[Distributed] Generic reqs must be forwarded to accessor from enclosing actor

If we don't do this, the generic parameter has no requirements at all,
which a) is incorrect to begin with, it should have the exact same
signature as the method it is the accessor for, and b) it would trip up
verification which is enabled on linux in snapshot builds -- causing
crashes.

Resolves rdar://115497090

Author: ktoso

lib/IRGen/GenDistributed.cpp

@@ -269,9 +269,17 @@ static CanSILFunctionType getAccessorType(IRGenModule &IGM,
     auto *actor = getDistributedActorOf(Target);
     assert(actor);
 
-    for (auto *genericParam : actor->getInnermostGenericParamTypes())
+    for (auto *genericParam : actor->getInnermostGenericParamTypes()) {
       genericParams.push_back(genericParam);
 
+      // and also forward all requirements this generic parameter might have.
+      for (auto req : actor->getGenericRequirements()) {
+        if (req.getFirstType()->isEqual(genericParam)) {
+          genericRequirements.push_back(req);
+        }
+      }
+    }
+
     // Add a generic parameter `D` which stands for decoder type in the
     // accessor signature - `inout D`.
     genericParams.push_back(decoderType);

test/Distributed/Runtime/distributed_actor_generic_constraint_issue_115497090.swift

@@ -0,0 +1,57 @@
+// 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-build-swift -module-name main  -Xfrontend -disable-availability-checking -j2 -parse-as-library -I %t %s %S/../Inputs/FakeDistributedActorSystems.swift -o %t/a.out
+// RUN: %target-run %t/a.out | %FileCheck %s --color
+
+// REQUIRES: executable_test
+// REQUIRES: concurrency
+// REQUIRES: distributed
+
+// rdar://76038845
+// UNSUPPORTED: use_os_stdlib
+// UNSUPPORTED: back_deployment_runtime
+
+import Distributed
+import FakeDistributedActorSystems
+
+import Distributed
+import FakeDistributedActorSystems
+
+typealias DefaultDistributedActorSystem = FakeActorSystem
+
+protocol SomeProtocol {
+  static var isInteger: Bool { get }
+}
+
+distributed actor TestActor<Value> where Value: Codable & Identifiable, Value.ID: SomeProtocol {
+  distributed func requirementsFromActor(value: Value) async throws {
+    print("OK: \(value)")
+  }
+  distributed func requirementsFromActorAndMethod(value: Value) async throws where Value: VerySpecific {
+    print("OK: \(value)")
+  }
+}
+
+protocol VerySpecific {}
+
+struct TheValue: Codable, Identifiable, VerySpecific {
+  let id: String
+  init() {
+    self.id = "id"
+  }
+}
+extension String: SomeProtocol {
+  static var isInteger: Bool { false }
+}
+
+@main struct Main {
+  static func main() async throws {
+    let ta: TestActor<TheValue> = TestActor(actorSystem: .init())
+    try await ta.requirementsFromActor(value: TheValue())
+    try await ta.requirementsFromActorAndMethod(value: TheValue())
+    // CHECK: OK
+  }
+}
+
+// FIXME: repro testing
+// export VER=5.9; swiftly install $VER && swiftly use $VER; swiftly list | grep use; swift build --build-tests; if [[ "$?" -eq 0 ]]; then echo "$VER: OK" >> ../checks; else echo "$VER: broken" >> ../checks; fi