RuleClosureContract.php

<?php


namespace App\Rules\Contracts;

use Closure;
use Illuminate\Contracts\Validation\Rule;

interface RuleClosureContract extends Rule
{
    public function getPassesClosure(): Closure;
}

ValidatorServiceProvider.php

<?php

namespace App\Providers;

use App\Rules\Contracts\RuleClosureContract;
use Illuminate\Contracts\Validation\Rule;
use Illuminate\Support\Facades\Validator;
use Illuminate\Support\ServiceProvider;
use Illuminate\Support\Str;

class ValidatorServiceProvider extends ServiceProvider
{
    /**
     * Register any application services.
     *
     * @return void
     */
    public function register()
    {
    }

    /**
     * Bootstrap any application services.
     *
     * @return void
     */
    public function boot()
    {
        $this->loadRules();
    }

    private function loadRules()
    {
        $dir = load_class_names_from_dir(app_path('Rules'));
        if (empty($dir)) {
            return;
        }

        $namespace = 'App\\Rules\\';

        foreach ($dir as $className) {
            $fullClassName = $namespace.$className;
            /** @var Rule|RuleClosureContract $instance */
            $instance = new $fullClassName();

            $ruleName = property_exists($instance, 'key') ? $instance->key : Str::snake($className);
            Validator::extend($ruleName, $instance->getPassesClosure(), $instance->message());
        }
    }
}