[Distributed] ID synthesis must be eager, or we run into issues in real projects

[ktoso]

Without this, in real, multi module, multi file, projects we end up with issues as follows:

Greeter.swift:9:19: error: type 'Greeter' does not conform to protocol 'DistributedActor'
distributed actor Greeter {
                  ^
Greeter.swift:9:19: error: 'DistributedActor' requires the types 'ObjectIdentifier' and 'BonjourActorSystem.ActorID' (aka 'ActorIdentity') be equivalent
distributed actor Greeter {
                  ^
Greeter.swift:9:19: note: requirement specified as 'Self.ID' == 'Self.ActorSystem.ActorID' [with Self = Greeter]
distributed actor Greeter {
                  ^
Greeter.swift:9:19: error: protocol 'DistributedActor' is broken; cannot derive conformance for type 'Greeter'
distributed actor Greeter {
                  ^

From debugging it seems that the reason is that the resolve by lookup triggers early and determines that the ID shall be taken from the extension Identifiable { var id: ObjectIdentifier {...} } and only then other synthesis is run.

In order to avoid such mixups, we can be eager about the ID type synthesis.

This is limited to distributed actor decls, because in all other cases the default would be right and follow the usual rules, but because we synthesize the ActorSystem typealias and ID types later on, things got tricky here.

If there is a cleaner way to do this I'd happily revisit but this seems not to terrible for now at least and unbreaks projects.

Resolves rdar://91020060

[ktoso]

@swift-ci please smoke test

[xedin]

Makes sense to me! Could you please add a couple more test cases with protocol that conform to a DistributedActor to make sure that fetching of the ActorSystem and other bits work correctly for that case too?

[ktoso]

Good idea, I actually don't do synthesis there but I guess I should maybe? Will think about it, thanks!

[ktoso]

@swift-ci please smoke test and merge

[ktoso]

Poked around a bit but protocols should not be impacted at all 👍

[xedin]

Sounds good!

[ktoso]

@swift-ci please smoke test and merge

CI stuck again...