[Distributed] Allow @resolvable to work with available on specific func

resolves rdar://147892011

Author: ktoso

lib/Macros/Sources/SwiftMacros/DistributedResolvableMacro.swift

@@ -78,8 +78,8 @@ extension DistributedResolvableMacro {
   static func stubMethodDecl(access: DeclModifierListSyntax, _ requirement: MemberBlockItemListSyntax.Element) -> String {
     // do we need to stub a computed variable?
     if let variable = requirement.decl.as(VariableDeclSyntax.self) {
+      
       var accessorStubs: [String] = []
-
       for binding in variable.bindings {
         if let accessorBlock = binding.accessorBlock {
           for accessor in accessorBlock.accessors.children(viewMode: .all) {
@@ -92,18 +92,27 @@ extension DistributedResolvableMacro {
       let name = variable.bindings.first!.pattern.trimmed
       let typeAnnotation = variable.bindings.first?.typeAnnotation.map { "\($0.trimmed)" } ?? "Any"
       return """
-             \(access)\(variable.modifiers)\(variable.bindingSpecifier) \(name) \(typeAnnotation) {
+             \(variable.attributes)
+             \(access)
+             \(variable.modifiers)\(variable.bindingSpecifier) \(name) \(typeAnnotation) {
                \(accessorStubs.joined(separator: "\n  "))
              }
              """
-    }
+    } else if var fun = requirement.decl.as(FunctionDeclSyntax.self) {
+      fun.modifiers = fun.modifiers.filter { !$0.isAccessControl }
+      fun.modifiers = fun.modifiers.prepending(DeclModifierSyntax(name: .keyword(.public)))
 
-    // normal function stub
-    return """
-           \(access)\(requirement) {
-             \(stubFunctionBody())
-           }
-           """
+      // normal function stub
+      return """
+             \(fun) {
+               \(stubFunctionBody())
+             }
+             """
+    } else {
+      // some declaration type we could not handle, let's silently ignore; we should not really need to emit
+      // anything others than var and func here, and it's cleaner to just ignore rather than crash here.
+      return ""
+    }
   }
 
   static func stubFunctionBody() -> DeclSyntax {

test/Distributed/Macros/distributed_macro_expansion_DistributedProtocol_availability.swift

@@ -0,0 +1,53 @@
+// REQUIRES: swift_swift_parser, asserts
+//
+// UNSUPPORTED: back_deploy_concurrency
+// REQUIRES: concurrency
+// REQUIRES: distributed
+//
+// RUN: %empty-directory(%t)
+// RUN: %empty-directory(%t-scratch)
+
+// RUN: %target-swift-frontend -typecheck -target %target-swift-6.0-abi-triple -plugin-path %swift-plugin-dir -I %t -dump-macro-expansions %s -dump-macro-expansions 2>&1 | %FileCheck %s --color
+
+import Distributed
+
+@Resolvable
+public protocol Greeter: DistributedActor where ActorSystem: DistributedActorSystem<any Codable> {
+  @available(iOS 6666, macOS 7777, tvOS 8888, visionOS 9999, *)
+  distributed func greet(name: String) -> String
+
+  @available(iOS 6666, macOS 7777, tvOS 8888, visionOS 9999, *)
+  distributed var name: String { get }
+}
+
+// @Resolvable ->
+
+// CHECK: public distributed actor $Greeter<ActorSystem>: Greeter,
+// CHECK:   Distributed._DistributedActorStub
+// CHECK:   where ActorSystem: DistributedActorSystem<any Codable>
+// CHECK: {
+// CHECK: }
+
+// CHECK: extension Greeter where Self: Distributed._DistributedActorStub {
+// CHECK:   @available(iOS 6666, macOS 7777, tvOS 8888, visionOS 9999, *) public
+// CHECK:   distributed func greet(name: String) -> String {
+// CHECK:     if #available(macOS 15.0, iOS 18.0, watchOS 11.0, tvOS 18.0, visionOS 2.0, *) {
+// CHECK:       Distributed._distributedStubFatalError()
+// CHECK:     } else {
+// CHECK:       fatalError()
+// CHECK:     }
+// CHECK:   }
+   
+// CHECK:   @available(iOS 6666, macOS 7777, tvOS 8888, visionOS 9999, *)
+// CHECK:   public
+// CHECK:   distributed var name : String {
+// CHECK:     get  {
+// CHECK:       if #available(macOS 15.0, iOS 18.0, watchOS 11.0, tvOS 18.0, visionOS 2.0, *) {
+// CHECK:         Distributed._distributedStubFatalError()
+// CHECK:       } else {
+// CHECK:         fatalError()
+// CHECK:       }
+// CHECK:     }
+// CHECK:   }
+   
+// CHECK: }