Implement very basic Objective-C interop

Also refactor StubGenerator

backend.native/tests/build.gradle

@@ -1995,6 +1995,13 @@ kotlinNativeInterop {
             linkerOpts '-framework', 'OpenGL', '-framework', 'GLUT'
             flavor 'native'
         }
+
+        objcSmoke {
+            defFile 'interop/objc/objcSmoke.def'
+            headers "$projectDir/interop/objc/smoke.h"
+            linkerOpts "-L$buildDir",  "-lobjcsmoke"
+            flavor 'native'
+        }
     }
 }
 
@@ -2057,4 +2064,19 @@ if (isMac()) {
         source = "interop/basics/opengl_teapot.kt"
         interop = 'opengl'
     }
+
+    task interop_objc_smoke(type: RunInteropKonanTest) {
+        goldValue = "Hello, World!\nKotlin says: Hello, everybody!\nHello from Kotlin\n2, 1\nDeallocated\nDeallocated\n"
+
+        source = "interop/objc/smoke.kt"
+        interop = 'objcSmoke'
+
+        doFirst {
+            execClang {
+                args "$projectDir/interop/objc/smoke.m"
+                args "-lobjc", '-fobjc-arc'
+                args '-fPIC', '-shared', '-o', "$buildDir/libobjcsmoke.dylib"
+            }
+        }
+    }
 }

backend.native/tests/interop/objc/objcSmoke.def

@@ -0,0 +1,2 @@
+language = Objective-C
+headerFilter = **/smoke.h

backend.native/tests/interop/objc/smoke.h

@@ -0,0 +1,24 @@
+#import <objc/NSObject.h>
+
+@protocol Printer
+@required
+-(void)print:(const char*)string;
+@end;
+
+@interface Foo : NSObject
+@property NSString* name;
+-(void)hello;
+-(void)helloWithPrinter:(id <Printer>)printer;
+@end;
+
+@protocol MutablePair
+@required
+@property (readonly) int first;
+@property (readonly) int second;
+
+-(void)update:(int)index add:(int)delta;
+-(void)update:(int)index sub:(int)delta;
+
+@end;
+
+void replacePairElements(id <MutablePair> pair, int first, int second);

backend.native/tests/interop/objc/smoke.kt

@@ -0,0 +1,55 @@
+import kotlinx.cinterop.*
+import objcSmoke.*
+
+fun main(args: Array<String>) {
+    autoreleasepool {
+        run()
+    }
+}
+
+fun run() {
+    val foo = Foo()
+    foo.hello()
+    foo.name = "everybody"
+    foo.helloWithPrinter(object : NSObject(), PrinterProtocol {
+        override fun print(string: CPointer<ByteVar>?) {
+            println("Kotlin says: " + string?.toKString())
+        }
+    })
+
+    Bar().hello()
+
+    val pair = MutablePairImpl(42, 17)
+    replacePairElements(pair, 1, 2)
+    pair.swap()
+    println("${pair.first}, ${pair.second}")
+}
+
+fun MutablePairProtocol.swap() {
+    update(0, add = second)
+    update(1, sub = first)
+    update(0, add = second)
+    update(1, sub = second*2)
+}
+
+class Bar : Foo() {
+    override fun helloWithPrinter(printer: PrinterProtocol) = memScoped {
+        printer.print("Hello from Kotlin".cstr.getPointer(memScope))
+    }
+}
+
+@Suppress("CONFLICTING_OVERLOADS")
+class MutablePairImpl(first: Int, second: Int) : NSObject(), MutablePairProtocol {
+    private var elements = intArrayOf(first, second)
+
+    override fun first() = elements.first()
+    override fun second() = elements.last()
+
+    override fun update(index: Int, add: Int) {
+        elements[index] += add
+    }
+
+    override fun update(index: Int, sub: Int) {
+        elements[index] -= sub
+    }
+}

backend.native/tests/interop/objc/smoke.m

@@ -0,0 +1,46 @@
+#import <stdio.h>
+#import <Foundation/NSString.h>
+#import "smoke.h"
+
+@interface CPrinter : NSObject <Printer>
+-(void)print:(const char*)string;
+@end;
+
+@implementation CPrinter
+-(void)print:(const char*)string {
+    printf("%s\n", string);
+    fflush(stdout);
+}
+@end;
+
+@implementation Foo
+
+@synthesize name;
+
+-(instancetype)init {
+    if (self = [super init]) {
+        self.name = @"World";
+    }
+    return self;
+}
+
+-(void)hello {
+    CPrinter* printer = [[CPrinter alloc] init];
+    [self helloWithPrinter:printer];
+}
+
+-(void)helloWithPrinter:(id <Printer>)printer {
+    NSString* message = [NSString stringWithFormat:@"Hello, %@!", self.name];
+    [printer print:message.UTF8String];
+}
+
+-(void)dealloc {
+    printf("Deallocated\n");
+}
+
+@end;
+
+void replacePairElements(id <MutablePair> pair, int first, int second) {
+    [pair update:0 add:(first - pair.first)];
+    [pair update:1 sub:(pair.second - second)];
+}