Improve kotlin.Unit support in produced framework

Make the Objective-C wrapper unique, and provide the method to get it

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/llvm/ContextUtils.kt

@@ -398,6 +398,7 @@ internal class Llvm(val context: Context, val llvmModule: LLVMModuleRef) {
     val Kotlin_ObjCExport_refFromObjC by lazyRtFunction
     val Kotlin_Interop_CreateNSStringFromKString by lazyRtFunction
     val Kotlin_Interop_CreateNSArrayFromKList by lazyRtFunction
+    val Kotlin_ObjCExport_convertUnit by lazyRtFunction
     val Kotlin_ObjCExport_GetAssociatedObject by lazyRtFunction
     val Kotlin_ObjCExport_AbstractMethodCalled by lazyRtFunction
 

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/llvm/objcexport/ObjCExportCodeGenerator.kt

@@ -254,6 +254,7 @@ internal class ObjCExportCodeGenerator(
             methodTable: List<RTTIGenerator.MethodTableRecord>,
             val objCName: String,
             directAdapters: List<ObjCToKotlinMethodAdapter>,
+            classAdapters: List<ObjCToKotlinMethodAdapter>,
             virtualAdapters: List<ObjCToKotlinMethodAdapter>,
             reverseAdapters: List<KotlinToObjCMethodAdapter>
     ) : Struct(
@@ -275,6 +276,13 @@ internal class ObjCExportCodeGenerator(
             ),
             Int32(directAdapters.size),
 
+            staticData.placeGlobalConstArray(
+                    "",
+                    runtime.objCToKotlinMethodAdapter,
+                    classAdapters
+            ),
+            Int32(classAdapters.size),
+
             staticData.placeGlobalConstArray(
                     "",
                     runtime.objCToKotlinMethodAdapter,
@@ -611,7 +619,8 @@ private fun ObjCExportCodeGenerator.createTypeAdapterForPackage(
             vtableSize = -1,
             methodTable = emptyList(),
             objCName = name,
-            directAdapters = adapters,
+            directAdapters = emptyList(),
+            classAdapters = adapters,
             virtualAdapters = emptyList(),
             reverseAdapters = emptyList()
     )
@@ -719,6 +728,12 @@ private fun ObjCExportCodeGenerator.createTypeAdapter(
         emptyList()
     }
 
+    val classAdapters = mutableListOf<ObjCExportCodeGenerator.ObjCToKotlinMethodAdapter>()
+
+    if (descriptor.isUnit()) {
+        classAdapters += createUnitInstanceAdapter()
+    }
+
     return ObjCTypeAdapter(
             descriptor,
             typeInfo,
@@ -727,11 +742,26 @@ private fun ObjCExportCodeGenerator.createTypeAdapter(
             methodTable,
             objCName,
             adapters,
+            classAdapters,
             virtualAdapters,
             reverseAdapters
     )
 }
 
+private fun ObjCExportCodeGenerator.createUnitInstanceAdapter(): ObjCExportCodeGenerator.ObjCToKotlinMethodAdapter {
+    val selector = "unit"
+    val methodBridge = MethodBridge(ReferenceBridge, listOf(ReferenceBridge, ReferenceBridge))
+    val encoding = getEncoding(methodBridge)
+
+    val imp = generateFunction(codegen, objCFunctionType(methodBridge), "") {
+        ret(callFromBridge(context.llvm.Kotlin_ObjCExport_convertUnit, listOf(codegen.theUnitInstanceRef.llvm)))
+    }
+
+    LLVMSetLinkage(imp, LLVMLinkage.LLVMPrivateLinkage)
+
+    return ObjCToKotlinMethodAdapter(selector, encoding, constPointer(imp))
+}
+
 private fun List<CallableMemberDescriptor>.toMethods(): List<FunctionDescriptor> = this.flatMap {
     when (it) {
         is PropertyDescriptor -> listOfNotNull(it.getter, it.setter)

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/objcexport/ObjCExportHeaderGenerator.kt

@@ -20,6 +20,7 @@ import org.jetbrains.kotlin.backend.konan.Context
 import org.jetbrains.kotlin.backend.konan.KonanCompilationException
 import org.jetbrains.kotlin.backend.konan.descriptors.getPackageFragments
 import org.jetbrains.kotlin.backend.konan.descriptors.isInterface
+import org.jetbrains.kotlin.backend.konan.descriptors.isUnit
 import org.jetbrains.kotlin.backend.konan.reportCompilationError
 import org.jetbrains.kotlin.builtins.getReceiverTypeFromFunctionType
 import org.jetbrains.kotlin.builtins.getReturnTypeFromFunctionType
@@ -201,6 +202,11 @@ internal class ObjCExportHeaderGenerator(val context: Context) {
 
             +"@interface $name : $superName${descriptor.superProtocolsClause}"
 
+            if (descriptor.isUnit()) {
+                +"+ (instancetype)unit NS_SWIFT_NAME(init());"
+                +""
+            }
+
             val presentConstructors = mutableSetOf<String>()
 
             descriptor.constructors.filter { mapper.shouldBeExposed(it) }.forEach {