scales_add_defaults: find discrete/date/datetime/continuous scale type

Previously, it used trans_type to find the appropriate transformation.
Now it uses scale_type to find the appropriate scale -- and the scale
definitions contain information about which trans to use ("date",
"time", "identity").

R/scales-.r

@@ -77,21 +77,14 @@ scales_add_defaults <- function(scales, data, aesthetics, env) {
   if (length(datacols) == 0) return()
 
   for(aes in new_aesthetics) {
-    disc <- is.discrete(datacols[[aes]])
-    type <- if (disc) "discrete" else "continuous"
+    type <- scale_type(datacols[[aes]])
     scale_name <- paste("scale", aes, type, sep="_")
 
     # Skip aesthetics with no scales (e.g. group, order, etc)
     scale_f <- find_global(scale_name)
     if (is.null(scale_f)) next
-
-    if (disc) {
-      args <- list()
-    } else {
-      args <- list(trans = trans_type(datacols[[aes]]))
-    }
-    scale <- do.call(scale_f, args)
-    scales$add(scale)
+
+    scales$add(scale_f())
   }
 
 }
@@ -112,13 +105,15 @@ find_global <- function(name) {
   NULL
 }
 
-# Determine default transformation for continuous scales
-trans_type <- function(x) {
-  if (inherits(x, "Date")) {
+# Determine default type of a scale
+scale_type <- function(x) {
+  if (is.discrete(x)) {
+    "discrete"
+  } else if (inherits(x, "Date")) {
     "date"
   } else if (inherits(x, "POSIXt")) {
-    "time"
+    "datetime"
   } else {
-    "identity"
+    "continuous"
   }
 }