[Macros] Reproduce issue with peer+extension macro extension's methods not being checked as witnesses

lib/AST/NameLookup.cpp

@@ -1844,13 +1844,18 @@ PotentialMacroExpansions PotentialMacroExpansionsInContextRequest::evaluate(
   auto containerDecl = container.getAsDecl();
   forEachPotentialAttachedMacro(containerDecl, MacroRole::Member, nameTracker);
 
-  // If the container is an extension that was created from an extension macro,
-  // look at the nominal declaration to find any extension macros.
-  if (auto ext = dyn_cast<ExtensionDecl>(containerDecl)) {
-    if (auto nominal = nominalForExpandedExtensionDecl(ext)) {
-      forEachPotentialAttachedMacro(
-          nominal, MacroRole::Extension, nameTracker);
-    }
+  // Extension macros on the type or extension.
+  {
+    NominalTypeDecl *nominal = nullptr;
+    // If the container is an extension that was created from an extension
+    // macro, look at the nominal declaration to find any extension macros.
+    if (auto ext = dyn_cast<ExtensionDecl>(containerDecl))
+      nominal = nominalForExpandedExtensionDecl(ext);
+    else
+      nominal = container.getBaseNominal();
+
+    if (nominal)
+      forEachPotentialAttachedMacro(nominal, MacroRole::Extension, nameTracker);
   }
 
   // Peer and freestanding declaration macros.
@@ -1911,15 +1916,20 @@ populateLookupTableEntryFromMacroExpansions(ASTContext &ctx,
   // names match.
   {
     MacroIntroducedNameTracker nameTracker;
-    if (auto ext = dyn_cast<ExtensionDecl>(container.getAsDecl())) {
-      if (auto nominal = nominalForExpandedExtensionDecl(ext)) {
-        forEachPotentialAttachedMacro(nominal, MacroRole::Extension, nameTracker);
-        if (nameTracker.shouldExpandForName(name)) {
-          (void)evaluateOrDefault(
-              ctx.evaluator,
-              ExpandExtensionMacros{nominal},
-              false);
-        }
+    NominalTypeDecl *nominal = nullptr;
+    // If the container is an extension that was created from an extension
+    // macro, look at the nominal declaration to find any extension macros.
+    if (auto ext = dyn_cast<ExtensionDecl>(container.getAsDecl()))
+      nominal = nominalForExpandedExtensionDecl(ext);
+    else
+      nominal = container.getBaseNominal();
+
+    if (nominal) {
+      forEachPotentialAttachedMacro(nominal,
+                                  MacroRole::Extension, nameTracker);
+      if (nameTracker.shouldExpandForName(name)) {
+        (void)evaluateOrDefault(ctx.evaluator, ExpandExtensionMacros{nominal},
+                                false);
       }
     }
   }

stdlib/public/Distributed/DistributedMacros.swift

@@ -17,7 +17,6 @@ import _Concurrency
 
 #if $Macros
 
-// FIXME: the fact tha this is peer and extension makes the extension's methods not found as witnesses
 @attached(peer, names: prefixed(`$`)) // provides $Greeter concrete stub type
 @attached(extension, names: arbitrary) // provides extension for Greeter & _DistributedActorStub
 public macro _DistributedProtocol() =

test/Distributed/Macros/distributed_macro_expansion_DistributedProtocol_simple.swift

@@ -11,29 +11,26 @@
 
 import Distributed
 
-// FIXME: the errors below are bugs: the added methods should be considered witnesses rdar://123012943
-// expected-note@+1{{in expansion of macro '_DistributedProtocol' on protocol 'Greeter' here}}
 @_DistributedProtocol
 protocol Greeter: DistributedActor where ActorSystem: DistributedActorSystem<any Codable> {
-  // FIXME: this is a bug
-  // expected-note@+1{{protocol requires function 'greet(name:)' with type '(String) -> String'}}
   distributed func greet(name: String) -> String
 }
 
 // @_DistributedProtocol ->
 
-// CHECK: distributed actor $Greeter<ActorSystem>: Greeter, _DistributedActorStub
-// CHECK:   where ActorSystem: DistributedActorSystem<any Codable>,
-// CHECK:   ActorSystem.ActorID: Codable
-// CHECK: {
-// CHECK: }
+// CHECK: distributed actor $Greeter<ActorSystem>: Greeter,
+// CHECK-NEXT: Distributed._DistributedActorStub
+// CHECK-NEXT: where ActorSystem: DistributedActorSystem<any Codable>,
+// CHECK-NEXT: ActorSystem.ActorID: Codable
+// CHECK-NEXT: {
+// CHECK-NEXT: }
 
-// CHECK: extension Greeter {
-// CHECK:   distributed func greet(name: String) -> String {
-// CHECK:     if #available (SwiftStdlib 5.11, *) {
-// CHECK:       Distributed._distributedStubFatalError()
-// CHECK:     } else {
-// CHECK:       fatalError()
-// CHECK:     }
-// CHECK:   }
-// CHECK: }
+// CHECK: extension Greeter where Self: Distributed._DistributedActorStub {
+// CHECK-NEXT:   distributed func greet(name: String) -> String {
+// CHECK-NEXT:     if #available (SwiftStdlib 5.11, *) {
+// CHECK-NEXT:       Distributed._distributedStubFatalError()
+// CHECK-NEXT:     } else {
+// CHECK-NEXT:       fatalError()
+// CHECK-NEXT:     }
+// CHECK-NEXT:   }
+// CHECK-NEXT: }

test/Macros/macro_expand_synthesized_members.swift

@@ -158,9 +158,10 @@ func callNestedExpansionMember() {
   NestedMacroExpansion.member()
 }
 
-@attached(peer, names: arbitrary) // introduces `__GenerateStubsForProtocolRequirements
+@attached(peer, names: prefixed(`__`)) // introduces `__GenerateStubsForProtocolRequirements
 @attached(extension, names: arbitrary) // introduces `extension GenerateStubsForProtocolRequirements`
 macro GenerateStubsForProtocolRequirements() = #externalMacro(module: "MacroDefinition", type: "GenerateStubsForProtocolRequirementsMacro")
+
 protocol _TestStub {} // used by 'GenerateStubsForProtocolRequirements'
 
 @GenerateStubsForProtocolRequirements
@@ -173,4 +174,4 @@ protocol MacroExpansionRequirements {
 func testWitnessStub() {
   let stub: any MacroExpansionRequirements = __MacroExpansionRequirements()
   _ = stub.hello(name: "Caplin")
-}
+}