Address review + reconcile with time-grain PR

Reconcile with #41456: that PR sets ``expression=None`` on SV
dimensions so a truthy ``expression`` (the "adhoc SQL column" signal)
does not hide the time-grain selector. As a consequence, SV
dimensions with empty ``expression`` land in the popover's Simple
list, not the Saved list — the split in ``ColumnSelectPopover.tsx``
is done purely on ``expression`` truthiness. Disabling Simple would
leave dimensions unreachable in the popover, so only Custom SQL
stays disabled.

- Drop ``'simple'`` from ``effectiveDisabledTabs`` in
  ``DndColumnSelect.tsx`` and ``DndColumnMetricSelect.tsx``; keep
  ``'sqlExpression'``. Update comments to explain the tie to #41456.
- Rewrite the popover test to assert the new SV behavior (Simple
  enabled and selected by default; Custom SQL disabled; Saved
  enabled but not initial). Drop the ``as any`` cast per review.
- Remove PR-added "Saved tab" comment blocks in ``models.py`` — they
  will be misleading once #41456 lands with its own ``expression``
  rationale.
- Remove the four ``expression == "..."`` assertions in
  ``models_test.py`` for the same reason.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

superset-frontend/src/explore/components/controls/DndColumnSelectControl/ColumnSelectPopover.test.tsx

@@ -128,6 +128,44 @@ test('open with Saved tab selected when there is a saved column selected', () =>
   expect(getByText('Custom SQL')).toHaveAttribute('aria-selected', 'false');
 });
 
+test('disables Custom SQL for semantic views but keeps Simple enabled', () => {
+  // Semantic-view contexts disable the Custom SQL tab (ad-hoc SQL doesn't
+  // apply to pre-defined semantic-model items). Simple stays enabled — SV
+  // dimensions carry ``expression=`` empty, which routes them into the
+  // Simple tab's list, and disabling that tab would leave the dimensions
+  // unreachable in the popover.
+  const store = mockStore({
+    explore: { datasource: { type: 'semantic_view' } },
+  });
+  const { getByText } = render(
+    <ColumnSelectPopover
+      columns={[{ column_name: 'year' }]}
+      editedColumn={undefined}
+      getCurrentTab={jest.fn()}
+      onChange={jest.fn()}
+      hasCustomLabel
+      isTemporal={false}
+      label="Custom Label"
+      onClose={jest.fn()}
+      setDatasetModal={jest.fn()}
+      setLabel={jest.fn()}
+      disabledTabs={new Set(['sqlExpression'])}
+    />,
+    { store },
+  );
+
+  // Simple is enabled and selected by default (no adhoc/saved column
+  // to steer initial selection elsewhere).
+  expect(getByText('Simple')).not.toHaveAttribute('aria-disabled', 'true');
+  expect(getByText('Simple')).toHaveAttribute('aria-selected', 'true');
+  // Saved remains enabled but is not the initial tab.
+  expect(getByText('Saved')).not.toHaveAttribute('aria-disabled', 'true');
+  expect(getByText('Saved')).toHaveAttribute('aria-selected', 'false');
+  // Custom SQL is greyed out and unselected.
+  expect(getByText('Custom SQL')).toHaveAttribute('aria-disabled', 'true');
+  expect(getByText('Custom SQL')).toHaveAttribute('aria-selected', 'false');
+});
+
 test('open with Custom SQL tab selected when there is a custom SQL selected', () => {
   const { getByText } = renderPopover({
     columns: [{ column_name: 'year' }],

superset-frontend/src/explore/components/controls/DndColumnSelectControl/ColumnSelectPopover.tsx

@@ -281,11 +281,20 @@ const ColumnSelectPopover = ({
     [columnMap, metricMap, onSimpleColumnChange, onSimpleMetricChange],
   );
 
-  const defaultActiveTabKey = initialAdhocColumn
-    ? 'sqlExpression'
-    : selectedCalculatedColumn
-      ? 'saved'
-      : 'simple';
+  // Pick the most natural starting tab, but never one that's disabled —
+  // semantic-view contexts disable Simple and Custom SQL, leaving Saved.
+  let defaultActiveTabKey: string;
+  if (initialAdhocColumn && !disabledTabs.has('sqlExpression')) {
+    defaultActiveTabKey = 'sqlExpression';
+  } else if (selectedCalculatedColumn && !disabledTabs.has('saved')) {
+    defaultActiveTabKey = 'saved';
+  } else if (!disabledTabs.has('simple')) {
+    defaultActiveTabKey = 'simple';
+  } else if (!disabledTabs.has('saved')) {
+    defaultActiveTabKey = 'saved';
+  } else {
+    defaultActiveTabKey = 'sqlExpression';
+  }
 
   useEffect(() => {
     getCurrentTab(defaultActiveTabKey);
@@ -501,8 +510,15 @@ const ColumnSelectPopover = ({
                 },
               ]),
           {
+            // The Simple tab is rendered even when disabled (mirroring how
+            // Custom SQL behaves below) so users see all the options that
+            // could exist in another context and understand why they're
+            // unavailable here. Semantic-view contexts disable it because
+            // dimensions there are pre-defined items in the semantic model,
+            // not physical columns to wrap.
             key: TABS_KEYS.SIMPLE,
             label: t('Simple'),
+            disabled: disabledTabs.has('simple'),
             children: (
               <>
                 {isTemporal && simpleColumns.length === 0 ? (

superset-frontend/src/explore/components/controls/DndColumnSelectControl/DndColumnMetricSelect.tsx

@@ -130,8 +130,12 @@ function DndColumnMetricSelect(props: DndColumnMetricSelectProps) {
     formData,
   } = props;
 
-  // Semantic views do not support arbitrary SQL expressions as dimensions.
-  // Merge 'sqlExpression' into disabledTabs so the Custom SQL tab is hidden.
+  // Semantic-view dimensions and metrics are pre-defined items in the
+  // semantic model, so the Custom SQL tab (ad-hoc SQL expressions) doesn't
+  // apply and is disabled. The Simple tab stays enabled: dimensions land
+  // there because ``expression`` is left unset (a truthy ``expression``
+  // triggers fx-icon treatment in the popover and hides the time-grain
+  // selector, which we need to keep reachable).
   const effectiveDisabledTabs = useMemo(
     () =>
       String(datasource?.type) === 'semantic_view'

superset-frontend/src/explore/components/controls/DndColumnSelectControl/DndColumnSelect.tsx

@@ -53,7 +53,12 @@ function DndColumnSelect(props: DndColumnSelectProps) {
     disabledTabs,
   } = props;
 
-  // Semantic views do not support arbitrary SQL expressions as dimensions.
+  // Semantic-view dimensions are pre-defined items in the semantic model,
+  // so the Custom SQL tab (ad-hoc SQL expressions) doesn't apply and is
+  // disabled. The Simple tab stays enabled: dimensions land there because
+  // ``expression`` is left unset (a truthy ``expression`` triggers fx-icon
+  // treatment in the popover and hides the time-grain selector, which we
+  // need to keep reachable).
   const datasourceType = useSelector<ExplorePageState, string | undefined>(
     state => state.explore.datasource?.type,
   );