Merge pull request swiftlang#26141 from devincoughlin/unavailable-extension-of-unavailable-in-pound-if

[Sema] Allow unavailable extension of unavailable type in #if

Author: devincoughlin

lib/Sema/TypeCheckAvailability.cpp

@@ -860,6 +860,13 @@ static const Decl *findContainingDeclaration(SourceRange ReferenceRange,
   auto ContainsReferenceRange = [&](const Decl *D) -> bool {
     if (ReferenceRange.isInvalid())
       return false;
+
+    // Members of an active #if are represented both inside the
+    // IfConfigDecl and in the enclosing context. Skip over the IfConfigDecl
+    // so that that the member declaration is found rather the #if itself.
+    if (isa<IfConfigDecl>(D))
+      return false;
+
     return SM.rangeContains(D->getSourceRange(), ReferenceRange);
   };
 

test/attr/attr_availability_osx.swift

@@ -198,3 +198,14 @@ extension TestStruct {
     introducedInExtensionMacOS()
   }
 }
+
+@available(macOS, unavailable)
+struct UnavailableStruct { }
+
+@available(macOS, unavailable)
+extension UnavailableStruct { } // no-error
+
+#if os(macOS)
+@available(macOS, unavailable)
+extension UnavailableStruct { } // no-error
+#endif