[8.x] Allow setting middleware on queued Mailables (#37568)

* allow setting middleware on queued mailables

* add tests

* fix style

src/Illuminate/Mail/Mailable.php

@@ -234,7 +234,13 @@ public function later($delay, Queue $queue)
      */
     protected function newQueuedJob()
     {
-        return new SendQueuedMailable($this);
+        return (new SendQueuedMailable($this))
+                    ->through(
+                        array_merge(
+                            method_exists($this, 'middleware') ? $this->middleware() : [],
+                            $this->middleware ?? []
+                        )
+                    );
     }
 
     /**

tests/Integration/Mail/SendingQueuedMailTest.php

@@ -0,0 +1,53 @@
+<?php
+
+namespace Illuminate\Tests\Integration\Mail;
+
+use Illuminate\Mail\Mailable;
+use Illuminate\Mail\SendQueuedMailable;
+use Illuminate\Queue\Middleware\RateLimited;
+use Illuminate\Support\Facades\Mail;
+use Illuminate\Support\Facades\Queue;
+use Illuminate\Support\Facades\View;
+use Orchestra\Testbench\TestCase;
+
+/**
+ * @group integration
+ */
+class SendingQueuedMailTest extends TestCase
+{
+    protected function getEnvironmentSetUp($app)
+    {
+        $app['config']->set('mail.driver', 'array');
+
+        View::addLocation(__DIR__.'/Fixtures');
+    }
+
+    public function testMailIsSentWithDefaultLocale()
+    {
+        Queue::fake();
+
+        Mail::to('test@mail.com')->queue(new SendingQueuedMailTestMail);
+
+        Queue::assertPushed(SendQueuedMailable::class, function ($job) {
+            return $job->middleware[0] instanceof RateLimited;
+        });
+    }
+}
+
+class SendingQueuedMailTestMail extends Mailable
+{
+    /**
+     * Build the message.
+     *
+     * @return $this
+     */
+    public function build()
+    {
+        return $this->view('view');
+    }
+
+    public function middleware()
+    {
+        return [new RateLimited('limiter')];
+    }
+}