Re: [PATCH] Add pg_get_policy_ddl() function to reconstruct CREATE POLICY statement

hi. I still can not compile your v2.

../../Desktop/pg_src/src1/postgres/src/backend/utils/adt/ruleutils.c:
In function ‘get_formatted_string’:
../../Desktop/pg_src/src1/postgres/src/backend/utils/adt/ruleutils.c:13770:9:
error: function ‘get_formatted_string’ might be a candidate for
‘gnu_printf’ format attribute [-Werror=suggest-attribute=format]
13770 | appendStringInfoVA(buf, fmt, args);
| ^~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

Maybe you can register your patch on https://commitfest.postgresql.org/
then it will run all CI tests on all kinds of OS.

row security policy qual and with_check_qual can contain sublink/subquery.
but pg_get_expr can not cope with sublink/subquery.

see pg_get_expr comments below:
* Currently, the expression can only refer to a single relation, namely
* the one specified by the second parameter. This is sufficient for
* partial indexes, column default expressions, etc. We also support
* Var-free expressions, for which the OID can be InvalidOid.

see commit 6867f96 and
https://www.postgresql.org/message-id/flat/20211219205422.GT17618%40telsasoft.com

I guess (because I can not compile, mentioned above):
"ERROR: expression contains variables"
can be triggered by the following setup:

create table t(a int);
CREATE POLICY p1 ON t AS RESTRICTIVE FOR ALL
USING (a IS NOT NULL AND (SELECT 1 = 1 FROM pg_rewrite WHERE
pg_get_function_arg_default(ev_class, 1) !~~ pg_get_expr(ev_qual, 0,
false)));
SELECT pg_get_policy_ddl('t', 'p1', true);

You can also check my patch at https://commitfest.postgresql.org/patch/6054/
which similarly needs to build the POLICY definition for reconstruction.

see RelationBuildRowSecurity, checkExprHasSubLink also.