This function make a validation and setErrors to the form, without the need of creating a StateMatcher to setErrors

passwordMatchValidation.ts

import { AbstractControl } from "@angular/forms";

export function passwordMatchValidator(control: AbstractControl): {[key: string]: boolean} | null {
    const password = control.get('password');
    const passwordRepeat = control.get('passwordRepeat');
    const passwordErrors = { ...password.errors };
    const passwordRepeatErrors = { ...passwordRepeat.errors };
    if (password.value !== passwordRepeat.value) {
        password.setErrors({passwordMatchValidator: true});
        passwordRepeat.setErrors({passwordMatchValidator: true});
        return {passwordMatchValidator: true};
    } else {
        delete passwordErrors.passwordMatchValidator;
        delete passwordRepeatErrors.passwordMatchValidator;
        if(Object.keys(passwordRepeatErrors).length > 0) {
            passwordRepeat.setErrors({...passwordRepeatErrors});
        } else {
            passwordRepeat.setErrors(null);
        }
        if(Object.keys(passwordErrors).length > 0) {
            password.setErrors({...passwordErrors});
        } else {
            password.setErrors(null);
        }
        return null;
    }
}