From 25d5532ba36001b82ea341c48e477a2dcd90f10a Mon Sep 17 00:00:00 2001
From: Teun van den Brand <49372158+teunbrand@users.noreply.github.com>
Date: Tue, 7 Nov 2023 17:27:12 +0100
Subject: [PATCH 01/19] remove element mechanism from guide constructor

---
 R/guide-.R | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/R/guide-.R b/R/guide-.R
index bdf360db8e..c722bbaf1d 100644
--- a/R/guide-.R
+++ b/R/guide-.R
@@ -25,13 +25,8 @@ new_guide <- function(..., available_aes = "any", super) {
   params <- intersect(names(args), param_names)
   params <- defaults(args[params], super$params)
 
-  # Set elements
-  elems_names <- names(super$elements)
-  elems  <- intersect(names(args), elems_names)
-  elems  <- defaults(args[elems], super$elements)
-
   # Warn about extra arguments
-  extra_args <- setdiff(names(args), union(param_names, elems_names))
+  extra_args <- setdiff(names(args), param_names)
   if (length(extra_args) > 0) {
     cli::cli_warn(paste0(
       "Ignoring unknown {cli::qty(extra_args)} argument{?s} to ",
@@ -56,8 +51,7 @@ new_guide <- function(..., available_aes = "any", super) {
 
   ggproto(
     NULL, super,
-    params   = params,
-    elements = elems,
+    params = params,
     available_aes = available_aes
   )
 }

From 8be1ab5e8007885f5a8bbba9f8095d69d04fb53e Mon Sep 17 00:00:00 2001
From: Teun van den Brand <49372158+teunbrand@users.noreply.github.com>
Date: Tue, 7 Nov 2023 17:29:18 +0100
Subject: [PATCH 02/19] cleanup legend code

---
 R/guide-legend.R | 107 +++++++++++++++++++----------------------------
 1 file changed, 44 insertions(+), 63 deletions(-)

diff --git a/R/guide-legend.R b/R/guide-legend.R
index 341bee47c8..dd0315336d 100644
--- a/R/guide-legend.R
+++ b/R/guide-legend.R
@@ -168,25 +168,32 @@ guide_legend <- function(
   if (!is.null(label.position)) {
     label.position <- arg_match0(label.position, .trbl)
   }
+  label.theme <- if (!isFALSE(label)) label.theme else element_blank()
+
+  internal_theme <- theme(
+    legend.text = combine_elements(
+      label.theme,
+      element_text(hjust = label.hjust, vjust = label.vjust, inherit.blank = TRUE)
+    ),
+    legend.title = combine_elements(
+      title.theme,
+      element_text(hjust = title.hjust, vjust = title.vjust, inherit.blank = TRUE)
+    ),
+    legend.key.width  = keywidth,
+    legend.key.height = keyheight,
+    legend.direction  = direction
+  )
 
   new_guide(
     # Title
     title = title,
     title.position = title.position,
-    title.theme = title.theme,
-    title.hjust = title.hjust,
-    title.vjust = title.vjust,
 
     # Label
-    label = label,
     label.position = label.position,
-    label.theme = label.theme,
-    label.hjust = label.hjust,
-    label.vjust = label.vjust,
 
-    # Key size
-    keywidth  = keywidth,
-    keyheight = keyheight,
+    # Theme
+    internal_theme = internal_theme,
 
     # General
     direction = direction,
@@ -214,21 +221,12 @@ GuideLegend <- ggproto(
   params = list(
     title = waiver(),
     title.position = NULL,
-    title.theme = NULL,
-    title.hjust = NULL,
-    title.vjust = NULL,
 
-    label = TRUE,
     label.position = NULL,
-    label.theme = NULL,
-    label.hjust = NULL,
-    label.vjust = NULL,
 
-    keywidth  = NULL,
-    keyheight = NULL,
+    internal_theme = NULL,
 
     # General
-    direction = NULL,
     override.aes = list(),
     nrow = NULL,
     ncol = NULL,
@@ -256,7 +254,7 @@ GuideLegend <- ggproto(
     key.height  = "legend.key.height",
     key.width   = "legend.key.width",
     text        = "legend.text",
-    theme.title = "legend.title"
+    title       = "legend.title"
   ),
 
   extract_params = function(scale, params,
@@ -390,50 +388,25 @@ GuideLegend <- ggproto(
     params
   },
 
-  override_elements = function(params, elements, theme) {
+  setup_elements = function(params, elements, theme) {
+    default_just <- legend_label_just(params$label.position)
 
-    # Title
-    title <- combine_elements(params$title.theme, elements$theme.title)
-    title$hjust <- params$title.hjust %||% title$hjust %||% 0
-    title$vjust <- params$title.vjust %||% title$vjust %||% 0.5
-    elements$title <- title
-
-    # Labels
-    if (!is.null(elements$text)) {
-      label <- combine_elements(params$label.theme, elements$text)
-      if (!params$label || is.null(params$key$.label)) {
-        label <- element_blank()
-      } else {
-        hjust <- unname(label_hjust_defaults[params$label.position])
-        vjust <- unname(label_vjust_defaults[params$label.position])
-        # Expressions default to right-justified
-        if (hjust == 0 && any(is.expression(params$key$.label))) {
-          hjust <- 1
-        }
-        # Breaking justification inheritance for intuition purposes.
-        if (is.null(params$label.theme$hjust) &&
-            is.null(theme$legend.text$hjust)) {
-          label$hjust <- NULL
-        }
-        if (is.null(params$label.theme$vjust) &&
-            is.null(theme$legend.text$vjust)) {
-          label$vjust <- NULL
-        }
-        label$hjust <- params$label.hjust %||% label$hjust %||% hjust
-        label$vjust <- params$label.vjust %||% label$vjust %||% vjust
-      }
-      elements$text <- label
-    }
+    # We break inheritance of text justification for intuition purposes
+    theme$legend.text$hjust <- theme$legend.text$hjust %||% default_just[1]
+    theme$legend.text$vjust <- theme$legend.text$vjust %||% default_just[2]
 
-    # Keys
-    if (any(c("key.width", "key.height") %in% names(elements))) {
-      elements$key.width  <- width_cm( params$keywidth  %||% elements$key.width)
-      elements$key.height <- height_cm(params$keyheight %||% elements$key.height)
-    }
+    theme <- theme + compact(params$internal_theme)
+
+    Guide$setup_elements(params, elements, theme)
+  },
+
+  override_elements = function(params, elements, theme) {
+
+    elements$key.width  <- width_cm(elements$key.width)
+    elements$key.height <- height_cm(elements$key.height)
 
     # Spacing
-    gap <- title$size %||% elements$theme.title$size %||%
-      elements$text$size %||% 11
+    gap <- elements$title$size %||% elements$text$size %||% 11
     gap <- unit(gap * 0.5, "pt")
     # Should maybe be elements$spacing.{x/y} instead of the theme's spacing?
     elements$hgap <- width_cm( theme$legend.spacing.x %||% gap)
@@ -725,8 +698,16 @@ GuideLegend <- ggproto(
   }
 )
 
-label_hjust_defaults <- c(top = 0.5, bottom = 0.5, left = 1,   right = 0)
-label_vjust_defaults <- c(top = 0,   bottom = 1,   left = 0.5, right = 0.5)
+legend_label_just <- function(position) {
+  default_just <- switch(
+    position,
+    top    = c(0.5, 0),
+    bottom = c(0.5, 0),
+    left   = c(1, 0.5),
+    right  = c(0, 0.5),
+    arg_match0(position, .trbl, arg = "label.position")
+  )
+}
 
 measure_legend_keys <- function(decor, n, dim, byrow = FALSE,
                                 default_width = 1, default_height = 1) {

From aa15ae3e09c07824a511dbfbbecb20830eff1f03 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <49372158+teunbrand@users.noreply.github.com>
Date: Tue, 7 Nov 2023 17:36:14 +0100
Subject: [PATCH 03/19] cleanup colourbar code

---
 R/guide-colorbar.R | 71 +++++++++++++++++++++++-----------------------
 1 file changed, 35 insertions(+), 36 deletions(-)

diff --git a/R/guide-colorbar.R b/R/guide-colorbar.R
index 7e71eaba0c..690fe4ed01 100644
--- a/R/guide-colorbar.R
+++ b/R/guide-colorbar.R
@@ -205,6 +205,25 @@ guide_colourbar <- function(
     ticks$linewidth <- ticks.linewidth %||% ticks$linewidth %||% (0.5 / .pt)
   }
 
+  label.theme <- if (!isFALSE(label)) label.theme else element_blank()
+
+  internal_theme <- theme(
+    legend.text = combine_elements(
+      label.theme,
+      element_text(hjust = label.hjust, vjust = label.vjust)
+    ),
+    legend.title = combine_elements(
+      title.theme,
+      element_text(hjust = title.hjust, vjust = title.vjust)
+    ),
+    legend.key.width  = barwidth,
+    legend.key.height = barheight,
+    legend.direction  = direction,
+    frame = frame,
+    ticks = ticks,
+    ticks.length = ticks.length
+  )
+
   # Trick to re-use this constructor in `guide_coloursteps()`.
   args  <- list2(...)
   super <- args$super %||% GuideColourbar
@@ -214,29 +233,14 @@ guide_colourbar <- function(
     # title
     title = title,
     title.position = title.position,
-    title.theme = title.theme,
-    title.hjust = title.hjust,
-    title.vjust = title.vjust,
-
-    # label
-    label = label,
     label.position = label.position,
-    label.theme = label.theme,
-    label.hjust = label.hjust,
-    label.vjust = label.vjust,
+
+    # theme
+    internal_theme = internal_theme,
 
     # bar
-    keywidth = barwidth,
-    keyheight = barheight,
     nbin = nbin,
     raster = raster,
-
-    # frame
-    frame = frame,
-
-    # ticks
-    ticks = ticks,
-    ticks_length = ticks.length,
     draw_lim = c(isTRUE(draw.llim), isTRUE(draw.ulim)),
 
     # general
@@ -267,20 +271,10 @@ GuideColourbar <- ggproto(
     # title
     title = waiver(),
     title.position = NULL,
-    title.theme = NULL,
-    title.hjust = NULL,
-    title.vjust = NULL,
-
-    # label
-    label = TRUE,
     label.position = NULL,
-    label.theme = NULL,
-    label.hjust = NULL,
-    label.vjust = NULL,
 
     # bar
-    keywidth  = NULL,
-    keyheight = NULL,
+    internal_theme = NULL,
     nbin = 300,
     raster = TRUE,
 
@@ -314,7 +308,7 @@ GuideColourbar <- ggproto(
     key.height  = "legend.key.height",
     key.width   = "legend.key.width",
     text        = "legend.text",
-    theme.title = "legend.title"
+    title       = "legend.title"
   ),
 
   extract_key = function(scale, aesthetic, ...) {
@@ -395,15 +389,20 @@ GuideColourbar <- ggproto(
     params
   },
 
-  override_elements = function(params, elements, theme) {
-    # These key sizes are the defaults, the GuideLegend method may overrule this
+  setup_elements = function(params, elements, theme) {
+    # Key sizes are already calculated before `Guides$draw()`
     if (params$direction == "horizontal") {
-      elements$key.width <- elements$key.width * 5
+      theme$legend.key.width  <- theme$legend.key.width * 5
     } else {
-      elements$key.height <- elements$key.height * 5
+      theme$legend.key.height <- theme$legend.key.height * 5
     }
-    elements$ticks <- combine_elements(elements$ticks, theme$line)
-    elements$frame <- combine_elements(elements$frame, theme$rect)
+    GuideLegend$setup_elements(params, elements, theme)
+  },
+
+  override_elements = function(params, elements, theme) {
+    itheme <- params$internal_theme
+    elements$ticks <- combine_elements(itheme$ticks, elements$ticks)
+    elements$frame <- combine_elements(itheme$frame, elements$frame)
     GuideLegend$override_elements(params, elements, theme)
   },
 

From d363f10387b02c7525b8a4089016159beb2731d7 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <49372158+teunbrand@users.noreply.github.com>
Date: Tue, 7 Nov 2023 17:40:43 +0100
Subject: [PATCH 04/19] cleanup guide_bins code

---
 R/guide-bins.R | 68 +++++++++++++++++++++-----------------------------
 1 file changed, 28 insertions(+), 40 deletions(-)

diff --git a/R/guide-bins.R b/R/guide-bins.R
index f20adee759..fb7cea567d 100644
--- a/R/guide-bins.R
+++ b/R/guide-bins.R
@@ -144,29 +144,33 @@ guide_bins <- function(
     ticks$arrow <- NULL
   }
 
+  label.theme <- if (!isFALSE(label)) label.theme else element_blank()
+
+  internal_theme <- theme(
+    legend.text = combine_elements(
+      label.theme,
+      element_text(hjust = label.hjust, vjust = label.vjust)
+    ),
+    legend.title = combine_elements(
+      title.theme,
+      element_text(hjust = title.hjust, vjust = title.vjust)
+    ),
+    legend.key.width  = keywidth,
+    legend.key.height = keyheight,
+    legend.direction  = direction,
+    axis_line  = axis,
+    ticks     = ticks,
+    ticks_length = ticks.length
+  )
+
   new_guide(
     # title
     title = title,
     title.position = title.position,
-    title.theme = title.theme,
-    title.hjust = title.hjust,
-    title.vjust = title.vjust,
-
-    # label
-    label = label,
     label.position = label.position,
-    label.theme = label.theme,
-    label.hjust = label.hjust,
-    label.vjust = label.vjust,
-
-    # key
-    keywidth  = keywidth,
-    keyheight = keyheight,
 
-    # ticks
-    line  = axis,
-    ticks = ticks,
-    ticks_length = ticks.length,
+    # theme
+    internal_theme = internal_theme,
 
     # general
     direction = direction,
@@ -193,20 +197,11 @@ GuideBins <- ggproto(
   params = list(
     title = waiver(),
     title.position = NULL,
-    title.theme = NULL,
-    title.hjust = NULL,
-    title.vjust = NULL,
-
-    label = TRUE,
     label.position = NULL,
-    label.theme = NULL,
-    label.hjust = NULL,
-    label.vjust = NULL,
 
-    keywidth  = NULL,
-    keyheight = NULL,
+    internal_theme = NULL,
 
-    direction = NULL,
+    # direction = NULL,
     override.aes = list(),
     reverse = FALSE,
     order = 0,
@@ -221,8 +216,8 @@ GuideBins <- ggproto(
   elements = c(
     GuideLegend$elements,
     list(
-      line  = "line",
-      ticks = "line",
+      axis_line = "line",
+      ticks     = "line",
       ticks_length = unit(0.2, "npc")
     )
   ),
@@ -329,8 +324,9 @@ GuideBins <- ggproto(
   },
 
   override_elements = function(params, elements, theme) {
-    elements$ticks <- combine_elements(elements$ticks, theme$line)
-    elements$line  <- combine_elements(elements$line,  theme$line)
+    itheme <- params$internal_theme
+    elements$ticks <- combine_elements(itheme$ticks, elements$ticks)
+    elements$line  <- combine_elements(itheme$axis_line, elements$axis_line)
     GuideLegend$override_elements(params, elements, theme)
   },
 
@@ -341,13 +337,6 @@ GuideBins <- ggproto(
     }
     key$.label[c(1, n_labels)[!params$show.limits]] <- ""
 
-    just <- switch(
-      params$direction,
-      horizontal = elements$text$vjust,
-      vertical   = elements$text$hjust,
-      0.5
-    )
-
     if (params$direction == "vertical") {
       key$.value <- 1 - key$.value
     }
@@ -356,7 +345,6 @@ GuideBins <- ggproto(
       elements$text,
       label = key$.label,
       x = unit(key$.value, "npc"),
-      y = rep(just, nrow(key)),
       margin_x = FALSE,
       margin_y = TRUE,
       flip = params$direction == "vertical"

From d2a99772c885fc85b3468a40cc8625ce0fd89485 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <49372158+teunbrand@users.noreply.github.com>
Date: Wed, 8 Nov 2023 10:02:35 +0100
Subject: [PATCH 05/19] utility function for common pattern

---
 R/utilities-grid.R | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/R/utilities-grid.R b/R/utilities-grid.R
index 389dad3eea..72ccfddf33 100644
--- a/R/utilities-grid.R
+++ b/R/utilities-grid.R
@@ -35,3 +35,10 @@ height_cm <- function(x) {
     cli::cli_abort("Don't know how to get height of {.cls {class(x)}} object")
   }
 }
+
+set_default_unit <- function(x, default.unit) {
+  if (is.null(x) || is.unit(x)) {
+    return(x)
+  }
+  unit(x, default.unit)
+}

From c46fb12115c6cc1096a7e2b650e16c9cae81fee6 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <49372158+teunbrand@users.noreply.github.com>
Date: Wed, 8 Nov 2023 10:32:46 +0100
Subject: [PATCH 06/19] Add logic for merging themes

---
 R/guide-.R       |  1 +
 R/guide-legend.R |  4 +---
 R/theme.R        | 22 ++++++++++++++++++++++
 3 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/R/guide-.R b/R/guide-.R
index c722bbaf1d..76b975e17b 100644
--- a/R/guide-.R
+++ b/R/guide-.R
@@ -268,6 +268,7 @@ Guide <- ggproto(
   # Converts the `elements` field to proper elements to be accepted by
   # `element_grob()`. String-interpolates aesthetic/position dependent elements.
   setup_elements = function(params, elements, theme) {
+    theme <- add_theme_preserve_blank(theme, params$internal_theme)
     is_char  <- vapply(elements, is.character, logical(1))
     elements[is_char] <- lapply(elements[is_char], calc_element, theme = theme)
     elements
diff --git a/R/guide-legend.R b/R/guide-legend.R
index dd0315336d..79dd80743d 100644
--- a/R/guide-legend.R
+++ b/R/guide-legend.R
@@ -389,14 +389,12 @@ GuideLegend <- ggproto(
   },
 
   setup_elements = function(params, elements, theme) {
-    default_just <- legend_label_just(params$label.position)
 
     # We break inheritance of text justification for intuition purposes
+    default_just <- legend_label_just(params$label.position)
     theme$legend.text$hjust <- theme$legend.text$hjust %||% default_just[1]
     theme$legend.text$vjust <- theme$legend.text$vjust %||% default_just[2]
 
-    theme <- theme + compact(params$internal_theme)
-
     Guide$setup_elements(params, elements, theme)
   },
 
diff --git a/R/theme.R b/R/theme.R
index e07fd29214..32ecc1edb2 100644
--- a/R/theme.R
+++ b/R/theme.R
@@ -560,6 +560,28 @@ add_theme <- function(t1, t2, t2name, call = caller_env()) {
   t1
 }
 
+# Calls `add_theme()`, but drops the elements of the new theme that inherit
+# blank and that are blank in the old theme.
+add_theme_preserve_blank <- function(old, new, new_name = caller_arg(new)) {
+  if (is.null(new)) {
+    return(old)
+  }
+  # Get non empty names of new theme
+  nms <- names(new)[!vapply(new, is.null, logical(1))]
+
+  # Does any of the new theme elements carry over blank elements?
+  inherit_blank <- vapply(
+    new[nms], FUN.VALUE = logical(1),
+    function(x) is.list(x) && isTRUE(x$inherit.blank)
+  )
+  # Are their equivalents in the old theme blank?
+  is_blank <- vapply(old[nms], inherits, logical(1), what = "element_blank")
+
+  # Only merge in elements that shouldn't become blank
+  new[] <- new[!(inherit_blank & is_blank)]
+  add_theme(old, new, t2name = new_name)
+}
+
 
 #' Calculate the element properties, by inheriting properties from its parents
 #'

From 53da3f625cf69b15e874595e1270a942d3abe6a9 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <49372158+teunbrand@users.noreply.github.com>
Date: Wed, 8 Nov 2023 10:37:07 +0100
Subject: [PATCH 07/19] More cleanup

---
 R/guide-bins.R     | 47 ++++++++++++++++++----------------------------
 R/guide-colorbar.R | 39 +++++++++++++++-----------------------
 R/guide-legend.R   | 31 ++++++++++++------------------
 3 files changed, 45 insertions(+), 72 deletions(-)

diff --git a/R/guide-bins.R b/R/guide-bins.R
index fb7cea567d..71a938cf8e 100644
--- a/R/guide-bins.R
+++ b/R/guide-bins.R
@@ -108,16 +108,6 @@ guide_bins <- function(
   show.limits  = NULL,
   ...
 ) {
-
-  if (!(is.null(keywidth) || is.unit(keywidth))) {
-    keywidth <- unit(keywidth, default.unit)
-  }
-  if (!(is.null(keyheight) || is.unit(keyheight))) {
-    keyheight <- unit(keyheight, default.unit)
-  }
-  if (!is.unit(ticks.length)) {
-    ticks.length <- unit(ticks.length, default.unit)
-  }
   if (!is.null(title.position)) {
     title.position <- arg_match0(title.position, .trbl)
   }
@@ -127,13 +117,12 @@ guide_bins <- function(
   if (!is.null(label.position)) {
     label.position <- arg_match0(label.position, .trbl)
   }
-
   if (is.logical(axis)) {
-    axis <- if (axis) element_line() else element_rect()
+    axis <- if (!isFALSE(axis)) element_line() else element_blank()
   }
   if (inherits(axis, "element_line")) {
-    axis$colour    <- axis.colour    %||% axis$colour      %||% "black"
-    axis$linewidth <- axis.linewidth %||% axis$linewidth   %||% (0.5 / .pt)
+    axis$colour    <- axis.colour    %||% axis$colour    %||% "black"
+    axis$linewidth <- axis.linewidth %||% axis$linewidth %||% (0.5 / .pt)
     axis$arrow     <- axis.arrow     %||% axis$arrow
   } else {
     axis <- element_blank()
@@ -145,22 +134,23 @@ guide_bins <- function(
   }
 
   label.theme <- if (!isFALSE(label)) label.theme else element_blank()
+  label.theme <- combine_elements(
+    label.theme,
+    element_text(hjust = label.hjust, vjust = label.vjust, inherit.blank = TRUE)
+  )
+  title.theme <- combine_elements(
+    title.theme,
+    element_text(hjust = title.hjust, vjust = title.vjust, inherit.blank = TRUE)
+  )
 
   internal_theme <- theme(
-    legend.text = combine_elements(
-      label.theme,
-      element_text(hjust = label.hjust, vjust = label.vjust)
-    ),
-    legend.title = combine_elements(
-      title.theme,
-      element_text(hjust = title.hjust, vjust = title.vjust)
-    ),
-    legend.key.width  = keywidth,
-    legend.key.height = keyheight,
-    legend.direction  = direction,
-    axis_line  = axis,
-    ticks     = ticks,
-    ticks_length = ticks.length
+    legend.text       = label.theme,
+    legend.title      = title.theme,
+    legend.key.width  = set_default_unit(keywidth,  default.unit),
+    legend.key.height = set_default_unit(keyheight, default.unit),
+    axis_line         = axis,
+    ticks             = ticks,
+    ticks_length      = set_default_unit(ticks.length, default.unit)
   )
 
   new_guide(
@@ -198,7 +188,6 @@ GuideBins <- ggproto(
     title = waiver(),
     title.position = NULL,
     label.position = NULL,
-
     internal_theme = NULL,
 
     # direction = NULL,
diff --git a/R/guide-colorbar.R b/R/guide-colorbar.R
index 690fe4ed01..8c634703e1 100644
--- a/R/guide-colorbar.R
+++ b/R/guide-colorbar.R
@@ -158,16 +158,6 @@ guide_colourbar <- function(
   available_aes = c("colour", "color", "fill"),
   ...
 ) {
-  if (!(is.null(barwidth) || is.unit(barwidth))) {
-    barwidth <- unit(barwidth, default.unit)
-  }
-  if (!(is.null(barheight) || is.unit(barheight))) {
-    barheight <- unit(barheight, default.unit)
-  }
-  if (!is.unit(ticks.length)) {
-    ticks.length <- unit(ticks.length, default.unit)
-  }
-
   if (!is.null(title.position)) {
     title.position <- arg_match0(title.position, .trbl)
   }
@@ -206,22 +196,23 @@ guide_colourbar <- function(
   }
 
   label.theme <- if (!isFALSE(label)) label.theme else element_blank()
+  label.theme <- combine_elements(
+    label.theme,
+    element_text(hjust = label.hjust, vjust = label.vjust)
+  )
+  title.theme <- combine_elements(
+    title.theme,
+    element_text(hjust = title.hjust, vjust = title.vjust)
+  )
 
   internal_theme <- theme(
-    legend.text = combine_elements(
-      label.theme,
-      element_text(hjust = label.hjust, vjust = label.vjust)
-    ),
-    legend.title = combine_elements(
-      title.theme,
-      element_text(hjust = title.hjust, vjust = title.vjust)
-    ),
-    legend.key.width  = barwidth,
-    legend.key.height = barheight,
-    legend.direction  = direction,
-    frame = frame,
-    ticks = ticks,
-    ticks.length = ticks.length
+    legend.text       = label.theme,
+    legend.title      = title.theme,
+    legend.key.width  = set_default_unit(barwidth,  default.unit),
+    legend.key.height = set_default_unit(barheight, default.unit),
+    frame             = frame,
+    ticks             = ticks,
+    ticks.length      = set_default_unit(ticks.length, default.unit)
   )
 
   # Trick to re-use this constructor in `guide_coloursteps()`.
diff --git a/R/guide-legend.R b/R/guide-legend.R
index 79dd80743d..7ea9c7efee 100644
--- a/R/guide-legend.R
+++ b/R/guide-legend.R
@@ -156,12 +156,6 @@ guide_legend <- function(
   ...
 ) {
   # Resolve key sizes
-  if (!inherits(keywidth, c("NULL", "unit"))) {
-    keywidth <- unit(keywidth, default.unit)
-  }
-  if (!inherits(keyheight, c("NULL", "unit"))) {
-    keyheight <- unit(keyheight, default.unit)
-  }
   if (!is.null(title.position)) {
     title.position <- arg_match0(title.position, .trbl)
   }
@@ -169,19 +163,20 @@ guide_legend <- function(
     label.position <- arg_match0(label.position, .trbl)
   }
   label.theme <- if (!isFALSE(label)) label.theme else element_blank()
+  label.theme <- combine_elements(
+    label.theme,
+    element_text(hjust = label.hjust, vjust = label.vjust, inherit.blank = TRUE)
+  )
+  title.theme <- combine_elements(
+    title.theme,
+    element_text(hjust = title.hjust, vjust = label.vjust, inherit.blank = TRUE)
+  )
 
   internal_theme <- theme(
-    legend.text = combine_elements(
-      label.theme,
-      element_text(hjust = label.hjust, vjust = label.vjust, inherit.blank = TRUE)
-    ),
-    legend.title = combine_elements(
-      title.theme,
-      element_text(hjust = title.hjust, vjust = title.vjust, inherit.blank = TRUE)
-    ),
-    legend.key.width  = keywidth,
-    legend.key.height = keyheight,
-    legend.direction  = direction
+    legend.text       = label.theme,
+    legend.title      = title.theme,
+    legend.key.width  = set_default_unit(keywidth,  default.unit),
+    legend.key.height = set_default_unit(keyheight, default.unit),
   )
 
   new_guide(
@@ -221,9 +216,7 @@ GuideLegend <- ggproto(
   params = list(
     title = waiver(),
     title.position = NULL,
-
     label.position = NULL,
-
     internal_theme = NULL,
 
     # General

From c11b594bca789d48f8f609f0f6e9872c188e748c Mon Sep 17 00:00:00 2001
From: Teun van den Brand <49372158+teunbrand@users.noreply.github.com>
Date: Wed, 8 Nov 2023 10:44:26 +0100
Subject: [PATCH 08/19] Fix bug

---
 R/theme.R | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/R/theme.R b/R/theme.R
index 32ecc1edb2..54d7f69a29 100644
--- a/R/theme.R
+++ b/R/theme.R
@@ -578,8 +578,8 @@ add_theme_preserve_blank <- function(old, new, new_name = caller_arg(new)) {
   is_blank <- vapply(old[nms], inherits, logical(1), what = "element_blank")
 
   # Only merge in elements that shouldn't become blank
-  new[] <- new[!(inherit_blank & is_blank)]
-  add_theme(old, new, t2name = new_name)
+  keep <- nms[!(inherit_blank & is_blank)]
+  add_theme(old, new[keep], t2name = new_name)
 }
 
 

From 9028521d3da61a825bf373f958aaa14c073df5c0 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <49372158+teunbrand@users.noreply.github.com>
Date: Wed, 8 Nov 2023 10:45:01 +0100
Subject: [PATCH 09/19] Document a bit

---
 R/guide-.R             |  5 +++++
 R/theme.R              | 19 +++++++++++++++++--
 man/ggplot2-ggproto.Rd | 12 +++++++++---
 3 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/R/guide-.R b/R/guide-.R
index 76b975e17b..cabd2abdb2 100644
--- a/R/guide-.R
+++ b/R/guide-.R
@@ -122,6 +122,11 @@ new_guide <- function(..., available_aes = "any", super) {
 #'   It can be used to overrule user-supplied parameters or perform checks on
 #'   the `params` property.
 #'
+#' - `setup_elements()` Used to extract elements from the theme. The base
+#'   `Guide` uses this method to merge a potential `internal_theme` with the
+#'   global theme and to calculate the elements declared in `Guide$elements`.
+#'   For other guides, this is a good place to intervene in theme inheritance.
+#'
 #' - `override_elements()` Take populated theme elements derived from the
 #'   `elements` property and allows overriding these theme settings.
 #'
diff --git a/R/theme.R b/R/theme.R
index 54d7f69a29..7d516e2012 100644
--- a/R/theme.R
+++ b/R/theme.R
@@ -560,8 +560,23 @@ add_theme <- function(t1, t2, t2name, call = caller_env()) {
   t1
 }
 
-# Calls `add_theme()`, but drops the elements of the new theme that inherit
-# blank and that are blank in the old theme.
+#' Combine themes while preserving blank elements
+#'
+#' This calls `add_theme()` but with the following modifications:
+#'
+#' * Elements in `new` that have `inherit.blank = TRUE` and are blank in `old`
+#'   will remain blank.
+#' * `NULL` elements in `new` are ignored.
+#'
+#' This logic is used in the guide system to merge theme settings provided
+#' at the guide level with theme settings provided at the plot level.
+#'
+#' @param old A theme object, typically the plot level theme.
+#' @param new A theme object
+#' @param new_name A name to display in error messages
+#'
+#' @keywords internal
+#' @noRd
 add_theme_preserve_blank <- function(old, new, new_name = caller_arg(new)) {
   if (is.null(new)) {
     return(old)
diff --git a/man/ggplot2-ggproto.Rd b/man/ggplot2-ggproto.Rd
index 37a042dd68..e6f9f25210 100644
--- a/man/ggplot2-ggproto.Rd
+++ b/man/ggplot2-ggproto.Rd
@@ -421,12 +421,18 @@ range.
 \item \code{merge()} Combines information from multiple guides with the same
 \code{params$hash}. This ensures that e.g. \code{guide_legend()} can display both
 \code{shape} and \code{colour} in the same guide.
-\item \code{get_layer_key()} Extract information from layers. This can be used to
-check that the guide's aesthetic is actually in use, or to gather
-information about how legend keys should be displayed.
+\item \code{process_layers()} Extract information from layers. This acts mostly
+as a filter for which layers to include and these are then (typically)
+forwarded to \code{get_layer_key()}.
+\item \code{get_layer_key()} This can be used to gather information about how legend
+keys should be displayed.
 \item \code{setup_params()} Set up parameters at the beginning of drawing stages.
 It can be used to overrule user-supplied parameters or perform checks on
 the \code{params} property.
+\item \code{setup_elements()} Used to extract elements from the theme. The base
+\code{Guide} uses this method to merge a potential \code{internal_theme} with the
+global theme and to calculate the elements declared in \code{Guide$elements}.
+For other guides, this is a good place to intervene in theme inheritance.
 \item \code{override_elements()} Take populated theme elements derived from the
 \code{elements} property and allows overriding these theme settings.
 \item \code{build_title()} Render the guide's title.

From e93bde9b9a9be7939da674f000962b85c0ee95a5 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <49372158+teunbrand@users.noreply.github.com>
Date: Wed, 8 Nov 2023 11:15:33 +0100
Subject: [PATCH 10/19] Drop the 'expressions are right-aligned' bit from the
 docs

---
 R/guide-legend.R         | 3 +--
 man/guide_bins.Rd        | 3 +--
 man/guide_colourbar.Rd   | 3 +--
 man/guide_coloursteps.Rd | 3 +--
 man/guide_legend.Rd      | 3 +--
 5 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/R/guide-legend.R b/R/guide-legend.R
index 7ea9c7efee..f651512489 100644
--- a/R/guide-legend.R
+++ b/R/guide-legend.R
@@ -32,8 +32,7 @@
 #'   object of [element_text()] is expected. By default, the theme is
 #'   specified by `legend.text` in [theme()].
 #' @param label.hjust A numeric specifying horizontal justification of the
-#'   label text. The default for standard text is 0 (left-aligned) and 1
-#'   (right-aligned) for expressions.
+#'   label text.
 #' @param label.vjust A numeric specifying vertical justification of the label
 #'   text.
 #' @param keywidth A numeric or a [grid::unit()] object specifying
diff --git a/man/guide_bins.Rd b/man/guide_bins.Rd
index 6eeada9598..dcca3c5a33 100644
--- a/man/guide_bins.Rd
+++ b/man/guide_bins.Rd
@@ -64,8 +64,7 @@ object of \code{\link[=element_text]{element_text()}} is expected. By default, t
 specified by \code{legend.text} in \code{\link[=theme]{theme()}}.}
 
 \item{label.hjust}{A numeric specifying horizontal justification of the
-label text. The default for standard text is 0 (left-aligned) and 1
-(right-aligned) for expressions.}
+label text.}
 
 \item{label.vjust}{A numeric specifying vertical justification of the label
 text.}
diff --git a/man/guide_colourbar.Rd b/man/guide_colourbar.Rd
index 7813c12b1c..3ae922e0dc 100644
--- a/man/guide_colourbar.Rd
+++ b/man/guide_colourbar.Rd
@@ -103,8 +103,7 @@ object of \code{\link[=element_text]{element_text()}} is expected. By default, t
 specified by \code{legend.text} in \code{\link[=theme]{theme()}}.}
 
 \item{label.hjust}{A numeric specifying horizontal justification of the
-label text. The default for standard text is 0 (left-aligned) and 1
-(right-aligned) for expressions.}
+label text.}
 
 \item{label.vjust}{A numeric specifying vertical justification of the label
 text.}
diff --git a/man/guide_coloursteps.Rd b/man/guide_coloursteps.Rd
index e97230b6f4..76f611ca79 100644
--- a/man/guide_coloursteps.Rd
+++ b/man/guide_coloursteps.Rd
@@ -92,8 +92,7 @@ label. One of "top", "bottom" (default for horizontal guide), "left", or
 object of \code{\link[=element_text]{element_text()}} is expected. By default, the theme is
 specified by \code{legend.text} in \code{\link[=theme]{theme()}}.}
     \item{\code{label.hjust}}{A numeric specifying horizontal justification of the
-label text. The default for standard text is 0 (left-aligned) and 1
-(right-aligned) for expressions.}
+label text.}
     \item{\code{label.vjust}}{A numeric specifying vertical justification of the label
 text.}
     \item{\code{order}}{positive integer less than 99 that specifies the order of
diff --git a/man/guide_legend.Rd b/man/guide_legend.Rd
index 21dcbe7833..d3831b0c4d 100644
--- a/man/guide_legend.Rd
+++ b/man/guide_legend.Rd
@@ -60,8 +60,7 @@ object of \code{\link[=element_text]{element_text()}} is expected. By default, t
 specified by \code{legend.text} in \code{\link[=theme]{theme()}}.}
 
 \item{label.hjust}{A numeric specifying horizontal justification of the
-label text. The default for standard text is 0 (left-aligned) and 1
-(right-aligned) for expressions.}
+label text.}
 
 \item{label.vjust}{A numeric specifying vertical justification of the label
 text.}

From 83b4142700257824d0dc7967a220371583acdb54 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <49372158+teunbrand@users.noreply.github.com>
Date: Mon, 20 Nov 2023 21:10:43 +0100
Subject: [PATCH 11/19] Simplify margin adjustment

---
 R/guide-legend.R | 29 +++++++++++++++--------------
 1 file changed, 15 insertions(+), 14 deletions(-)

diff --git a/R/guide-legend.R b/R/guide-legend.R
index a9bc02a8ad..e4e0e537cc 100644
--- a/R/guide-legend.R
+++ b/R/guide-legend.R
@@ -400,6 +400,13 @@ GuideLegend <- ggproto(
     theme$legend.text$hjust <- theme$legend.text$hjust %||% default_just[1]
     theme$legend.text$vjust <- theme$legend.text$vjust %||% default_just[2]
 
+    # We break inheritance of the text margins to add small spacings between
+    # labels and keys.
+    # We set the global text's margin to NULL here, so that a NULL in the
+    # computed elements indicates that no explicit margin has been set in
+    # neither the guide nor the theme's legend.text/legend.title.
+    theme$text$margin <- NULL
+
     Guide$setup_elements(params, elements, theme)
   },
 
@@ -426,22 +433,16 @@ GuideLegend <- ggproto(
       "cm", valueOnly = TRUE
     )
 
-    # When no explicit margin has been set, either in this guide or in the
-    # theme, we add a default text margin to leave a small gap in between
-    # the label and the key.
-    margin_absent <- is.null(
-      params$internal_theme$legend.text$margin %||% theme$legend.text$margin
-    )
-    if (margin_absent && !inherits(elements$text, "element_blank")) {
-      i <- match(params$label.position, .trbl[c(3, 4, 1, 2)])
-      elements$text$margin[i] <- elements$text$margin[i] + gap
+    # When no explicit margin has been set, we set a default text margin
+    # to leave a small gap in between the label and the key.
+    margin <- theme$text$margin %||% margin()
+    if (is.null(elements$text$margin)) {
+      i <- match(params$label.position, .trbl[c(3, 4, 1, 2)]) # match opposite
+      elements$text$margin <- replace(margin, i, margin[i] + gap)
     }
-    margin_absent <- is.null(
-      params$internal_theme$legend.title$margin %||% theme$legend.title$margin
-    )
-    if (margin_absent && !inherits(elements$title, "element_blank")) {
+    if (is.null(elements$title$margin)) {
       i <- match(params$title.position, .trbl[c(3, 4, 1, 2)])
-      elements$title$margin[i] <- elements$title$margin[i] + gap
+      elements$title$margin <- replace(margin, i, margin[i] + gap)
     }
 
     # Evaluate backgrounds early

From 06bf5c968e490186b5080c200a59d3415ad857cb Mon Sep 17 00:00:00 2001
From: Teun van den Brand <49372158+teunbrand@users.noreply.github.com>
Date: Wed, 22 Nov 2023 12:14:24 +0100
Subject: [PATCH 12/19] fix text just bug

---
 R/guide-legend.R | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/R/guide-legend.R b/R/guide-legend.R
index e4e0e537cc..ebcdf8d0d3 100644
--- a/R/guide-legend.R
+++ b/R/guide-legend.R
@@ -737,7 +737,7 @@ legend_label_just <- function(position) {
   default_just <- switch(
     position,
     top    = c(0.5, 0),
-    bottom = c(0.5, 0),
+    bottom = c(0.5, 1),
     left   = c(1, 0.5),
     right  = c(0, 0.5),
     arg_match0(position, .trbl, arg = "label.position")

From 59d1b9398846f1c741b20c3b0dc4127d5b590bdf Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Mon, 27 Nov 2023 12:01:49 +0100
Subject: [PATCH 13/19] match opposite more explicitly

---
 R/guide-legend.R | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/R/guide-legend.R b/R/guide-legend.R
index ebcdf8d0d3..65f0e380f8 100644
--- a/R/guide-legend.R
+++ b/R/guide-legend.R
@@ -437,11 +437,11 @@ GuideLegend <- ggproto(
     # to leave a small gap in between the label and the key.
     margin <- theme$text$margin %||% margin()
     if (is.null(elements$text$margin)) {
-      i <- match(params$label.position, .trbl[c(3, 4, 1, 2)]) # match opposite
+      i <- match(opposite_position(params$label.position), .trbl) # match opposite
       elements$text$margin <- replace(margin, i, margin[i] + gap)
     }
     if (is.null(elements$title$margin)) {
-      i <- match(params$title.position, .trbl[c(3, 4, 1, 2)])
+      i <- match(opposite_position(params$title.position), .trbl)
       elements$title$margin <- replace(margin, i, margin[i] + gap)
     }
 

From 148006f3039183240c67251c8072263405c84552 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Mon, 27 Nov 2023 12:49:37 +0100
Subject: [PATCH 14/19] use merge_element instead of combine_elements

---
 R/guide-legend.R | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/R/guide-legend.R b/R/guide-legend.R
index 65f0e380f8..f42552398b 100644
--- a/R/guide-legend.R
+++ b/R/guide-legend.R
@@ -169,13 +169,13 @@ guide_legend <- function(
     label.position <- arg_match0(label.position, .trbl)
   }
   label.theme <- if (!isFALSE(label)) label.theme else element_blank()
-  label.theme <- combine_elements(
-    label.theme,
-    element_text(hjust = label.hjust, vjust = label.vjust, inherit.blank = TRUE)
+  label.theme <- merge_element(
+    element_text(hjust = label.hjust, vjust = label.vjust, inherit.blank = TRUE),
+    label.theme
   )
-  title.theme <- combine_elements(
-    title.theme,
-    element_text(hjust = title.hjust, vjust = label.vjust, inherit.blank = TRUE)
+  title.theme <- merge_element(
+    element_text(hjust = title.hjust, vjust = label.vjust, inherit.blank = TRUE),
+    title.theme
   )
 
   internal_theme <- theme(
@@ -184,6 +184,7 @@ guide_legend <- function(
     legend.key.width  = set_default_unit(keywidth,  default.unit),
     legend.key.height = set_default_unit(keyheight, default.unit),
   )
+  internal_theme <- compact(internal_theme)
 
   # Resolve spacing
   key.spacing.x <- set_default_unit(key.spacing.x %||% key.spacing, default.unit)

From 36993dc1d094e9674533deee5990f61efaca7d4f Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Mon, 27 Nov 2023 14:19:33 +0100
Subject: [PATCH 15/19] rewire theme merging logic

---
 R/guide-.R | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
 R/theme.R  | 38 -------------------------------------
 2 files changed, 54 insertions(+), 39 deletions(-)

diff --git a/R/guide-.R b/R/guide-.R
index 5c86c06b03..b6a01796cf 100644
--- a/R/guide-.R
+++ b/R/guide-.R
@@ -273,7 +273,7 @@ Guide <- ggproto(
   # Converts the `elements` field to proper elements to be accepted by
   # `element_grob()`. String-interpolates aesthetic/position dependent elements.
   setup_elements = function(params, elements, theme) {
-    theme <- add_theme_preserve_blank(theme, params$internal_theme)
+    theme <- merge_internal_theme(theme, params$internal_theme)
     is_char  <- vapply(elements, is.character, logical(1))
     elements[is_char] <- lapply(elements[is_char], calc_element, theme = theme)
     elements
@@ -457,3 +457,56 @@ validate_labels <- function(labels) {
     unlist(labels)
   }
 }
+
+# This logic is similar to `add_theme()` with the following exceptions:
+#
+# 1. Elements in `new` that have `inherit.blank = TRUE` and are blank in `old`
+#    will remain blank.
+# 2. `NULL` elements in `new` are ignored.
+# 3. When an `old` element is a subclass of the `new` element, that subclass
+#    is preserved.
+merge_internal_theme <- function(old, new, new_name = caller_arg(new)) {
+  if (is.null(new)) {
+    return(old)
+  }
+  # Get non empty names of new theme
+  nms <- names(new)[!vapply(new, is.null, logical(1))]
+
+  # Does any of the new theme elements carry over blank elements?
+  inherit_blank <- vapply(
+    new[nms], FUN.VALUE = logical(1),
+    function(x) is.list(x) && isTRUE(x$inherit.blank)
+  )
+  # Are their equivalents in the old theme blank?
+  is_blank <- vapply(old[nms], inherits, logical(1), what = "element_blank")
+
+  # Only merge in elements that shouldn't become blank
+  keep <- nms[!(inherit_blank & is_blank)]
+
+  try_fetch(
+    for (item in keep) {
+      x <- merge_subclass(new[[item]], old[[item]])
+      old[item] <- list(x)
+    },
+    error = function(cnd) {
+      cli::cli_abort(
+        "Problem merging the {.var {item}} theme element.",
+        parent = cnd
+      )
+    }
+  )
+  old
+}
+
+merge_subclass <- function(new, old) {
+  if (!is.subclass(old, new)) {
+    return(merge_element(new, old))
+  }
+  if (is.null(old)) {
+    return(new)
+  }
+  idx <- !vapply(new, is.null, logical(1))
+  idx <- names(new)[idx]
+  old[idx] <- new[idx]
+  old
+}
diff --git a/R/theme.R b/R/theme.R
index 7d516e2012..f1315e0881 100644
--- a/R/theme.R
+++ b/R/theme.R
@@ -560,44 +560,6 @@ add_theme <- function(t1, t2, t2name, call = caller_env()) {
   t1
 }
 
-#' Combine themes while preserving blank elements
-#'
-#' This calls `add_theme()` but with the following modifications:
-#'
-#' * Elements in `new` that have `inherit.blank = TRUE` and are blank in `old`
-#'   will remain blank.
-#' * `NULL` elements in `new` are ignored.
-#'
-#' This logic is used in the guide system to merge theme settings provided
-#' at the guide level with theme settings provided at the plot level.
-#'
-#' @param old A theme object, typically the plot level theme.
-#' @param new A theme object
-#' @param new_name A name to display in error messages
-#'
-#' @keywords internal
-#' @noRd
-add_theme_preserve_blank <- function(old, new, new_name = caller_arg(new)) {
-  if (is.null(new)) {
-    return(old)
-  }
-  # Get non empty names of new theme
-  nms <- names(new)[!vapply(new, is.null, logical(1))]
-
-  # Does any of the new theme elements carry over blank elements?
-  inherit_blank <- vapply(
-    new[nms], FUN.VALUE = logical(1),
-    function(x) is.list(x) && isTRUE(x$inherit.blank)
-  )
-  # Are their equivalents in the old theme blank?
-  is_blank <- vapply(old[nms], inherits, logical(1), what = "element_blank")
-
-  # Only merge in elements that shouldn't become blank
-  keep <- nms[!(inherit_blank & is_blank)]
-  add_theme(old, new[keep], t2name = new_name)
-}
-
-
 #' Calculate the element properties, by inheriting properties from its parents
 #'
 #' @param element The name of the theme element to calculate

From eaab63eec2913e885a1a1d2301f74acfa79920ab Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Mon, 27 Nov 2023 14:20:48 +0100
Subject: [PATCH 16/19] prevent 0-length size/linewidth

---
 R/theme.R | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/R/theme.R b/R/theme.R
index f1315e0881..1b36401dc7 100644
--- a/R/theme.R
+++ b/R/theme.R
@@ -774,12 +774,12 @@ combine_elements <- function(e1, e2) {
 
   # Calculate relative sizes
   if (is.rel(e1$size)) {
-    e1$size <- e2$size * unclass(e1$size)
+    e1$size <- (e2$size %||% rel(1)) * unclass(e1$size)
   }
 
   # Calculate relative linewidth
   if (is.rel(e1$linewidth)) {
-    e1$linewidth <- e2$linewidth * unclass(e1$linewidth)
+    e1$linewidth <- (e2$linewidth %||% rel(1)) * unclass(e1$linewidth)
   }
 
   # If e2 is 'richer' than e1, fill e2 with e1 parameters

From a513fdf6968f93fc617b7eff0baae874c0e60cfb Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Mon, 27 Nov 2023 14:21:28 +0100
Subject: [PATCH 17/19] Revert "use merge_element instead of combine_elements"

This reverts commit 148006f3039183240c67251c8072263405c84552.
---
 R/guide-legend.R | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/R/guide-legend.R b/R/guide-legend.R
index f42552398b..65f0e380f8 100644
--- a/R/guide-legend.R
+++ b/R/guide-legend.R
@@ -169,13 +169,13 @@ guide_legend <- function(
     label.position <- arg_match0(label.position, .trbl)
   }
   label.theme <- if (!isFALSE(label)) label.theme else element_blank()
-  label.theme <- merge_element(
-    element_text(hjust = label.hjust, vjust = label.vjust, inherit.blank = TRUE),
-    label.theme
+  label.theme <- combine_elements(
+    label.theme,
+    element_text(hjust = label.hjust, vjust = label.vjust, inherit.blank = TRUE)
   )
-  title.theme <- merge_element(
-    element_text(hjust = title.hjust, vjust = label.vjust, inherit.blank = TRUE),
-    title.theme
+  title.theme <- combine_elements(
+    title.theme,
+    element_text(hjust = title.hjust, vjust = label.vjust, inherit.blank = TRUE)
   )
 
   internal_theme <- theme(
@@ -184,7 +184,6 @@ guide_legend <- function(
     legend.key.width  = set_default_unit(keywidth,  default.unit),
     legend.key.height = set_default_unit(keyheight, default.unit),
   )
-  internal_theme <- compact(internal_theme)
 
   # Resolve spacing
   key.spacing.x <- set_default_unit(key.spacing.x %||% key.spacing, default.unit)

From aaaf17e5c0a6b74467d4fec2ca8f1497ff4064db Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Mon, 27 Nov 2023 14:23:39 +0100
Subject: [PATCH 18/19] should not receive NULL

---
 R/guide-.R | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/R/guide-.R b/R/guide-.R
index b6a01796cf..543d23b03e 100644
--- a/R/guide-.R
+++ b/R/guide-.R
@@ -502,9 +502,6 @@ merge_subclass <- function(new, old) {
   if (!is.subclass(old, new)) {
     return(merge_element(new, old))
   }
-  if (is.null(old)) {
-    return(new)
-  }
   idx <- !vapply(new, is.null, logical(1))
   idx <- names(new)[idx]
   old[idx] <- new[idx]

From 56401d1550b64c86d8871ecb6257dfad4ad191d7 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Mon, 27 Nov 2023 14:33:50 +0100
Subject: [PATCH 19/19] early exit empty themes as well

---
 R/guide-.R | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/R/guide-.R b/R/guide-.R
index 543d23b03e..f3047a450a 100644
--- a/R/guide-.R
+++ b/R/guide-.R
@@ -466,7 +466,7 @@ validate_labels <- function(labels) {
 # 3. When an `old` element is a subclass of the `new` element, that subclass
 #    is preserved.
 merge_internal_theme <- function(old, new, new_name = caller_arg(new)) {
-  if (is.null(new)) {
+  if (length(new) == 0) {
     return(old)
   }
   # Get non empty names of new theme