Discrete position scales use palette

---
 R/scale-discrete-.R | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/R/scale-discrete-.R b/R/scale-discrete-.R
index 1a8228e318..1fc7773b40 100644
--- a/R/scale-discrete-.R
+++ b/R/scale-discrete-.R
@@ -134,7 +134,21 @@ ScaleDiscretePosition <- ggproto("ScaleDiscretePosition", ScaleDiscrete,
 
   map = function(self, x, limits = self$get_limits()) {
     if (is.discrete(x)) {
-      x <- seq_along(limits)[match(as.character(x), limits)]
+      values <- self$palette(limits)
+      if (!is.numeric(values)) {
+        cli::cli_abort(
+          "The {.arg palette} function must return a {.cls numeric} vector.",
+          call = self$call
+        )
+      }
+      if (length(values) < length(limits)) {
+        cli::cli_abort(
+          "The {.arg palette} function must return at least \\
+            {length(limits)} values.",
+          call = self$call
+        )
+      }
+      x <- values[match(as.character(x), limits)]
     }
     mapped_discrete(x)
   },

From 0fd6f37d38cfad91c2af0e8221ff08c86772a70c Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Tue, 12 Mar 2024 16:00:22 +0100
Subject: [PATCH 2/9] Plumbing for `palette` argument

---
 R/scale-discrete-.R   | 12 ++++++++----
 man/scale_discrete.Rd |  8 +++++---
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/R/scale-discrete-.R b/R/scale-discrete-.R
index 1fc7773b40..8f36c22c00 100644
--- a/R/scale-discrete-.R
+++ b/R/scale-discrete-.R
@@ -12,6 +12,8 @@
 #'
 #' @inheritDotParams discrete_scale
 #' @inheritParams discrete_scale
+#' @param palette A function that takes the limits as input and provides
+#'   numerical values as output.
 #' @rdname scale_discrete
 #' @family position scales
 #' @seealso
@@ -63,11 +65,12 @@
 #'   geom_point() +
 #'   scale_x_discrete(labels = abbreviate)
 #' }
-scale_x_discrete <- function(name = waiver(), ..., expand = waiver(),
+scale_x_discrete <- function(name = waiver(), ..., palette = seq_along,
+                             expand = waiver(),
                              guide = waiver(), position = "bottom") {
   sc <- discrete_scale(
     aesthetics = c("x", "xmin", "xmax", "xend"), name = name,
-    palette = identity, ...,
+    palette = palette, ...,
     expand = expand, guide = guide, position = position,
     super = ScaleDiscretePosition
   )
@@ -77,11 +80,12 @@ scale_x_discrete <- function(name = waiver(), ..., expand = waiver(),
 }
 #' @rdname scale_discrete
 #' @export
-scale_y_discrete <- function(name = waiver(), ..., expand = waiver(),
+scale_y_discrete <- function(name = waiver(), ..., palette = seq_along,
+                             expand = waiver(),
                              guide = waiver(), position = "left") {
   sc <- discrete_scale(
     aesthetics = c("y", "ymin", "ymax", "yend"), name = name,
-    palette = identity, ...,
+    palette = palette, ...,
     expand = expand, guide = guide, position = position,
     super = ScaleDiscretePosition
   )
diff --git a/man/scale_discrete.Rd b/man/scale_discrete.Rd
index 3955316322..4cd85a4fd6 100644
--- a/man/scale_discrete.Rd
+++ b/man/scale_discrete.Rd
@@ -8,6 +8,7 @@
 scale_x_discrete(
   name = waiver(),
   ...,
+  palette = seq_along,
   expand = waiver(),
   guide = waiver(),
   position = "bottom"
@@ -16,6 +17,7 @@ scale_x_discrete(
 scale_y_discrete(
   name = waiver(),
   ...,
+  palette = seq_along,
   expand = waiver(),
   guide = waiver(),
   position = "left"
@@ -30,9 +32,6 @@ omitted.}
 \item{...}{
   Arguments passed on to \code{\link[=discrete_scale]{discrete_scale}}
   \describe{
-    \item{\code{palette}}{A palette function that when called with a single integer
-argument (the number of levels in the scale) returns the values that
-they should take (e.g., \code{\link[scales:pal_hue]{scales::pal_hue()}}).}
     \item{\code{breaks}}{One of:
 \itemize{
 \item \code{NULL} for no breaks
@@ -78,6 +77,9 @@ notation.
     \item{\code{super}}{The super class to use for the constructed scale}
   }}
 
+\item{palette}{A function that takes the limits as input and provides
+numerical values as output.}
+
 \item{expand}{For position scales, a vector of range expansion constants used to add some
 padding around the data to ensure that they are placed some distance
 away from the axes. Use the convenience function \code{\link[=expansion]{expansion()}}

From 74bfb9358bec6a7a8dfb37676c7f2c8017cc7a85 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Tue, 12 Mar 2024 16:01:10 +0100
Subject: [PATCH 3/9] discrete range derived from mapped limits

---
 R/coord-transform.R |  2 +-
 R/scale-expansion.R | 19 +++++++++++--------
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/R/coord-transform.R b/R/coord-transform.R
index 81f06afad3..83ffd7b9ee 100644
--- a/R/coord-transform.R
+++ b/R/coord-transform.R
@@ -198,7 +198,7 @@ view_scales_from_scale_with_coord_trans <- function(scale, coord_limits, trans,
 
   if (scale$is_discrete()) {
     continuous_ranges <- expand_limits_discrete_trans(
-      scale_limits,
+      scale$map(scale_limits),
       expansion,
       coord_limits,
       trans,
diff --git a/R/scale-expansion.R b/R/scale-expansion.R
index 9ede4c1400..8ec72c2a78 100644
--- a/R/scale-expansion.R
+++ b/R/scale-expansion.R
@@ -137,7 +137,7 @@ expand_limits_scale <- function(scale, expand = expansion(0, 0), limits = waiver
   if (scale$is_discrete()) {
     coord_limits <- coord_limits %||% c(NA_real_, NA_real_)
     expand_limits_discrete(
-      limits,
+      scale$map(limits),
       expand,
       coord_limits,
       range_continuous = scale$range_c$range
@@ -201,14 +201,17 @@ expand_limits_continuous_trans <- function(limits, expand = expansion(0, 0),
 expand_limits_discrete_trans <- function(limits, expand = expansion(0, 0),
                                          coord_limits = c(NA, NA), trans = transform_identity(),
                                          range_continuous = NULL) {
-  if (is.discrete(limits)) {
-    n_discrete_limits <- length(limits)
-  } else {
-    n_discrete_limits <- 0
+  discrete_limits <- NULL
+  if (length(limits) > 0) {
+    if (is.discrete(limits)) {
+      discrete_limits <- c(1, length(limits)) # for backward compatibility
+    } else {
+      discrete_limits <- range(limits)
+    }
   }
 
   is_empty <- is.null(limits) && is.null(range_continuous)
-  is_only_continuous <- n_discrete_limits == 0
+  is_only_continuous <- is.null(discrete_limits)
   is_only_discrete <- is.null(range_continuous)
 
   if (is_empty) {
@@ -216,10 +219,10 @@ expand_limits_discrete_trans <- function(limits, expand = expansion(0, 0),
   } else if (is_only_continuous) {
     expand_limits_continuous_trans(range_continuous, expand, coord_limits, trans)
   } else if (is_only_discrete) {
-    expand_limits_continuous_trans(c(1, n_discrete_limits), expand, coord_limits, trans)
+    expand_limits_continuous_trans(discrete_limits, expand, coord_limits, trans)
   } else {
     # continuous and discrete
-    limit_info_discrete <- expand_limits_continuous_trans(c(1, n_discrete_limits), expand, coord_limits, trans)
+    limit_info_discrete <- expand_limits_continuous_trans(discrete_limits, expand, coord_limits, trans)
 
     # don't expand continuous range if there is also a discrete range
     limit_info_continuous <- expand_limits_continuous_trans(

From 47ce0ba0ed6a7a8c7aa038aa275c4757322ac7f7 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Tue, 12 Mar 2024 16:01:22 +0100
Subject: [PATCH 4/9] adjust test

---
 tests/testthat/test-scale-expansion.R | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/testthat/test-scale-expansion.R b/tests/testthat/test-scale-expansion.R
index 7d1b5b30ae..26d25abfdc 100644
--- a/tests/testthat/test-scale-expansion.R
+++ b/tests/testthat/test-scale-expansion.R
@@ -116,6 +116,6 @@ test_that("expand_limits_scale_discrete() begrudgingly handles numeric limits",
       coord_limits = c(NA, NA),
       range_continuous = c(-15, -2)
     ),
-    c(-15, -2)
+    c(-16, -1)
   )
 })

From d74f39daf25a0f8245945679001d73464b9b94b4 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Tue, 12 Mar 2024 16:16:28 +0100
Subject: [PATCH 5/9] add tests

---
 tests/testthat/test-scale-discrete.R | 42 ++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/tests/testthat/test-scale-discrete.R b/tests/testthat/test-scale-discrete.R
index d9ce98c494..cd8c2da933 100644
--- a/tests/testthat/test-scale-discrete.R
+++ b/tests/testthat/test-scale-discrete.R
@@ -162,3 +162,45 @@ test_that("mapped_discrete vectors behaves as predicted", {
   x[5:7] <- mapped_discrete(seq_len(3))
   expect_s3_class(x, "mapped_discrete")
 })
+
+# Palettes ----------------------------------------------------------------
+
+test_that("palettes work for discrete scales", {
+
+  df <- data.frame(x = c("A", "B", "C"), y = 1:3)
+  values <- c(1, 10, 100)
+
+  p <- ggplot(df, aes(x, y)) +
+    geom_point() +
+    scale_x_discrete(palette = function(x) values)
+
+  # Check limits are translated to correct values
+  ld <- layer_data(p)
+  expect_equal(ld$x, values, ignore_attr = TRUE)
+
+  # Check discsrete expansion is applied
+  b <- ggplot_build(p)
+  expect_equal(
+    b$layout$panel_params[[1]]$x.range,
+    range(values) + c(-0.6, 0.6)
+  )
+})
+
+test_that("invalid palettes trigger errors", {
+
+  df <- data.frame(x = c("A", "B", "C"), y = 1:3)
+
+  p <- ggplot(df, aes(x, y)) +
+    geom_point()
+
+  expect_error(
+    ggplot_build(p + scale_x_discrete(palette = function(x) LETTERS[1:3])),
+    "must return a .+ vector\\."
+  )
+
+  expect_error(
+    ggplot_build(p + scale_x_discrete(palette = function(x) 1:2)),
+    "must return at least 3 values"
+  )
+})
+

From 9e0e25d4239fc268b63949058228fc331862bc5c Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Fri, 22 Mar 2024 09:53:29 +0100
Subject: [PATCH 6/9] palettes take `n` just like other scales

---
 R/scale-discrete-.R | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/R/scale-discrete-.R b/R/scale-discrete-.R
index 8f36c22c00..d6dfdd7284 100644
--- a/R/scale-discrete-.R
+++ b/R/scale-discrete-.R
@@ -65,7 +65,7 @@
 #'   geom_point() +
 #'   scale_x_discrete(labels = abbreviate)
 #' }
-scale_x_discrete <- function(name = waiver(), ..., palette = seq_along,
+scale_x_discrete <- function(name = waiver(), ..., palette = seq_len,
                              expand = waiver(),
                              guide = waiver(), position = "bottom") {
   sc <- discrete_scale(
@@ -80,7 +80,7 @@ scale_x_discrete <- function(name = waiver(), ..., palette = seq_along,
 }
 #' @rdname scale_discrete
 #' @export
-scale_y_discrete <- function(name = waiver(), ..., palette = seq_along,
+scale_y_discrete <- function(name = waiver(), ..., palette = seq_len,
                              expand = waiver(),
                              guide = waiver(), position = "left") {
   sc <- discrete_scale(
@@ -138,7 +138,7 @@ ScaleDiscretePosition <- ggproto("ScaleDiscretePosition", ScaleDiscrete,
 
   map = function(self, x, limits = self$get_limits()) {
     if (is.discrete(x)) {
-      values <- self$palette(limits)
+      values <- self$palette(length(limits))
       if (!is.numeric(values)) {
         cli::cli_abort(
           "The {.arg palette} function must return a {.cls numeric} vector.",

From cf3b28a136ea9a12b59e09984c68fc2d7cd5f1fd Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Thu, 4 Apr 2024 09:48:12 +0200
Subject: [PATCH 7/9] reoxygenate

---
 man/scale_discrete.Rd | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/man/scale_discrete.Rd b/man/scale_discrete.Rd
index 4cd85a4fd6..02359d1f67 100644
--- a/man/scale_discrete.Rd
+++ b/man/scale_discrete.Rd
@@ -8,7 +8,7 @@
 scale_x_discrete(
   name = waiver(),
   ...,
-  palette = seq_along,
+  palette = seq_len,
   expand = waiver(),
   guide = waiver(),
   position = "bottom"
@@ -17,7 +17,7 @@ scale_x_discrete(
 scale_y_discrete(
   name = waiver(),
   ...,
-  palette = seq_along,
+  palette = seq_len,
   expand = waiver(),
   guide = waiver(),
   position = "left"

From f6fef113f83a843980da24867539d1441ffc2225 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Mon, 20 May 2024 13:05:45 +0200
Subject: [PATCH 8/9] rephrase palette arg

---
 R/scale-discrete-.R   | 5 +++--
 man/scale_discrete.Rd | 5 +++--
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/R/scale-discrete-.R b/R/scale-discrete-.R
index 684c549549..b957b97b97 100644
--- a/R/scale-discrete-.R
+++ b/R/scale-discrete-.R
@@ -12,8 +12,9 @@
 #'
 #' @inheritDotParams discrete_scale -scale_name
 #' @inheritParams discrete_scale
-#' @param palette A function that takes the limits as input and provides
-#'   numerical values as output.
+#' @param palette A palette function that when called with a single integer
+#'   argument (the number of levels in the scale) returns the numerical values
+#'   that they should take.
 #' @param sec.axis [dup_axis()] is used to specify a secondary axis.
 #' @rdname scale_discrete
 #' @family position scales
diff --git a/man/scale_discrete.Rd b/man/scale_discrete.Rd
index 8cb7f0644a..381c09254e 100644
--- a/man/scale_discrete.Rd
+++ b/man/scale_discrete.Rd
@@ -78,8 +78,9 @@ notation.
     \item{\code{super}}{The super class to use for the constructed scale}
   }}
 
-\item{palette}{A function that takes the limits as input and provides
-numerical values as output.}
+\item{palette}{A palette function that when called with a single integer
+argument (the number of levels in the scale) returns the numerical values
+that they should take.}
 
 \item{expand}{For position scales, a vector of range expansion constants used to add some
 padding around the data to ensure that they are placed some distance

From db0dfdc940612c2ebd9670bdcf7d083ee9144b67 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Mon, 20 May 2024 13:07:35 +0200
Subject: [PATCH 9/9] add news bullet

---
 NEWS.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/NEWS.md b/NEWS.md
index 633a46172b..4e8216504e 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,7 @@
 # ggplot2 (development version)
 
+* Discrete position scales now expose the `palette` argument, which can be used 
+  to customise spacings between levels (@teunbrand, #5770).
 * The default `se` parameter in layers with `geom = "smooth"` will be `TRUE` 
   when the data has `ymin` and `ymax` parameters and `FALSE` if these are 
   absent. Note that this does not affect the default of `geom_smooth()` or