Revert "Allow msg_send_id![obj, init] to non-option wrapped Id"

It makes error messages and documentation worse (which _is_ a big deal), and I doubt it'll really be useful. Besides, we can always re-add it without breaking changes!

objc2/src/__macro_helpers.rs

@@ -78,14 +78,12 @@ impl<T: ?Sized + Message, O: Ownership> MsgSendId<&'_ Class, Id<T, O>>
 }
 
 // `init`, should mark the input value as "allocated, not initialized" somehow
-//
-// The generic bound allows `init` to take both `Option<Id>` and `Id`.
-impl<X: Into<Option<Id<T, O>>>, T: ?Sized + Message, O: Ownership> MsgSendId<X, Id<T, O>>
+impl<T: ?Sized + Message, O: Ownership> MsgSendId<Option<Id<T, O>>, Id<T, O>>
     for RetainSemantics<false, false, true, false>
 {
     #[inline(always)]
     unsafe fn send_message_id<A: MessageArguments>(
-        obj: X,
+        obj: Option<Id<T, O>>,
         sel: Sel,
         args: A,
     ) -> Result<Option<Id<T, O>>, MessageError> {
@@ -242,7 +240,7 @@ mod tests {
         expected.alloc += 1;
         // Check allocation error before init
         let obj = obj.unwrap();
-        let _obj: Id<RcTestObject, Shared> = unsafe { msg_send_id![obj, init].unwrap() };
+        let _obj: Id<RcTestObject, Shared> = unsafe { msg_send_id![Some(obj), init].unwrap() };
         expected.init += 1;
         expected.assert_current();
     }

objc2/src/macros.rs

@@ -325,10 +325,9 @@ macro_rules! msg_send_bool {
 /// - The `alloc` family: The receiver must be `&Class`, and the return type
 ///   is a generic `Option<Id<T, O>>`. (This will change, see [#172]).
 ///
-/// - The `init` family: The receiver must be either `Id<T, O>` or
-///   `Option<Id<T, O>>` as returned from `alloc`. The receiver is consumed,
-///   and a the now-initialized `Option<Id<T, O>>` (with the same `T` and `O`)
-///   is returned.
+/// - The `init` family: The receiver must be `Option<Id<T, O>>` as returned
+///   from `alloc`. The receiver is consumed, and a the now-initialized
+///   `Option<Id<T, O>>` (with the same `T` and `O`) is returned.
 ///
 /// - The `copy` family: The receiver may be anything that implements
 ///   [`MessageReceiver`] and the return type is a generic `Option<Id<T, O>>`.

tests/ui/msg_send_id_invalid_receiver.stderr

@@ -32,33 +32,39 @@ note: associated function defined here
    |     unsafe fn send_message_id<A: MessageArguments>(
    |               ^^^^^^^^^^^^^^^
 
-error[E0277]: the trait bound `Option<Id<_, _>>: From<&objc2::runtime::Object>` is not satisfied
-  --> ui/msg_send_id_invalid_receiver.rs:10:42
+error[E0308]: mismatched types
+  --> ui/msg_send_id_invalid_receiver.rs:10:55
    |
 10 |     let _: Id<Object, Shared> = unsafe { msg_send_id![obj, init].unwrap() };
-   |                                          ^^^^^^^^^^^^^^^^^^^^^^^ the trait `From<&objc2::runtime::Object>` is not implemented for `Option<Id<_, _>>`
+   |                                          -------------^^^-------
+   |                                          |            |
+   |                                          |            expected enum `Option`, found `&objc2::runtime::Object`
+   |                                          arguments to this function are incorrect
    |
-   = help: the following other types implement trait `From<T>`:
-             <Option<&'a T> as From<&'a Option<T>>>
-             <Option<&'a mut T> as From<&'a mut Option<T>>>
-             <Option<T> as From<T>>
-   = note: required because of the requirements on the impl of `Into<Option<Id<_, _>>>` for `&objc2::runtime::Object`
-   = note: required because of the requirements on the impl of `MsgSendId<&objc2::runtime::Object, Id<_, _>>` for `RetainSemantics<false, false, true, false>`
-   = note: this error originates in the macro `msg_send_id` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note:   expected enum `Option<Id<_, _>>`
+           found reference `&objc2::runtime::Object`
+note: associated function defined here
+  --> $WORKSPACE/objc2/src/__macro_helpers.rs
+   |
+   |     unsafe fn send_message_id<A: MessageArguments>(
+   |               ^^^^^^^^^^^^^^^
 
-error[E0277]: the trait bound `Option<Id<_, _>>: From<&objc2::runtime::Class>` is not satisfied
-  --> ui/msg_send_id_invalid_receiver.rs:13:42
+error[E0308]: mismatched types
+  --> ui/msg_send_id_invalid_receiver.rs:13:55
    |
 13 |     let _: Id<Object, Shared> = unsafe { msg_send_id![cls, init].unwrap() };
-   |                                          ^^^^^^^^^^^^^^^^^^^^^^^ the trait `From<&objc2::runtime::Class>` is not implemented for `Option<Id<_, _>>`
+   |                                          -------------^^^-------
+   |                                          |            |
+   |                                          |            expected enum `Option`, found `&objc2::runtime::Class`
+   |                                          arguments to this function are incorrect
    |
-   = help: the following other types implement trait `From<T>`:
-             <Option<&'a T> as From<&'a Option<T>>>
-             <Option<&'a mut T> as From<&'a mut Option<T>>>
-             <Option<T> as From<T>>
-   = note: required because of the requirements on the impl of `Into<Option<Id<_, _>>>` for `&objc2::runtime::Class`
-   = note: required because of the requirements on the impl of `MsgSendId<&objc2::runtime::Class, Id<_, _>>` for `RetainSemantics<false, false, true, false>`
-   = note: this error originates in the macro `msg_send_id` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note:   expected enum `Option<Id<_, _>>`
+           found reference `&objc2::runtime::Class`
+note: associated function defined here
+  --> $WORKSPACE/objc2/src/__macro_helpers.rs
+   |
+   |     unsafe fn send_message_id<A: MessageArguments>(
+   |               ^^^^^^^^^^^^^^^
 
 error[E0277]: the trait bound `Id<objc2::runtime::Object, Shared>: MessageReceiver` is not satisfied
   --> ui/msg_send_id_invalid_receiver.rs:16:42