app: [macOS] make the app delegate optional

Inspired by the discussion at golang.org/issue/70089, this change makes
our particular NSApplicationDelegate implementation optional.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/os_macos.go

@@ -40,6 +40,7 @@ import (
 #define MOUSE_SCROLL 4
 
 __attribute__ ((visibility ("hidden"))) void gio_main(void);
+__attribute__ ((visibility ("hidden"))) void gio_init(void);
 __attribute__ ((visibility ("hidden"))) CFTypeRef gio_createView(int presentWithTrans);
 __attribute__ ((visibility ("hidden"))) CFTypeRef gio_createWindow(CFTypeRef viewRef, CGFloat width, CGFloat height);
 __attribute__ ((visibility ("hidden"))) void gio_viewSetHandle(CFTypeRef viewRef, uintptr_t handle);
@@ -334,6 +335,8 @@ import "C"
 func init() {
 	// Darwin requires that UI operations happen on the main thread only.
 	runtime.LockOSThread()
+	// Register launch finished listener.
+	C.gio_init()
 }
 
 // AppKitViewEvent notifies the client of changes to the window AppKit handles.

app/os_macos.m

@@ -420,7 +420,6 @@ void gio_viewSetHandle(CFTypeRef viewRef, uintptr_t handle) {
 - (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
 	[NSApp setActivationPolicy:NSApplicationActivationPolicyRegular];
 	[NSApp activateIgnoringOtherApps:YES];
-	gio_onFinishLaunching();
 }
 @end
 
@@ -451,3 +450,25 @@ void gio_main() {
 		[NSApp run];
 	}
 }
+
+@interface AppListener : NSObject
+@end
+
+static AppListener *appListener;
+
+@implementation AppListener
+- (void)launchFinished:(NSNotification *)notification {
+	appListener = nil;
+	gio_onFinishLaunching();
+}
+@end
+
+void gio_init() {
+	@autoreleasepool {
+		appListener = [[AppListener alloc] init];
+		[[NSNotificationCenter defaultCenter] addObserver:appListener
+												 selector:@selector(launchFinished:)
+													 name:NSApplicationDidFinishLaunchingNotification
+												   object:nil];
+	}
+}