Parameterless nullsFirst and nullsLast and misc comparator combining functions.

libraries/stdlib/test/OrderingTest.kt

@@ -53,6 +53,20 @@ class OrderingTest {
         assertEquals(v1, items[1])
     }
 
+    Test fun combineComparators() {
+        val byName = compareBy<Item> { it.name }
+        val byRating = compareBy<Item> { it.rating }
+        val v3 = Item(v1.name, v1.rating + 1)
+        val v4 = Item(v2.name + "_", v2.rating)
+        assertTrue( (byName then byRating).compare(v1, v2) > 0 )
+        assertTrue( (byName then byRating).compare(v1, v3) < 0 )
+        assertTrue( (byName thenDescending byRating).compare(v1, v3) > 0 )
+
+        assertTrue( (byRating then byName).compare(v1, v2) < 0 )
+        assertTrue( (byRating then byName).compare(v4, v2) > 0 )
+        assertTrue( (byRating thenDescending byName).compare(v4, v2) < 0 )
+    }
+
     Test fun sortByThenBy() {
         val comparator = compareBy<Item> { it.rating } thenBy { it.name }
 

libraries/stdlib/test/collections/CollectionTest.kt

@@ -584,7 +584,7 @@ class CollectionTest {
         listOf("", "sort", "abc").let {
             assertEquals(listOf("", "abc", "sort"), it.sortedBy { it.nonEmptyLength() })
             assertEquals(listOf("sort", "abc", ""), it.sortedByDescending { it.nonEmptyLength() })
-            assertEquals(listOf("abc", "sort", ""), it.sortedWith(compareBy(nullsLast(compareBy<Int> {it})) { it.nonEmptyLength()}))
+            assertEquals(listOf("abc", "sort", ""), it.sortedWith(compareBy(nullsLast<Int>()) { it.nonEmptyLength()}))
         }
     }