fix(trigger): avoid flushSync for synchronous-call dedup

`internalTriggerOpen` wrapped `setInternalOpen` / `onOpenChange` /
`onPopupVisibleChange` in `flushSync` (introduced in #601) to dedup
within a single user interaction batch, because reading `mergedOpen`
between two synchronous calls would otherwise see the stale value.

Under React 19 that emits

    flushSync was called from inside a lifecycle method. React cannot
    flush when React is already rendering.

whenever `internalTriggerOpen` is reached from inside a render/commit —
for example clicking a `<Tooltip trigger="focus">`-wrapped button that
opens a Modal: the click updates Modal state (entering React's render
phase) and the focus event in the same batch routes into Trigger's
`internalTriggerOpen`, so `flushSync` fires mid-render.

Replace the flushSync gate with a single `useRef` that tracks the last
synchronously dispatched `nextOpen`, plus a `useLayoutEffect` that
syncs that ref to `mergedOpen` after each commit so controlled updates
from outside (and the `lastTriggerRef`-leak case #601 originally fixed)
remain handled without depending on a render reset.

Adds `tests/no-flush-sync-warning.test.tsx` covering:

- No `flushSync was called from inside a lifecycle` warning when open
  is triggered from inside a commit (the antd#57789 scenario).
- Structural guard: `src/index.tsx` no longer imports or calls
  `flushSync`.

Existing `tests/open-change.test.tsx` (the dedup coverage added in
#601) keeps passing, so the synchronous pointer+focus / pointerleave+
blur dedup behaviour is preserved.

Refs ant-design/ant-design#57789

Author: hippye99

src/index.tsx

@@ -41,7 +41,6 @@ export type {
 
 import UniqueProvider, { type UniqueProviderProps } from './UniqueProvider';
 import { useControlledState } from '@rc-component/util';
-import { flushSync } from 'react-dom';
 
 export { UniqueProvider };
 export type { UniqueProviderProps };
@@ -382,14 +381,34 @@ export function generateTrigger(
     const openRef = React.useRef(mergedOpen);
     openRef.current = mergedOpen;
 
+    // Track the last synchronously dispatched `nextOpen` so multiple events
+    // firing in the same batch (e.g. `pointerenter` + `focus`, or `pointerleave`
+    // + `blur`) only emit one `onOpenChange`. We can't read `mergedOpen` here
+    // because React state updates are async — within a single batch the second
+    // call would still see the stale value. A simple `useRef` avoids that
+    // without requiring `flushSync`, which would emit a React 19 warning when
+    // `internalTriggerOpen` is reached from inside a render/lifecycle (e.g.
+    // a child commit triggered by clicking a `<Tooltip trigger="focus">`-
+    // wrapped button that also opens a Modal).
+    // See https://github.com/ant-design/ant-design/issues/57789
+    const lastDispatchedOpenRef = React.useRef(mergedOpen);
+
+    // Keep the ref in sync with `mergedOpen` after each render so that
+    // controlled updates from outside (or any internal state change that
+    // already committed) reset the dedup baseline. This preserves the
+    // behaviour fixed in #601 where the dedup state could leak across user
+    // interactions in controlled mode without re-renders.
+    useLayoutEffect(() => {
+      lastDispatchedOpenRef.current = mergedOpen;
+    }, [mergedOpen]);
+
     const internalTriggerOpen = useEvent((nextOpen: boolean) => {
-      flushSync(() => {
-        if (mergedOpen !== nextOpen) {
-          setInternalOpen(nextOpen);
-          onOpenChange?.(nextOpen);
-          onPopupVisibleChange?.(nextOpen);
-        }
-      });
+      if (lastDispatchedOpenRef.current !== nextOpen) {
+        lastDispatchedOpenRef.current = nextOpen;
+        setInternalOpen(nextOpen);
+        onOpenChange?.(nextOpen);
+        onPopupVisibleChange?.(nextOpen);
+      }
     });
 
     // Trigger for delay

tests/no-flush-sync-warning.test.tsx

@@ -0,0 +1,142 @@
+/**
+ * Regression coverage for https://github.com/ant-design/ant-design/issues/57789
+ *
+ * Trigger used to wrap `setInternalOpen` / `onOpenChange` in `flushSync` for
+ * synchronous-call dedup (introduced in #601). React 19 warns
+ *
+ *   `flushSync was called from inside a lifecycle method. React cannot flush
+ *    when React is already rendering.`
+ *
+ * whenever `internalTriggerOpen` is reached from inside a render/commit phase
+ * — e.g. clicking a button wrapped by `<Tooltip trigger="focus">` that also
+ * opens a Modal: the click handler updates Modal state (entering React's
+ * render phase), the focus event in the same batch routes into Trigger's
+ * `internalTriggerOpen`, and `flushSync` then fires inside the render.
+ *
+ * This test pins the fix: opening a Trigger while React is mid-commit must
+ * not emit the warning.
+ */
+import { act, cleanup, fireEvent, render } from '@testing-library/react';
+import { spyElementPrototypes } from '@rc-component/util/lib/test/domHook';
+import * as React from 'react';
+import Trigger from '../src';
+
+const flush = async () => {
+  for (let i = 0; i < 10; i += 1) {
+    act(() => {
+      jest.runAllTimers();
+    });
+    await act(async () => {
+      await Promise.resolve();
+    });
+  }
+};
+
+describe('Trigger.NoFlushSyncWarning', () => {
+  let eleRect = { width: 100, height: 100 };
+  let spanRect = { x: 0, y: 0, left: 0, top: 0, width: 1, height: 1 };
+  let popupRect = { x: 0, y: 0, left: 0, top: 0, width: 100, height: 100 };
+
+  beforeAll(() => {
+    spyElementPrototypes(HTMLElement, {
+      clientWidth: { get: () => eleRect.width },
+      clientHeight: { get: () => eleRect.height },
+      offsetWidth: { get: () => eleRect.width },
+      offsetHeight: { get: () => eleRect.height },
+      offsetParent: { get: () => document.body },
+    });
+    spyElementPrototypes(HTMLDivElement, {
+      getBoundingClientRect() {
+        return popupRect;
+      },
+    });
+    spyElementPrototypes(HTMLSpanElement, {
+      getBoundingClientRect() {
+        return spanRect;
+      },
+    });
+  });
+
+  beforeEach(() => {
+    eleRect = { width: 100, height: 100 };
+    spanRect = { x: 0, y: 0, left: 0, top: 0, width: 1, height: 1 };
+    popupRect = { x: 0, y: 0, left: 0, top: 0, width: 100, height: 100 };
+    jest.useFakeTimers();
+  });
+
+  afterEach(() => {
+    cleanup();
+    jest.useRealTimers();
+  });
+
+  it('does not emit a flushSync warning when open is triggered from inside a render/commit', async () => {
+    // Spy console.error so we can fail the test on the React 19 flushSync warning.
+    const errorSpy = jest.spyOn(console, 'error').mockImplementation(() => {});
+
+    // Sibling whose commit cycle "owns" the render: when its `count` state
+    // increases it re-renders, and within that commit we synchronously fire a
+    // focus event on the Trigger target. That mirrors the Modal+Tooltip case
+    // in #57789 where focus handling lands inside React's render phase.
+    const Reproducer: React.FC = () => {
+      const targetRef = React.useRef<HTMLSpanElement>(null);
+      const [count, setCount] = React.useState(0);
+
+      React.useEffect(() => {
+        if (count === 1 && targetRef.current) {
+          // Synchronously focus the trigger target while we are still inside
+          // an effect that ran during commit.
+          targetRef.current.focus();
+        }
+      }, [count]);
+
+      return (
+        <>
+          <button
+            type="button"
+            className="opener"
+            onClick={() => setCount((c) => c + 1)}
+          >
+            open
+          </button>
+          <Trigger action={['focus']} popup={<strong>popup</strong>}>
+            <span className="target" ref={targetRef} tabIndex={0} />
+          </Trigger>
+        </>
+      );
+    };
+
+    const { container } = render(<Reproducer />);
+
+    act(() => {
+      fireEvent.click(container.querySelector('.opener') as HTMLButtonElement);
+    });
+
+    await flush();
+
+    const flushSyncWarnings = errorSpy.mock.calls.filter((call) =>
+      String(call[0]).includes('flushSync was called from inside a lifecycle'),
+    );
+    expect(flushSyncWarnings).toEqual([]);
+
+    errorSpy.mockRestore();
+  });
+
+  it('does not import flushSync from react-dom (structural guard)', () => {
+    // Soft guard: if anyone re-introduces flushSync in src/index.tsx the
+    // structural intent of this fix should be reviewed alongside #57789.
+    // eslint-disable-next-line @typescript-eslint/no-require-imports, global-require
+    const fs = require('node:fs') as typeof import('node:fs');
+    const path = require('node:path') as typeof import('node:path');
+    const source = fs.readFileSync(
+      path.resolve(__dirname, '../src/index.tsx'),
+      'utf8',
+    );
+    // Strip block + line comments so the explanatory comment that *mentions*
+    // flushSync doesn't trip the guard.
+    const code = source
+      .replace(/\/\*[\s\S]*?\*\//g, '')
+      .replace(/(^|[^:])\/\/.*$/gm, '$1');
+    expect(code).not.toMatch(/from\s+['"]react-dom['"]/);
+    expect(code).not.toMatch(/\bflushSync\s*\(/);
+  });
+});