fix(overlay): do not hide overlay if toast is presented (#29140)

Issue number: resolves #29139 

---------

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issue. -->

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## What is the current behavior?
<!-- Please describe the current behavior that you are modifying. -->

When implementing
https://github.com/ionic-team/ionic-framework/pull/28997 we did not
consider the case where a Toast could be presented. When presenting a
Toast after presenting a Modal the linked change causes the Modal to be
hidden from screen readers.

## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->

- If the top-most overlay is a Toast then the closest non-Toast overlay
is also not hidden from screen readers.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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below.
  2. Update the BREAKING.md file with the breaking change.
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## Other information

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screenshots of how the component looks before and after the change. -->

Dev build: `7.7.5-dev.11710260658.1fc29a6c`

---------

Co-authored-by: Amanda Johnston <90629384+amandaejohnston@users.noreply.github.com>

core/src/utils/overlays.ts

@@ -541,16 +541,7 @@ export const present = async <OverlayPresentOptions>(
   }
 
   setRootAriaHidden(true);
-
-  /**
-   * Hide all other overlays from screen readers so only this one
-   * can be read. Note that presenting an overlay always makes
-   * it the topmost one.
-   */
-  if (doc !== undefined) {
-    const presentedOverlays = getPresentedOverlays(doc);
-    presentedOverlays.forEach((o) => o.setAttribute('aria-hidden', 'true'));
-  }
+  hideOverlaysFromScreenReaders(overlay.el);
 
   overlay.presented = true;
   overlay.willPresent.emit();
@@ -723,13 +714,7 @@ export const dismiss = async <OverlayDismissOptions>(
 
   overlay.el.remove();
 
-  /**
-   * If there are other overlays presented, unhide the new
-   * topmost one from screen readers.
-   */
-  if (doc !== undefined) {
-    getPresentedOverlay(doc)?.removeAttribute('aria-hidden');
-  }
+  revealOverlaysToScreenReaders();
 
   return true;
 };
@@ -966,3 +951,65 @@ export const createTriggerController = () => {
     removeClickListener,
   };
 };
+
+/**
+ * Ensure that underlying overlays have aria-hidden if necessary so that screen readers
+ * cannot move focus to these elements. Note that we cannot rely on focus/focusin/focusout
+ * events here because those events do not fire when the screen readers moves to a non-focusable
+ * element such as text.
+ * Without this logic screen readers would be able to move focus outside of the top focus-trapped overlay.
+ *
+ * @param newTopMostOverlay - The overlay that is being presented. Since the overlay has not been
+ * fully presented yet at the time this function is called it will not be included in the getPresentedOverlays result.
+ */
+const hideOverlaysFromScreenReaders = (newTopMostOverlay: HTMLIonOverlayElement) => {
+  if (doc === undefined) return;
+
+  const overlays = getPresentedOverlays(doc);
+
+  for (let i = overlays.length - 1; i >= 0; i--) {
+    const presentedOverlay = overlays[i];
+    const nextPresentedOverlay = overlays[i + 1] ?? newTopMostOverlay;
+
+    /**
+     * If next overlay has aria-hidden then all remaining overlays will have it too.
+     * Or, if the next overlay is a Toast that does not have aria-hidden then current overlay
+     * should not have aria-hidden either so focus can remain in the current overlay.
+     */
+    if (nextPresentedOverlay.hasAttribute('aria-hidden') || nextPresentedOverlay.tagName !== 'ION-TOAST') {
+      presentedOverlay.setAttribute('aria-hidden', 'true');
+    }
+  }
+};
+
+/**
+ * When dismissing an overlay we need to reveal the new top-most overlay to screen readers.
+ * If the top-most overlay is a Toast we potentially need to reveal more overlays since
+ * focus is never automatically moved to the Toast.
+ */
+const revealOverlaysToScreenReaders = () => {
+  if (doc === undefined) return;
+
+  const overlays = getPresentedOverlays(doc);
+
+  for (let i = overlays.length - 1; i >= 0; i--) {
+    const currentOverlay = overlays[i];
+
+    /**
+     * If the current we are looking at is a Toast then we can remove aria-hidden.
+     * However, we potentially need to keep looking at the overlay stack because there
+     * could be more Toasts underneath. Additionally, we need to unhide the closest non-Toast
+     * overlay too so focus can move there since focus is never automatically moved to the Toast.
+     */
+    currentOverlay.removeAttribute('aria-hidden');
+
+    /**
+     * If we found a non-Toast element then we can just remove aria-hidden and stop searching entirely
+     * since this overlay should always receive focus. As a result, all underlying overlays should still
+     * be hidden from screen readers.
+     */
+    if (currentOverlay.tagName !== 'ION-TOAST') {
+      break;
+    }
+  }
+};

core/src/utils/test/overlays/overlays.spec.ts

@@ -1,6 +1,7 @@
 import { newSpecPage } from '@stencil/core/testing';
 
 import { Modal } from '../../../components/modal/modal';
+import { Toast } from '../../../components/toast/toast';
 import { Nav } from '../../../components/nav/nav';
 import { RouterOutlet } from '../../../components/router-outlet/router-outlet';
 import { setRootAriaHidden } from '../../overlays';
@@ -193,4 +194,70 @@ describe('aria-hidden on individual overlays', () => {
     await modalOne.present();
     expect(modalOne.hasAttribute('aria-hidden')).toEqual(false);
   });
+
+  it('should not hide previous overlay if top-most overlay is toast', async () => {
+    const page = await newSpecPage({
+      components: [Modal, Toast],
+      html: `
+        <ion-modal id="m-one"></ion-modal>
+        <ion-modal id="m-two"></ion-modal>
+        <ion-toast id="t-one"></ion-toast>
+        <ion-toast id="t-two"></ion-toast>
+      `,
+    });
+
+    const modalOne = page.body.querySelector<HTMLIonModalElement>('ion-modal#m-one')!;
+    const modalTwo = page.body.querySelector<HTMLIonModalElement>('ion-modal#m-two')!;
+    const toastOne = page.body.querySelector<HTMLIonModalElement>('ion-toast#t-one')!;
+    const toastTwo = page.body.querySelector<HTMLIonModalElement>('ion-toast#t-two')!;
+
+    await modalOne.present();
+    await modalTwo.present();
+    await toastOne.present();
+    await toastTwo.present();
+
+    expect(modalOne.hasAttribute('aria-hidden')).toEqual(true);
+    expect(modalTwo.hasAttribute('aria-hidden')).toEqual(false);
+    expect(toastOne.hasAttribute('aria-hidden')).toEqual(false);
+    expect(toastTwo.hasAttribute('aria-hidden')).toEqual(false);
+
+    await toastTwo.dismiss();
+
+    expect(modalOne.hasAttribute('aria-hidden')).toEqual(true);
+    expect(modalTwo.hasAttribute('aria-hidden')).toEqual(false);
+    expect(toastOne.hasAttribute('aria-hidden')).toEqual(false);
+
+    await toastOne.dismiss();
+
+    expect(modalOne.hasAttribute('aria-hidden')).toEqual(true);
+    expect(modalTwo.hasAttribute('aria-hidden')).toEqual(false);
+  });
+
+  it('should hide previous overlay even with a toast that is not the top-most overlay', async () => {
+    const page = await newSpecPage({
+      components: [Modal, Toast],
+      html: `
+        <ion-modal id="m-one"></ion-modal>
+        <ion-toast id="t-one"></ion-toast>
+        <ion-modal id="m-two"></ion-modal>
+      `,
+    });
+
+    const modalOne = page.body.querySelector<HTMLIonModalElement>('ion-modal#m-one')!;
+    const modalTwo = page.body.querySelector<HTMLIonModalElement>('ion-modal#m-two')!;
+    const toastOne = page.body.querySelector<HTMLIonModalElement>('ion-toast#t-one')!;
+
+    await modalOne.present();
+    await toastOne.present();
+    await modalTwo.present();
+
+    expect(modalOne.hasAttribute('aria-hidden')).toEqual(true);
+    expect(toastOne.hasAttribute('aria-hidden')).toEqual(true);
+    expect(modalTwo.hasAttribute('aria-hidden')).toEqual(false);
+
+    await modalTwo.dismiss();
+
+    expect(modalOne.hasAttribute('aria-hidden')).toEqual(false);
+    expect(toastOne.hasAttribute('aria-hidden')).toEqual(false);
+  });
 });