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

The following review has been posted through the commitfest application:
make installcheck-world:  not tested
Implements feature:       tested, failed
Spec compliant:           not tested
Documentation:            not tested

Hi,

I looked at v10, focused on whether the generated CREATE POLICY statement
can be executed again.

The patch applies cleanly on current master at
8a86aa313a714adc56c74e4b08793e4e6102b5ca.

git diff --check reports no issues.

I built with:

./configure --prefix="$PWD/pg-install" --without-readline --without-zlib --without-icu
make -s -j8
make -s install

make -C src/test/regress check TESTS=rowsecurity

ended up running the full parallel_schedule in this makefile; all 245 tests
passed, including rowsecurity.

I found one correctness issue in the generated non-pretty DDL.  The code
assumes that pg_get_expr_ext(..., false) already returns the parentheses
required by CREATE POLICY syntax, but that is not true for simple boolean
constants.

For example:

CREATE TABLE t(a int);
CREATE POLICY p_true ON t USING (true);
SELECT ddl FROM pg_get_policy_ddl('t', 'p_true', 'pretty', 'false') AS ddl;

returns:

CREATE POLICY p_true ON public.t USING true;

If I drop the policy and execute that generated statement, it fails:

ERROR:  syntax error at or near "true"
LINE 1: CREATE POLICY p_true ON public.t USING true;
                                               ^

The same issue reproduces for WITH CHECK:

CREATE POLICY p_check ON t FOR INSERT WITH CHECK (false);

is reconstructed as:

CREATE POLICY p_check ON public.t FOR INSERT WITH CHECK false;

and executing it fails at "false".

So I think USING and WITH CHECK need to be parenthesized in non-pretty mode
too, or the tests should include a round-trip execution check for generated
DDL with simple boolean expressions.

I used two small SQL reproducers for the manual checks; the complete repro is
included above.

I have not reviewed the broader pg_get_*_ddl API design or every possible
policy expression form.

Regards,
Ilmar Yunusov

The new status of this patch is: Waiting on Author