From a54f7dd04d8a00d67286a1715c668414d6ab6e09 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Thu, 5 Sep 2024 11:31:51 +0200
Subject: [PATCH 1/4] guides merge aesthetics

---
 R/guide-colorbar.R | 1 +
 R/guide-legend.R   | 1 +
 2 files changed, 2 insertions(+)

diff --git a/R/guide-colorbar.R b/R/guide-colorbar.R
index 586caee124..c7c424c2ac 100644
--- a/R/guide-colorbar.R
+++ b/R/guide-colorbar.R
@@ -273,6 +273,7 @@ GuideColourbar <- ggproto(
   merge = function(self, params, new_guide, new_params) {
     new_params$key$.label <- new_params$key$.value <- NULL
     params$key <- vec_cbind(params$key, new_params$key)
+    params$aesthetic <- union(params$aesthetic, new_params$aesthetic)
     return(list(guide = self, params = params))
   },
 
diff --git a/R/guide-legend.R b/R/guide-legend.R
index 671acf1a1c..37aad2e3f0 100644
--- a/R/guide-legend.R
+++ b/R/guide-legend.R
@@ -204,6 +204,7 @@ GuideLegend <- ggproto(
       cli::cli_warn("Duplicated {.arg override.aes} is ignored.")
     }
     params$override.aes <- params$override.aes[!duplicated(nms)]
+    params$aesthetic <- union(params$aesthetic, new_params$aesthetic)
 
     list(guide = self, params = params)
   },

From d952f381224e16b6c9fa2ff4443b5a443150075d Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Thu, 5 Sep 2024 11:43:57 +0200
Subject: [PATCH 2/4] add getter for completed plot labels

---
 R/labels.R | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/R/labels.R b/R/labels.R
index 20cc929d37..16dfa2da3a 100644
--- a/R/labels.R
+++ b/R/labels.R
@@ -179,6 +179,34 @@ ggtitle <- function(label, subtitle = waiver()) {
   labs(title = label, subtitle = subtitle)
 }
 
+get_labs <- function(plot = get_last_plot()) {
+  plot <- ggplot_build(plot)
+
+  labs <- plot$plot$labels
+
+  xy_labs <- rename(
+    c(x = plot$layout$resolve_label(plot$layout$panel_scales_x[[1]], labs),
+      y = plot$layout$resolve_label(plot$layout$panel_scales_y[[1]], labs)),
+    c(x.primary = "x", x.secondary = "x.sec",
+      y.primary = "y", y.secondary = "y.sec")
+  )
+
+  labs <- defaults(xy_labs, labs)
+
+  guides <- plot$plot$guides
+  if (length(guides$aesthetics) == 0) {
+    return(labs)
+  }
+
+  for (aes in guides$aesthetics) {
+    param <- guides$get_params(aes)
+    aes   <- param$aesthetic # Can have length > 1 when guide was merged
+    title <- vec_set_names(rep(list(param$title), length(aes)), aes)
+    labs  <- defaults(title, labs)
+  }
+  labs
+}
+
 #' Extract alt text from a plot
 #'
 #' This function returns a text that can be used as alt-text in webpages etc.

From 48e7dcf897e884386b6ca70550ccfe5b45206312 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Thu, 5 Sep 2024 11:44:10 +0200
Subject: [PATCH 3/4] incorporate getter in tests

---
 tests/testthat/test-labels.R | 71 +++++++++++++-----------------------
 1 file changed, 25 insertions(+), 46 deletions(-)

diff --git a/tests/testthat/test-labels.R b/tests/testthat/test-labels.R
index 60f5165c1b..6a26578c0b 100644
--- a/tests/testthat/test-labels.R
+++ b/tests/testthat/test-labels.R
@@ -52,15 +52,13 @@ test_that("setting guide labels works", {
 test_that("Labels from default stat mapping are overwritten by default labels", {
   p <- ggplot(mpg, aes(displ, hwy)) +
     geom_density2d()
-  labels <- ggplot_build(p)$plot$labels
 
+  labels <- get_labs(p)
   expect_equal(labels$colour[1], "colour")
   expect_true(attr(labels$colour, "fallback"))
 
   p <- p + geom_smooth(aes(color = drv), method = "lm", formula = y ~ x)
-  labels <- ggplot_build(p)$plot$labels
-
-  expect_equal(labels$colour, "drv")
+  expect_equal(get_labs(p)$colour, "drv")
 })
 
 test_that("Labels can be extracted from attributes", {
@@ -68,8 +66,8 @@ test_that("Labels can be extracted from attributes", {
   attr(df$mpg, "label") <- "Miles per gallon"
 
   p <- ggplot(df, aes(mpg, disp)) + geom_point()
-  labels <- ggplot_build(p)$plot$labels
 
+  labels <- get_labs(p)
   expect_equal(labels$x, "Miles per gallon")
   expect_equal(labels$y, "disp")
 })
@@ -79,14 +77,10 @@ test_that("Labels from static aesthetics are ignored (#6003)", {
   df <- data.frame(x = 1, y = 1, f = 1)
 
   p <- ggplot(df, aes(x, y, colour = f)) + geom_point()
-  labels <- ggplot_build(p)$plot$labels
-
-  expect_equal(labels$colour, "f")
+  expect_equal(get_labs(p)$colour, "f")
 
   p <- ggplot(df, aes(x, y, colour = f)) + geom_point(colour = "blue")
-  labels <- ggplot_build(p)$plot$labels
-
-  expect_null(labels$colour)
+  expect_null(get_labs(p)$colour)
 })
 
 test_that("alt text is returned", {
@@ -140,24 +134,25 @@ test_that("position axis label hierarchy works as intended", {
     geom_point(size = 5)
 
   p <- ggplot_build(p)
+  resolve_label <- function(x) p$layout$resolve_label(x, p$plot$labels)
 
   # In absence of explicit title, get title from mapping
   expect_identical(
-    p$layout$resolve_label(p$layout$panel_scales_x[[1]], p$plot$labels),
+    resolve_label(p$layout$panel_scales_x[[1]]),
     list(secondary = NULL, primary = "foo")
   )
   expect_identical(
-    p$layout$resolve_label(p$layout$panel_scales_y[[1]], p$plot$labels),
+    resolve_label(p$layout$panel_scales_y[[1]]),
     list(primary = "bar", secondary = NULL)
   )
 
   # Scale name overrules mapping label
   expect_identical(
-    p$layout$resolve_label(scale_x_continuous("Baz"), p$plot$labels),
+    resolve_label(scale_x_continuous("Baz")),
     list(secondary = NULL, primary = "Baz")
   )
   expect_identical(
-    p$layout$resolve_label(scale_y_continuous("Qux"), p$plot$labels),
+    resolve_label(scale_y_continuous("Qux")),
     list(primary = "Qux", secondary = NULL)
   )
 
@@ -167,23 +162,23 @@ test_that("position axis label hierarchy works as intended", {
     p$plot$layers
   )
   expect_identical(
-    p$layout$resolve_label(scale_x_continuous("Baz"), p$plot$labels),
+    resolve_label(scale_x_continuous("Baz")),
     list(secondary = NULL, primary = "quuX")
   )
   expect_identical(
-    p$layout$resolve_label(scale_y_continuous("Qux"), p$plot$labels),
+    resolve_label(scale_y_continuous("Qux")),
     list(primary = "corgE", secondary = NULL)
   )
 
   # Secondary axis names work
   xsec <- scale_x_continuous("Baz", sec.axis = dup_axis(name = "grault"))
   expect_identical(
-    p$layout$resolve_label(xsec, p$plot$labels),
+    resolve_label(xsec),
     list(secondary = "grault", primary = "quuX")
   )
   ysec <- scale_y_continuous("Qux", sec.axis = dup_axis(name = "garply"))
   expect_identical(
-    p$layout$resolve_label(ysec, p$plot$labels),
+    resolve_label(ysec),
     list(primary = "corgE", secondary = "garply")
   )
 
@@ -194,12 +189,12 @@ test_that("position axis label hierarchy works as intended", {
     p$plot$layers
   )
   expect_identical(
-    p$layout$resolve_label(xsec, p$plot$labels),
+    resolve_label(xsec),
     list(secondary = "waldo", primary = "quuX")
   )
   ysec <- scale_y_continuous("Qux", sec.axis = dup_axis(name = "garply"))
   expect_identical(
-    p$layout$resolve_label(ysec, p$plot$labels),
+    resolve_label(ysec),
     list(primary = "corgE", secondary = "fred")
   )
 })
@@ -220,16 +215,11 @@ test_that("moving guide positions lets titles follow", {
     ),
     p$plot$layers
   )
-  expect_identical(
-    p$layout$resolve_label(p$layout$panel_scales_x[[1]], p$plot$labels),
-    list(secondary = NULL, primary = "baz")
-  )
-  expect_identical(
-    p$layout$resolve_label(p$layout$panel_scales_y[[1]], p$plot$labels),
-    list(primary = "qux", secondary = NULL)
-  )
+  labs <- get_labs(p)
+  expect <- list(x = "baz", x.sec = NULL, y = "qux", y.sec = NULL)
+  expect_identical(labs[names(expect)], expect)
 
-  # Guides at secondary positions (changes order of primary/secondary)
+  # Guides at secondary positions
   p$layout$setup_panel_guides(
     guides_list(
       list(x = guide_axis("baz", position = "top"),
@@ -237,14 +227,8 @@ test_that("moving guide positions lets titles follow", {
     ),
     p$plot$layers
   )
-  expect_identical(
-    p$layout$resolve_label(p$layout$panel_scales_x[[1]], p$plot$labels),
-    list(primary = "baz", secondary = NULL)
-  )
-  expect_identical(
-    p$layout$resolve_label(p$layout$panel_scales_y[[1]], p$plot$labels),
-    list(secondary = NULL, primary = "qux")
-  )
+  labs <- get_labs(p)
+  expect_identical(labs[names(expect)], expect)
 
   # Primary guides at secondary positions with
   # secondary guides at primary positions
@@ -257,14 +241,9 @@ test_that("moving guide positions lets titles follow", {
     ),
     p$plot$layers
   )
-  expect_identical(
-    p$layout$resolve_label(p$layout$panel_scales_x[[1]], p$plot$labels),
-    list(primary = "baz", secondary = "quux")
-  )
-  expect_identical(
-    p$layout$resolve_label(p$layout$panel_scales_y[[1]], p$plot$labels),
-    list(secondary = "corge", primary = "qux")
-  )
+  labs <- get_labs(p)
+  expect[c("x.sec", "y.sec")] <- list("quux", "corge")
+  expect_identical(labs[names(expect)], expect)
 })
 
 # Visual tests ------------------------------------------------------------

From 1ca6a390406a33c23bfa3ad4b2414871b1aa0da1 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Thu, 5 Sep 2024 11:50:01 +0200
Subject: [PATCH 4/4] document

---
 NAMESPACE   | 1 +
 NEWS.md     | 2 ++
 R/labels.R  | 5 +++++
 man/labs.Rd | 7 +++++++
 4 files changed, 15 insertions(+)

diff --git a/NAMESPACE b/NAMESPACE
index f0ccf3bec1..1220e7e6ef 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -426,6 +426,7 @@ export(get_alt_text)
 export(get_element_tree)
 export(get_geom_defaults)
 export(get_guide_data)
+export(get_labs)
 export(get_last_plot)
 export(get_layer_data)
 export(get_layer_grob)
diff --git a/NEWS.md b/NEWS.md
index 40bdb3d156..75579e6fc6 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,7 @@
 # ggplot2 (development version)
 
+* New `get_labs()` function for retrieving completed plot labels 
+  (@teunbrand, #6008).
 * `guide_bins()`, `guide_colourbar()` and `guide_coloursteps()` gain an `angle`
   argument to overrule theme settings, similar to `guide_axis(angle)` 
   (@teunbrand, #4594).
diff --git a/R/labels.R b/R/labels.R
index 16dfa2da3a..50e3776555 100644
--- a/R/labels.R
+++ b/R/labels.R
@@ -179,6 +179,11 @@ ggtitle <- function(label, subtitle = waiver()) {
   labs(title = label, subtitle = subtitle)
 }
 
+#' @rdname labs
+#' @export
+#' @param plot A ggplot object
+#' @description
+#' `get_labs()` retrieves completed labels from a plot.
 get_labs <- function(plot = get_last_plot()) {
   plot <- ggplot_build(plot)
 
diff --git a/man/labs.Rd b/man/labs.Rd
index 6fc7e9aa08..5d6fb93b52 100644
--- a/man/labs.Rd
+++ b/man/labs.Rd
@@ -5,6 +5,7 @@
 \alias{xlab}
 \alias{ylab}
 \alias{ggtitle}
+\alias{get_labs}
 \title{Modify axis, legend, and plot labels}
 \usage{
 labs(
@@ -22,6 +23,8 @@ xlab(label)
 ylab(label)
 
 ggtitle(label, subtitle = waiver())
+
+get_labs(plot = get_last_plot())
 }
 \arguments{
 \item{...}{A list of new name-value pairs. The name should be an aesthetic.}
@@ -44,6 +47,8 @@ rlang \link[rlang:as_function]{lambda} function notation.}
 
 \item{label}{The title of the respective axis (for \code{xlab()} or \code{ylab()}) or
 of the plot (for \code{ggtitle()}).}
+
+\item{plot}{A ggplot object}
 }
 \description{
 Good labels are critical for making your plots accessible to a wider
@@ -52,6 +57,8 @@ variable name. Use the plot \code{title} and \code{subtitle} to explain the
 main findings. It's common to use the \code{caption} to provide information
 about the data source. \code{tag} can be used for adding identification tags
 to differentiate between multiple plots.
+
+\code{get_labs()} retrieves completed labels from a plot.
 }
 \details{
 You can also set axis and legend labels in the individual scales (using