Macro agnes::declare_fields

macro_rules! declare_fields {
    (@step($tbl:ty)($prev_label:ident)()) => { ... };
    (@step
        ($tbl:ty)
        ($prev_label:ident)
        ($label:ident: $dtype:ident = $name:expr, $($rest:tt)*)
    ) => { ... };
    (@step($tbl:ty)($prev_label:ident)($label:ident: $dtype:ident = $name:expr)) => { ... };
    (@start
        ($tbl:ty)
        ($label:ident: $dtype:ident = $name:expr, $($rest:tt)*)
    ) => { ... };
    (@start($tbl:ty)($label:ident: $dtype:ident = $name:expr)) => { ... };
    ($tbl:ty; $($fields:tt)*) => { ... };
}

Macro for declaring field labels. Used by tablespace macro.