Check for occurence of infinite values

Add scale name to warning

Clean up warning

Author: thomasp85

NEWS.md

@@ -75,6 +75,9 @@
 * Only one warning is issued when asking for too many levels in 
   `scale_discrete()` (#1674)
 
+* A warning is now issued when a scale transformation introduces infinite 
+  values in a scale (#1696)
+
 # ggplot2 2.1.0
 
 ## New features

R/scale-.r

@@ -187,7 +187,13 @@ ScaleContinuous <- ggproto("ScaleContinuous", Scale,
   },
 
   transform = function(self, x) {
-     self$trans$transform(x)
+     new_x <- self$trans$transform(x)
+     if (any(is.finite(x) != is.finite(new_x))) {
+       type <- if (self$scale_name == "position_c") "continuous" else "discrete"
+       axis <- if ("x" %in% self$aesthetics) "x" else "y"
+       warning("Transformation introduced infinite values in ", type, " ", axis, "-axis", call. = FALSE)
+     }
+     new_x
   },
 
   map = function(self, x, limits = self$get_limits()) {

tests/testthat/test-scales.r

@@ -167,3 +167,13 @@ test_that("find_global searches in the right places", {
   expect_identical(find_global("scale_colour_hue", emptyenv()),
     ggplot2::scale_colour_hue)
 })
+
+test_that("Scales warn when transforms introduces non-finite values", {
+  df <- data.frame(x = c(1e1, 1e5), y = c(0, 100))
+
+  p <- ggplot(df, aes(x, y)) +
+    geom_point(size = 5) +
+    scale_y_log10()
+
+  expect_warning(ggplot_build(p), "Transformation introduced infinite values")
+})