fix(dropdown-container): prevent empty popover from opening when alwaysShowDropdownButton is set

Gates popover open state and onOpenChange on popoverContent existence,
addressing review feedback that the button could trigger an empty popover
during layout recalculation. Adds a test covering this behavior.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

superset-frontend/packages/superset-ui-core/src/components/DropdownContainer/DropdownContainer.test.tsx

@@ -16,7 +16,7 @@
  * specific language governing permissions and limitations
  * under the License.
  */
-import { screen, render } from '@superset-ui/core/spec';
+import { screen, render, fireEvent } from '@superset-ui/core/spec';
 import { Button, DropdownContainer, Icons } from '..';
 
 const generateItems = (n: number) =>
@@ -158,6 +158,36 @@ test('accepts custom style props', () => {
   expect(container).toHaveStyle('padding: 10px');
 });
 
+test('shows dropdown button when alwaysShowDropdownButton is true even without overflow', () => {
+  render(
+    <DropdownContainer items={generateItems(3)} alwaysShowDropdownButton />,
+  );
+  expect(screen.getByTestId('dropdown-container-btn')).toBeInTheDocument();
+});
+
+test('does not open popover when alwaysShowDropdownButton is true but there is no popover content', () => {
+  render(
+    <DropdownContainer items={generateItems(3)} alwaysShowDropdownButton />,
+  );
+  const btn = screen.getByTestId('dropdown-container-btn');
+  expect(btn).toBeInTheDocument();
+  fireEvent.click(btn);
+  // No popover content exists, so the popover should not open
+  expect(screen.queryByRole('tooltip')).not.toBeInTheDocument();
+});
+
+test('does not show dropdown button when alwaysShowDropdownButton is false and not overflowing', () => {
+  render(
+    <DropdownContainer
+      items={generateItems(3)}
+      alwaysShowDropdownButton={false}
+    />,
+  );
+  expect(
+    screen.queryByTestId('dropdown-container-btn'),
+  ).not.toBeInTheDocument();
+});
+
 // Integration test that doesn't rely on specific overflow behavior
 test('component renders and functions without throwing errors', () => {
   const onOverflowingStateChange = jest.fn();

superset-frontend/packages/superset-ui-core/src/components/DropdownContainer/DropdownContainer.tsx

@@ -53,6 +53,7 @@ export const DropdownContainer = forwardRef(
       dropdownTriggerTooltip = null,
       forceRender,
       style,
+      alwaysShowDropdownButton,
     }: DropdownContainerProps,
     outerRef: RefObject<DropdownRef>,
   ) => {
@@ -314,7 +315,7 @@ export const DropdownContainer = forwardRef(
         >
           {notOverflowedItems.map(item => item.element)}
         </div>
-        {popoverContent && (
+        {(popoverContent || alwaysShowDropdownButton) && (
           <>
             <Global
               styles={css`
@@ -348,8 +349,13 @@ export const DropdownContainer = forwardRef(
               }}
               content={popoverContent}
               trigger="click"
-              open={popoverVisible}
-              onOpenChange={visible => setPopoverVisible(visible)}
+              open={popoverVisible && !!popoverContent}
+              onOpenChange={visible => {
+                // When alwaysShowDropdownButton is set but there is no content
+                // yet (e.g. during layout recalculation), ignore open attempts
+                // so the button stays visible without opening an empty popover.
+                if (popoverContent) setPopoverVisible(visible);
+              }}
               placement="bottom"
               forceRender={forceRender}
             >

superset-frontend/packages/superset-ui-core/src/components/DropdownContainer/types.ts

@@ -87,6 +87,11 @@ export interface DropdownContainerProps {
    * Force render popover content before it's first opened
    */
   forceRender?: boolean;
+  /**
+   * Always show the dropdown button, even when no items are overflowing.
+   * Useful to prevent button flickering during layout recalculations.
+   */
+  alwaysShowDropdownButton?: boolean;
 }
 
 export type DropdownRef = HTMLDivElement & { open: () => void };

superset-frontend/src/dashboard/components/nativeFilters/FilterBar/FilterControls/FilterControls.tsx

@@ -630,6 +630,7 @@ const FilterControls: FC<FilterControlsProps> = ({
               : undefined
           }
           forceRender={hasRequiredFirst}
+          alwaysShowDropdownButton={items.length > 0}
           ref={popoverRef}
           onOverflowingStateChange={({ overflowed: nextOverflowedIds }) => {
             if (