Add regression test for DROP OWNED BY with default ACLs

DROP OWNED BY has a specific code path to remove ACLs stored in
pg_default_acl when cleaning up shared dependencies that had no
coverage with the existing tests.  This issue has been found while
digging into the bug fixed by 21378e1.

As ALTER DEFAULT PRIVILEGES impacts the ACLs of all objects created
while the default permissions are visible, the test uses a transaction
rollback to isolate the test and avoid any impact with other sessions
running in parallel.

Reviewed-by: Álvaro Herrera
Discussion: https://postgr.es/m/YAbQ1OD+3ip4lRv8@paquier.xyz

src/test/regress/expected/privileges.out

@@ -1760,6 +1760,35 @@ SELECT has_schema_privilege('regress_priv_user2', 'testns4', 'CREATE'); -- yes
 
 ALTER DEFAULT PRIVILEGES REVOKE ALL ON SCHEMAS FROM regress_priv_user2;
 COMMIT;
+-- Test for DROP OWNED BY with shared dependencies.  This is done in a
+-- separate, rollbacked, transaction to avoid any trouble with other
+-- regression sessions.
+BEGIN;
+ALTER DEFAULT PRIVILEGES GRANT ALL ON FUNCTIONS TO regress_priv_user2;
+ALTER DEFAULT PRIVILEGES GRANT ALL ON SCHEMAS TO regress_priv_user2;
+ALTER DEFAULT PRIVILEGES GRANT ALL ON SEQUENCES TO regress_priv_user2;
+ALTER DEFAULT PRIVILEGES GRANT ALL ON TABLES TO regress_priv_user2;
+ALTER DEFAULT PRIVILEGES GRANT ALL ON TYPES TO regress_priv_user2;
+SELECT count(*) FROM pg_shdepend
+  WHERE deptype = 'a' AND
+        refobjid = 'regress_priv_user2'::regrole AND
+	classid = 'pg_default_acl'::regclass;
+ count 
+-------
+     5
+(1 row)
+
+DROP OWNED BY regress_priv_user2, regress_priv_user2;
+SELECT count(*) FROM pg_shdepend
+  WHERE deptype = 'a' AND
+        refobjid = 'regress_priv_user2'::regrole AND
+	classid = 'pg_default_acl'::regclass;
+ count 
+-------
+     0
+(1 row)
+
+ROLLBACK;
 CREATE SCHEMA testns5;
 SELECT has_schema_privilege('regress_priv_user2', 'testns5', 'USAGE'); -- no
  has_schema_privilege 

src/test/regress/sql/privileges.sql

@@ -1049,6 +1049,26 @@ ALTER DEFAULT PRIVILEGES REVOKE ALL ON SCHEMAS FROM regress_priv_user2;
 
 COMMIT;
 
+-- Test for DROP OWNED BY with shared dependencies.  This is done in a
+-- separate, rollbacked, transaction to avoid any trouble with other
+-- regression sessions.
+BEGIN;
+ALTER DEFAULT PRIVILEGES GRANT ALL ON FUNCTIONS TO regress_priv_user2;
+ALTER DEFAULT PRIVILEGES GRANT ALL ON SCHEMAS TO regress_priv_user2;
+ALTER DEFAULT PRIVILEGES GRANT ALL ON SEQUENCES TO regress_priv_user2;
+ALTER DEFAULT PRIVILEGES GRANT ALL ON TABLES TO regress_priv_user2;
+ALTER DEFAULT PRIVILEGES GRANT ALL ON TYPES TO regress_priv_user2;
+SELECT count(*) FROM pg_shdepend
+  WHERE deptype = 'a' AND
+        refobjid = 'regress_priv_user2'::regrole AND
+	classid = 'pg_default_acl'::regclass;
+DROP OWNED BY regress_priv_user2, regress_priv_user2;
+SELECT count(*) FROM pg_shdepend
+  WHERE deptype = 'a' AND
+        refobjid = 'regress_priv_user2'::regrole AND
+	classid = 'pg_default_acl'::regclass;
+ROLLBACK;
+
 CREATE SCHEMA testns5;
 
 SELECT has_schema_privilege('regress_priv_user2', 'testns5', 'USAGE'); -- no