[Distributed] Implicit Codable conformance for distributed actors

[ktoso]

Codable conformance is synthesized for any concrete DistributedActor when the ID it has is Codable.

This would not be implementable in "normal" swift due to the need to assign to self in the initializer.

[ktoso]

So we have the conformance in place but I can't figure out where or how to ensure the witness symbols get emitted

Undefined symbols for architecture arm64:
  "_$s4main6WorkerCSEAAMc", referenced from:
      _$s4main6WorkerCACSEAAWl in distributed_actor_encode_roundtrip-3b6d09.o
  "_$s4main6WorkerCSeAAMc", referenced from:
      _$s4main6WorkerCACSeAAWl in distributed_actor_encode_roundtrip-3b6d09.o
ld: symbol(s) not found for architecture arm64

Undefined symbols for architecture arm64:
  "protocol conformance descriptor for main.Worker : Swift.Encodable in main", referenced from:
      lazy protocol witness table accessor for type main.Worker and conformance main.Worker : Swift.Encodable in main in distributed_actor_encode_roundtrip-3b6d09.o
  "protocol conformance descriptor for main.Worker : Swift.Decodable in main", referenced from:
      lazy protocol witness table accessor for type main.Worker and conformance main.Worker : Swift.Decodable in main in distributed_actor_encode_roundtrip-3b6d09.o

Technically we have the

@available(SwiftStdlib 5.7, *)
extension DistributedActor /*: implicitly Encodable */ where Self.ID: Encodable {
  nonisolated public func encode(to encoder: Encoder) throws {

so i was hoping to not have to do anything extra but that does not seem to be the case.

I tried setting the witness when we create the conformance explicitly as well but that does no good either.

We cannot find the above extension on the protocol either because getExtensions() returns nothing since we're too early so we can't grab the impl from the extension on DistributedActor either way... I'd be ok to synthesize it if we have to, but when I tried this does not seem to solve the missing symbol anyway.

[ktoso]

@swift-ci please smoke test

[ktoso]

Rebased :)

[ktoso]

@swift-ci please smoke test

[ktoso]

Actual issue, fixing it.

• Swift(linux-x86_64) :: Concurrency/require-explicit-sendable.swift
  • was a real issue, fixed
• Swift(linux-x86_64) :: IDE/complete_actorisolation.swift
• Swift(linux-x86_64) :: IDE/complete_diagnostics_concurrency.swift
• seem just flaky...?

[ktoso]

@swift-ci please smoke test

[ktoso]

Only reason this failed was because #41602 got merged in between...
Some new errors are reported by the combination of the two heh.

[ktoso]

@swift-ci please smoke test and merge