macro_rules! register_error {
($ctx:expr, crate($krate:expr), $span: expr, $($fmt:tt)*) => { ... };
($ctx:expr, $span: expr, $($fmt:tt)*) => { ... };
}macro_rules! register_error {
($ctx:expr, crate($krate:expr), $span: expr, $($fmt:tt)*) => { ... };
($ctx:expr, $span: expr, $($fmt:tt)*) => { ... };
}