fix(db_engine_specs): map var_string to STRING for MySQL/StarRocks

The MySQL and StarRocks column type mappings did not recognize the
`var_string` native type (returned for varchar-backed columns), so
these columns fell through unmatched and were not classified as
GenericDataType.STRING. As a result, controls that gate on column
type (e.g. the "Force categorical" / y-axis sort control) were
incorrectly hidden for such columns.

Add a `^var_string` regex mapping resolving to GenericDataType.STRING
in both engine specs, matching the workaround confirmed by the issue
reporter, plus regression cases in the parameterized column-spec tests.

Fixes #30282

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

superset/db_engine_specs/mysql.py

@@ -238,6 +238,11 @@ class MySQLEngineSpec(BasicParametersMixin, BaseEngineSpec):
             LONGTEXT(),
             GenericDataType.STRING,
         ),
+        (
+            re.compile(r"^var_string", re.IGNORECASE),
+            types.VARCHAR(),
+            GenericDataType.STRING,
+        ),
     )
     column_type_mutators: dict[types.TypeEngine, Callable[[Any], Any]] = {
         DECIMAL: lambda val: Decimal(val) if isinstance(val, str) else val

superset/db_engine_specs/starrocks.py

@@ -238,6 +238,11 @@ class StarRocksEngineSpec(MySQLEngineSpec):
         (re.compile(r"^array.*", re.IGNORECASE), ARRAY(), GenericDataType.STRING),
         (re.compile(r"^map.*", re.IGNORECASE), MAP(), GenericDataType.STRING),
         (re.compile(r"^struct.*", re.IGNORECASE), STRUCT(), GenericDataType.STRING),
+        (
+            re.compile(r"^var_string", re.IGNORECASE),
+            types.VARCHAR(),
+            GenericDataType.STRING,
+        ),
     )
 
     custom_errors: dict[Pattern[str], tuple[str, SupersetErrorType, dict[str, Any]]] = {

tests/unit_tests/db_engine_specs/test_mysql.py

@@ -65,6 +65,7 @@ from tests.unit_tests.fixtures.common import dttm  # noqa: F401
         ("TINYTEXT", TINYTEXT, None, GenericDataType.STRING, False),
         ("MEDIUMTEXT", MEDIUMTEXT, None, GenericDataType.STRING, False),
         ("LONGTEXT", LONGTEXT, None, GenericDataType.STRING, False),
+        ("var_string", types.VARCHAR, None, GenericDataType.STRING, False),
         # Temporal
         ("DATE", types.Date, None, GenericDataType.TEMPORAL, True),
         ("DATETIME", types.DateTime, None, GenericDataType.TEMPORAL, True),

tests/unit_tests/db_engine_specs/test_starrocks.py

@@ -50,6 +50,7 @@ from tests.unit_tests.db_engine_specs.utils import assert_column_spec
         ("char(10)", types.CHAR, None, GenericDataType.STRING, False),
         ("varchar(65533)", types.VARCHAR, None, GenericDataType.STRING, False),
         ("binary", types.String, None, GenericDataType.STRING, False),
+        ("var_string", types.VARCHAR, None, GenericDataType.STRING, False),
         # Complex type
         ("array<varchar(65533)>", ARRAY, None, GenericDataType.STRING, False),
         ("map<string,int>", MAP, None, GenericDataType.STRING, False),