Change null handling in compareValuesBy(a, b, functions). Provide nullsFirst() and nullsLast() to extend Comparator<T> to Comparator<T?>.

libraries/stdlib/test/OrderingTest.kt

@@ -34,12 +34,21 @@ class OrderingTest {
         assertTrue(diff == 0)
     }
 
+    Test fun compareNullables() {
+        val v1: Item? = this.v1
+        val v2: Item? = null
+        val diff = compareValuesBy(v1, v2) { it?.rating }
+        assertTrue(diff > 0)
+        val diff2 = compareBy<Item> { it.rating }.thenBy { it.name }.nullsLast().compare(v1, v2)
+        assertTrue(diff2 < 0)
+    }
+
     Test fun sortComparatorThenComparator() {
         val comparator = comparator<Item> { a, b -> a.name.compareTo(b.name) } thenComparator { a, b -> a.rating.compareTo(b.rating) }
 
         val diff = comparator.compare(v1, v2)
         assertTrue(diff > 0)
-        val items = arrayListOf(v1, v2).sortBy(comparator)
+        val items = arrayListOf(v1, v2).sortedWith(comparator)
         assertEquals(v2, items[0])
         assertEquals(v1, items[1])
     }
@@ -49,7 +58,7 @@ class OrderingTest {
 
         val diff = comparator.compare(v1, v2)
         assertTrue(diff < 0)
-        val items = arrayListOf(v1, v2).sortBy(comparator)
+        val items = arrayListOf(v1, v2).sortedWith(comparator)
         assertEquals(v1, items[0])
         assertEquals(v2, items[1])
     }
@@ -59,7 +68,7 @@ class OrderingTest {
 
         val diff = comparator.compare(v1, v2)
         assertTrue(diff < 0)
-        val items = arrayListOf(v1, v2).sortBy(comparator)
+        val items = arrayListOf(v1, v2).sortedWith(comparator)
         assertEquals(v1, items[0])
         assertEquals(v2, items[1])
     }
@@ -68,7 +77,7 @@ class OrderingTest {
         val comparator = compareBy<Item>({ it.name }, { it.rating })
         val diff = comparator.compare(v1, v2)
         assertTrue(diff > 0)
-        val items = arrayListOf(v1, v2).sortBy(comparator)
+        val items = arrayListOf(v1, v2).sortedWith(comparator)
         assertEquals(v2, items[0])
         assertEquals(v1, items[1])
     }
@@ -85,7 +94,7 @@ class OrderingTest {
         }
         val diff = comparator.compare(v1, v2)
         assertTrue(diff > 0)
-        val items = arrayListOf(v1, v2).sortBy(comparator)
+        val items = arrayListOf(v1, v2).sortedWith(comparator)
         assertEquals(v2, items[0])
         assertEquals(v1, items[1])
     }