refactor: make status a const function in rejection handling

[TheAwiteb]

Fix #3167, Updated the status method to be a const function for improved performance and compile-time evaluation.

Motivation

Allows the status code to be evaluated at compile time

Solution

-pub fn status(&self) -> http::StatusCode {
+pub const fn status(&self) -> http::StatusCode {

[Turbo87]

could you add the const keyword for the second macro variant too?

and do you know if we could do the same for __composite_rejection?

[TheAwiteb]

could you add the const keyword for the second macro variant too?

No, because it uses ToString::to_string, which is not a const function.

and do you know if we could do the same for __composite_rejection?

Yes I can, for the status function only

[Turbo87]

No, because it uses ToString::to_string, which is not a const function.

I'm talking about the function in line 115, and I don't see a to_string() call in there :)

[TheAwiteb]

FailedToDeserializePathParams and InvalidUtf8InPathParam are used in the __composite_rejection macro, but their status functions are not implemented by the __define_rejection macro. Therefore, I made their status functions const.

[jplatte]

Makes sense to me, but please note that this does not impact performance in any way. const fn means it can be evaluated in const contexts such as const ITEMs and statics, it has no influence on whether optimizations like constant folding are applied in code outside of a const context.

resolved

[jplatte]

Could you add changelog entries to axum and axum-extra (where the macro-generated methods live)?

[jplatte]

Thanks!