Sema: Only diagnose unavailable attr when it is active for the target.

An attribute may be "active" but also not the most specific attribute for the
current target and therefore ignored.

Resolves rdar://107678512

Author: tshortli

lib/Sema/TypeCheckAttr.cpp

@@ -1906,6 +1906,16 @@ void AttributeChecker::visitAvailableAttr(AvailableAttr *attr) {
       !attr->isPackageDescriptionVersionSpecific())
     return;
 
+  // Make sure there isn't a more specific attribute we should be using instead.
+  // findMostSpecificActivePlatform() is O(N), so only do this if we're checking
+  // an iOS attribute while building for macCatalyst.
+  if (attr->Platform == PlatformKind::iOS &&
+      isPlatformActive(PlatformKind::macCatalyst, Ctx.LangOpts)) {
+    if (attr != D->getAttrs().findMostSpecificActivePlatform(Ctx)) {
+      return;
+    }
+  }
+
   SourceLoc attrLoc = attr->getLocation();
   auto versionAvailability = attr->getVersionAvailability(Ctx);
   if (versionAvailability == AvailableVersionComparison::Obsoleted ||
@@ -1932,16 +1942,6 @@ void AttributeChecker::visitAvailableAttr(AvailableAttr *attr) {
   if (!attr->hasPlatform() || !attr->Introduced.has_value())
     return;
 
-  // Make sure there isn't a more specific attribute we should be using instead.
-  // findMostSpecificActivePlatform() is O(N), so only do this if we're checking
-  // an iOS attribute while building for macCatalyst.
-  if (attr->Platform == PlatformKind::iOS &&
-      isPlatformActive(PlatformKind::macCatalyst, Ctx.LangOpts)) {
-    if (attr != D->getAttrs().findMostSpecificActivePlatform(Ctx)) {
-      return;
-    }
-  }
-
   // Find the innermost enclosing declaration with an availability
   // range annotation and ensure that this attribute's available version range
   // is fully contained within that declaration's range. If there is no such

test/Sema/availability_stored_unavailable_maccatalyst.swift

@@ -0,0 +1,13 @@
+// RUN: %target-typecheck-verify-swift -target %target-cpu-apple-ios13.1-macabi -parse-as-library -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import
+
+// REQUIRES: OS=macosx
+
+struct BadStruct {
+  @available(macCatalyst 13.1, *)
+  @available(iOS, unavailable) // This attribute is inactive so we don't expect a diagnostic
+  var availableOnCatalyst: Int
+
+  @available(macCatalyst, unavailable) // expected-error {{stored properties cannot be marked unavailable with '@available'}}
+  @available(iOS 13, *)
+  var unavailableOnCatalyst: Int
+}