Add KClass.sealedSubclasses to get direct subclasses of sealed class

#KT-14657 Fixed

compiler/testData/codegen/box/reflection/classes/sealedSubclasses.kt

@@ -0,0 +1,41 @@
+// IGNORE_BACKEND: JS, JS_IR, JVM_IR, NATIVE
+// WITH_REFLECT
+
+import kotlin.reflect.KClass
+import kotlin.reflect.jvm.*
+import kotlin.test.assertEquals
+
+// --
+
+sealed class SealedClassWithTopLevelSubclasses {
+    class NotASealedSubclass : TL2()
+}
+object TL1 : SealedClassWithTopLevelSubclasses()
+open class TL2 : SealedClassWithTopLevelSubclasses()
+
+// --
+
+sealed class SealedClassWithNestedSubclasses {
+    data class N1(val x: Unit) : SealedClassWithNestedSubclasses()
+    object N2 : SealedClassWithNestedSubclasses()
+}
+
+// --
+
+sealed class SealedClassWithNoSubclasses
+
+// --
+
+fun sealedSubclassNames(c: KClass<*>) = c.sealedSubclasses.map { it.simpleName ?: throw AssertionError("Unnamed class: ${it.java}") }.sorted()
+
+fun box(): String {
+    assertEquals(listOf("TL1", "TL2"), sealedSubclassNames(SealedClassWithTopLevelSubclasses::class))
+    assertEquals(listOf("N1", "N2"), sealedSubclassNames(SealedClassWithNestedSubclasses::class))
+    assertEquals(emptyList(), sealedSubclassNames(SealedClassWithNoSubclasses::class))
+
+    assertEquals(emptyList(), sealedSubclassNames(String::class))
+    assertEquals(emptyList(), sealedSubclassNames(Thread::class))
+    assertEquals(emptyList(), sealedSubclassNames(FloatArray::class))
+
+    return "OK"
+}

compiler/tests/org/jetbrains/kotlin/codegen/BlackBoxCodegenTestGenerated.java

@@ -17844,6 +17844,11 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
                 runTest("compiler/testData/codegen/box/reflection/classes/qualifiedNameOfStandardClasses.kt");
             }
 
+            @TestMetadata("sealedSubclasses.kt")
+            public void testSealedSubclasses() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/classes/sealedSubclasses.kt");
+            }
+
             @TestMetadata("starProjectedType.kt")
             public void testStarProjectedType() throws Exception {
                 runTest("compiler/testData/codegen/box/reflection/classes/starProjectedType.kt");

compiler/tests/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java

@@ -17844,6 +17844,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
                 runTest("compiler/testData/codegen/box/reflection/classes/qualifiedNameOfStandardClasses.kt");
             }
 
+            @TestMetadata("sealedSubclasses.kt")
+            public void testSealedSubclasses() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/classes/sealedSubclasses.kt");
+            }
+
             @TestMetadata("starProjectedType.kt")
             public void testStarProjectedType() throws Exception {
                 runTest("compiler/testData/codegen/box/reflection/classes/starProjectedType.kt");

compiler/tests/org/jetbrains/kotlin/codegen/ir/IrBlackBoxCodegenTestGenerated.java

@@ -17844,6 +17844,11 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
                 runTest("compiler/testData/codegen/box/reflection/classes/qualifiedNameOfStandardClasses.kt");
             }
 
+            @TestMetadata("sealedSubclasses.kt")
+            public void testSealedSubclasses() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/classes/sealedSubclasses.kt");
+            }
+
             @TestMetadata("starProjectedType.kt")
             public void testStarProjectedType() throws Exception {
                 runTest("compiler/testData/codegen/box/reflection/classes/starProjectedType.kt");