CAST silently accepts compact date ending in T without warning 1292

MariaDB 12.3.3 silently accepts the incomplete compact date string '20010101T' in permissive mode. CAST(... AS DATE) returns 2001-01-01 without warning 1292, although the equivalent delimited form '2001-01-01T' produces that warning.

Reproduction

Save the following four files and run each in a fresh client session. Separate sessions are necessary because earlier diagnostics can otherwise remain visible after later table-free statements.

compact.sql:

SET sql_mode='';

SELECT CAST('20010101T' AS DATE) AS parsed_value;

SHOW WARNINGS;

delimited.sql:

SET sql_mode='';

SELECT CAST('2001-01-01T' AS DATE) AS parsed_value;

SHOW WARNINGS;

valid.sql:

SET sql_mode='';

SELECT CAST('20010101T010203' AS DATETIME) AS parsed_value;

SHOW WARNINGS;

date_only.sql:

SET sql_mode='';

SELECT CAST('20010101' AS DATE) AS parsed_value;

SHOW WARNINGS;

Run the files with:

mariadb < compact.sql

mariadb < delimited.sql

mariadb < valid.sql

mariadb < date_only.sql

Decisive observation

The incomplete compact form returns a date and no warnings:

parsed_value

2001-01-01

The incomplete delimited form returns the same date but reports the expected diagnostic:

parsed_value

2001-01-01

Level    Code  Message

Warning  1292  Truncated incorrect date value: '2001-01-01T'

The two valid controls produce no warnings:

'20010101T010203' -> 2001-01-01 01:02:03

'20010101'        -> 2001-01-01

Semantic mismatch

The trailing T denotes a date-time separator, but '20010101T' contains no time component after it. In permissive mode, both incomplete forms should report warning 1292; preserving the parsed date is not itself the defect. The valid compact datetime and compact date-only forms should continue to produce no warnings.

This occurs when an incomplete compact date ends with the date-time separator T but contains no following time component.