Don’t declare async methods with alternatives in headers

If Swift sees this pattern of methods in an @objc protocol:

```
    func hello() async -> Int

    @available(*, renamed: “hello()”)
    func hello(completion: @escaping (Int) -> Void)
```

Then PrintAsClang will print only the completion-handler-based method, not the async one, into a generated header, on the assumption that the completion-handler method may have greater availability.

Fixes rdar://94175167.

Author: beccadax

lib/PrintAsClang/DeclAndTypePrinter.cpp

@@ -2017,12 +2017,31 @@ auto DeclAndTypePrinter::getImpl() -> Implementation {
   return Implementation(os, *this, outputLang);
 }
 
+static bool isAsyncAlternativeOfOtherDecl(const ValueDecl *VD) {
+  auto AFD = dyn_cast<AbstractFunctionDecl>(VD);
+  if (!AFD || !AFD->isAsyncContext() || !AFD->getObjCSelector())
+    return false;
+
+  auto type = AFD->getDeclContext()->getSelfNominalTypeDecl();
+  if (!type)
+    return false;
+  auto others = type->lookupDirect(AFD->getObjCSelector(),
+                                   AFD->isInstanceMember());
+
+  for (auto other : others)
+    if (other->getAsyncAlternative() == AFD)
+      return true;
+
+  return false;
+}
+
 bool DeclAndTypePrinter::shouldInclude(const ValueDecl *VD) {
   return !VD->isInvalid() &&
          (outputLang == OutputLanguageMode::Cxx
               ? cxx_translation::isVisibleToCxx(VD, minRequiredAccess)
               : isVisibleToObjC(VD, minRequiredAccess)) &&
-         !VD->getAttrs().hasAttribute<ImplementationOnlyAttr>();
+         !VD->getAttrs().hasAttribute<ImplementationOnlyAttr>() &&
+         !isAsyncAlternativeOfOtherDecl(VD);
 }
 
 void DeclAndTypePrinter::print(const Decl *D) {

test/PrintAsObjC/protocols.swift

@@ -27,6 +27,20 @@ import objc_generics
 // CHECK-NEXT: @end
 @objc protocol B : A {}
 
+// CHECK-LABEL: @protocol CompletionAndAsync
+// CHECK-NEXT: - (void)helloWithCompletion:(void (^ _Nonnull)(BOOL))completion;
+// CHECK-NEXT: @end
+@objc protocol CompletionAndAsync {
+  // We don't want this one printed because it has more limited availability.
+  @available(SwiftStdlib 5.7, *)
+  @objc(helloWithCompletion:)
+  func hello() async -> Bool
+
+  @available(*, renamed: "hello()")
+  @objc(helloWithCompletion:)
+  func hello(completion: @escaping (Bool) -> Void)
+}
+
 // CHECK: @protocol CustomName2;
 // CHECK-LABEL: SWIFT_PROTOCOL_NAMED("CustomName")
 // CHECK-NEXT: @protocol CustomName{{$}}