From 1bb923099e5d44b21615431f07bb99894e7a7dfd Mon Sep 17 00:00:00 2001
From: Teun van den Brand <49372158+teunbrand@users.noreply.github.com>
Date: Mon, 2 Dec 2024 11:14:57 +0100
Subject: [PATCH] Scale palettes from theme (#5946)

* add palette theme elements

* set palettes

* expand options for numeric palettes

* backward compatibility for `options()` default scales

* use explicit scales in tests

* standard colour scales have `palette = NULL`

* document

* properly document this time

* misc fixes

* more palettes in theme

* use binned versions of discrete palettes for continuous linetype/shape

* Set default palettes to `NULL`

* tweak test to populate palettes

* try registered theme palettes

* document

* remove redundant call to `plot_theme()`

* simplify `fallback_palette()` args

* Put in shims for scales/#427

* Streamline `ScalesList$set_palettes()` method

* try to match first non-null aesthetic

* add news bullet
---
 NEWS.md                                       |   3 +
 R/geom-text.R                                 |   2 +-
 R/plot-build.R                                |   1 +
 R/scale-.R                                    |   1 +
 R/scale-alpha.R                               |  35 +--
 R/scale-colour.R                              | 216 ++++++++++--------
 R/scale-hue.R                                 |  57 ++---
 R/scale-linetype.R                            |   4 +-
 R/scale-linewidth.R                           |  35 +--
 R/scale-shape.R                               |   8 +-
 R/scale-size.R                                |  38 +--
 R/scales-.R                                   |  33 +++
 R/theme-elements.R                            |  15 ++
 R/utilities.R                                 |  62 ++++-
 man/geom_text.Rd                              |   2 +-
 man/scale_alpha.Rd                            |   8 +-
 man/scale_colour_continuous.Rd                |  45 +++-
 man/scale_colour_discrete.Rd                  |  20 +-
 man/scale_linewidth.Rd                        |   4 +-
 man/scale_shape.Rd                            |   2 +-
 man/scale_size.Rd                             |   4 +-
 .../_snaps/scale-colour-continuous.md         |   2 -
 tests/testthat/_snaps/scale-discrete.md       |   8 +-
 tests/testthat/test-guide-colorbar.R          |   2 +-
 tests/testthat/test-guide-legend.R            |  13 +-
 tests/testthat/test-scales.R                  |  24 ++
 26 files changed, 427 insertions(+), 217 deletions(-)

diff --git a/NEWS.md b/NEWS.md
index 36ab09933e..2bd655a5c1 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -215,6 +215,9 @@
 * Added `keep.zeroes` argument to `stat_bin()` (@teunbrand, #3449)
 * `coord_sf()` no longer errors when dealing with empty graticules (@teunbrand, #6052)
 * Added `theme_transparent()` with transparent backgrounds (@topepo).
+* New theme elements `palette.{aes}.discrete` and `palette.{aes}.continuous`. 
+  Theme palettes replace palettes in scales where `palette = NULL`, which is 
+  the new default in many scales (@teunbrand, #4696).
 
 # ggplot2 3.5.1
 
diff --git a/R/geom-text.R b/R/geom-text.R
index ed378734ba..78e601f8f9 100644
--- a/R/geom-text.R
+++ b/R/geom-text.R
@@ -95,7 +95,7 @@
 #' # Add aesthetic mappings
 #' p + geom_text(aes(colour = factor(cyl)))
 #' p + geom_text(aes(colour = factor(cyl))) +
-#'   scale_colour_discrete(l = 40)
+#'   scale_colour_hue(l = 40)
 #' p + geom_label(aes(fill = factor(cyl)), colour = "white", fontface = "bold")
 #'
 #' # Scale size of text, and change legend key glyph from a to point
diff --git a/R/plot-build.R b/R/plot-build.R
index 873f79a32c..b55c599198 100644
--- a/R/plot-build.R
+++ b/R/plot-build.R
@@ -106,6 +106,7 @@ ggplot_build.ggplot <- function(plot) {
   # Train and map non-position scales and guides
   npscales <- scales$non_position_scales()
   if (npscales$n() > 0) {
+    npscales$set_palettes(plot$theme)
     lapply(data, npscales$train_df)
     plot$guides <- plot$guides$build(npscales, plot$layers, plot$labels, data, plot$theme)
     data <- lapply(data, npscales$map_df)
diff --git a/R/scale-.R b/R/scale-.R
index 33752f9ec2..f345310e4b 100644
--- a/R/scale-.R
+++ b/R/scale-.R
@@ -528,6 +528,7 @@ Scale <- ggproto("Scale", NULL,
     if (empty(df)) {
       return()
     }
+    self$palette <- self$palette %||% fallback_palette(self)
 
     aesthetics <- intersect(self$aesthetics, names(df))
     names(aesthetics) <- aesthetics
diff --git a/R/scale-alpha.R b/R/scale-alpha.R
index 53344f23be..5e22937e88 100644
--- a/R/scale-alpha.R
+++ b/R/scale-alpha.R
@@ -31,8 +31,9 @@
 #'
 #' # Changing the title
 #' p + scale_alpha("cylinders")
-scale_alpha <- function(name = waiver(), ..., range = c(0.1, 1)) {
-  continuous_scale("alpha", name = name, palette = pal_rescale(range), ...)
+scale_alpha <- function(name = waiver(), ..., range = NULL) {
+  palette <- if (!is.null(range)) pal_rescale(range) else NULL
+  continuous_scale("alpha", name = name, palette = palette, ...)
 }
 
 #' @rdname scale_alpha
@@ -41,8 +42,9 @@ scale_alpha_continuous <- scale_alpha
 
 #' @rdname scale_alpha
 #' @export
-scale_alpha_binned <- function(name = waiver(), ..., range = c(0.1, 1)) {
-  binned_scale("alpha", name = name, palette = pal_rescale(range), ...)
+scale_alpha_binned <- function(name = waiver(), ..., range = NULL) {
+  palette <- if (!is.null(range)) pal_rescale(range) else NULL
+  binned_scale("alpha", name = name, palette = palette, ...)
 }
 
 #' @rdname scale_alpha
@@ -56,32 +58,33 @@ scale_alpha_discrete <- function(...) {
 
 #' @rdname scale_alpha
 #' @export
-scale_alpha_ordinal <- function(name = waiver(), ..., range = c(0.1, 1)) {
-  discrete_scale(
-    "alpha", name = name,
-    palette = function(n) seq(range[1], range[2], length.out = n),
-    ...
-  )
+scale_alpha_ordinal <- function(name = waiver(), ..., range = NULL) {
+  palette <- if (!is.null(range)) {
+    function(n) seq(range[1], range[2], length.out = n)
+  } else {
+    NULL
+  }
+  discrete_scale("alpha", name = name, palette = palette, ...)
 }
 
 #' @rdname scale_alpha
 #' @export
 #' @usage NULL
-scale_alpha_datetime <- function(name = waiver(), ..., range = c(0.1, 1)) {
+scale_alpha_datetime <- function(name = waiver(), ..., range = NULL) {
+  palette <- if (!is.null(range)) pal_rescale(range) else NULL
   datetime_scale(
     aesthetics = "alpha", transform = "time", name = name,
-    palette = pal_rescale(range),
-    ...
+    palette = palette, ...
   )
 }
 
 #' @rdname scale_alpha
 #' @export
 #' @usage NULL
-scale_alpha_date <- function(name = waiver(), ..., range = c(0.1, 1)){
+scale_alpha_date <- function(name = waiver(), ..., range = NULL){
+  palette <- if (!is.null(range)) pal_rescale(range) else NULL
   datetime_scale(
     aesthetics = "alpha", transform = "date", name = name,
-    palette = pal_rescale(range),
-    ...
+    palette = palette, ...
   )
 }
diff --git a/R/scale-colour.R b/R/scale-colour.R
index 19cdda1396..a17d872dbe 100644
--- a/R/scale-colour.R
+++ b/R/scale-colour.R
@@ -27,6 +27,7 @@
 #' you want to manually set the colors of a scale, consider using
 #' [scale_colour_gradient()] or [scale_colour_steps()].
 #'
+#' @inheritParams continuous_scale
 #' @param ... Additional parameters passed on to the scale type
 #' @param type One of the following:
 #'   * "gradient" (the default)
@@ -77,122 +78,81 @@
 #' v
 #' options(ggplot2.continuous.fill = tmp) # restore previous setting
 #' @export
-scale_colour_continuous <- function(...,
+scale_colour_continuous <- function(..., aesthetics = "colour",
+                                    guide = "colourbar", na.value = "grey50",
                                     type = getOption("ggplot2.continuous.colour")) {
-  type <- type %||% "gradient"
-  args <- list2(...)
-  args$call <- args$call %||% current_call()
 
-  if (is.function(type)) {
-    if (!any(c("...", "call") %in% fn_fmls_names(type))) {
-      args$call <- NULL
-    }
-    check_scale_type(exec(type, !!!args), "scale_colour_continuous", "colour")
-  } else if (identical(type, "gradient")) {
-    exec(scale_colour_gradient, !!!args)
-  } else if (identical(type, "viridis")) {
-    exec(scale_colour_viridis_c, !!!args)
-  } else {
-    cli::cli_abort(c(
-      "Unknown scale type: {.val {type}}",
-      "i" = "Use either {.val gradient} or {.val viridis}."
-    ))
+  if (!is.null(type)) {
+    scale <- scale_backward_compatibility(
+      ..., guide = guide, na.value = na.value, scale = type,
+      aesthetic = "colour", type = "continuous"
+    )
+    return(scale)
   }
+
+  continuous_scale(
+    aesthetics, palette = NULL, guide = guide, na.value = na.value,
+    ...
+  )
 }
 
 #' @rdname scale_colour_continuous
 #' @export
-scale_fill_continuous <- function(...,
+scale_fill_continuous <- function(..., aesthetics = "fill", guide = "colourbar",
+                                  na.value = "grey50",
                                   type = getOption("ggplot2.continuous.fill")) {
-  type <- type %||% "gradient"
-  args <- list2(...)
-  args$call <- args$call %||% current_call()
 
-  if (is.function(type)) {
-    if (!any(c("...", "call") %in% fn_fmls_names(type))) {
-      args$call <- NULL
-    }
-    check_scale_type(exec(type, !!!args), "scale_fill_continuous", "fill")
-  } else if (identical(type, "gradient")) {
-    exec(scale_fill_gradient, !!!args)
-  } else if (identical(type, "viridis")) {
-    exec(scale_fill_viridis_c, !!!args)
-  } else {
-    cli::cli_abort(c(
-      "Unknown scale type: {.val {type}}",
-      "i" = "Use either {.val gradient} or {.val viridis}."
-    ))
+  if (!is.null(type)) {
+    scale <- scale_backward_compatibility(
+      ..., guide = guide, na.value = na.value, scale = type,
+      aesthetic = "fill", type = "continuous"
+    )
+    return(scale)
   }
+
+  continuous_scale(
+    aesthetics, palette = NULL, guide = guide, na.value = na.value,
+    ...
+  )
 }
 
 #' @export
 #' @rdname scale_colour_continuous
-scale_colour_binned <- function(...,
+scale_colour_binned <- function(..., aesthetics = "colour", guide = "coloursteps",
+                                na.value = "grey50",
                                 type = getOption("ggplot2.binned.colour")) {
-  args <- list2(...)
-  args$call <- args$call %||% current_call()
-  if (is.function(type)) {
-    if (!any(c("...", "call") %in% fn_fmls_names(type))) {
-      args$call <- NULL
-    }
-    check_scale_type(exec(type, !!!args), "scale_colour_binned", "colour")
-  } else {
-    type_fallback <- getOption("ggplot2.continuous.colour", default = "gradient")
-    # don't use fallback from scale_colour_continuous() if it is
-    # a function, since that would change the type of the color
-    # scale from binned to continuous
-    if (is.function(type_fallback)) {
-      type_fallback <- "gradient"
-    }
-    type <- type %||% type_fallback
-
-    if (identical(type, "gradient")) {
-      exec(scale_colour_steps, !!!args)
-    } else if (identical(type, "viridis")) {
-      exec(scale_colour_viridis_b, !!!args)
-    } else {
-      cli::cli_abort(c(
-        "Unknown scale type: {.val {type}}",
-        "i" = "Use either {.val gradient} or {.val viridis}."
-      ))
-    }
+  if (!is.null(type)) {
+    scale <- scale_backward_compatibility(
+      ..., guide = guide, na.value = na.value, scale = type,
+      aesthetic = "colour", type = "binned"
+    )
+    return(scale)
   }
+
+  binned_scale(
+    aesthetics, palette = NULL, guide = guide, na.value = na.value,
+    ...
+  )
 }
 
 #' @export
 #' @rdname scale_colour_continuous
-scale_fill_binned <- function(...,
+scale_fill_binned <- function(..., aesthetics = "fill", guide = "coloursteps",
+                              na.value = "grey50",
                               type = getOption("ggplot2.binned.fill")) {
-  args <- list2(...)
-  args$call <- args$call %||% current_call()
-  if (is.function(type)) {
-    if (!any(c("...", "call") %in% fn_fmls_names(type))) {
-      args$call <- NULL
-    }
-    check_scale_type(exec(type, !!!args), "scale_fill_binned", "fill")
-  } else {
-    type_fallback <- getOption("ggplot2.continuous.fill", default = "gradient")
-    # don't use fallback from scale_colour_continuous() if it is
-    # a function, since that would change the type of the color
-    # scale from binned to continuous
-    if (is.function(type_fallback)) {
-      type_fallback <- "gradient"
-    }
-    type <- type %||% type_fallback
-
-    if (identical(type, "gradient")) {
-      exec(scale_fill_steps, !!!args)
-    } else if (identical(type, "viridis")) {
-      exec(scale_fill_viridis_b, !!!args)
-    } else {
-      cli::cli_abort(c(
-        "Unknown scale type: {.val {type}}",
-        "i" = "Use either {.val gradient} or {.val viridis}."
-      ))
-    }
+  if (!is.null(type)) {
+    scale <- scale_backward_compatibility(
+      ..., guide = guide, na.value = na.value, scale = type,
+      aesthetic = "fill", type = "binned"
+    )
+    return(scale)
   }
-}
 
+  binned_scale(
+    aesthetics, palette = NULL, guide = guide, na.value = na.value,
+    ...
+  )
+}
 
 # helper function to make sure that the provided scale is of the correct
 # type (i.e., is continuous and works with the provided aesthetic)
@@ -222,3 +182,73 @@ check_scale_type <- function(scale, name, aesthetic, scale_is_discrete = FALSE,
 
   scale
 }
+
+# helper function for backwards compatibility through setting defaults
+# scales through `options()` instead of `theme()`.
+scale_backward_compatibility <- function(..., scale, aesthetic, type) {
+  aesthetic <- standardise_aes_names(aesthetic[1])
+
+  args <- list2(...)
+  args$call <- args$call %||% caller_call() %||% current_call()
+
+  if (type == "binned") {
+    fallback <- getOption(
+      paste("ggplot2", type, aesthetic, sep = "."),
+      default = "gradient"
+    )
+    if (is.function(fallback)) {
+      fallback <- "gradient"
+    }
+    scale <- scale %||% fallback
+  }
+
+  if (is_bare_string(scale)) {
+    if (scale == "continuous") {
+      scale <- "gradient"
+    }
+    if (scale == "discrete") {
+      scale <- "hue"
+    }
+    if (scale == "viridis") {
+      scale <- switch(
+        type, discrete = "viridis_d", binned = "viridis_b", "viridis_c"
+      )
+    }
+
+    candidates <- paste("scale", aesthetic, scale, sep = "_")
+    for (candi in candidates) {
+      f <- find_global(candi, env = caller_env(), mode = "function")
+      if (!is.null(f)) {
+        scale <- f
+        break
+      }
+    }
+  }
+
+  if (!is.function(scale) && type == "discrete") {
+    args$type <- scale
+    scale <- switch(
+      aesthetic,
+      colour = scale_colour_qualitative,
+      fill   = scale_fill_qualitative
+    )
+  }
+
+  if (is.function(scale)) {
+    if (!any(c("...", "call") %in% fn_fmls_names(scale))) {
+      args$call <- NULL
+    }
+    if (!"..." %in% fn_fmls_names(scale)) {
+      args <- args[intersect(names(args), fn_fmls_names(scale))]
+    }
+    scale <- check_scale_type(
+      exec(scale, !!!args),
+      paste("scale", aesthetic, type, sep = "_"),
+      aesthetic,
+      scale_is_discrete = type == "discrete"
+    )
+    return(scale)
+  }
+
+  cli::cli_abort("Unknown scale type: {.val {scale}}")
+}
diff --git a/R/scale-hue.R b/R/scale-hue.R
index 414f10864e..b95938ceb6 100644
--- a/R/scale-hue.R
+++ b/R/scale-hue.R
@@ -86,6 +86,7 @@ scale_fill_hue <- function(name = waiver(), ..., h = c(0, 360) + 15, c = 100,
 #' is specified.
 #'
 #' @param ... Additional parameters passed on to the scale type,
+#' @inheritParams discrete_scale
 #' @param type One of the following:
 #'   * A character vector of color codes. The codes are used for a 'manual' color
 #'   scale as long as the number of codes exceeds the number of data levels
@@ -134,48 +135,36 @@ scale_fill_hue <- function(name = waiver(), ..., h = c(0, 360) + 15, c = 100,
 #'   print(cty_by_var(fl))
 #' })
 #'
-scale_colour_discrete <- function(..., type = getOption("ggplot2.discrete.colour")) {
-  # TODO: eventually `type` should default to a set of colour-blind safe color codes (e.g. Okabe-Ito)
-  type <- type %||% scale_colour_hue
-  args <- list2(...)
-  args$call <- args$call %||% current_call()
-
-  if (is.function(type)) {
-    if (!any(c("...", "call") %in% fn_fmls_names(type))) {
-      args$call <- NULL
-    }
-    check_scale_type(
-      exec(type, !!!args),
-      "scale_colour_discrete",
-      "colour",
-      scale_is_discrete = TRUE
+scale_colour_discrete <- function(..., aesthetics = "colour", na.value = "grey50",
+                                  type = getOption("ggplot2.discrete.colour")) {
+  if (!is.null(type)) {
+    scale <- scale_backward_compatibility(
+      ..., na.value = na.value, scale = type,
+      aesthetic = "colour", type = "discrete"
     )
-  } else {
-    exec(scale_colour_qualitative, !!!args, type = type)
+    return(scale)
   }
+  discrete_scale(
+    aesthetics, palette = NULL, na.value = na.value,
+    ...
+  )
 }
 
 #' @rdname scale_colour_discrete
 #' @export
-scale_fill_discrete <- function(..., type = getOption("ggplot2.discrete.fill")) {
-  # TODO: eventually `type` should default to a set of colour-blind safe color codes (e.g. Okabe-Ito)
-  type <- type %||% scale_fill_hue
-  args <- list2(...)
-  args$call <- args$call %||% current_call()
-
-  if (is.function(type)) {
-    if (!any(c("...", "call") %in% fn_fmls_names(type))) {
-      args$call <- NULL
-    }
-    check_scale_type(
-      exec(type, !!!args),
-      "scale_fill_discrete",
-      "fill",
-      scale_is_discrete = TRUE
+scale_fill_discrete <- function(..., aesthetics = "fill", na.value = "grey50",
+                                type = getOption("ggplot2.discrete.fill")) {
+  if (!is.null(type)) {
+    scale <- scale_backward_compatibility(
+      ..., na.value = na.value, scale = type,
+      aesthetic = "fill", type = "discrete"
     )
-  } else {
-    exec(scale_fill_qualitative, !!!args, type = type)
+    return(scale)
   }
+  discrete_scale(
+    aesthetics, palette = NULL, na.value = na.value,
+    ...
+  )
 }
 
 scale_colour_qualitative <- function(name = waiver(), ..., type = NULL,
diff --git a/R/scale-linetype.R b/R/scale-linetype.R
index d4ea6df26d..8f8c62e30e 100644
--- a/R/scale-linetype.R
+++ b/R/scale-linetype.R
@@ -38,7 +38,7 @@
 scale_linetype <- function(name = waiver(), ..., na.value = NA) {
   discrete_scale(
     "linetype", name = name,
-    palette = pal_linetype(),
+    palette = NULL,
     na.value = na.value,
     ...
   )
@@ -49,7 +49,7 @@ scale_linetype <- function(name = waiver(), ..., na.value = NA) {
 scale_linetype_binned <- function(name = waiver(), ..., na.value = NA) {
   binned_scale(
     "linetype", name = name,
-    palette = pal_binned(pal_linetype()),
+    palette = NULL,
     na.value = na.value,
     ...
   )
diff --git a/R/scale-linewidth.R b/R/scale-linewidth.R
index 801df22b3a..9bf05b3913 100644
--- a/R/scale-linewidth.R
+++ b/R/scale-linewidth.R
@@ -31,10 +31,11 @@ NULL
 #' @usage NULL
 scale_linewidth_continuous <- function(name = waiver(), breaks = waiver(),
                                        labels = waiver(), limits = NULL,
-                                       range = c(1, 6), transform = "identity",
+                                       range = NULL, transform = "identity",
                                        trans = deprecated(),
                                        guide = "legend") {
-  continuous_scale("linewidth", palette = pal_rescale(range), name = name,
+  palette <- if (!is.null(range)) pal_rescale(range) else NULL
+  continuous_scale("linewidth", palette = palette, name = name,
                    breaks = breaks, labels = labels, limits = limits,
                    transform = transform, trans = trans, guide = guide)
 }
@@ -46,10 +47,11 @@ scale_linewidth <- scale_linewidth_continuous
 #' @rdname scale_linewidth
 #' @export
 scale_linewidth_binned <- function(name = waiver(), breaks = waiver(), labels = waiver(),
-                              limits = NULL, range = c(1, 6), n.breaks = NULL,
+                              limits = NULL, range = NULL, n.breaks = NULL,
                               nice.breaks = TRUE, transform = "identity",
                               trans = deprecated(), guide = "bins") {
-  binned_scale("linewidth", palette = pal_rescale(range), name = name,
+  palette <- if (!is.null(range)) pal_rescale(range) else NULL
+  binned_scale("linewidth", palette = palette, name = name,
                breaks = breaks, labels = labels, limits = limits,
                transform = transform, trans = trans, n.breaks = n.breaks,
                nice.breaks = nice.breaks, guide = guide)
@@ -68,32 +70,33 @@ scale_linewidth_discrete <- function(...) {
 #' @rdname scale_linewidth
 #' @export
 #' @usage NULL
-scale_linewidth_ordinal <- function(name = waiver(), ..., range = c(2, 6)) {
-  force(range)
-
-  discrete_scale(
-    "linewidth", name = name,
-    palette = function(n) seq(range[1], range[2], length.out = n),
-    ...
-  )
+scale_linewidth_ordinal <- function(name = waiver(), ..., range = NULL) {
+  palette <- if (!is.null(range)) {
+    function(n) seq(range[1], range[2], length.out = n)
+  } else {
+    NULL
+  }
+  discrete_scale("linewidth", name = name, palette = palette, ...)
 }
 
 #' @rdname scale_linewidth
 #' @export
 #' @usage NULL
-scale_linewidth_datetime <- function(name = waiver(), ..., range = c(1, 6)) {
+scale_linewidth_datetime <- function(name = waiver(), ..., range = NULL) {
+  palette <- if (!is.null(range)) pal_rescale(range) else NULL
   datetime_scale(
     "linewidth", transform = "time", name = name,
-    palette = pal_rescale(range), ...
+    palette = palette, ...
   )
 }
 
 #' @rdname scale_linewidth
 #' @export
 #' @usage NULL
-scale_linewidth_date <- function(name = waiver(), ..., range = c(1, 6)) {
+scale_linewidth_date <- function(name = waiver(), ..., range = NULL) {
+  palette <- if (!is.null(range)) pal_rescale(range) else NULL
   datetime_scale(
     "linewidth", transform = "date", name = name,
-    palette = pal_rescale(range), ...
+    palette = palette, ...
   )
 }
diff --git a/R/scale-shape.R b/R/scale-shape.R
index ecb8a2a2a1..effa0a0b2f 100644
--- a/R/scale-shape.R
+++ b/R/scale-shape.R
@@ -42,14 +42,16 @@
 #'   scale_shape_identity() +
 #'   facet_wrap(~shape) +
 #'   theme_void()
-scale_shape <- function(name = waiver(), ..., solid = TRUE) {
-  discrete_scale("shape", name = name, palette = pal_shape(solid), ...)
+scale_shape <- function(name = waiver(), ..., solid = NULL) {
+  palette <- if (!is.null(solid)) pal_shape(solid) else NULL
+  discrete_scale("shape", name = name, palette = palette, ...)
 }
 
 #' @rdname scale_shape
 #' @export
 scale_shape_binned <- function(name = waiver(), ..., solid = TRUE) {
-  binned_scale("shape", name = name, palette = pal_binned(pal_shape(solid)), ...)
+  palette <- if (!is.null(solid)) pal_binned(pal_shape(solid)) else NULL
+  binned_scale("shape", name = name, palette = palette, ...)
 }
 
 #' @rdname scale_shape
diff --git a/R/scale-size.R b/R/scale-size.R
index 33f14d4834..525f378e15 100644
--- a/R/scale-size.R
+++ b/R/scale-size.R
@@ -52,11 +52,12 @@ NULL
 #' @export
 #' @usage NULL
 scale_size_continuous <- function(name = waiver(), breaks = waiver(), labels = waiver(),
-                                  limits = NULL, range = c(1, 6),
+                                  limits = NULL, range = NULL,
                                   transform = "identity",
                                   trans = deprecated(),
                                   guide = "legend") {
-  continuous_scale("size", palette = pal_area(range), name = name,
+  palette <- if (!is.null(range)) pal_area(range) else NULL
+  continuous_scale("size", palette = palette, name = name,
     breaks = breaks, labels = labels, limits = limits,
     transform = transform, trans = trans, guide = guide)
 }
@@ -79,10 +80,11 @@ scale_radius <- function(name = waiver(), breaks = waiver(), labels = waiver(),
 #' @rdname scale_size
 #' @export
 scale_size_binned <- function(name = waiver(), breaks = waiver(), labels = waiver(),
-                              limits = NULL, range = c(1, 6), n.breaks = NULL,
+                              limits = NULL, range = NULL, n.breaks = NULL,
                               nice.breaks = TRUE, transform = "identity",
                               trans = deprecated(), guide = "bins") {
-  binned_scale("size", palette = pal_area(range), name = name,
+  palette <- if (!is.null(range)) pal_area(range) else NULL
+  binned_scale("size", palette = palette, name = name,
                breaks = breaks, labels = labels, limits = limits,
                transform = transform, trans = trans, n.breaks = n.breaks,
                nice.breaks = nice.breaks, guide = guide)
@@ -101,17 +103,13 @@ scale_size_discrete <- function(...) {
 #' @rdname scale_size
 #' @export
 #' @usage NULL
-scale_size_ordinal <- function(name = waiver(), ..., range = c(2, 6)) {
-  force(range)
-
-  discrete_scale(
-    "size", name = name,
-    palette = function(n) {
-      area <- seq(range[1] ^ 2, range[2] ^ 2, length.out = n)
-      sqrt(area)
-    },
-    ...
-  )
+scale_size_ordinal <- function(name = waiver(), ..., range = NULL) {
+  palette <- if (!is.null(range)) {
+    function(n) sqrt(seq(range[1]^2, range[2]^2, length.out = n))
+  } else {
+    NULL
+  }
+  discrete_scale("size", name = name, palette = palette, ...)
 }
 
 #' @inheritDotParams continuous_scale -aesthetics -scale_name -palette -rescaler -expand -position
@@ -139,13 +137,15 @@ scale_size_binned_area <- function(name = waiver(), ..., max_size = 6) {
 #' @rdname scale_size
 #' @export
 #' @usage NULL
-scale_size_datetime <- function(name = waiver(), ..., range = c(1, 6)) {
-  datetime_scale("size", "time", name = name, palette = pal_area(range), ...)
+scale_size_datetime <- function(name = waiver(), ..., range = NULL) {
+  palette <- if (!is.null(range)) pal_area(range) else NULL
+  datetime_scale("size", "time", name = name, palette = palette, ...)
 }
 
 #' @rdname scale_size
 #' @export
 #' @usage NULL
-scale_size_date <- function(name = waiver(), ..., range = c(1, 6)) {
-  datetime_scale("size", "date", name = name, palette = pal_area(range), ...)
+scale_size_date <- function(name = waiver(), ..., range = NULL) {
+  palette <- if (!is.null(range)) pal_area(range) else NULL
+  datetime_scale("size", "date", name = name, palette = palette, ...)
 }
diff --git a/R/scales-.R b/R/scales-.R
index e62eb0e8cb..769613a2d8 100644
--- a/R/scales-.R
+++ b/R/scales-.R
@@ -168,6 +168,39 @@ ScalesList <- ggproto("ScalesList", NULL,
       scale_name <- paste("scale", aes, "continuous", sep = "_")
       self$add(find_global(scale_name, env, mode = "function")())
     }
+  },
+
+  set_palettes = function(self, theme) {
+    for (scale in self$scales) {
+      if (!is.null(scale$palette)) {
+        next
+      }
+
+      # Resolve palette theme setting for this scale
+      type <- if (scale$is_discrete()) "discrete" else "continuous"
+      elem <- paste0("palette.", scale$aesthetics, ".", type)
+      elem <- compact(lapply(elem, calc_element, theme))[1][[1]]
+
+      # Resolve the palette itself
+      elem <- elem %||% fallback_palette(scale)
+      palette <- switch(
+        type,
+        discrete   = as_discrete_pal(elem),
+        continuous = as_continuous_pal(elem)
+      )
+      if (!is.function(palette)) {
+        cli::cli_warn(
+          "Failed to find palette for {.field {scale$aesthetics[1]}} scale."
+        )
+      }
+
+      # Set palette to scale
+      # Note: while direct assignment is not ideal, we've already cloned the
+      # scale at the beginning of the plot build method, so it doesn't affect
+      # other plots
+      scale$palette <- palette
+      invisible()
+    }
   }
 )
 
diff --git a/R/theme-elements.R b/R/theme-elements.R
index fb3341bf49..c51134216f 100644
--- a/R/theme-elements.R
+++ b/R/theme-elements.R
@@ -666,6 +666,21 @@ el_def <- function(class = NULL, inherit = NULL, description = NULL) {
   plot.tag.location   = el_def("character"),
   plot.margin         = el_def(c("margin", "unit", "rel"), "margins"),
 
+  palette.colour.discrete   = el_def(c("character", "function")),
+  palette.colour.continuous = el_def(c("character", "function")),
+  palette.fill.discrete   = el_def(c("character", "function"), "palette.colour.discrete"),
+  palette.fill.continuous = el_def(c("character", "function"), "palette.colour.continuous"),
+  palette.alpha.discrete   = el_def(c("character", "numeric", "integer", "function")),
+  palette.alpha.continuous = el_def(c("character", "numeric", "integer", "function")),
+  palette.linewidth.discrete = el_def(c("character", "numeric", "integer", "function")),
+  palette.linewidth.continuous = el_def(c("character", "numeric", "integer", "function")),
+  palette.size.discrete = el_def(c("character", "numeric", "integer", "function")),
+  palette.size.continuous = el_def(c("character", "numeric", "integer", "function")),
+  palette.shape.discrete = el_def(c("character", "numeric", "integer", "function")),
+  palette.shape.continuous = el_def(c("character", "numeric", "integer", "function")),
+  palette.linetype.discrete = el_def(c("character", "numeric", "integer", "function")),
+  palette.linetype.continuous = el_def(c("character", "numeric", "integer", "function")),
+
   aspect.ratio        = el_def(c("numeric", "integer"))
 )
 
diff --git a/R/utilities.R b/R/utilities.R
index 039376f4df..cbb403da4e 100644
--- a/R/utilities.R
+++ b/R/utilities.R
@@ -781,6 +781,34 @@ as_unordered_factor <- function(x) {
   x
 }
 
+fallback_palette <- function(scale) {
+  aes <- scale$aesthetics[1]
+  discrete <- scale$is_discrete()
+  if (discrete) {
+    pal <- switch(
+      aes,
+      colour = , fill = pal_hue(),
+      alpha = function(n) seq(0.1, 1, length.out = n),
+      linewidth = function(n) seq(2, 6, length.out = n),
+      linetype = pal_linetype(),
+      shape = pal_shape(),
+      size = function(n) sqrt(seq(4, 36, length.out = n)),
+      ggplot_global$theme_default[[paste0("palette.", aes, ".discrete")]]
+    )
+    return(pal)
+  }
+  switch(
+    aes,
+    colour = , fill = pal_seq_gradient("#132B43", "#56B1F7"),
+    alpha = pal_rescale(c(0.1, 1)),
+    linewidth = pal_rescale(c(1, 6)),
+    linetype = pal_binned(pal_linetype()),
+    shape = pal_binned(pal_shape()),
+    size = pal_area(),
+    ggplot_global$theme_default[[paste0("palette.", aes, ".continuous")]]
+  )
+}
+
 warn_dots_used <- function(env = caller_env(), call = caller_env()) {
   check_dots_used(
     env = env, call = call,
@@ -793,6 +821,8 @@ warn_dots_used <- function(env = caller_env(), call = caller_env()) {
   )
 }
 
+# TODO: delete shims when {scales} releases >1.3.0.9000
+# and bump {scales} version requirements
 # Shim for scales/#424
 col_mix <- function(a, b, amount = 0.5) {
   input <- vec_recycle_common(a = a, b = b, amount = amount)
@@ -805,10 +835,40 @@ col_mix <- function(a, b, amount = 0.5) {
   )
 }
 
+# Shim for scales/#427
+as_discrete_pal <- function(x, ...) {
+  if (is.function(x)) {
+    return(x)
+  }
+  pal_manual(x)
+}
+
+# Shim for scales/#427
+as_continuous_pal <- function(x, ...) {
+  if (is.function(x)) {
+    return(x)
+  }
+  is_color <- grepl("^#(([[:xdigit:]]{2}){3,4}|([[:xdigit:]]){3,4})$", x) |
+    x %in% grDevices::colours()
+  if (all(is_color)) {
+    colour_ramp(x)
+  } else {
+    approxfun(seq(0, 1, length.out = length(x)), x)
+  }
+}
+
+# Replace shims by actual scales function when available
 on_load({
-  if ("col_mix" %in% getNamespaceExports("scales")) {
+  nse <- getNamespaceExports("scales")
+  if ("col_mix" %in% nse) {
     col_mix <- scales::col_mix
   }
+  if ("as_discrete_pal" %in% nse) {
+    as_discrete_pal <- scales::as_discrete_pal
+  }
+  if ("as_continuous_pal" %in% nse) {
+    as_continuous_pal <- scales::as_continuous_pal
+  }
 })
 
 # TODO: Replace me if rlang/#1730 gets implemented
diff --git a/man/geom_text.Rd b/man/geom_text.Rd
index 1b06e73ae1..e88e45a0e1 100644
--- a/man/geom_text.Rd
+++ b/man/geom_text.Rd
@@ -246,7 +246,7 @@ p +
 # Add aesthetic mappings
 p + geom_text(aes(colour = factor(cyl)))
 p + geom_text(aes(colour = factor(cyl))) +
-  scale_colour_discrete(l = 40)
+  scale_colour_hue(l = 40)
 p + geom_label(aes(fill = factor(cyl)), colour = "white", fontface = "bold")
 
 # Scale size of text, and change legend key glyph from a to point
diff --git a/man/scale_alpha.Rd b/man/scale_alpha.Rd
index 28defef0de..6833a08002 100644
--- a/man/scale_alpha.Rd
+++ b/man/scale_alpha.Rd
@@ -10,15 +10,15 @@
 \alias{scale_alpha_date}
 \title{Alpha transparency scales}
 \usage{
-scale_alpha(name = waiver(), ..., range = c(0.1, 1))
+scale_alpha(name = waiver(), ..., range = NULL)
 
-scale_alpha_continuous(name = waiver(), ..., range = c(0.1, 1))
+scale_alpha_continuous(name = waiver(), ..., range = NULL)
 
-scale_alpha_binned(name = waiver(), ..., range = c(0.1, 1))
+scale_alpha_binned(name = waiver(), ..., range = NULL)
 
 scale_alpha_discrete(...)
 
-scale_alpha_ordinal(name = waiver(), ..., range = c(0.1, 1))
+scale_alpha_ordinal(name = waiver(), ..., range = NULL)
 }
 \arguments{
 \item{name}{The name of the scale. Used as the axis or legend title. If
diff --git a/man/scale_colour_continuous.Rd b/man/scale_colour_continuous.Rd
index 36f3427746..d88a74f399 100644
--- a/man/scale_colour_continuous.Rd
+++ b/man/scale_colour_continuous.Rd
@@ -9,17 +9,48 @@
 \alias{scale_color_binned}
 \title{Continuous and binned colour scales}
 \usage{
-scale_colour_continuous(..., type = getOption("ggplot2.continuous.colour"))
-
-scale_fill_continuous(..., type = getOption("ggplot2.continuous.fill"))
-
-scale_colour_binned(..., type = getOption("ggplot2.binned.colour"))
-
-scale_fill_binned(..., type = getOption("ggplot2.binned.fill"))
+scale_colour_continuous(
+  ...,
+  aesthetics = "colour",
+  guide = "colourbar",
+  na.value = "grey50",
+  type = getOption("ggplot2.continuous.colour")
+)
+
+scale_fill_continuous(
+  ...,
+  aesthetics = "fill",
+  guide = "colourbar",
+  na.value = "grey50",
+  type = getOption("ggplot2.continuous.fill")
+)
+
+scale_colour_binned(
+  ...,
+  aesthetics = "colour",
+  guide = "coloursteps",
+  na.value = "grey50",
+  type = getOption("ggplot2.binned.colour")
+)
+
+scale_fill_binned(
+  ...,
+  aesthetics = "fill",
+  guide = "coloursteps",
+  na.value = "grey50",
+  type = getOption("ggplot2.binned.fill")
+)
 }
 \arguments{
 \item{...}{Additional parameters passed on to the scale type}
 
+\item{aesthetics}{The names of the aesthetics that this scale works with.}
+
+\item{guide}{A function used to create a guide or its name. See
+\code{\link[=guides]{guides()}} for more information.}
+
+\item{na.value}{Missing values will be replaced with this value.}
+
 \item{type}{One of the following:
 \itemize{
 \item "gradient" (the default)
diff --git a/man/scale_colour_discrete.Rd b/man/scale_colour_discrete.Rd
index 0c7883fb6e..ff8fe3f9e7 100644
--- a/man/scale_colour_discrete.Rd
+++ b/man/scale_colour_discrete.Rd
@@ -6,13 +6,29 @@
 \alias{scale_color_discrete}
 \title{Discrete colour scales}
 \usage{
-scale_colour_discrete(..., type = getOption("ggplot2.discrete.colour"))
+scale_colour_discrete(
+  ...,
+  aesthetics = "colour",
+  na.value = "grey50",
+  type = getOption("ggplot2.discrete.colour")
+)
 
-scale_fill_discrete(..., type = getOption("ggplot2.discrete.fill"))
+scale_fill_discrete(
+  ...,
+  aesthetics = "fill",
+  na.value = "grey50",
+  type = getOption("ggplot2.discrete.fill")
+)
 }
 \arguments{
 \item{...}{Additional parameters passed on to the scale type,}
 
+\item{aesthetics}{The names of the aesthetics that this scale works with.}
+
+\item{na.value}{If \code{na.translate = TRUE}, what aesthetic value should the
+missing values be displayed as? Does not apply to position scales
+where \code{NA} is always placed at the far right.}
+
 \item{type}{One of the following:
 \itemize{
 \item A character vector of color codes. The codes are used for a 'manual' color
diff --git a/man/scale_linewidth.Rd b/man/scale_linewidth.Rd
index 275f860582..5c9a842da9 100644
--- a/man/scale_linewidth.Rd
+++ b/man/scale_linewidth.Rd
@@ -15,7 +15,7 @@ scale_linewidth(
   breaks = waiver(),
   labels = waiver(),
   limits = NULL,
-  range = c(1, 6),
+  range = NULL,
   transform = "identity",
   trans = deprecated(),
   guide = "legend"
@@ -26,7 +26,7 @@ scale_linewidth_binned(
   breaks = waiver(),
   labels = waiver(),
   limits = NULL,
-  range = c(1, 6),
+  range = NULL,
   n.breaks = NULL,
   nice.breaks = TRUE,
   transform = "identity",
diff --git a/man/scale_shape.Rd b/man/scale_shape.Rd
index 8c8b8320fc..85b991fd9a 100644
--- a/man/scale_shape.Rd
+++ b/man/scale_shape.Rd
@@ -8,7 +8,7 @@
 \alias{scale_shape_continuous}
 \title{Scales for shapes, aka glyphs}
 \usage{
-scale_shape(name = waiver(), ..., solid = TRUE)
+scale_shape(name = waiver(), ..., solid = NULL)
 
 scale_shape_binned(name = waiver(), ..., solid = TRUE)
 }
diff --git a/man/scale_size.Rd b/man/scale_size.Rd
index 753ecfa790..2ba6a1e295 100644
--- a/man/scale_size.Rd
+++ b/man/scale_size.Rd
@@ -18,7 +18,7 @@ scale_size(
   breaks = waiver(),
   labels = waiver(),
   limits = NULL,
-  range = c(1, 6),
+  range = NULL,
   transform = "identity",
   trans = deprecated(),
   guide = "legend"
@@ -40,7 +40,7 @@ scale_size_binned(
   breaks = waiver(),
   labels = waiver(),
   limits = NULL,
-  range = c(1, 6),
+  range = NULL,
   n.breaks = NULL,
   nice.breaks = TRUE,
   transform = "identity",
diff --git a/tests/testthat/_snaps/scale-colour-continuous.md b/tests/testthat/_snaps/scale-colour-continuous.md
index a5410a8799..14d6e6a95d 100644
--- a/tests/testthat/_snaps/scale-colour-continuous.md
+++ b/tests/testthat/_snaps/scale-colour-continuous.md
@@ -21,10 +21,8 @@
 ---
 
     Unknown scale type: "abc"
-    i Use either "gradient" or "viridis".
 
 ---
 
     Unknown scale type: "abc"
-    i Use either "gradient" or "viridis".
 
diff --git a/tests/testthat/_snaps/scale-discrete.md b/tests/testthat/_snaps/scale-discrete.md
index a3251c4c4e..6a49fa9fdf 100644
--- a/tests/testthat/_snaps/scale-discrete.md
+++ b/tests/testthat/_snaps/scale-discrete.md
@@ -3,7 +3,7 @@
     Code
       scale_colour_discrete(type = scale_colour_gradient)
     Condition
-      Error in `scale_colour_discrete()`:
+      Error in `scale_backward_compatibility()`:
       ! The `type` argument must return a discrete scale for the colour aesthetic.
       x The provided scale is continuous.
 
@@ -12,7 +12,7 @@
     Code
       scale_fill_discrete(type = scale_fill_gradient)
     Condition
-      Error in `scale_fill_discrete()`:
+      Error in `scale_backward_compatibility()`:
       ! The `type` argument must return a discrete scale for the fill aesthetic.
       x The provided scale is continuous.
 
@@ -21,7 +21,7 @@
     Code
       scale_colour_discrete(type = scale_fill_hue)
     Condition
-      Error in `scale_colour_discrete()`:
+      Error in `scale_backward_compatibility()`:
       ! The `type` argument must return a continuous scale for the colour aesthetic.
       x The provided scale works with the following aesthetics: fill.
 
@@ -30,7 +30,7 @@
     Code
       scale_fill_discrete(type = scale_colour_hue)
     Condition
-      Error in `scale_fill_discrete()`:
+      Error in `scale_backward_compatibility()`:
       ! The `type` argument must return a continuous scale for the fill aesthetic.
       x The provided scale works with the following aesthetics: colour.
 
diff --git a/tests/testthat/test-guide-colorbar.R b/tests/testthat/test-guide-colorbar.R
index 9f44adb371..7cfd96a2f1 100644
--- a/tests/testthat/test-guide-colorbar.R
+++ b/tests/testthat/test-guide-colorbar.R
@@ -2,7 +2,7 @@ skip_on_cran() # This test suite is long-running (on cran) and is skipped
 
 test_that("colourbar trains without labels", {
   g <- guide_colorbar()
-  sc <- scale_colour_continuous(limits = c(0, 4), labels = NULL)
+  sc <- scale_colour_gradient(limits = c(0, 4), labels = NULL)
 
   out <- g$train(scale = sc)
   expect_named(out$key, c("colour", ".value"))
diff --git a/tests/testthat/test-guide-legend.R b/tests/testthat/test-guide-legend.R
index ff79bd7aa7..d4a47c145e 100644
--- a/tests/testthat/test-guide-legend.R
+++ b/tests/testthat/test-guide-legend.R
@@ -38,6 +38,7 @@ test_that("guide merging for guide_legend() works as expected", {
     scales <- scales_list()
     scales$add(scale1)
     scales$add(scale2)
+    scales$set_palettes(NULL)
     scales <- scales$scales
 
     aesthetics <- lapply(scales, `[[`, "aesthetics")
@@ -52,34 +53,34 @@ test_that("guide merging for guide_legend() works as expected", {
   }
 
   different_limits <- merge_test_guides(
-    scale_colour_discrete(limits = c("a", "b", "c", "d")),
+    scale_colour_hue(limits = c("a", "b", "c", "d")),
     scale_linetype_discrete(limits = c("a", "b", "c"))
   )
   expect_length(different_limits, 2)
 
   same_limits <- merge_test_guides(
-    scale_colour_discrete(limits = c("a", "b", "c")),
+    scale_colour_hue(limits = c("a", "b", "c")),
     scale_linetype_discrete(limits = c("a", "b", "c"))
   )
   expect_length(same_limits, 1)
   expect_equal(same_limits[[1]]$key$.label, c("a", "b", "c"))
 
   same_labels_different_limits <- merge_test_guides(
-    scale_colour_discrete(limits = c("a", "b", "c")),
+    scale_colour_hue(limits = c("a", "b", "c")),
     scale_linetype_discrete(limits = c("one", "two", "three"), labels = c("a", "b", "c"))
   )
   expect_length(same_labels_different_limits, 1)
   expect_equal(same_labels_different_limits[[1]]$key$.label, c("a", "b", "c"))
 
   same_labels_different_scale <- merge_test_guides(
-    scale_colour_continuous(limits = c(0, 4), breaks = 1:3, labels = c("a", "b", "c")),
+    scale_colour_gradient(limits = c(0, 4), breaks = 1:3, labels = c("a", "b", "c")),
     scale_linetype_discrete(limits = c("a", "b", "c"))
   )
   expect_length(same_labels_different_scale, 1)
   expect_equal(same_labels_different_scale[[1]]$key$.label, c("a", "b", "c"))
 
   repeated_identical_labels <- merge_test_guides(
-    scale_colour_discrete(limits = c("one", "two", "three"), labels = c("label1", "label1", "label2")),
+    scale_colour_hue(limits = c("one", "two", "three"), labels = c("label1", "label1", "label2")),
     scale_linetype_discrete(limits = c("1", "2", "3"), labels = c("label1", "label1", "label2"))
   )
   expect_length(repeated_identical_labels, 1)
@@ -99,7 +100,7 @@ test_that("size = NA doesn't throw rendering errors", {
 
 test_that("legend reverse argument reverses the key", {
 
-  scale <- scale_colour_discrete()
+  scale <- scale_colour_hue()
   scale$train(LETTERS[1:4])
 
   guides <- guides_list(NULL)
diff --git a/tests/testthat/test-scales.R b/tests/testthat/test-scales.R
index d9286b513f..514cb392a3 100644
--- a/tests/testthat/test-scales.R
+++ b/tests/testthat/test-scales.R
@@ -734,6 +734,30 @@ test_that("continuous scales warn about faulty `limits`", {
   expect_snapshot(scale_x_continuous(limits = 1:3), error = TRUE)
 })
 
+test_that("populating palettes works", {
+
+  scl <- scales_list()
+  scl$add(scale_colour_discrete(aesthetics = c("colour", "fill")))
+
+  my_theme <- theme(
+    palette.colour.discrete = c("white", "black"),
+    palette.fill.discrete = c("red", "blue")
+  )
+
+  scl$set_palettes(my_theme)
+  expect_equal(scl$scales[[1]]$palette(2), c("white", "black"))
+
+  # Scales with >1 aesthetic
+  scl <- scales_list()
+  scl$add(scale_colour_discrete(aesthetics = c("colour", "fill")))
+
+  my_theme$palette.colour.discrete <- NULL
+
+  scl$set_palettes(my_theme)
+  expect_equal(scl$scales[[1]]$palette(2), c("red", "blue"))
+
+})
+
 test_that("discrete scales work with NAs in arbitrary positions", {
   # Prevents intermediate caching of palettes
   map <- function(x, limits) {