Bug: false positive in RemoveUnusedPrivatePropertyRector for usage in closure

[Levivb]

Subject	Details
PHP version	PHP 7.2
Full Command	vendor/bin/rector --config ci/config/rector.yml process Tests/Unit/Exceptions/HandlerTest.php -n

parameters:
  php_version_features: '7.2'

services:
  Rector\DeadCode\Rector\Property\RemoveUnusedPrivatePropertyRector: ~

Current Behaviour

Rector v0.5.5
Config file: ci/config/rector.yml

 3/3 [▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓] 100%

1 file with changes
===================

1) Tests/Unit/Exceptions/HandlerTest.php

    ---------- begin diff ----------
--- Original
+++ New
@@ -52,9 +52,6 @@
     /** @var LoggerInterface */
     private $logger;

-    /** @var Message */
-    private $message;
-
     /** @var Redirector */
     private $redirector;

@@ -72,7 +69,6 @@
         parent::setUp();

         $this->request = Mockery::mock(Request::class);
-        $this->message = $this->createMock(Message::class);
         $this->sentry = $this->createMock(Raven_Client::class);
         $this->container = $this->createMock(Container::class);
         $this->mailer = $this->createMock(Mailer::class);
    ----------- end diff -----------

Applied rectors:

 * Rector\DeadCode\Rector\Property\RemoveUnusedPrivatePropertyRector

 [OK] Rector is done! 1 changed files

Minimal PHP Code Causing Issue

<?php
declare(strict_types=1);

namespace Tests\Unit\Exceptions;

use App\Exceptions\Handler;
use Closure;
use Exception;
use Illuminate\Contracts\Container\Container;
use Illuminate\Contracts\Mail\Mailer;
use Illuminate\Contracts\Translation\Translator;
use Illuminate\Contracts\View\Factory;
use Illuminate\Mail\Message;
use Modules\Core\Tests\LaravelTestCase;
use Raven_Client;

class HandlerTest extends LaravelTestCase
{
    /** @var Handler */
    private $handler;

    /** @var Mailer */
    private $mailer;

    /** @var Message */
    private $message;

    public function setUp()
    {
        parent::setUp();

        $this->message = $this->createMock(Message::class);
        $this->mailer = $this->createMock(Mailer::class);

        $this->handler = new Handler(
            $this->createMock(Container::class),
            $this->createMock(Raven_Client::class),
            $this->mailer,
            $this->createMock(Factory::class),
            $this->createMock(Translator::class),
            'some app',
            false
        );
    }

    public function testReportWillMailIfReportToSentryFails(): void
    {
        $this->mailer
            ->method('raw')
            ->with($this->identicalTo('Sentry has crashed!!!'), $this->callback(function (Closure $closure): bool {
                $this->message
                    ->expects($this->once())
                    ->method('to')
                    ->with($this->identicalTo('developers@maximum.nl'), $this->identicalTo('Developers'));

                $closure->call($this->handler, $this->message);

                return true;
            }));

        $this->handler->report(new Exception('Nice exception message!'));
    }
}

Expected Behaviour

Rector reports the $this->message property as unused, but it's used in an anonymous function. Behaviour of report is pretty weird because if any of the following diffs are applied, rector doesn't report any dead code, even though there isn't really changed anything significant with regards to the usage of $this->message:

$this->mailer
            ->method('raw')
-          ->with($this->identicalTo('Sentry has crashed!!!'), $this->callback(function (Closure $closure): bool {
+          ->with($this->callback(function (Closure $closure): bool {

                $this->message
-                   ->expects($this->once())
                    ->method('to')
                    ->with($this->identicalTo('developers@maximum.nl'), $this->identicalTo('Developers'));

               $closure->call($this->handler, $this->message);

                $this->message
                   ->expects($this->once())
-                  ->method('to')
                    ->with($this->identicalTo('developers@maximum.nl'), $this->identicalTo('Developers'));

               $closure->call($this->handler, $this->message);

                $this->message
                   ->expects($this->once())
                  ->method('to')
-                ->with($this->identicalTo('developers@maximum.nl'), $this->identicalTo('Developers'));

               $closure->call($this->handler, $this->message);

                $this->message
                   ->expects($this->once())
                  ->method('to')
                  ->with($this->identicalTo('developers@maximum.nl'), $this->identicalTo('Developers'));

-               $closure->call($this->handler, $this->message);

[TomasVotruba]

This is probably already covered in https://github.com/rectorphp/rector/pull/1641/files

Could you verify it still fails on master?

[Levivb]

Tested in master, unfortunately same issue. Even though test case looks similar. Event tested on keep-anonymous-property branch, but got same behaviour as described in initial report

[TomasVotruba]

Could you send failing test case?