[Distributed] Handle composite type in generic bound in distributed accessor

rdar://111664985

Author: ktoso

lib/IRGen/GenDistributed.cpp

@@ -616,6 +616,8 @@ void DistributedAccessor::emit() {
 
   auto params = IGF.collectParameters();
 
+  GenericContextScope scope(IGM, targetTy->getInvocationGenericSignature());
+
   auto directResultTy = targetConv.getSILResultType(expansionContext);
   const auto &directResultTI = IGM.getTypeInfo(directResultTy);
 
@@ -652,8 +654,6 @@ void DistributedAccessor::emit() {
   // Witness table for decoder conformance to DistributedTargetInvocationDecoder
   auto *decoderProtocolWitness = params.claimNext();
 
-  GenericContextScope scope(IGM, targetTy->getInvocationGenericSignature());
-
   // Preliminary: Setup async context for this accessor.
   {
     auto fpKind = FunctionPointerKind::defaultAsync();

test/IRGen/distributed_actor.swift

@@ -12,3 +12,27 @@ public distributed actor MyActor {
   public typealias ActorSystem = LocalTestingDistributedActorSystem
   // nothing
 }
+
+public protocol Kappa {}
+
+/// This combination of DistributedActor + Codable used to trigger a crash in DistributedAccessor::emit (rdar://111664985)
+/// So returning it from distributed methods in the types below covers this radar.
+public protocol ClusterSingleton: DistributedActor, Codable {}
+
+@available(SwiftStdlib 5.6, *)
+public distributed actor MyActorGenerics {
+  public typealias ActorSystem = LocalTestingDistributedActorSystem
+
+  distributed func find<Act: ClusterSingleton>(byName name: String) -> Act {
+    fatalError("mock impl")
+  }
+}
+
+@available(SwiftStdlib 5.6, *)
+public distributed actor MyActorGenericsOnType<Act: ClusterSingleton> {
+  public typealias ActorSystem = LocalTestingDistributedActorSystem
+
+  distributed func find(byName name: String) -> Act {
+    fatalError("mock impl")
+  }
+}