Flip labels input before modifying them (#4441)

Author: thomasp85

R/coord-flip.r

@@ -62,7 +62,7 @@ CoordFlip <- ggproto("CoordFlip", CoordCartesian,
   },
 
   labels = function(labels, panel_params) {
-    flip_axis_labels(CoordCartesian$labels(labels, panel_params))
+    CoordCartesian$labels(flip_axis_labels(labels), panel_params)
   },
 
   setup_layout = function(layout, params) {

tests/figs/test-coord-flip-r/turning-off-secondary-title-with-coord-flip.svg

@@ -0,0 +1,11 @@
+context("test-coord-flip.r")
+
+test_that("secondary labels are correctly turned off", {
+  # Using a visual test because the labels are only generated during rendering
+  expect_doppelganger("turning off secondary title with coord_flip",
+    ggplot(mtcars, aes(x = mpg, y = cyl)) +
+      geom_point() +
+      scale_x_continuous(sec.axis = dup_axis(guide = guide_axis(title = NULL))) +
+      coord_flip()
+  )
+})