Macro define_codes 

macro_rules! define_codes {
    (
        $(
            $(#[$meta:meta])*
            $name:ident = $num:literal, $sev:ident, $cat:ident, $slug:literal, $owner:literal, $summary:literal;
        )*
    ) => { ... };
}

Define the entire diagnostic registry.

Each line expands to a pub static DiagnosticDef plus an entry in ALL. The macro is the only mint site for codes and defs, and it generates the invariant tests (unique numbers, unique slugs, the static’s name matches its rendered code, MOS + four digits).