It seems that there is a missing implementation of std::fmt::Pointer on some function pointers:

function pointers like fn test() -> f32 can be passed as argument to println!("{:p}", ...)
but function pointers like fn test(Vec<T> a) -> f32 can't because it's a HRTB variant.

see https://users.rust-lang.org/t/display-function-pointer/17073 for more details.