Function first_field_without_column 

pub const fn first_field_without_column(
    columns: &'static [(&'static str, &'static str)],
    fields: &'static [&'static str],
) -> Option<&'static str>

The first of fields without a column in the (domain field, column) table, if any. Usable in const code, which is how assert_columns! checks coverage at compile time.