Fix self-referencing foreign keys with partitioned tables

There are a number of bugs in this area.  Two of them are fixed here,
namely:
1. get_relation_idx_constraint_oid does not restrict the type of
   constraint that's returned, so with sufficient bad luck it can
   return the OID of a foreign key constraint.  This has the effect that
   a primary key in a partition can end up as a child of a foreign key,
   which makes no sense (it needs to be the child of the equivalent
   primary key.)
   Change the API contract so that only index-backed constraints are
   returned, mimicking get_constraint_index().

2. Both CloneFkReferenced and CloneFkReferencing clone a
   self-referencing foreign key, so the partition ends up with
   a duplicate foreign key.  Change the former function to ignore such
   constraints.

Add some tests to verify that things are better now.  (However, these
new tests show some additional misbehavior that will be fixed later --
namely that there's a constraint marked NOT VALID.)

Backpatch to 12, where these constraints are possible at all.

Author: Jehan-Guillaume de Rorthais <jgdr@dalibo.com>
Discussion: https://postgr.es/m/20220603154232.1715b14c@karst

1 files changed, 12 insertions, 1 deletions

diff --git a/src/backend/catalog/pg_constraint.c b/src/backend/catalog/pg_constraint.c
index 489f0b2818e..c269ac251ac 100644
--- a/src/backend/catalog/pg_constraint.c
+++ b/src/backend/catalog/pg_constraint.c
@@ -992,8 +992,12 @@ get_relation_constraint_attnos(Oid relid, const char *conname,
 }
 
 /*
- * Return the OID of the constraint associated with the given index in the
+ * Return the OID of the constraint enforced by the given index in the
  * given relation; or InvalidOid if no such index is catalogued.
+ *
+ * Much like get_constraint_index, this function is concerned only with the
+ * one constraint that "owns" the given index.  Therefore, constraints of
+ * types other than unique, primary-key, and exclusion are ignored.
  */
 Oid
 get_relation_idx_constraint_oid(Oid relationId, Oid indexId)
@@ -1018,6 +1022,13 @@ get_relation_idx_constraint_oid(Oid relationId, Oid indexId)
 		Form_pg_constraint constrForm;
 
 		constrForm = (Form_pg_constraint) GETSTRUCT(tuple);
+
+		/* See above */
+		if (constrForm->contype != CONSTRAINT_PRIMARY &&
+			constrForm->contype != CONSTRAINT_UNIQUE &&
+			constrForm->contype != CONSTRAINT_EXCLUSION)
+			continue;
+
 		if (constrForm->conindid == indexId)
 		{
 			constraintId = constrForm->oid;