Function bare_prefix_operand_needs_parens 

fn bare_prefix_operand_needs_parens<T: AstInfo>(operand: &Expr<T>) -> bool

Whether the operand of a bare prefix -/+ must be parenthesized to round-trip. Such a prefix op binds tighter than COLLATE/AT TIME ZONE and the binary/comparison operators, but looser than the postfix ::/[…] forms, and - <number> additionally lexes as a negative literal. So peel the tight postfixes (::/[…]). If the chain bottoms out at a numeric literal, the sign would fold into it, and if it bottoms out at anything other than a self-delimiting non-COLLATE primary (a COLLATE, a binary op, …), the prefix op would re-associate. Both need parens. (a + b COLLATE c reparses as a + (b COLLATE c), and - x COLLATE c as (- x) COLLATE c.)