Function precompile_date_units 

fn precompile_date_units<F>(
    e: &mut MirScalarExpr,
    column_types: &[ReprColumnType],
    build_unary: F,
)
where
    F: FnOnce(DateTimeUnits) -> UnaryFunc,

Specializes a binary date/time function call whose units argument is a literal string. Produces either a unary call with the parsed units baked in, or a literal UnknownUnits error.