bug(CDK a11y, Tooltip, SortHeader): AriaDescriber not working inside Shadow DOM
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- TypeScript
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描述
### Is this a regression?
- [ ] Yes, this behavior used to work in the previous version
### The previous version in which this bug was not present was
_No response_
### Description
The AriaDescriber service creates a container element and appends it to the body. The messages inside the container are linked with the host element using `aria-describedby` when calling `ariaDescriber.describe()`.
When the host element is inside Shadow DOM this will not work properly because the hidden message element (that is referenced via `aria-describedby`) is outside of the Shadow DOM and will be ignored by the browser.
### Reproduction
I actually had the problem with Angular Material Tooltips and Table Sort Header (which use AriaDescriber) but for the repro I use the AriaDescriber service directly. I set a description on a button in the Example component which uses `ViewEncapsulation.ShadowDom`.
Steps to reproduce:
1. Open the repro https://stackblitz.com/edit/components-issue-rxwpmf?file=src/app/example-component.ts
2. Inspect the "Action" button
3. Open the "Accessibility" tab in the inspector
### Expected Behavior
The button should have the description "Some description" which was created via AriaDescriber service.
### Actual Behavior
The button has no description.

The `aria-describedby` attribute is there but the referenced element is ignored because it's outside of the Shadow DOM. It works if I set `encapsulation` on the component to `Emulated`.
### Environment
- Angular: 13.3.0
- CDK/Material: 13.3.0
- Browser(s): Brave
- Operating System (e.g. Windows, macOS, Ubuntu): macOS
贡献指南
调研方向
从 AriaDescriber 服务开始,使用链接的、采用 ViewEncapsulation.ShadowDom 的 StackBlitz 示例重现该问题。通过浏览器的 Accessibility 检查器验证行为;当按钮公开“Some description”且仍保留 Shadow DOM 封装时,即表示完成。
由索引模型根据 Issue 内容生成。
评估
- 技术栈
- angular, typescript
- 领域
- accessibility, frontend
- Issue 类型
- 缺陷
- 难度
- 3/5
- 预计耗时
- 1-2 天
- 活跃度
- 活跃
- 描述清晰度
- 基本清楚
- 新手友好度
- 55/100