Add ggplot_build() method for <ggplot_built> class (#5803)

* Add `ggplot_build.ggplot_built` method

* small simplification in `get_guide_data()`

* add news bullet

Author: teunbrand

NAMESPACE

@@ -67,6 +67,7 @@ S3method(ggplot_add,list)
 S3method(ggplot_add,theme)
 S3method(ggplot_add,uneval)
 S3method(ggplot_build,ggplot)
+S3method(ggplot_build,ggplot_built)
 S3method(ggplot_gtable,ggplot_built)
 S3method(grid.draw,absoluteGrob)
 S3method(grid.draw,ggplot)

NEWS.md

@@ -71,6 +71,8 @@
   alignment is not necessary (#5788).
 * `position_stack()` skips computation when all `x` values are unique and 
   therefore stacking is not necessary (#5788).
+* A new `ggplot_build()` S3 method for <ggplot_built> classes was added, which
+  returns input unaltered (@teunbrand, #5800).
 
 # ggplot2 3.5.1
 

R/guides-.R

@@ -792,9 +792,7 @@ get_guide_data <- function(plot = get_last_plot(), aesthetic, panel = 1L) {
   check_string(aesthetic, allow_empty = FALSE)
   aesthetic <- standardise_aes_names(aesthetic)
 
-  if (!inherits(plot, "ggplot_built")) {
-    plot <- ggplot_build(plot)
-  }
+  plot <- ggplot_build(plot)
 
   if (!aesthetic %in% c("x", "y", "x.sec", "y.sec", "theta", "r")) {
     # Non position guides: check if aesthetic in colnames of key

R/plot-build.R

@@ -30,6 +30,12 @@ ggplot_build <- function(plot) {
   UseMethod('ggplot_build')
 }
 
+#' @export
+ggplot_build.ggplot_built <- function(plot) {
+  # This is a no-op
+  plot
+}
+
 #' @export
 ggplot_build.ggplot <- function(plot) {
   plot <- plot_clone(plot)