Coord flip grid (#6319)

* swap x/y when using `coord_flip()`

* include grid in snapshot

* add news bullet

Author: teunbrand

NEWS.md

@@ -1,5 +1,7 @@
 # ggplot2 (development version)
 
+* Fixed regression with incorrectly drawn gridlines when using `coord_flip()` 
+  (@teunbrand, #6293).
 * Deprecated functions and arguments prior to ggplot2 3.0.0 throw errors instead 
   of warnings. 
 * Functions and arguments that were soft-deprecated up to ggplot2 3.4.0 now 

R/guides-grid.R

@@ -12,7 +12,11 @@ guide_grid <- function(theme, panel_params, coord, square = TRUE) {
   y_minor <- setdiff(panel_params$y$mapped_breaks_minor(), y_major)
 
   transform <- if (isTRUE(square)) {
-    function(x) coord$transform(x, panel_params)
+    if (inherits(coord, "CoordFlip")) {
+      function(x) coord$transform(flip_axis_labels(x), panel_params)
+    } else {
+      function(x) coord$transform(x, panel_params)
+    }
   } else {
     function(x) coord_munch(coord, x, panel_params)
   }

tests/testthat/_snaps/coord-flip/turning-off-secondary-title-with-coord-flip.svg

@@ -4,7 +4,12 @@ test_that("secondary labels are correctly turned off", {
     ggplot(mtcars, aes(x = mpg, y = cyl)) +
       geom_point() +
       scale_x_continuous(sec.axis = dup_axis(guide = guide_axis(title = NULL))) +
-      coord_flip()
+      coord_flip() +
+      theme_test() +
+      theme(
+        panel.grid.major.y = element_line(colour = "grey80"),
+        panel.grid.major.x = element_line(colour = "grey90")
+      )
   )
 })