Rule: Add a new rule to check constructor for OM

Extdn/Samples/Classes/ObjectManager.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace Extdn\Samples\Classes;
+
+use Magento\Framework\App\ObjectManager as CoreObjectManager;
+use Magento\Framework\ObjectManagerInterface;
+
+class ObjectManager
+{
+    public function __construct(
+        ObjectManagerInterface $objectManager1,
+        CoreObjectManager $objectManager2
+    ) {
+    }
+}

Extdn/Sniffs/Classes/ObjectManagerSniff.md

@@ -0,0 +1,16 @@
+# Rule: Do not inject the Object Manager
+## Background
+The Object Manager should never be injected as a dependency into a class constructor. Injecting the Object Manager directly bypasses the DI mechanism that Magento makes flexible. Therefore, injecting the Object Manager in any kind of class is a code smell that leads to inflexibility.
+
+## Reasoning
+Whenever the Object Manager is directly injected into the constructor, it should be refactored into something else. 
+
+## How it works
+This rule uses PHP Reflection to determine the constructor arguments of a parsed class. If one of the arguments contains the word `ObjectManager`, the rule gives a warning.
+
+However, if the parsed class matches one of the following circumstances, the rule is bypassed:
+- When the class has a namespace that contains `/Test/`, indicating a test-class;
+- When the class has a name ending with `Factory`, `Proxy` or `Builder`;
+
+## How to fix
+If there is a match with this rule, the class constructor needs to be refactored so that dependencies are injected directly as a constructor argument, instead of via the Object Manager. Alternatively, this class needs to be created via a `Factory` class so that the `Factory` is able to use the Object Manager as needed.

Extdn/Sniffs/Classes/ObjectManagerSniff.php

@@ -0,0 +1,93 @@
+<?php
+/**
+ * Copyright © ExtDN. All rights reserved.
+ */
+
+declare(strict_types=1);
+
+namespace Extdn\Sniffs\Classes;
+
+use PHP_CodeSniffer\Files\File;
+use PHP_CodeSniffer\Sniffs\Sniff;
+use Extdn\Utils\Reflection;
+
+/**
+ * Class ObjectManagerSniff
+ *
+ * @package Extdn\Sniffs\Classes
+ */
+class ObjectManagerSniff implements Sniff
+{
+    /**
+     * @var string
+     */
+    protected $message = 'The ObjectManager should not be injected into the constructor';
+
+    /**
+     * @inheritdoc
+     */
+    public function register()
+    {
+        return [T_CLASS];
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function process(File $phpcsFile, $stackPtr)
+    {
+        $className = Reflection::findClassName($phpcsFile);
+        if (empty($className)) {
+            return false;
+        }
+
+        // Make sure to load the file itself, so that autoloading can be skipped
+        include_once($phpcsFile->getFilename());
+
+        $dependencyClasses = Reflection::getClassDependencies($className);
+        foreach ($dependencyClasses as $dependencyClass) {
+            if ($this->isObjectManagerAllowedWithClass($className)) {
+                continue;
+            }
+
+            if (!$this->isInstanceOfObjectManager($dependencyClass->getName())) {
+                continue;
+            }
+
+            $warning = 'The dependency "\\' . $dependencyClass->getName() . '" is not allowed here.';
+            $phpcsFile->addWarning($warning, null, 'warning');
+        }
+    }
+
+    /**
+     * @param string $className
+     *
+     * @return bool
+     */
+    private function isObjectManagerAllowedWithClass(string $className): bool
+    {
+        if (preg_match('/([a-zA-Z]+)(Factory|Builder)$/', $className)) {
+            return true;
+        }
+
+        if (preg_match('/Proxy$/', $className)) {
+            return true;
+        }
+
+        return false;
+    }
+
+    /**
+     * @param string $className
+     *
+     * @return bool
+     */
+    private function isInstanceOfObjectManager(string $className): bool
+    {
+        if (strstr($className, 'ObjectManager')) {
+            return true;
+        }
+
+        return false;
+    }
+}

Extdn/Tests/Classes/ObjectManagerUnitTest.1.inc

@@ -0,0 +1,13 @@
+<?php
+namespace Extdn\Samples\Classes;
+
+use Magento\Framework\ObjectManager\ObjectManager;
+
+class ObjectManagerUnitTest
+{
+    public function __construct(
+        ObjectManager $objectManager
+    ) {
+
+    }
+}

Extdn/Tests/Classes/ObjectManagerUnitTest.php

@@ -0,0 +1,42 @@
+<?php
+/**
+ * Copyright © ExtDN. All rights reserved.
+ */
+declare(strict_types=1);
+
+namespace Extdn\Tests\Classes;
+
+use PHP_CodeSniffer\Tests\Standards\AbstractSniffUnitTest;
+
+/**
+ * Class ObjectManagerUnitTest
+ *
+ * @package Extdn\Tests\Classes
+ */
+class ObjectManagerUnitTest extends AbstractSniffUnitTest
+{
+    protected function setUp()
+    {
+        parent::setUp();
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function getErrorList()
+    {
+        return [];
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function getWarningList($testFile = '')
+    {
+        if ($testFile === 'ObjectManagerUnitTest.2.inc') {
+            return [];
+        }
+
+        return [1 => 1];
+    }
+}

Extdn/ruleset.xml

@@ -8,5 +8,6 @@
     </rule>
     <rule ref="Extdn.Blocks.SetTemplateInBlock"/>
     <rule ref="Extdn.Classes.StrictTypes"/>
+    <rule ref="Extdn.Classes.ObjectManager"/>
     <rule ref="Extdn.Templates.TemplateObjectManager"/>
 </ruleset>