Generated Pb files fail to compile with the new Default Actor Isolation flag set to MainActor

[mylaluna]

After watching the WWDC 2025, Embracing Swift concurrency, I try to play with the new concurrency flags which you can find on the Xcode 26 beta.

Following is the recommended flag settings from the tutorial video:

I find my existing project that contains generated *.pb.swift files have hundreds of compile time errors, if I set the Default Actor Isolation to the MainActor.

Some typical errors are like: Conformance of "Pb_Person" to protocol 'Enum' crosses into main actor-isolated code and can cause data races.

The fix is to set the flag to nonisolated which I believe was the default before Swift 6.2.

This makes sense because the generated code is created with the nonisolated as default actor isolation.
Since Apple has recommended the new default isolation, the current generated code will be a road block for those who want to switch to the MainActor default.
What is the solution here for the existing projects and new projects?

[Lukasa]

In the short term, the easiest solution is to generate the protobuf files into a separate target that does not have approachable concurrency enabled. In the medium term we should consider enhancing the code generator to produce appropriate compiler guards to annotate the various protobuf types as having nonisolated conformances and nonisolated types.

[mylaluna]

In the short term, the easiest solution is to generate the protobuf files into a separate target that does not have approachable concurrency enabled. In the medium term we should consider enhancing the code generator to produce appropriate compiler guards to annotate the various protobuf types as having nonisolated conformances and nonisolated types.

Thanks for the swift feedback, I will give it a shot and see what happens.

[mylaluna]

I have been trying to fix my code base by creating a new Service target.
Moving the non-UI related code into this target indeed solved the problem.
The only extra thing I need to do was to mark these code public.

However, I gave up in the end because I have too much non-UI related code.
I feel I would rather manually mark my UI related code with @mainactor, which seems to be a lesser work.

It is not worth the effort for me but I can imagine the benefit for new concurrency learners.