[Modal] Fix stale aria-hidden when the container changes

packages/mui-material/src/Modal/Modal.test.js

@@ -799,6 +799,29 @@ describe('<Modal />', () => {
       setProps({ anchorEl: document.body });
     });
 
+    it('should remove aria-hidden from the previous container when the container changes', () => {
+      const root = document.createElement('div');
+      root.setAttribute('id', 'root');
+      document.body.appendChild(root);
+
+      try {
+        const { setProps } = render(
+          <Modal open>
+            <div data-testid="modal-content" />
+          </Modal>,
+        );
+
+        // The modal is mounted in the body, making #root an aria-hidden sibling.
+        expect(root).toBeInaccessible();
+
+        // Moving the modal into #root must remove the stale aria-hidden from it.
+        setProps({ container: root });
+        expect(root).not.toBeInaccessible();
+      } finally {
+        document.body.removeChild(root);
+      }
+    });
+
     it('should finish closing when the container changes during the exit transition', () => {
       function TestCase(props) {
         const firstContainerRef = React.useRef(null);

packages/mui-material/src/Modal/ModalManager.test.ts

@@ -438,5 +438,36 @@ describe('ModalManager', () => {
       expect(container2.children[1]).toBeInaccessible();
       expect(container2.children[2]).not.toBeInaccessible();
     });
+
+    it('should restore aria-hidden when a modal is re-registered to a nested container', () => {
+      const containerA = document.createElement('div');
+      const containerB = document.createElement('div');
+      const sibling = document.createElement('div');
+      const modalRef = document.createElement('div');
+      containerA.appendChild(sibling);
+      containerA.appendChild(containerB);
+      containerA.appendChild(modalRef);
+      document.body.appendChild(containerA);
+
+      try {
+        const modal = { mount: containerA, modalRef };
+        modalManager.add(modal, containerA);
+        modalManager.mount(modal, {});
+        expect(containerB).toBeInaccessible();
+        expect(sibling).toBeInaccessible();
+
+        // Simulates the portal having moved into containerB before the manager is notified.
+        modal.mount = containerB;
+
+        modalManager.remove(modal);
+        modalManager.add(modal, containerB);
+
+        expect(containerB).not.toBeInaccessible();
+        expect(sibling).not.toBeInaccessible();
+        expect(modalRef).not.toBeInaccessible();
+      } finally {
+        document.body.removeChild(containerA);
+      }
+    });
   });
 });

packages/mui-material/src/Modal/ModalManager.ts

@@ -268,7 +268,7 @@ export class ModalManager {
 
       ariaHiddenSiblings(
         containerInfo.container,
-        modal.mount,
+        containerInfo.container,
         modal.modalRef,
         containerInfo.hiddenSiblings,
         false,

packages/mui-material/src/Modal/useModal.ts

@@ -46,6 +46,7 @@ function useModal(parameters: UseModalParameters): UseModalReturnValue {
   const mountNodeRef = React.useRef<HTMLElement>(null);
   const lastMountNodeRef = React.useRef<HTMLElement>(null);
   const modalRef = React.useRef<HTMLDivElement>(null);
+  const registeredContainerRef = React.useRef<HTMLElement>(null);
   const handleRef = useForkRef(modalRef, rootRef);
   const [exited, setExited] = React.useState(!open);
   const hasTransition = getHasTransition(children);
@@ -74,7 +75,16 @@ function useModal(parameters: UseModalParameters): UseModalReturnValue {
   const handleOpen = useEventCallback(() => {
     const resolvedContainer = getContainer(container) || getDoc().body;
 
+    // When the container changes while the modal stays open, the previous container
+    // keeps the `aria-hidden` state computed for the previous sibling set.
+    // Unregister the modal first so the new container is evaluated against its own siblings.
+    if (registeredContainerRef.current && registeredContainerRef.current !== resolvedContainer) {
+      manager.remove(getModal(), ariaHiddenProp);
+      registeredContainerRef.current = null;
+    }
+
     manager.add(getModal(), resolvedContainer as HTMLElement);
+    registeredContainerRef.current = resolvedContainer as HTMLElement;
 
     // The element was already mounted.
     if (modalRef.current) {
@@ -101,6 +111,7 @@ function useModal(parameters: UseModalParameters): UseModalReturnValue {
   });
 
   const handleClose = React.useCallback(() => {
+    registeredContainerRef.current = null;
     manager.remove(getModal(), ariaHiddenProp);
   }, [ariaHiddenProp]);
 
@@ -116,7 +127,7 @@ function useModal(parameters: UseModalParameters): UseModalReturnValue {
     } else if (!hasTransition || !closeAfterTransition) {
       handleClose();
     }
-  }, [open, handleClose, hasTransition, closeAfterTransition, handleOpen]);
+  }, [open, handleClose, hasTransition, closeAfterTransition, handleOpen, container]);
 
   const createHandleKeyDown = (otherHandlers: EventHandlers) => (event: React.KeyboardEvent) => {
     otherHandlers.onKeyDown?.(event);