Add setOfNotNull function #KT-35851

libraries/stdlib/samples/test/samples/collections/collections.kt

@@ -334,6 +334,18 @@ class Collections {
             assertPrints(set, "[1, 2, 4, 5]")
         }
 
+        @Sample
+        fun setOfNotNull() {
+            val empty = setOfNotNull<Any>(null)
+            assertPrints(empty, "[]")
+
+            val singleton = setOfNotNull(42)
+            assertPrints(singleton, "[42]")
+
+            val set = setOfNotNull(1, null, 2, null, 3)
+            assertPrints(set, "[1, 2, 3]")
+        }
+
         @Sample
         fun emptyLinkedHashSet() {
             val set: LinkedHashSet<Int> = linkedSetOf<Int>()

libraries/stdlib/src/kotlin/collections/Sets.kt

@@ -90,6 +90,25 @@ public inline fun <T> linkedSetOf(): LinkedHashSet<T> = LinkedHashSet()
  */
 public fun <T> linkedSetOf(vararg elements: T): LinkedHashSet<T> = elements.toCollection(LinkedHashSet(mapCapacity(elements.size)))
 
+/**
+ * Returns a new read-only set either with single given element, if it is not null, or empty set if the element is null.
+ * The returned set is serializable (JVM).
+ * @sample samples.collections.Collections.Sets.setOfNotNull
+ */
+@SinceKotlin("1.4")
+public fun <T : Any> setOfNotNull(element: T?): Set<T> = if (element != null) setOf(element) else emptySet()
+
+/**
+ * Returns a new read-only set only with those given elements, that are not null.
+ * Elements of the set are iterated in the order they were specified.
+ * The returned set is serializable (JVM).
+ * @sample samples.collections.Collections.Sets.setOfNotNull
+ */
+@SinceKotlin("1.4")
+public fun <T : Any> setOfNotNull(vararg elements: T?): Set<T> {
+    return elements.filterNotNullTo(LinkedHashSet())
+}
+
 /**
  * Builds a new read-only [Set] by populating a [MutableSet] using the given [builderAction]
  * and returning a read-only set with the same elements.

libraries/stdlib/test/collections/CollectionTest.kt

@@ -71,6 +71,18 @@ class CollectionTest {
         assertEquals(listOf("value1", "value2"), l3)
     }
 
+    @Test fun setOfNotNull() {
+        val l1: Set<Int> = setOfNotNull(null)
+        assertTrue(l1.isEmpty())
+
+        val s: String? = "value"
+        val l2: Set<String> = setOfNotNull(s)
+        assertEquals(s, l2.single())
+
+        val l3: Set<String> = setOfNotNull("value1", null, "value2")
+        assertEquals(setOf("value1", "value2"), l3)
+    }
+
     @Test fun filterIntoSet() {
         val data = listOf("foo", "bar")
         val foo = data.filterTo(hashSetOf<String>()) { it.startsWith("f") }

libraries/tools/binary-compatibility-validator/reference-public-api/kotlin-stdlib-runtime-merged.txt

@@ -2369,6 +2369,8 @@ public final class kotlin/collections/SetsKt {
 	public static final fun plus (Ljava/util/Set;[Ljava/lang/Object;)Ljava/util/Set;
 	public static final fun setOf (Ljava/lang/Object;)Ljava/util/Set;
 	public static final fun setOf ([Ljava/lang/Object;)Ljava/util/Set;
+	public static final fun setOfNotNull (Ljava/lang/Object;)Ljava/util/Set;
+	public static final fun setOfNotNull ([Ljava/lang/Object;)Ljava/util/Set;
 	public static final fun sortedSetOf (Ljava/util/Comparator;[Ljava/lang/Object;)Ljava/util/TreeSet;
 	public static final fun sortedSetOf ([Ljava/lang/Object;)Ljava/util/TreeSet;
 }