Fix NSApplication initialization to prevent some issues on macOS

os/osx/app.mm

@@ -52,7 +52,25 @@ void setAppMode(AppMode appMode)
 
   void finishLaunching()
   {
-    [m_app finishLaunching];
+    id runningApp = [NSRunningApplication currentApplication];
+    // [m_app run] must be called once, if the app didn't finish launching yet.
+    if (![runningApp isFinishedLaunching]) {
+      // The run method must be called in GUI mode only, otherwise the
+      // [AppDelegateOSX applicationDidFinishLaunching] doesn't get called
+      // and [m_app run] ends up blocking the app.
+      if ([runningApp activationPolicy] == NSApplicationActivationPolicyRegular) {
+        // Note that the [m_app run] call doesn't block because we are calling
+        // [NSApp stop] from [AppDelegateOSX applicationDidFinishLaunching]. We only
+        // need the application's initialization done inside run to prevent issues
+        // such as: https://github.com/aseprite/aseprite/issues/4795
+        [m_app run];
+      }
+      else {
+        // The app is running in CLI mode, then we just call finishLaunching.
+        [m_app finishLaunching];
+      }
+    }
+
     [m_appDelegate resetCliFiles];
   }
 

os/osx/app_delegate.h

@@ -29,6 +29,7 @@
 - (BOOL)applicationShouldTerminateAfterLastWindowClosed:(NSApplication*)app;
 - (void)applicationWillTerminate:(NSNotification*)notification;
 - (void)applicationWillResignActive:(NSNotification*)notification;
+- (void)applicationDidFinishLaunching:(NSNotification*)notification;
 - (void)applicationDidBecomeActive:(NSNotification*)notification;
 - (void)applicationDidHide:(NSNotification*)notification;
 - (void)applicationDidUnhide:(NSNotification*)notification;

os/osx/app_delegate.mm

@@ -106,6 +106,13 @@ - (void)applicationWillResignActive:(NSNotification*)notification
     [ViewOSX updateKeyFlags:event];
 }
 
+- (void)applicationDidFinishLaunching:(NSNotification*)notification
+{
+  // We do not want that the [NSApplication run] call made from
+  // AppOSX::Impl::finishLaunching() blocks.
+  [NSApp stop:nil];
+}
+
 - (void)applicationDidBecomeActive:(NSNotification*)notification
 {
   for (id window : [NSApp windows]) {

os/system.h

@@ -93,15 +93,16 @@ class System : public RefCount {
   // files that were processed from the CLI arguments directly.
   virtual void markCliFileAsProcessed(const std::string& cliFile) = 0;
 
-  // On macOS it calls [NSApplication finishLaunching] that will
-  // produce some extra events like [NSApplicationDelegate
-  // application:openFiles:] which generates os::Event::DropFiles
-  // events for each file specified in the command line.
+  // On macOS it calls [NSApplication run], which in turn does two things:
+  // - It calls [NSApplication finishLaunching], which will produce some extra
+  // events like [NSApplicationDelegate application:openFiles:] which generates
+  // os::Event::DropFiles events for each file specified in the command line.
+  // - It initializes internal state of the NSApplication instance to make it
+  // behave as expected under some circumstances.
   //
-  // You can ignore those DropFiles events if you've already
-  // processed through the CLI arguments (app_main(argc, argv)) or
-  // you can use markCliFileAsProcessed() before calling this
-  // function.
+  // About the first point: you can ignore those DropFiles events if you've
+  // already processed through the CLI arguments (app_main(argc, argv)) or
+  // you can use markCliFileAsProcessed() before calling this function.
   virtual void finishLaunching() = 0;
 
   // We might need to call this function when the app is launched