Apply pg_get_serial_sequence() to identity column sequences as well

Bug: #14813

src/backend/utils/adt/ruleutils.c

@@ -2322,7 +2322,7 @@ pg_get_userbyid(PG_FUNCTION_ARGS)
 
 /*
  * pg_get_serial_sequence
- *		Get the name of the sequence used by a serial column,
+ *		Get the name of the sequence used by an identity or serial column,
  *		formatted suitably for passing to setval, nextval or currval.
  *		First parameter is not treated as double-quoted, second parameter
  *		is --- see documentation for reason.
@@ -2380,13 +2380,14 @@ pg_get_serial_sequence(PG_FUNCTION_ARGS)
 		Form_pg_depend deprec = (Form_pg_depend) GETSTRUCT(tup);
 
 		/*
-		 * We assume any auto dependency of a sequence on a column must be
-		 * what we are looking for.  (We need the relkind test because indexes
-		 * can also have auto dependencies on columns.)
+		 * Look for an auto dependency (serial column) or internal dependency
+		 * (identity column) of a sequence on a column.  (We need the relkind
+		 * test because indexes can also have auto dependencies on columns.)
 		 */
 		if (deprec->classid == RelationRelationId &&
 			deprec->objsubid == 0 &&
-			deprec->deptype == DEPENDENCY_AUTO &&
+			(deprec->deptype == DEPENDENCY_AUTO ||
+			 deprec->deptype == DEPENDENCY_INTERNAL) &&
 			get_rel_relkind(deprec->objid) == RELKIND_SEQUENCE)
 		{
 			sequenceId = deprec->objid;

src/test/regress/expected/identity.out

@@ -26,6 +26,12 @@ SELECT sequence_name FROM information_schema.sequences WHERE sequence_name LIKE
 ---------------
 (0 rows)
 
+SELECT pg_get_serial_sequence('itest1', 'a');
+ pg_get_serial_sequence 
+------------------------
+ public.itest1_a_seq
+(1 row)
+
 CREATE TABLE itest4 (a int, b text);
 ALTER TABLE itest4 ALTER COLUMN a ADD GENERATED ALWAYS AS IDENTITY;  -- error, requires NOT NULL
 ERROR:  column "a" of relation "itest4" must be declared NOT NULL before identity can be added

src/test/regress/expected/sequence.out

@@ -79,6 +79,12 @@ SELECT * FROM serialTest1;
  force | 100
 (3 rows)
 
+SELECT pg_get_serial_sequence('serialTest1', 'f2');
+  pg_get_serial_sequence   
+---------------------------
+ public.serialtest1_f2_seq
+(1 row)
+
 -- test smallserial / bigserial
 CREATE TABLE serialTest2 (f1 text, f2 serial, f3 smallserial, f4 serial2,
   f5 bigserial, f6 serial8);

src/test/regress/sql/identity.sql

@@ -12,6 +12,8 @@ SELECT table_name, column_name, column_default, is_nullable, is_identity, identi
 -- internal sequences should not be shown here
 SELECT sequence_name FROM information_schema.sequences WHERE sequence_name LIKE 'itest%';
 
+SELECT pg_get_serial_sequence('itest1', 'a');
+
 CREATE TABLE itest4 (a int, b text);
 ALTER TABLE itest4 ALTER COLUMN a ADD GENERATED ALWAYS AS IDENTITY;  -- error, requires NOT NULL
 ALTER TABLE itest4 ALTER COLUMN a SET NOT NULL;

src/test/regress/sql/sequence.sql

@@ -61,6 +61,8 @@ INSERT INTO serialTest1 VALUES ('wrong', NULL);
 
 SELECT * FROM serialTest1;
 
+SELECT pg_get_serial_sequence('serialTest1', 'f2');
+
 -- test smallserial / bigserial
 CREATE TABLE serialTest2 (f1 text, f2 serial, f3 smallserial, f4 serial2,
   f5 bigserial, f6 serial8);