DISTINCT silently dropped from a plugin aggregate function with VIEW / EXPLAIN EXTENDED

INSTALL SONAME 'func_test';

CREATE TABLE t (g INT, v INT);

INSERT INTO t VALUES (1,1),(1,1),(1,2),(1,2),(1,2),(2,3),(2,3),(2,NULL),(2,4);

-- 9 rows, 8 non-NULL, 4 distinct non-NULL values

-- correct when run directly:

SELECT COUNT(DISTINCT v), test_plugin_count(DISTINCT v) FROM t;  --> 4, 4

-- WRONG through a view:

CREATE VIEW vw AS SELECT COUNT(DISTINCT v) AS b, test_plugin_count(DISTINCT v) AS pl FROM t;

SELECT b, pl FROM vw; --> 4, 8        <=== pl must be 4; it silently became the TOTAL count

-- Stored view shows that the `DISTINCT` is retained in the built-in implementation but not in the plugin.

SELECT VIEW_DEFINITION FROM information_schema.VIEWS WHERE TABLE_NAME='vw';

13.1.0-opt>INSTALL SONAME 'func_test';

Query OK, 0 rows affected (0.002 sec)

13.1.0-opt>CREATE TABLE t (g INT, v INT);

Query OK, 0 rows affected (0.008 sec)

13.1.0-opt>INSERT INTO t VALUES (1,1),(1,1),(1,2),(1,2),(1,2),(2,3),(2,3),(2,NULL),(2,4);

Query OK, 9 rows affected (0.001 sec)

Records: 9  Duplicates: 0  Warnings: 0

13.1.0-opt>-- 9 rows, 8 non-NULL, 4 distinct non-NULL values

13.1.0-opt>-- correct when run directly:

13.1.0-opt>SELECT COUNT(DISTINCT v), test_plugin_count(DISTINCT v) FROM t;  --> 4, 4

+-------------------+-------------------------------+

| COUNT(DISTINCT v) | test_plugin_count(DISTINCT v) |

+-------------------+-------------------------------+

|                 4 |                             4 |

+-------------------+-------------------------------+

1 row in set (0.000 sec)

13.1.0-opt>

13.1.0-opt>-- WRONG through a view:

13.1.0-opt>CREATE VIEW vw AS SELECT COUNT(DISTINCT v) AS b, test_plugin_count(DISTINCT v) AS pl FROM t;

Query OK, 0 rows affected (0.004 sec)

13.1.0-opt>SELECT b, pl FROM vw; --> 4, 8        <=== pl must be 4; it silently became the TOTAL count

+---+----+

| b | pl |

+---+----+

| 4 |  8 |

+---+----+

1 row in set (0.000 sec)

13.1.0-opt>-- Stored view shows that the `DISTINCT` is retained in the built-in implementation but not in the plugin.

13.1.0-opt>SELECT VIEW_DEFINITION FROM information_schema.VIEWS WHERE TABLE_NAME='vw';

+--------------------------------------------------------------------------------------------------------+

| VIEW_DEFINITION                                                                                        |

+--------------------------------------------------------------------------------------------------------+

| select count(distinct `test`.`t`.`v`) AS `b`,test_plugin_count(`test`.`t`.`v`) AS `pl` from `test`.`t` |

+--------------------------------------------------------------------------------------------------------+

1 row in set (0.001 sec)

13.1.0-opt>

Same issue is visible with EXPLAIN EXTENDED / SHOW WARNINGS

13.1.0-opt>EXPLAIN EXTENDED SELECT test_plugin_count(DISTINCT v) as b FROM t;

+------+-------------+-------+------+---------------+------+---------+------+------+----------+-------+

| id   | select_type | table | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra |

+------+-------------+-------+------+---------------+------+---------+------+------+----------+-------+

|    1 | SIMPLE      | t     | ALL  | NULL          | NULL | NULL    | NULL | 9    |   100.00 |       |

+------+-------------+-------+------+---------------+------+---------+------+------+----------+-------+

1 row in set, 1 warning (0.000 sec)

13.1.0-opt>SHOW WARNINGS;

+-------+------+-----------------------------------------------------------------+

| Level | Code | Message                                                         |

+-------+------+-----------------------------------------------------------------+

| Note  | 1003 | select test_plugin_count(`test`.`t`.`v`) AS `b` from `test`.`t` |

+-------+------+-----------------------------------------------------------------+

1 row in set (0.000 sec)

13.1.0-opt>