[Distributed] Test for distributed protocols + method defaults (#75609)

Author: ktoso

test/Distributed/distributed_actor_conform_protocol_with_default_impl.swift

@@ -0,0 +1,43 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend-emit-module -emit-module-path %t/FakeDistributedActorSystems.swiftmodule -module-name FakeDistributedActorSystems -disable-availability-checking %S/Inputs/FakeDistributedActorSystems.swift
+// RUN: %target-swift-frontend -typecheck -verify -disable-availability-checking -I %t 2>&1 %s
+
+// REQUIRES: concurrency
+// REQUIRES: distributed
+
+import Distributed
+import FakeDistributedActorSystems
+
+protocol Device: DistributedActor {
+  distributed func fetch() async -> String?
+
+  distributed func fetch2() async -> String?
+  distributed func fetch5() async -> String?
+}
+
+distributed actor Impl: Device {
+  typealias ActorSystem = FakeActorSystem
+
+  init(actorSystem: ActorSystem) {
+    self.actorSystem = actorSystem
+  }
+
+  // fetch() uses default impl
+
+  distributed func fetch2() async -> String? {
+    ""
+  }
+
+  distributed func fetch5() async -> String? {
+    ""
+  }
+}
+
+// MARK: - Device default implementation
+
+extension Device {
+  distributed func fetch() async -> String? { "" }
+
+  distributed func fetch2() async -> String? { "" }
+  distributed func fetch5() async -> String? { "" }
+}