Consume ManuallyDrop<Id<T, O>> in msg_send!

If you do not want to consume it, the possibility of doing `msg_send![&*obj]` exists, but most of the time that is indeed what you want (I mean, why else would you wrap it in `ManuallyDrop`?)

Author: madsmtm

objc2/src/message/mod.rs

@@ -83,8 +83,7 @@ pub(crate) mod private {
     impl<'a, T: Message + ?Sized, O: Ownership> Sealed for &'a Id<T, O> {}
     impl<'a, T: Message + ?Sized> Sealed for &'a mut Id<T, Owned> {}
 
-    impl<'a, T: Message + ?Sized, O: Ownership> Sealed for &'a ManuallyDrop<Id<T, O>> {}
-    impl<'a, T: Message + ?Sized> Sealed for &'a mut ManuallyDrop<Id<T, Owned>> {}
+    impl<T: Message + ?Sized, O: Ownership> Sealed for ManuallyDrop<Id<T, O>> {}
 }
 
 /// Types that can directly be used as the receiver of Objective-C messages.
@@ -267,17 +266,10 @@ unsafe impl<'a, T: Message + ?Sized> MessageReceiver for &'a mut Id<T, Owned> {
     }
 }
 
-unsafe impl<'a, T: Message + ?Sized, O: Ownership> MessageReceiver for &'a ManuallyDrop<Id<T, O>> {
+unsafe impl<T: Message + ?Sized, O: Ownership> MessageReceiver for ManuallyDrop<Id<T, O>> {
     #[inline]
     fn as_raw_receiver(self) -> *mut Object {
-        Id::as_ptr(&**self) as *mut Object
-    }
-}
-
-unsafe impl<'a, T: Message + ?Sized> MessageReceiver for &'a mut ManuallyDrop<Id<T, Owned>> {
-    #[inline]
-    fn as_raw_receiver(self) -> *mut Object {
-        Id::as_mut_ptr(&mut **self) as *mut Object
+        Id::consume_as_ptr(self) as *mut Object
     }
 }
 
@@ -481,17 +473,11 @@ mod tests {
 
     #[test]
     fn test_send_message_manuallydrop() {
-        let obj = test_utils::custom_object();
-        let mut obj = ManuallyDrop::new(obj);
-        let result: u32 = unsafe {
-            let _: () = msg_send![&mut obj, setFoo: 4u32];
-            msg_send![&obj, foo]
+        let obj = ManuallyDrop::new(test_utils::custom_object());
+        unsafe {
+            let _: () = msg_send![obj, release];
         };
-        assert_eq!(result, 4);
-
-        let obj: *const ManuallyDrop<Object> = obj.as_ptr().cast();
-        let result: u32 = unsafe { msg_send![obj, foo] };
-        assert_eq!(result, 4);
+        // `obj` is consumed, can't use here
     }
 
     #[test]

objc2/src/rc/id.rs

@@ -199,6 +199,11 @@ impl<T: Message + ?Sized, O: Ownership> Id<T, O> {
     pub fn as_ptr(this: &Id<T, O>) -> *const T {
         this.ptr.as_ptr()
     }
+
+    #[inline]
+    pub(crate) fn consume_as_ptr(this: ManuallyDrop<Self>) -> *mut T {
+        this.ptr.as_ptr()
+    }
 }
 
 impl<T: Message + ?Sized> Id<T, Owned> {

objc2/src/test_utils.rs

@@ -23,34 +23,26 @@ impl CustomObject {
 // TODO: Remove the need for this hack
 impl crate::message::private::Sealed for &CustomObject {}
 impl crate::message::private::Sealed for &mut CustomObject {}
-impl crate::message::private::Sealed for &ManuallyDrop<CustomObject> {}
-impl crate::message::private::Sealed for &mut ManuallyDrop<CustomObject> {}
+impl crate::message::private::Sealed for ManuallyDrop<CustomObject> {}
 
 unsafe impl MessageReceiver for &CustomObject {
     #[inline]
     fn as_raw_receiver(self) -> *mut Object {
-        (&**self).as_raw_receiver()
+        self.obj
     }
 }
 
 unsafe impl MessageReceiver for &mut CustomObject {
     #[inline]
     fn as_raw_receiver(self) -> *mut Object {
-        (&**self).as_raw_receiver()
+        self.obj
     }
 }
 
-unsafe impl MessageReceiver for &ManuallyDrop<CustomObject> {
+unsafe impl MessageReceiver for ManuallyDrop<CustomObject> {
     #[inline]
     fn as_raw_receiver(self) -> *mut Object {
-        (&**self).as_raw_receiver()
-    }
-}
-
-unsafe impl MessageReceiver for &mut ManuallyDrop<CustomObject> {
-    #[inline]
-    fn as_raw_receiver(self) -> *mut Object {
-        (&**self).as_raw_receiver()
+        self.obj
     }
 }
 
@@ -106,6 +98,11 @@ pub(crate) fn custom_class() -> &'static Class {
         builder.add_protocol(proto);
         builder.add_ivar::<u32>("_foo");
 
+        unsafe extern "C" fn custom_obj_release(this: *mut Object, _cmd: Sel) {
+            // Drop the value
+            let _ = CustomObject { obj: this };
+        }
+
         extern "C" fn custom_obj_set_foo(this: &mut Object, _cmd: Sel, foo: u32) {
             unsafe {
                 this.set_ivar::<u32>("_foo", foo);
@@ -145,6 +142,9 @@ pub(crate) fn custom_class() -> &'static Class {
         }
 
         unsafe {
+            let release: unsafe extern "C" fn(*mut Object, Sel) = custom_obj_release;
+            builder.add_method(sel!(release), release);
+
             let set_foo: extern "C" fn(&mut Object, Sel, u32) = custom_obj_set_foo;
             builder.add_method(sel!(setFoo:), set_foo);
             let get_foo: extern "C" fn(&Object, Sel) -> u32 = custom_obj_get_foo;

tests/ui/msg_send_only_message.stderr

@@ -6,12 +6,11 @@ error[E0277]: the trait bound `{integer}: MessageReceiver` is not satisfied
   |
   = help: the following other types implement trait `MessageReceiver`:
             &'a Id<T, O>
-            &'a ManuallyDrop<Id<T, O>>
             &'a T
             &'a mut Id<T, objc2::rc::Owned>
-            &'a mut ManuallyDrop<Id<T, objc2::rc::Owned>>
             &'a mut T
             *const T
             *mut T
+            ManuallyDrop<Id<T, O>>
             NonNull<T>
   = note: this error originates in the macro `msg_send` (in Nightly builds, run with -Z macro-backtrace for more info)