You have to write some code that does the migration in the custom migration stage's willMigrate / didMigrate. There is a sample here: https://www.hackingwithswift.com/quick-start/swiftdata/how-to-store-swiftdata-attributes-in-an-external-file - although I'm not finding any more detailed resources on how to migrate and when to use will- or did-Migrate, so I guess we'll just have to try it out.

I had the same question and tried it out. Using ProcessInfo.processInfo.environment to access Xcode Cloud Environment Variable Secrets like I'm used to with Environment Variables defined in Xcode Schemas did not work for me. the docs don't go into much detail on the Xcode Cloud Environment Variables but reference that they can be used in custom build scripts: https://developer.apple.com/documentation/xcode/xcode-cloud-workflow-reference#Custom-environment-variables

For anyone running into this, in-case you have your app and local package together in the same Xcode workspace, make sure you select to run the Xcode Cloud workflow in the workspace (not app project). This was the issue for me that caused "Missing package product 'MyPackageName'" on Xcode Cloud builds. See this screenshot for the setting on the Xcode Cloud workflow:

Just in case someone wants to use a Data Set from an XCAsset, your should use NSDataAsset for loading it: https://stackoverflow.com/a/33370596/499113

I had the same issue: It works fine on the Simulator but fails on the device with SIGABRT after logging the Symbol not found error as @kkyr shared in his post. To solve this, make sure your iOS device version is aligned with the Xcode version. To debug with an iPhone running iOS 17 beta 4, you need Xcode 15 beta 5 (beta 4 will fail with the symbol error).

Same here, going back to beta 4 allows uploading and publishing to TestFlight again. This seems to be a common issue for new Xcode versions which Apple usually resolves in one or two days according to this thread: https://developer.apple.com/forums/thread/61855