Function pretty_expr 

pub fn pretty_expr(e: &Expr) -> String

v7.39 (round 311, V32) — PG’s PRETTY deparse of an expression, the form pg_get_constraintdef(oid, true) and friends return.

The default fmt::Display parenthesises every operator node, which is what PG’s non-pretty deparse does and what makes the text round-trip. Pretty drops the pairs the grammar can put back, and the rule is NOT plain precedence minimisation — measured against PG 18.4 across 37 shapes:

• the boolean layer follows precedence (NOT > AND > OR): an OR under an AND keeps its parens, an AND under an OR does not, and a comparison under any of them does not (NOT a > 1);
• an associative chain flattens completely, even where the source nested it to the right (a AND (b AND c) prints as one chain);
• but an operand of a comparison or arithmetic operator keeps its parens whenever it is itself an operator expression — so (a + b) > 10 and (- a) + b, even though precedence alone would not require either. A cast, function call, column or literal in that position does not (a::text = t, length(code) > 2); a cast counts as compound exactly when the thing it casts is (((a + b)::text) = t).

Anything outside that layer defers to Display, which is never wrong — only more parenthesised than PG would print.