Test that msg_send! consumes the receiver

tests/ui/msg_send_mutable.rs

@@ -0,0 +1,14 @@
+//! Test that `msg_send!` consumes their arguments, including the receiver.
+//!
+//! Ideally, it shouldn't be so, but that's how it works currently.
+use objc2::{msg_send, class};
+use objc2::runtime::Object;
+
+fn main() {
+    let cls = class!(NSObject);
+    let obj: &mut Object = unsafe { msg_send![cls, new] };
+
+    let _: () = unsafe { msg_send![obj, selector] };
+    // Could be solved with a reborrow
+    let _: () = unsafe { msg_send![obj, selector] };
+}

tests/ui/msg_send_mutable.stderr

@@ -0,0 +1,17 @@
+error[E0382]: use of moved value: `obj`
+   --> ui/msg_send_mutable.rs:13:36
+    |
+9   |     let obj: &mut Object = unsafe { msg_send![cls, new] };
+    |         --- move occurs because `obj` has type `&mut objc2::runtime::Object`, which does not implement the `Copy` trait
+10  |
+11  |     let _: () = unsafe { msg_send![obj, selector] };
+    |                          ------------------------ `obj` moved due to this method call
+12  |     // Could be solved with a reborrow
+13  |     let _: () = unsafe { msg_send![obj, selector] };
+    |                                    ^^^ value used here after move
+    |
+note: this function takes ownership of the receiver `self`, which moves `obj`
+   --> $WORKSPACE/objc2/src/message/mod.rs
+    |
+    |     unsafe fn send_message<A, R>(self, sel: Sel, args: A) -> Result<R, MessageError>
+    |                                  ^^^^

tests/ui/msg_send_not_encode.rs

@@ -1,9 +1,12 @@
-//! Test that return types that are not `Encode` are not accepted.
+//! Test that types that are not `Encode` are not accepted.
 use objc2::{class, msg_send};
 
 fn main() {
+    let cls = class!(NSData);
     unsafe {
-        let cls = class!(NSData);
         let _: Vec<u8> = msg_send![cls, new];
+
+        let x: Vec<u8>;
+        let _: () = msg_send![cls, newWith: x];
     }
 }

tests/ui/msg_send_not_encode.stderr

@@ -20,3 +20,27 @@ note: required by a bound in `send_message`
     |         R: Encode,
     |            ^^^^^^ required by this bound in `send_message`
     = note: this error originates in the macro `msg_send` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the trait bound `Vec<u8>: Encode` is not satisfied
+   --> ui/msg_send_not_encode.rs:10:21
+    |
+10  |         let _: () = msg_send![cls, newWith: x];
+    |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Encode` is not implemented for `Vec<u8>`
+    |
+    = help: the following other types implement trait `Encode`:
+              &'a T
+              &'a mut T
+              ()
+              *const T
+              *const c_void
+              *mut T
+              *mut c_void
+              ManuallyDrop<T>
+            and 142 others
+    = note: required because of the requirements on the impl of `MessageArguments` for `(Vec<u8>,)`
+note: required by a bound in `send_message`
+   --> $WORKSPACE/objc2/src/message/mod.rs
+    |
+    |         A: MessageArguments,
+    |            ^^^^^^^^^^^^^^^^ required by this bound in `send_message`
+    = note: this error originates in the macro `msg_send` (in Nightly builds, run with -Z macro-backtrace for more info)