Components: No valuechange when invalid date

[lousley]

Bug, feature request, or proposal:

Bug
What is the expected behavior?

https://github.com/angular/material2/blob/8050f633b56b6c048fc72dad2ab79304afdfad19/src/lib/datepicker/datepicker-input.ts#L332

This line of code produces a problem. If an invalidate is returned by a MomenDateAdpater in the parse method and the value was previously zero, no event is thrown.

What are the steps to reproduce?

Go to https://material.angular.io/components/datepicker/overview and navigate to "Datepicker that uses Moment.js dates". Clean the value and input 'asdf'. No error is displayed.

What is the use-case or motivation for changing an existing behavior?

I want enter a invalid date after cleaning the input field and will see an error

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

Angular 6
Material 6.3.0
Typescript: 2.7.2
All browswers

[lousley]

Why is this bug low?
This error also occurs in the initial case..that means, if the user still has no value in his date field, he can enter an invalid value and does not see that .. with an input mask where the user must enter his date of birth, that is very problematic

[lemoinem]

This issue also trigger the other way around.
If a date picker field with an invalid is cleared, the field remained marked as error (invalid date).
I have no validator (e.g., required) on the field.

Coalescing null and invalid values does not sound like the correct behavior.

[Pamasich]

Why is this only at low priority? Is there some workaround or something?

[lemoinem]

This is linked to, if not a duplicate of: #13346 (That's classified as P1/regression)

[crisbeto]

Looks like the related PR got merged in, but it wasn't labelled properly so the issue didn't close on its own.

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