note to future self

library/core/src/ptr/mod.rs

@@ -26,6 +26,7 @@
 //!   some memory happens to exist at that address and gets deallocated. This corresponds to writing
 //!   your own allocator: allocating zero-sized objects is not very hard. The canonical way to
 //!   obtain a pointer that is valid for zero-sized accesses is [`NonNull::dangling`].
+//FIXME: mention `ptr::invalid` above, once it is stable.
 //! * All accesses performed by functions in this module are *non-atomic* in the sense
 //!   of [atomic operations] used to synchronize between threads. This means it is
 //!   undefined behavior to perform two concurrent accesses to the same location from different