But `panic!()` is just a macro invocation that needs to expand to something, and the question here is what that something ought to be in order to produce a vali

But `panic!()` is just a macro invocation that needs to expand to something, and the question here is what that something ought to be in order to produce a valid program. Currently it expands to this: https://github.com/rust-lang/rust/blob/98fd715edd3a0a5aa8f2041d7e20a3143b0fc0d3/library/core/src/panicking.rs#L138 https://github.com/rust-lang/rust/blob/98fd715edd3a0a5aa8f20... , which is a function with a return type of `!`, which has indicated a diverging function since long before Rust even considered having a first-class never type.