fix(select): errors not shown on submit

[crisbeto]

Fixes mat-select error messages not being shown when the parent form is submitted.

Fixes #7634.

@mmalerba this is more or less what the input does already. I was considering moving it into the MatFormFieldControl, but having lifecycle hooks in there might look weird. What do you think?

[mmalerba]

I was thinking we should just move all the ErrorStateMatcher stuff into mat-form-field anyways. It's essentially all the same logic duplicated between input and select, and anyone who implements a custom control is probably going to want similar behavior. (but also fine if you just want to do this for now to fix select)

[crisbeto]

My issue with having it there is that some bindings on the form field control depend on it (e.g. the aria-invalid on the input). We'd have to introduce another subject like stateChanges, but on the form field, which could make things even more convoluted.

[mmalerba]

Hmmm I see, what if we changed to, instead of an @Input to a @Directive: [matErrorStateMatcher] which would basically do this:

@Directive({
  ...
  providers: [{provide: ErrorStateMatcher, useExisting: MatErrorStateMatcherDirective}]
})
export class MatErrorStateMatcherDirective implements ErrorStateMatcher {
  @Input('matErrorStateMatcher') errorStateMatcher: ErrorStateMatcher;

  isErrorState(...) {
    return this.errorStateMatcher.isErrorState(...);
  }
}

This way form field and input could both just inject the token and not worry about dealing with the @Input. It also has a cool side-effect of being able to do this:

<form class="my-special-error-group" [matErrorStateMatcher]="myMatcher">
  <!-- bunch of form fields that all get my custom matcher -->
</form>

[crisbeto]

I don't think that would react to changes either. Angular marks it for checking if the @Input value changes. Since the input is the error matcher itself, it won't do anything when the error state changes.

[mmalerba]

Ok then, let's do this for now, I'll keep thinking if there's any good way to move this common logic somewhere else...

[listepo-alterpost]

@crisbeto when will this fix be released?

[harshi1991]

Is this fix released?

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