Postgres schema: Constrain sequence search classid

The pk_an_sequence_for query previously joined against pg_class's oid
for rows in pg_depend, but pg_depend's objid may point to other system
tables, such as pg_attrdef.  If a row in one of those other tables
coincidentally has the same oid as an (unrelated) sequence, that
sequence name may be returned instead of the real one.

This ensures that only the pg_depend entries pointing to pg_class are
considered.

activerecord/CHANGELOG.md

@@ -6,6 +6,11 @@
 
     *Matthew Draper*
 
+*   `pk_and_sequence_for` now ensures that only the pg_depend entries
+    pointing to pg_class, and thus only sequence objects, are considered.
+
+    *Josh Williams*
+
 *   `where.not` adds `references` for `includes` like normal `where` calls do.
 
     Fixes #14406.

activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb

@@ -327,6 +327,7 @@ module ActiveRecord
               AND attr.attrelid     = cons.conrelid
               AND attr.attnum       = cons.conkey[1]
               AND cons.contype      = 'p'
+              AND dep.classid       = 'pg_class'::regclass
               AND dep.refobjid      = '#{quote_table_name(table)}'::regclass
           end_sql
 

activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb

@@ -176,6 +176,51 @@ module ActiveRecord
         assert_nil @connection.pk_and_sequence_for('unobtainium')
       end
 
+      def test_pk_and_sequence_for_with_collision_pg_class_oid
+        @connection.exec_query('create table ex(id serial primary key)')
+        @connection.exec_query('create table ex2(id serial primary key)')
+
+        correct_depend_record = [
+          "'pg_class'::regclass",
+          "'ex_id_seq'::regclass",
+          '0',
+          "'pg_class'::regclass",
+          "'ex'::regclass",
+          '1',
+          "'a'"
+        ]
+
+        collision_depend_record = [
+          "'pg_attrdef'::regclass",
+          "'ex2_id_seq'::regclass",
+          '0',
+          "'pg_class'::regclass",
+          "'ex'::regclass",
+          '1',
+          "'a'"
+        ]
+
+        @connection.exec_query(
+          "DELETE FROM pg_depend WHERE objid = 'ex_id_seq'::regclass AND refobjid = 'ex'::regclass AND deptype = 'a'"
+        )
+        @connection.exec_query(
+          "INSERT INTO pg_depend VALUES(#{collision_depend_record.join(',')})"
+        )
+        @connection.exec_query(
+          "INSERT INTO pg_depend VALUES(#{correct_depend_record.join(',')})"
+        )
+
+        seq = @connection.pk_and_sequence_for('ex').last
+        assert_equal 'ex_id_seq', seq
+
+        @connection.exec_query(
+          "DELETE FROM pg_depend WHERE objid = 'ex2_id_seq'::regclass AND refobjid = 'ex'::regclass AND deptype = 'a'"
+        )
+      ensure
+        @connection.exec_query('DROP TABLE IF EXISTS ex')
+        @connection.exec_query('DROP TABLE IF EXISTS ex2')
+      end
+
       def test_exec_insert_number
         with_example_table do
           insert(@connection, 'number' => 10)