bug(checkbox): Tri-state checkbox runs out of sync with its input after a change event
- Dominant language
- TypeScript
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Description
### 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
I think the direct implementation with the `(change)` checkbox output (represented in https://stackblitz.com/edit/angular-tzjh4u?file=src%2Fmain.ts) has never worked.
With the Legacy checkbox, we had a workaround that relied on `click` and `keyup.space` DOM events instead of relying on the component's `change` output.
After migrating to MDC, this workaround no longer works, too.
### Reproduction
https://stackblitz.com/edit/angular-tzjh4u?file=src%2Fmain.ts
Steps to reproduce:
1. Click checkbox to toggle between "checked" and "unchecked" - see how the checkbox state (checkmark) is always in sync with the app state (`this.state`)
2. Click the "Set to indeterminate" button
3. Click the checkbox, which is currently in the indeterminate state
### Expected Behavior
Checkbox becomes "unchecked"
### Actual Behavior
Checkbox becomes "checked", despite `this.state` is "unchecked". Checkbox is now out of sync with its input. Note how `ng-reflect-checked="false"`, while the classname includes `mat-mdc-checkbox-checked`
### Environment
- Angular 16.0.2
- CDK/Material: 16.0.1
- Browser(s): Firefox, Chrome
- Operating System (e.g. Windows, macOS, Ubuntu): macOS
Contributor guide
Research direction
Start with the linked StackBlitz reproduction at src/main.ts and reproduce the transition from indeterminate to unchecked through the checkbox change event. Trace the tri-state checkbox behavior and verify that the visual state and input state remain synchronized after the change.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- angular, typescript
- Domain
- frontend
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100