Macro const_format_args 

macro_rules! const_format_args {
    ($fmt:expr) => { ... };
    ($fmt:expr, $($args:tt)*) => { ... };
}

🔬This is a nightly-only experimental API. (const_format_args)

Same as format_args, but can be used in some const contexts.

This macro is used by the panic macros for the const_panic feature.

This macro will be removed once format_args is allowed in const contexts.