[5.8] Add Deferred interface for service providers

src/Illuminate/Contracts/Support/Deferred.php

@@ -0,0 +1,13 @@
+<?php
+
+namespace Illuminate\Contracts\Support;
+
+interface Deferred
+{
+    /**
+     * Get the services provided by the provider.
+     *
+     * @return array
+     */
+    public function provides();
+}

src/Illuminate/Support/ServiceProvider.php

@@ -2,6 +2,7 @@
 
 namespace Illuminate\Support;
 
+use Illuminate\Contracts\Support\Deferred;
 use Illuminate\Console\Application as Artisan;
 
 abstract class ServiceProvider
@@ -16,6 +17,8 @@ abstract class ServiceProvider
     /**
      * Indicates if loading of the provider is deferred.
      *
+     * @deprecated 5.8 Implement the \Illuminate\Contracts\Support\Deferred interface instead.
+     *
      * @var bool
      */
     protected $defer = false;
@@ -297,6 +300,6 @@ public function when()
      */
     public function isDeferred()
     {
-        return $this->defer;
+        return $this->defer || $this instanceof Deferred;
     }
 }