fix(sqla): annotate main_dttm_column local in dttm_cols

Add an explicit type annotation per project type-hint conventions,
per codeant-ai review feedback on #41964.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

superset/connectors/sqla/models.py

@@ -1516,7 +1516,18 @@ class SqlaTable(
     def dttm_cols(self) -> list[str]:
         l = [c.column_name for c in self.columns if c.is_dttm]  # noqa: E741
         if self.main_dttm_col and self.main_dttm_col not in l:
-            l.append(self.main_dttm_col)
+            # Only treat ``main_dttm_col`` as a datetime column when the column it
+            # points to is actually temporal. A column whose "Is Temporal" flag was
+            # removed must not keep being reported as a datetime column just because
+            # it is still referenced by ``main_dttm_col`` (#30510). When the column
+            # is not present on the dataset, fall back to the legacy behavior of
+            # trusting ``main_dttm_col``.
+            main_dttm_column: TableColumn | None = next(
+                (c for c in self.columns if c.column_name == self.main_dttm_col),
+                None,
+            )
+            if main_dttm_column is None or main_dttm_column.is_dttm:
+                l.append(self.main_dttm_col)
         return l
 
     @property

tests/unit_tests/connectors/sqla/models_test.py

@@ -1177,3 +1177,46 @@ def test_validate_stored_expression_rejects_subquery_around_jinja(
             None,
             "(SELECT password FROM ab_user LIMIT 1) {# x #}",
         )
+
+
+def test_dttm_cols_excludes_column_after_temporal_flag_removed(
+    session: Session,
+) -> None:
+    """
+    Regression for #30510: when a column is mistakenly marked temporal, set as the
+    dataset's default datetime (``main_dttm_col``) and saved, then later has its
+    ``is_dttm`` flag removed, the dataset must stop treating that column as temporal.
+
+    Otherwise ``dttm_cols`` (which feeds time-column selection and the default time
+    filter for every chart built on the dataset) keeps returning a non-temporal
+    column, corrupting the dataset with a time filter that cannot be removed.
+    """
+    Database.metadata.create_all(session.bind)
+    database = Database(database_name="my_db", sqlalchemy_uri="sqlite://")
+
+    # A column the user mistakenly marks as temporal ("Is Temporal") and then picks
+    # as the dataset "Default Datetime" (``main_dttm_col``).
+    column = TableColumn(column_name="not_really_a_date", type="VARCHAR", is_dttm=True)
+    dataset = SqlaTable(
+        database=database,
+        table_name="my_table",
+        columns=[column],
+        main_dttm_col="not_really_a_date",
+    )
+    session.add(dataset)
+    session.commit()
+
+    # While flagged temporal, the column is (expectedly) exposed as a datetime column.
+    assert dataset.dttm_cols == ["not_really_a_date"]
+
+    # The user realizes the mistake and unchecks "Is Temporal", then saves. Persisting
+    # the update clears ``is_dttm`` on the column.
+    column.is_dttm = False
+    session.commit()
+
+    # The column is no longer temporal...
+    assert column.is_temporal is False
+    # ...so it must no longer be reported as a datetime column. On master
+    # ``main_dttm_col`` is never cleared, so ``dttm_cols`` still contains the stale,
+    # non-temporal column and this assertion fails (bug reproduced).
+    assert "not_really_a_date" not in dataset.dttm_cols