Make NSObject !Send and !Sync

Similar to objc2::runtime::Object

objc2-foundation/CHANGELOG.md

@@ -25,6 +25,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ### Fixed
 * Soundness issue with `NSValue`, `NSDictionary`, `NSArray` and
   `NSMutableArray` not being `#[repr(C)]`.
+* **BREAKING**: `NSObject` is no longer `Send` and `Sync` (because its
+  subclasses may not be).
 
 ## 0.2.0-alpha.2 - 2021-11-22
 

objc2-foundation/src/array.rs

@@ -184,6 +184,16 @@ unsafe impl<T: Sync + Send> Send for NSArray<T, Shared> {}
 unsafe impl<T: Sync> Sync for NSArray<T, Owned> {}
 unsafe impl<T: Send> Send for NSArray<T, Owned> {}
 
+/// ```compile_fail
+/// use objc2::rc::Shared;
+/// use objc2::runtime::Object;
+/// use objc2_foundation::NSArray;
+/// fn needs_send_sync<T: Send + Sync>() {}
+/// needs_send_sync::<NSArray<Object, Shared>>();
+/// ```
+#[cfg(doctest)]
+pub struct NSArrayWithObjectNotSendSync;
+
 unsafe impl<T: INSObject, O: Ownership> INSArray for NSArray<T, O> {
     /// The `NSArray` itself (length and number of items) is always immutable,
     /// but we would like to know when we're the only owner of the array, to

objc2-foundation/src/object.rs

@@ -1,8 +1,9 @@
+use core::marker::PhantomData;
 use core::ptr::NonNull;
 
 use objc2::msg_send;
 use objc2::rc::{Id, Owned, Shared};
-use objc2::runtime::{Bool, Class};
+use objc2::runtime::{Bool, Class, Object};
 use objc2::Message;
 
 use super::NSString;
@@ -37,7 +38,22 @@ pub unsafe trait INSObject: Sized + Message {
     }
 }
 
-object!(unsafe pub struct NSObject);
+object!(unsafe pub struct NSObject<> {
+    p: PhantomData<Object>, // Temporary
+});
+
+/// ```compile_fail
+/// use objc2_foundation::NSObject;
+/// fn needs_sync<T: Sync>() {}
+/// needs_sync::<NSObject>();
+/// ```
+/// ```compile_fail
+/// use objc2_foundation::NSObject;
+/// fn needs_send<T: Send>() {}
+/// needs_send::<NSObject>();
+/// ```
+#[cfg(doctest)]
+pub struct NSObjectNotSendNorSync;
 
 impl NSObject {
     unsafe_def_fn!(pub fn new -> Owned);