62f34097c8
This follows in the spirit of commit dfb75e478, which created primary key and uniqueness constraints to improve the visibility of constraints imposed on the system catalogs. While our catalogs contain many foreign-key-like relationships, they don't quite follow SQL semantics, in that the convention for an omitted reference is to write zero not NULL. Plus, we have some cases in which there are arrays each of whose elements is supposed to be an FK reference; SQL has no way to model that. So we can't create actual foreign key constraints to describe the situation. Nonetheless, we can collect and use knowledge about these relationships. This patch therefore adds annotations to the catalog header files to declare foreign-key relationships. (The BKI_LOOKUP annotations cover simple cases, but we weren't previously distinguishing which such columns are allowed to contain zeroes; we also need new markings for multi-column FK references.) Then, Catalog.pm and genbki.pl are taught to collect this information into a table in a new generated header "system_fk_info.h". The only user of that at the moment is a new SQL function pg_get_catalog_foreign_keys(), which exposes the table to SQL. The oidjoins regression test is rewritten to use pg_get_catalog_foreign_keys() to find out which columns to check. Aside from removing the need for manual maintenance of that test script, this allows it to cover numerous relationships that were not checked by the old implementation based on findoidjoins. (As of this commit, 217 relationships are checked by the test, versus 181 before.) Discussion: https://postgr.es/m/3240355.1612129197@sss.pgh.pa.us
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