More precisely note status of unstable-apple-new

crates/objc2/Cargo.toml

@@ -65,7 +65,7 @@ unstable-c-unwind = []
 # For better documentation on docs.rs
 unstable-docsrs = []
 
-# Enable new features available on ARM64 on:
+# Enable some new features available on ARM64 on:
 # - macOS 13.0
 # - iOS 16.0
 # - tvOS 16.0
@@ -74,7 +74,9 @@ unstable-docsrs = []
 # See https://developer.apple.com/videos/play/wwdc2022/110363/ for an overview
 # of the features.
 #
-# Currently untested.
+# Currently untested, might be unsound or lead to confusing compiler errors.
+#
+# Additionally, the message sending improvements is not yet implemented.
 unstable-apple-new = ["apple"]
 
 # Runtime selection. See `objc-sys` for details.

crates/objc2/src/runtime/retain_release_fast.rs

@@ -35,7 +35,7 @@
 //!    allocator ends up using `x16`, `x17`, `x18`, `x29` or `x30`, we will
 //!    emit a call to e.g. `objc_retain_x29`, which will fail at link time.
 //!
-//!    Before this option can be stable, we need a way to prevent that!
+//!    TODO: Before this option can be stable, we need a way to prevent that!
 //!
 //! 2. We use the `clobber_abi("C")` since we're effectively calling a C
 //!    C function.