I wrote a nice little program. At some point, it is required to load a bundle with some additional functionality. I, too, am the author of the bundle, so I have the source code and Xcode-projects for both the main application and the bundle.
Until now, I simply dragged the bundle into the resources-folder in the main application, which works fine for running it, but I can't debug it (and of course there is an error in it).
Is there a way to set up Xcode so that I can debug the bundle?
In your bundle project, you should add a custom executable. That executable will launch in the debugger when you do a Build & Debug.
To do this, right-click on the Executables section in the Groups and Files list in your project and choose Add > New Custom Executable…
You can then select your application in the open dialog.
You will also need to change your build settings so that the build products are placed in your application's plug-ins folder when the plug-in is built, so that when you Build & Debug the application contains the latest version of your bundle.