Unable to pass hook to panic::set_hook as a variable or without specifying type

[wooster0]

I tried this code:

use std::panic;

fn main() {
    let new_hook = Box::new(|_| {});
    panic::set_hook(new_hook);
}

I expected it to compile successfully.

Instead, this happened:

error[E0308]: mismatched types
 --> src/main.rs:5:21
  |
5 |     panic::set_hook(new_hook);
  |                     ^^^^^^^^ one type is more general than the other
  |
  = note: expected type `FnOnce<(&PanicInfo<'_>,)>`
             found type `FnOnce<(&PanicInfo<'_>,)>`
note: this closure does not fulfill the lifetime requirements
 --> src/main.rs:4:29
  |
4 |     let new_hook = Box::new(|_| {});
  |                             ^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.
error: could not compile `playground`

To learn more, run the command again with --verbose.

If I however not assign the Box to a variable and instead directly pass it to panic::set_hook, it compiles:

use std::panic;

fn main() {
    panic::set_hook(Box::new(|_| {}));
}

I believe it should be allowed to assign it to a variable beforehand.

That, or if you explicitly specify the type, it compiles too:

use std::panic;

type Hook = Box<dyn Fn(&panic::PanicInfo<'_>) + Sync + Send + 'static>;

fn main() {
    let new_hook: Hook = Box::new(|_| {});
    panic::set_hook(new_hook);
}

I believe it should be able to infer the type on its own.

Meta

rustc --version --verbose:

rustc 1.51.0 (2fd73fabe 2021-03-23)
binary: rustc
commit-hash: 2fd73fabe469357a12c2c974c140f67e7cdd76d0
commit-date: 2021-03-23
host: x86_64-unknown-linux-gnu
release: 1.51.0
LLVM version: 11.0.1

Note that on beta and nightly the error is different.