Code cleanup: several inspections applied

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/LocalFunctionsLowering.kt

@@ -239,8 +239,7 @@ class LocalFunctionsLowering(val context: BackendContext): DeclarationContainerL
                         functionDescriptor.parentsWithSelf
                                 .takeWhile { it is FunctionDescriptor }
                                 .toList().reversed()
-                                .map { suggestLocalName(it) }
-                                .joinToString(separator = "$")
+                                .joinToString(separator = "$") { suggestLocalName(it) }
                         )
 
         private fun createTransformedDescriptor(localFunctionContext: LocalFunctionContext): FunctionDescriptor {

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/ClassLowerWithContext.kt

@@ -33,7 +33,7 @@ abstract class ClassLowerWithContext : FileLoweringPass, IrElementTransformer<Ir
     private val irClass2Context = hashMapOf<IrClass, IrClassContext>()
 
     override fun lower(irFile: IrFile) {
-        val packageIr = irFile.declarations.filter { it.descriptor is FileClassDescriptor }.singleOrNull()
+        val packageIr = irFile.declarations.singleOrNull { it.descriptor is FileClassDescriptor }
         if (packageIr != null) {
             visitClass(packageIr as IrClass, null)
             irFile.declarations.filterNot { it == packageIr }.forEach { it.accept(this, irClass2Context[packageIr]!!) }

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/InterfaceLowering.kt

@@ -54,7 +54,7 @@ class InterfaceLowering(val state: GenerationState) : IrElementTransformerVoid()
 
         val members = defaultImplsIrClass.declarations
 
-        irClass.declarations.filterIsInstance<IrFunction>().mapNotNull {
+        irClass.declarations.filterIsInstance<IrFunction>().forEach {
             val descriptor = it.descriptor
             if (descriptor.modality != Modality.ABSTRACT) {
                 val functionDescriptorImpl = createDefaultImplFunDescriptor(defaultImplsDescriptor, descriptor, interfaceDescriptor, state.typeMapper)