ipsos-components/src/material-examples/select-error-state-matcher/select-error-state-matcher-example.html

Material Design components for Angular

<mat-form-field>
  <mat-select placeholder="Choose one" [formControl]="selected" [errorStateMatcher]="matcher">
    <mat-option>Clear</mat-option>
    <mat-option value="valid">Valid option</mat-option>
    <mat-option value="invalid">Invalid option</mat-option>
  </mat-select>
  <mat-hint>Errors appear instantly!</mat-hint>
  <mat-error *ngIf="selected.hasError('required')">You must make a selection</mat-error>
  <mat-error *ngIf="selected.hasError('pattern') && !selected.hasError('required')">
    Your selection is invalid
  </mat-error>
</mat-form-field>