fix: 🐛 fix stale widget leak, prop-only re-render, and test expectation

- Unmount and clear lastStory when args.args.widget is falsy for the same
  story, preventing stale DOM/state leaks between Storybook loader calls
- Fix hasSetState && !hasSetProps branch to trigger a lifecycle update/render
  when only props change (else if), so Storybook controls re-render correctly
- Update test 'should not force widget.state to {}...' to reflect actual
  componentPlugin default (state is {} not undefined)

Author: Jiří Fencl

packages/tool-storybook/src/__tests__/indexSpec.js

@@ -324,6 +324,53 @@ describe('Merkur tool storybook', () => {
       expect(first.state).toEqual({ fromPreviousLoad: true });
     });
 
+    it('should call lifeCycle.update when only props change (hasSetState && !hasSetProps)', async () => {
+      let loader = createWidgetLoader({ widgetProperties, render });
+
+      let { widget: first } = await loader(storyArgs);
+      first.setProps = undefined; // force hasSetState && !hasSetProps branch
+      const lifeCycleUpdate = jest.fn().mockResolvedValue(undefined);
+      first.$in.component.lifeCycle.update = lifeCycleUpdate;
+      render.mockClear();
+
+      storyArgs.args.widget = { props: { title: 'New' } }; // no 'state' key
+      await loader(storyArgs);
+
+      expect(lifeCycleUpdate).toHaveBeenCalledWith(first);
+      expect(first.props).toEqual({ title: 'New' });
+    });
+
+    it('should call render when only props change and lifeCycle.update is unavailable (hasSetState && !hasSetProps)', async () => {
+      let loader = createWidgetLoader({ widgetProperties, render });
+
+      let { widget: first } = await loader(storyArgs);
+      first.setProps = undefined; // force hasSetState && !hasSetProps branch
+      first.$in.component.lifeCycle.update = undefined;
+      render.mockClear();
+
+      storyArgs.args.widget = { props: { title: 'New' } }; // no 'state' key
+      await loader(storyArgs);
+
+      expect(render).toHaveBeenCalledWith(first);
+      expect(first.props).toEqual({ title: 'New' });
+    });
+
+    it('should not trigger a render when neither props nor state key is present (hasSetState && !hasSetProps)', async () => {
+      let loader = createWidgetLoader({ widgetProperties, render });
+
+      let { widget: first } = await loader(storyArgs);
+      first.setProps = undefined; // force hasSetState && !hasSetProps branch
+      const lifeCycleUpdate = jest.fn().mockResolvedValue(undefined);
+      first.$in.component.lifeCycle.update = lifeCycleUpdate;
+      render.mockClear();
+
+      storyArgs.args.widget = {}; // no 'state' key, no 'props' key
+      await loader(storyArgs);
+
+      expect(lifeCycleUpdate).not.toHaveBeenCalled();
+      expect(render).not.toHaveBeenCalled();
+    });
+
     it('should not update props when props key is absent (hasSetState && !hasSetProps)', async () => {
       let loader = createWidgetLoader({ widgetProperties, render });
 

packages/tool-storybook/src/index.js

@@ -22,6 +22,10 @@ function createWidgetLoader({ render, widgetProperties }) {
     }
 
     if (!args?.args?.widget) {
+      if (lastStory.widget && lastStory.name === args.story) {
+        await lastStory.widget.unmount();
+        lastStory = {};
+      }
       return { widget: null };
     }
 
@@ -43,13 +47,20 @@ function createWidgetLoader({ render, widgetProperties }) {
       const hasSetState = typeof widget.setState === 'function';
       const hasSetProps = typeof widget.setProps === 'function';
       if (hasSetState && !hasSetProps) {
-        // Use setState as the single source of truth for triggering an update.
         if (hasNextProps) {
           widget.props = nextProps;
         }
         if (hasNextState) {
           widget.state = {};
           await widget.setState(nextState);
+        } else if (hasNextProps) {
+          // When only props change, manually trigger a lifecycle update/render so
+          // that Storybook controls that modify props still cause a re-render.
+          if (lifeCycle && typeof lifeCycle.update === 'function') {
+            await lifeCycle.update(widget);
+          } else {
+            await render(widget);
+          }
         }
         return { widget };
       }