User supplied minor breaks should be transformed.

Fixes #1385

Author: hadley

NEWS.md

@@ -425,6 +425,9 @@ version of ggplot.
 * New `layer_data()` function extracts the data used for plotting for a given
   layer. It's mostly useful for testing.
 
+* User supplied `minor_breaks` can now be supplied on the same scale as 
+  the data, and will be automatically transformed with by scale (#1385).
+
 * You can now suppress the appearance of an axis/legend title (and the space
   that would allocated for it) with `NULL` in the `scale_` function. To
   use the default lable, use `waiver()` (#1145).

R/scale-.r

@@ -266,7 +266,7 @@ ScaleContinuous <- ggproto("ScaleContinuous", Scale,
       breaks <- self$minor_breaks(self$trans$inverse(limits))
       breaks <- self$trans$transform(breaks)
     } else {
-      breaks <- self$minor_breaks
+      breaks <- self$trans$transform(self$minor_breaks)
     }
 
     # Any minor breaks outside the dimensions need to be thrown away

tests/testthat/test-scales-breaks-labels.r

@@ -248,3 +248,10 @@ test_that("only finite or NA values for breaks for transformed scales (#871)", {
   breaks <- sc$get_breaks()
   expect_true(all(is.finite(breaks) | is.na(breaks)))
 })
+
+test_that("minor breaks are transformed by scales", {
+  sc <- scale_y_continuous(limits = c(1, 100), trans = "log10",
+    minor_breaks = c(1, 10, 100))
+
+  expect_equal(sc$get_breaks_minor(), c(0, 1, 2))
+})