Add prelimitary support for using Objective-C types in framework API

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

@@ -172,10 +172,9 @@ internal class InteropBuiltIns(builtIns: KonanBuiltIns) {
 
     val getObjCClass = packageScope.getContributedFunctions("getObjCClass").single()
 
-    val objCObjectRawPtr = packageScope.getContributedVariables("rawPtr").single {
+    val objCObjectRawPtr = packageScope.getContributedFunctions("rawPtr").single {
         val extensionReceiverType = it.extensionReceiverParameter?.type
-        extensionReceiverType != null && !extensionReceiverType.isMarkedNullable &&
-                TypeUtils.getClassDescriptor(extensionReceiverType) == objCObject
+        extensionReceiverType != null && TypeUtils.getClassDescriptor(extensionReceiverType) == objCObject
     }
 
     val getObjCReceiverOrSuper = packageScope.getContributedFunctions("getReceiverOrSuper").single()

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

@@ -117,7 +117,7 @@ internal class KonanSymbols(context: Context, val symbolTable: SymbolTable): Sym
             symbolTable.referenceSimpleFunction(context.interopBuiltIns.objCObjectSuperInitCheck)
 
     val interopObjCObjectRawValueGetter =
-            symbolTable.referenceSimpleFunction(context.interopBuiltIns.objCObjectRawPtr.getter!!)
+            symbolTable.referenceSimpleFunction(context.interopBuiltIns.objCObjectRawPtr)
 
     val interopInvokeImpls = context.interopBuiltIns.invokeImpls.mapValues { (_, function) ->
         symbolTable.referenceSimpleFunction(function)

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

@@ -440,6 +440,15 @@ internal class Llvm(val context: Context, val llvmModule: LLVMModuleRef) {
         null
     }
 
+    val objCExportEnabled = if (context.config.produce.isNativeBinary) {
+        // Note: this defines the global declared in runtime (if any).
+        staticData.placeGlobal("objCExportEnabled", Int8(0), isExported = true).also {
+            it.setConstant(true)
+        }
+    } else {
+        null
+    }
+
     val tlsMode by lazy {
         when (target) {
             KonanTarget.WASM32, 

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

@@ -218,6 +218,7 @@ internal class ObjCExportCodeGenerator(
         emitSortedAdapters(placedInterfaceAdapters, "Kotlin_ObjCExport_sortedProtocolAdapters")
 
         context.llvm.kObjectReservedTailSize!!.setInitializer(Int32(runtime.pointerSize))
+        context.llvm.objCExportEnabled!!.setInitializer(Int8(1))
 
         dataGenerator.finishModule() // TODO: move to appropriate place.
     }
@@ -445,6 +446,11 @@ private fun ObjCExportCodeGenerator.emitSpecialClassesConvertions() {
         emitBoxConverter(it)
     }
 
+    setObjCExportTypeInfo(
+            context.interopBuiltIns.objCPointerHolder,
+            constPointer(codegen.llvmFunction(context.ir.symbols.objCPointerHolderValueGetter.owner))
+    )
+
     emitFunctionConverters()
 
     emitKotlinFunctionAdaptersToBlock()

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

@@ -92,8 +92,11 @@ internal class ObjCExportHeaderGenerator(val context: Context) {
     private val kotlinAnyName = namer.kotlinAnyName
 
     private val stubs = mutableListOf<Stub>()
-    private val classToName = mutableMapOf<ClassDescriptor, String>()
-    private val interfaceToName = mutableMapOf<ClassDescriptor, String>()
+    private val classOrInterfaceToName = mutableMapOf<ClassDescriptor, String>()
+
+    internal val classForwardDeclarations = mutableSetOf<String>()
+    internal val protocolForwardDeclarations = mutableSetOf<String>()
+
     private val extensions = mutableMapOf<ClassDescriptor, MutableList<CallableMemberDescriptor>>()
     val extraClassesToTranslate = mutableSetOf<ClassDescriptor>()
 
@@ -154,17 +157,11 @@ internal class ObjCExportHeaderGenerator(val context: Context) {
         }
     }
 
-    fun translateClassName(descriptor: ClassDescriptor): String {
-        val descriptorToName = if (descriptor.isInterface) interfaceToName else classToName
+    fun translateClassName(descriptor: ClassDescriptor): String = classOrInterfaceToName.getOrPut(descriptor) {
+        assert(mapper.shouldBeExposed(descriptor))
+        val forwardDeclarations = if (descriptor.isInterface) protocolForwardDeclarations else classForwardDeclarations
 
-        return descriptorToName.getOrPut(descriptor) {
-            if (!mapper.shouldBeExposed(descriptor)) {
-                context.reportCompilationError("Can't produce ${descriptor.fqNameSafe.asString()} to framework API")
-                throw KonanCompilationException()
-            }
-
-            namer.getClassOrProtocolName(descriptor)
-        }
+        namer.getClassOrProtocolName(descriptor).also { forwardDeclarations += it }
     }
 
     private fun translateInterface(descriptor: ClassDescriptor) {
@@ -555,13 +552,13 @@ internal class ObjCExportHeaderGenerator(val context: Context) {
         add("#import <Foundation/Foundation.h>")
         add("")
 
-        if (classToName.isNotEmpty()) {
-            add("@class ${classToName.values.joinToString()};")
+        if (classForwardDeclarations.isNotEmpty()) {
+            add("@class ${classForwardDeclarations.joinToString()};")
             add("")
         }
 
-        if (interfaceToName.isNotEmpty()) {
-            add("@protocol ${interfaceToName.values.joinToString()};")
+        if (protocolForwardDeclarations.isNotEmpty()) {
+            add("@protocol ${protocolForwardDeclarations.joinToString()};")
             add("")
         }
 
@@ -790,6 +787,10 @@ private fun ObjCExportHeaderGenerator.mapReferenceTypeIgnoringNullability(
         return ObjCIdType
     }
 
+    if (classDescriptor.defaultType.isObjCObjectType()) {
+        return mapObjCObjectReferenceTypeIgnoringNullability(classDescriptor)
+    }
+
     scheduleClassToBeGenerated(classDescriptor)
 
     return if (classDescriptor.isInterface) {
@@ -799,6 +800,32 @@ private fun ObjCExportHeaderGenerator.mapReferenceTypeIgnoringNullability(
     }
 }
 
+private tailrec fun ObjCExportHeaderGenerator.mapObjCObjectReferenceTypeIgnoringNullability(
+        descriptor: ClassDescriptor
+): ObjCNonNullReferenceType {
+    // TODO: more precise types can be used.
+
+    if (descriptor.isObjCMetaClass()) return ObjCIdType
+
+    if (descriptor.isExternalObjCClass()) {
+        return if (descriptor.isInterface) {
+            val name = descriptor.name.asString().removeSuffix("Protocol")
+            protocolForwardDeclarations += name
+            ObjCProtocolType(name)
+        } else {
+            val name = descriptor.name.asString()
+            classForwardDeclarations += name
+            ObjCClassType(name)
+        }
+    }
+
+    if (descriptor.isKotlinObjCClass()) {
+        return mapObjCObjectReferenceTypeIgnoringNullability(descriptor.getSuperClassOrAny())
+    }
+
+    return ObjCIdType
+}
+
 private fun ObjCExportHeaderGenerator.scheduleClassToBeGenerated(classDescriptor: ClassDescriptor) {
     if (classDescriptor !in generatedClasses) {
         extraClassesToTranslate += classDescriptor

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

@@ -49,6 +49,8 @@ internal fun ObjCExportMapper.getClassIfCategory(descriptor: CallableMemberDescr
 
     val extensionReceiverType = descriptor.extensionReceiverParameter?.type ?: return null
 
+    if (extensionReceiverType.isObjCObjectType()) return null
+
     val erasedClass = extensionReceiverType.getErasedTypeClass()
     return if (this.isRepresentedAsObjCInterface(erasedClass)) {
         erasedClass