Macro dw_code 

macro_rules! dw_code {
    (
        $(#[$meta:meta])*
        $vis:vis const $name:ident : DwCode = DwCode::new($id:literal, ExitTier::$tier:ident)
            $(.$chain:ident())? ;
    ) => { ... };
    (
        $(#[$meta:meta])*
        $vis:vis const $name:ident : &str = $id:literal ;
    ) => { ... };
}

Declare a DW code — the only way to. Expands to the constant as written and registers it in DECLARED:

dw_code! {
    /// What the rule refuses.
    pub const <NAME>: DwCode = DwCode::new("<code>", ExitTier::<tier>);
}
dw_code! { pub const <NAME>: &str = "<code>"; }

The declaration inside the braces is spelled the way tools/ci/check-dw-codes.py’s CONST_RE reads it, so the source reading and the binary’s registry are two readings of one text.