Function prefix_operand_needs_parens 

pub fn prefix_operand_needs_parens<T: AstInfo>(
    op: &Op,
    operand: &Expr<T>,
) -> bool

Whether the operand of a prefix operator (an Op with no second operand) must be parenthesized so the printed expression reparses to the same tree. Both printers (AstDisplay and mz-sql-pretty) must use it, so they agree.