bug(MatSlideToggle): Unlabelled slide toggle cannot be labeled by a dynamically set aria-label

[wildcardalice]

Reproduction

https://angular-j8a87w.stackblitz.io

Steps to reproduce:

1. Open Chrome inspector and inspect the mat-slide-toggle, note that it doesn't have an aria-label
2. Expand the DOM tree and note that the nested input also doesn't have an aria-label
3. Inspect the checkbox on the page, which is similarly labeled, and note that the aria-label applies properly

Expected Behavior

[attr.aria-label]="..." should apply an aria-label to the slide toggle and the nested input element

Actual Behavior

Applying a dynamic aria-label to an unlabeled mat-slide-toggle does not currently seem possible

Environment

• Angular: Stackblitz was copied from the documentation at https://material.angular.io/components/slide-toggle
• Browser(s): Chrome Version 89.0.4389.114

[crisbeto]

The attr.aria-label won't work because we don't have a good way of picking it up. We do have an aria-label input so doing something like [aria-label]="..." should work.

[wildcardalice]

Ah I see. Are there any plans to support aria-describedby in a similar way to aria-label?

[crisbeto]

I've submitted #23104 to add support for it.

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