MarkGUCPrefixReserved() doesn't check all options

Hi hackers,

Ekaterina Sokolova and I have found a bug in PG 15. Since 88103567cb
MarkGUCPrefixReserved() is supposed not only reporting GUCs that haven't
been
defined by the extension, but also removing them. However, it removes them
in
a wrong way, so that a GUC that goes after the removed GUC is never checked.

To reproduce the bug add the following to the postgresql.conf

shared_preload_libraries = 'pg_stat_statements'
pg_stat_statements.nonexisting_option_1 = on
pg_stat_statements.nonexisting_option_2 = on
pg_stat_statements.nonexisting_option_3 = on
pg_stat_statements.nonexisting_option_4 = on

and start the server. In the logfile you'll see only first and third options
reported invalid and removed.

In master MarkGUCPrefixReserved() iterates a hash table, not an array as in
PG 15. I'm not sure whether it is safe to remove an entry from this hash
table
while iterating it, but at least I can't reproduce the bug on master.

I attached a bugfix for PG 15.

Best regards,
Karina Litskevich
Postgres Professional: http://postgrespro.com/