Future compatibility warning ("CloneToAny" cannot be made into an object)

[jonas-schievink]

Compiling anymap on the current nightly results in this warning: rust-lang/rust#51443

warning: the trait `any::CloneToAny` cannot be made into an object                                                                                                                
  --> src/any.rs:15:5                                                                                                                                                             
   |                                                                                                                                                                              
15 |     fn clone_to_any_send(&self) -> Box<CloneAny + Send> where Self: Send;                                                                                                    
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^                                                                                                    
   |                                                                                                                                                                              
   = note: #[warn(where_clauses_object_safety)] on by default                                                                                                                     
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!                                              
   = note: for more information, see issue #51443 <https://github.com/rust-lang/rust/issues/51443>                                                                                
   = note: method `clone_to_any_send` references the `Self` type in where clauses                                                                                                 

(same warning for all clone_to_any_X methods)

[chris-morgan]

I’ve assessed the situation in some detail in rust-lang/rust#51443 (comment). For now, I’m going to do nothing and see if I get any responses there.

What it’s doing should be absolutely fine, and if you don’t do Box<CloneAny + …> then you’re definitely fine.

[jonas-schievink]

Yeah that seems fine, thanks! FWIW the typemap crate is also affected and has a very unsafe fix here: reem/rust-typemap#41

[chris-morgan]

Well, although it’s acknowledged to be a spurious warning, nothing’s been done about it, so I’ve finally caved and implemented it a different way, adding some more unsafe, but avoiding this troublesome future-compatibility warning.

Fixed in 521fbfe.