How do I check if a trait is implemented in Rust?

I want to print a variable with the Display trait if it is implemented, or with the Debug trait otherwise.

let display = MyDisplayType::new(); // implements Display
let debug = MyDebugType::new(); // implements Debug

output!(display); // uses Display a.k.a. println!("{}", display);
output!(debug); // uses Debug a.k.a. println!("{:?}", debug);

What is the cleanest way?