[Sema] Add a helper function to get the innermost declaration with an

@available annotation.

Author: hborla

include/swift/AST/Decl.h

@@ -789,6 +789,9 @@ class alignas(1 << DeclAlignInBits) Decl {
     return Attrs;
   }
 
+  /// Returns the innermost enclosing decl with an availability annotation.
+  const Decl *getInnermostDeclWithAvailability() const;
+
   /// Returns the introduced OS version in the given platform kind specified
   /// by @available attribute.
   /// This function won't consider the parent context to get the information.

lib/AST/Decl.cpp

@@ -351,6 +351,19 @@ StringRef Decl::getDescriptiveKindName(DescriptiveDeclKind K) {
   llvm_unreachable("bad DescriptiveDeclKind");
 }
 
+const Decl *Decl::getInnermostDeclWithAvailability() const {
+  const Decl *enclosingDecl = this;
+  // Find the innermost enclosing declaration with an @available annotation.
+  while (enclosingDecl != nullptr) {
+    if (enclosingDecl->getAttrs().hasAttribute<AvailableAttr>())
+      return enclosingDecl;
+
+    enclosingDecl = enclosingDecl->getDeclContext()->getAsDecl();
+  }
+
+  return nullptr;
+}
+
 Optional<llvm::VersionTuple>
 Decl::getIntroducedOSVersion(PlatformKind Kind) const {
   for (auto *attr: getAttrs()) {

lib/Sema/CodeSynthesis.cpp

@@ -566,17 +566,15 @@ configureInheritedDesignatedInitAttributes(ClassDecl *classDecl,
   // If the superclass has its own availability, make sure the synthesized
   // constructor is only as available as its superclass's constructor.
   if (superclassCtor->getAttrs().hasAttribute<AvailableAttr>()) {
-    SmallVector<Decl *, 2> asAvailableAs;
+    SmallVector<const Decl *, 2> asAvailableAs;
 
     // We don't have to look at enclosing contexts of the superclass constructor,
     // because designated initializers must always be defined in the superclass
     // body, and we already enforce that a superclass is at least as available as
     // a subclass.
     asAvailableAs.push_back(superclassCtor);
-    Decl *parentDecl = classDecl;
-    while (parentDecl != nullptr) {
+    if (auto *parentDecl = classDecl->getInnermostDeclWithAvailability()) {
       asAvailableAs.push_back(parentDecl);
-      parentDecl = parentDecl->getDeclContext()->getAsDecl();
     }
     AvailabilityInference::applyInferredAvailableAttrs(
         ctor, asAvailableAs, ctx);

lib/Sema/TypeCheckStorage.cpp

@@ -1967,19 +1967,8 @@ static AccessorDecl *createSetterPrototype(AbstractStorageDecl *storage,
   assert(storage->requiresOpaqueAccessor(AccessorKind::Set));
 
   // Copy availability from the accessor we'll synthesize the setter from.
-  SmallVector<Decl *, 2> asAvailableAs;
-
-  auto addEnclosingScopeAvailability = [&]() {
-    Decl *enclosingDecl = storage;
-    // Find the innermost enclosing declaration with an @available annotation.
-    while ((enclosingDecl = enclosingDecl->getDeclContext()->getAsDecl())) {
-      if (enclosingDecl->getAttrs().hasAttribute<AvailableAttr>()) {
-        asAvailableAs.push_back(enclosingDecl);
-        break;
-      }
-    }
-  };
-  
+  SmallVector<const Decl *, 2> asAvailableAs;
+
   // That could be a property wrapper...
   if (auto var = dyn_cast<VarDecl>(storage)) {
     if (var->hasAttachedPropertyWrapper()) {
@@ -1989,7 +1978,8 @@ static AccessorDecl *createSetterPrototype(AbstractStorageDecl *storage,
       if (info.valueVar) {
         if (auto setter = info.valueVar->getOpaqueAccessor(AccessorKind::Set)) {
           asAvailableAs.push_back(setter);
-          addEnclosingScopeAvailability();
+          if (auto *enclosing = var->getInnermostDeclWithAvailability())
+            asAvailableAs.push_back(enclosing);
         }
       }
     } else if (auto wrapperSynthesizedKind
@@ -2007,7 +1997,8 @@ static AccessorDecl *createSetterPrototype(AbstractStorageDecl *storage,
             if (auto setter
                 = info.projectedValueVar->getOpaqueAccessor(AccessorKind::Set)){
               asAvailableAs.push_back(setter);
-              addEnclosingScopeAvailability();
+              if (auto *enclosing = var->getInnermostDeclWithAvailability())
+                asAvailableAs.push_back(enclosing);
             }
           }
         }