fn pointers taking references are not Clone

[sgrif]

The type fn(&'a T) implements Clone, while fn(&T) does not. This presumably applies to more traits than just Clone.

[ghost]

This is probably related to #28229

[petrochenkov]

More like #24000

The problem can probably be mitigated in practice to some extent by manually implementing fn pointer traits for a few most common cases involving references.
The place to add impls is here.

[sgrif]

Yes, I agree. I did check that adding

fnptr_impls_safety_abi! { extern "Rust" fn($(&$Arg),*) -> Ret, $($Arg),* }

compiles successfully. It does (e.g. no coherence issues). I didn't confirm whether it solved the problem I was encountering though.

[cjgillot]

This was fixed a long time ago.