Mark labels from default mappings and overwrite them if possible (#4414)

Author: thomasp85

NEWS.md

@@ -1,5 +1,9 @@
 # ggplot2 (development version)
 
+
+* Make sure that default labels from default mappings doesn't overwrite default
+  labels from explicit mappings (@thomasp85, #2406)
+  
 * `stat_count()` now computes width based on the full dataset instead of per 
   group (@thomasp85, #2047)
 

R/plot-construction.r

@@ -167,8 +167,16 @@ ggplot_add.Layer <- function(object, plot, object_name) {
 
   # Add any new labels
   mapping <- make_labels(object$mapping)
-  default <- make_labels(object$stat$default_aes)
+  default <- lapply(make_labels(object$stat$default_aes), function(l) {
+    attr(l, "fallback") <- TRUE
+    l
+  })
   new_labels <- defaults(mapping, default)
-  plot$labels <- defaults(plot$labels, new_labels)
+  current_labels <- plot$labels
+  current_fallbacks <- vapply(current_labels, function(l) isTRUE(attr(l, "fallback")), logical(1))
+  plot$labels <- defaults(current_labels[!current_fallbacks], new_labels)
+  if (any(current_fallbacks)) {
+    plot$labels <- defaults(plot$labels, current_labels)
+  }
   plot
 }

tests/testthat/test-labels.r

@@ -50,6 +50,18 @@ 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()
+
+  expect_equal(p$labels$colour[1], "colour")
+  expect_true(attr(p$labels$colour, "fallback"))
+
+  p <- p + geom_smooth(aes(color = drv))
+
+  expect_equal(p$labels$colour, "drv")
+})
+
 
 # Visual tests ------------------------------------------------------------