Support KClass.nestedClasses

core/reflection.jvm/src/kotlin/reflect/jvm/internal/KClassImpl.kt

@@ -16,15 +16,20 @@
 
 package kotlin.reflect.jvm.internal
 
-import org.jetbrains.kotlin.descriptors.ClassKind
-import org.jetbrains.kotlin.descriptors.ConstructorDescriptor
-import org.jetbrains.kotlin.descriptors.FunctionDescriptor
-import org.jetbrains.kotlin.descriptors.PropertyDescriptor
+import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.descriptors.annotations.Annotated
 import org.jetbrains.kotlin.incremental.components.NoLookupLocation
 import org.jetbrains.kotlin.load.java.JvmAbi
+import org.jetbrains.kotlin.load.java.reflect.tryLoadClass
+import org.jetbrains.kotlin.load.java.sources.JavaSourceElement
+import org.jetbrains.kotlin.load.java.structure.reflect.ReflectJavaClass
+import org.jetbrains.kotlin.load.java.structure.reflect.safeClassLoader
+import org.jetbrains.kotlin.load.kotlin.KotlinJvmBinarySourceElement
+import org.jetbrains.kotlin.load.kotlin.reflect.ReflectKotlinClass
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.platform.JavaToKotlinClassMap
+import org.jetbrains.kotlin.resolve.DescriptorUtils
 import org.jetbrains.kotlin.resolve.scopes.JetScope
 import org.jetbrains.kotlin.serialization.deserialization.findClassAcrossModuleDependencies
 import kotlin.reflect.KCallable
@@ -111,6 +116,27 @@ class KClassImpl<T : Any>(override val jClass: Class<T>) : KDeclarationContainer
             KFunctionImpl(this, it) as KFunction<T>
         }
 
+    override val nestedClasses: Collection<KClass<*>>
+        get() = descriptor.unsubstitutedInnerClassesScope.getAllDescriptors().map { nestedClass ->
+            val source = (nestedClass as DeclarationDescriptorWithSource).source
+            when (source) {
+                is KotlinJvmBinarySourceElement ->
+                    (source.binaryClass as ReflectKotlinClass).klass
+                is JavaSourceElement ->
+                    (source.javaElement as ReflectJavaClass).element
+                SourceElement.NO_SOURCE -> {
+                    // If neither a Kotlin class nor a Java class, it must be a built-in
+                    val classId = JavaToKotlinClassMap.INSTANCE.mapKotlinToJava(DescriptorUtils.getFqName(nestedClass))
+                                  ?: throw KotlinReflectionInternalError("Class with no source must be a built-in: $nestedClass")
+                    val packageName = classId.packageFqName.asString()
+                    val className = classId.relativeClassName.asString().replace('.', '$')
+                    // All pseudo-classes like String.Companion must be accessible from the current class loader
+                    javaClass.safeClassLoader.tryLoadClass("$packageName.$className")
+                }
+                else -> throw KotlinReflectionInternalError("Unsupported class: $nestedClass (source = $source)")
+            }
+        }.filterNotNull().map { KClassImpl(it) }
+
     @suppress("UNCHECKED_CAST")
     override val objectInstance: T? by ReflectProperties.lazy {
         val descriptor = descriptor