I tested v15 on current master (57f93af36f): builds, make check passes, and basic reconstruction, pretty mode, NULL handling, and default-clause omission all look good. Two things.
1) Back in the v3/v4 discussion you decided the ON <table> name should always be schema-qualified for safety (the pg_get_triggerdef_worker thread with jian he), and that pretty here only controls formatting, not schema (Phil's point). That reasoning didn't reach the USING / WITH CHECK expressions, though: object references inside them are still qualified only by the caller's search_path, so they can lose their schema and rebind to a different object when the DDL is replayed elsewhere:
CREATE FUNCTION s1.f(int) RETURNS bool LANGUAGE sql AS 'SELECT $1 > 0'; CREATE FUNCTION s2.f(int) RETURNS bool LANGUAGE sql AS 'SELECT $1 < 0'; CREATE POLICY pf ON t2 USING (s1.f(a));
SET search_path = public, s1; SELECT ddl FROM pg_get_policy_ddl('t2', 'pf') AS ddl; -- CREATE POLICY pf ON public.t2 USING (f(a)); -- s1. dropped
SET search_path = public, s2; CREATE POLICY pf ON t2 USING (f(a)); -- now s2.f, opposite meaning
So within one statement the ON clause is always qualified but the expression body isn't -- and as Phil noted, the pretty flag can't fix this, since pg_get_expr qualifies by search_path visibility regardless of pretty.
Worth settling the contract, given where this function sits. The old pg_get_viewdef / ruledef / indexdef functions are search_path-aware and leave qualification to the caller (pg_dump sets search_path empty around them so the output is portable). The new pg_get_*_ddl functions committed so far (role, database, tablespace) are on global, schemaless objects, so the question never came up -- pg_get_policy_ddl is the first of the family whose output embeds schema-qualifiable references. Your own pg_get_table_ddl patch already hit this and deparses under a controlled search_path (narrowed to pg_catalog), so the most consistent fix is to do the same here (NewGUCNestLevel + set_config); an empty search_path already yields the fully-qualified s1.f(a). If instead the intent is to follow the caller's search_path, that's fine too, but it should be documented (and SET search_path = '' noted as the way to get portable DDL).
2) The doc calls the second parameter policy_name, but the actual argument is policyname, so the documented named-argument call fails:
SELECT * FROM pg_get_policy_ddl("table" => 't'::regclass, policy_name => 'p_all'); ERROR: function pg_get_policy_ddl(table => regclass, policy_name => unknown) does not exist
