[Property Wrappers] If a property wrapper accessor is synthesized using the

enclosing-self subscript, infer availability from accessors on the subscript
declaration.

Author: hborla

lib/Sema/TypeCheckStorage.cpp

@@ -1930,11 +1930,17 @@ static void addPropertyWrapperAccessorAvailability(VarDecl *var, AccessorKind ac
                                                    SmallVectorImpl<const Decl *> &asAvailableAs) {
   AccessorDecl *synthesizedFrom = nullptr;
   if (var->hasAttachedPropertyWrapper()) {
+    AbstractStorageDecl *wrappedValueImpl;
+    if (auto access = getEnclosingSelfPropertyWrapperAccess(var, /*forProjected=*/false)) {
+      wrappedValueImpl = access->subscript;
+    } else {
+      wrappedValueImpl = var->getAttachedPropertyWrapperTypeInfo(0).valueVar;
+    }
+
     // The property wrapper info may not actually link back to a wrapper
     // implementation, if there was a semantic error checking the wrapper.
-    auto info = var->getAttachedPropertyWrapperTypeInfo(0);
-    if (info.valueVar) {
-      synthesizedFrom = info.valueVar->getOpaqueAccessor(accessorKind);
+    if (wrappedValueImpl) {
+      synthesizedFrom = wrappedValueImpl->getOpaqueAccessor(accessorKind);
     }
   } else if (auto wrapperSynthesizedKind
                = var->getPropertyWrapperSynthesizedPropertyKind()) {
@@ -1944,11 +1950,17 @@ static void addPropertyWrapperAccessorAvailability(VarDecl *var, AccessorKind ac
 
     case PropertyWrapperSynthesizedPropertyKind::Projection: {
       if (auto origVar = var->getOriginalWrappedProperty(wrapperSynthesizedKind)) {
+        AbstractStorageDecl *projectedValueImpl;
+        if (auto access = getEnclosingSelfPropertyWrapperAccess(origVar, /*forProjected=*/true)) {
+          projectedValueImpl = access->subscript;
+        } else {
+          projectedValueImpl = origVar->getAttachedPropertyWrapperTypeInfo(0).projectedValueVar;
+        }
+
         // The property wrapper info may not actually link back to a wrapper
         // implementation, if there was a semantic error checking the wrapper.
-        auto info = origVar->getAttachedPropertyWrapperTypeInfo(0);
-        if (info.projectedValueVar) {
-          synthesizedFrom = info.projectedValueVar->getOpaqueAccessor(accessorKind);
+        if (projectedValueImpl) {
+          synthesizedFrom = projectedValueImpl->getOpaqueAccessor(accessorKind);
         }
       }
       break;

test/Sema/generalized_accessors_availability.swift

@@ -110,3 +110,42 @@ func testInferredAvailability(x: inout LessAvailable) { // expected-error {{'Les
     x.nested.$wrapped_modify_more_available = 0
   }
 }
+
+@propertyWrapper
+struct Observable<Value> {
+  private var stored: Value
+
+  init(wrappedValue: Value) { self.stored = wrappedValue }
+
+  @available(*, unavailable)
+  var wrappedValue: Value {
+    get { fatalError() }
+    set { fatalError() }
+  }
+
+  static subscript<EnclosingSelf>(
+    _enclosingInstance observed: EnclosingSelf,
+    wrapped wrappedKeyPath: ReferenceWritableKeyPath<EnclosingSelf, Value>,
+    storage storageKeyPath: ReferenceWritableKeyPath<EnclosingSelf, Self>
+  ) -> Value {
+    get { observed[keyPath: storageKeyPath].stored }
+    set { observed[keyPath: storageKeyPath].stored = newValue }
+  }
+}
+
+protocol P {}
+
+class Base<T: P> {
+  @Observable var item: T?
+}
+
+struct Item: P {}
+
+class Subclass: Base<Item> {
+  // Make sure this override isn't incorrectly diagnosed as
+  // unavailable. Wrapper availability inference should infer
+  // availability from the static subscript in this case.
+  override var item: Item? {
+    didSet {}
+  }
+}