[wleeaf]

The paren_expr printer collapses nested parentheses into a single pair. That's fine for (((1 + 2))). But when the inner pair belongs to a subquery or a row constructor and the outer pair is part of the enclosing clause, both are needed, and the output is no longer valid SQL:

CREATE POLICY admin_only ON permissions
USING ((SELECT is_admin FROM users WHERE name = current_user))

is formatted with USING (SELECT is_admin FROM users WHERE name = current_user), which PostgreSQL rejects with a syntax error at SELECT. The same thing happens with:

• WITH CHECK ((SELECT ...));
• GENERATED ALWAYS AS ((SELECT ...)) STORED;
• a row in GENERATED ALWAYS AS ((a * 2, a * 3));
• PARTITION BY RANGE (((a, b))), which comes out as RANGE ((a, b)).

Nested parentheses are still collapsed, except when the inner pair contains a subquery (select_stmt or compound_select_stmt) or a list. Then both pairs are kept. In plain expressions this can leave a redundant pair, as in SELECT ((SELECT 1)), but it never removes one that is needed.

Test: "preserves parenthesis around subquery used as the USING condition" in test/ddl/policy.test.ts. It fails without the change and passes with it. yarn test passes (1060 passed, 1 skipped), as do yarn ts:check and prettier --check on the changed files.

I found this by formatting the statements of PostgreSQL's regression tests with the postgresql parser and comparing the libpg_query parse tree of each output with that of the input. Together with the separate row-constructor fix (#96), the 8 statements where formatting changed the meaning through parentheses now keep it, and no other statement changed.