Sema: Fix diagnostics for @available(noasync, swift).

Author: tshortli

lib/Sema/TypeCheckAttr.cpp

@@ -8271,7 +8271,6 @@ SemanticAvailableAttrRequest::evaluate(swift::Evaluator &evaluator,
   auto &diags = decl->getASTContext().Diags;
   auto attrLoc = attr->getLocation();
   auto attrName = attr->getAttrName();
-  auto attrKind = attr->getKind();
   auto domainLoc = attr->getDomainLoc();
   auto introducedVersion = attr->getRawIntroduced();
   auto deprecatedVersion = attr->getRawDeprecated();
@@ -8305,7 +8304,7 @@ SemanticAvailableAttrRequest::evaluate(swift::Evaluator &evaluator,
   auto domainName = domain->getNameForAttributePrinting();
 
   if (domain->isSwiftLanguage() || domain->isPackageDescription()) {
-    switch (attrKind) {
+    switch (attr->getKind()) {
     case AvailableAttr::Kind::Deprecated:
       diags.diagnose(attrLoc,
                      diag::attr_availability_expected_deprecated_version,
@@ -8320,7 +8319,8 @@ SemanticAvailableAttrRequest::evaluate(swift::Evaluator &evaluator,
     case AvailableAttr::Kind::NoAsync:
       diags.diagnose(attrLoc, diag::attr_availability_cannot_be_used_for_domain,
                      "noasync", attrName, domainName);
-      break;
+      return std::nullopt;
+
     case AvailableAttr::Kind::Default:
       break;
     }

test/attr/attr_availability_noasync.swift

@@ -18,13 +18,11 @@ func asyncReplacement() async -> Int { }
 @available(*, noasync, renamed: "IOActor.readString()")
 func readStringFromIO() -> String {}
 
-// expected-warning@+2 {{'noasync' cannot be used in 'available' attribute for platform 'swift'}}
-// expected-warning@+1 {{expected 'introduced', 'deprecated', or 'obsoleted' in 'available' attribute for platform 'swift'}}
+// expected-warning@+1 {{'noasync' cannot be used in 'available' attribute for platform 'swift'}}
 @available(swift, noasync)
 func swiftNoAsync() { }
 
-// expected-warning@+2 {{'noasync' cannot be used in 'available' attribute for platform '_PackageDescription'}}
-// expected-warning@+1 {{expected 'introduced', 'deprecated', or 'obsoleted' in 'available' attribute for platform '_PackageDescription'}}
+// expected-warning@+1 {{'noasync' cannot be used in 'available' attribute for platform '_PackageDescription'}}
 @available(_PackageDescription, noasync)
 func packageDescriptionNoAsync() { }