Fix regression in guide_bins(reverse)

NEWS.md

@@ -1,5 +1,6 @@
 # ggplot2 (development version)
 
+* Fixed regression in `guide_bins(reverse = TRUE)` (@teunbrand, #6183).
 * Custom and raster annotation now respond to scale transformations, and can
   use AsIs variables for relative placement (@teunbrand based on 
   @yutannihilation's prior work, #3120)

R/guide-bins.R

@@ -208,7 +208,10 @@ GuideBins <- ggproto(
     params$show.limits <- show.limits
 
     if (params$reverse) {
-      key <- key[rev(seq_len(nrow(key))), , drop = FALSE]
+      ord <- seq_len(nrow(key))
+      key <- vec_slice(key, rev(ord))
+      # Put NA back in the trailing position
+      key[params$aesthetic] <- vec_slice(key[params$aesthetic], c(ord[-1], ord[1]))
       key$.value <- 1 - key$.value
     }
 

tests/testthat/test-guides.R

@@ -378,6 +378,22 @@ test_that("guides title and text are positioned correctly", {
   expect_doppelganger("legends with all title justifications", p)
 })
 
+test_that("bin guide can be reversed", {
+
+  p <- ggplot(data.frame(x = c(0, 100)), aes(x, x, colour = x, fill = x)) +
+    geom_point() +
+    guides(
+      colour = guide_bins(reverse = TRUE, show.limits = TRUE,  order = 1),
+      fill   = guide_bins(
+        reverse = TRUE, show.limits = FALSE, order = 2,
+        override.aes = list(shape = 21)
+      )
+    )
+
+  expect_doppelganger("reversed guide_bins", p)
+
+})
+
 test_that("bin guide can be styled correctly", {
   df <- data_frame(x = c(1, 2, 3),
                    y = c(6, 5, 7))