Resolves #4. Add fixer to replace ::className() method usages with ::class keyword.

README.md

@@ -261,3 +261,19 @@ an anonymous class declaration in a case when said class constructor doesn't con
 
 * `remove_for_anonymous_classes` - if its set to `true`, then braces for anonymous classes without constructor
   arguments will be removed. **Default**: `false`.
+
+### `Ely/remove_class_name_method_usages` (Yii2)
+
+Replaces Yii2 [`BaseObject::className()`](https://github.com/yiisoft/yii2/blob/e53fc0ded1/framework/base/BaseObject.php#L84)
+usages with native `::class` keyword, introduced in PHP 5.5.
+
+```diff
+--- Original
++++ New
+@@ @@
+  <?php
+  use common\models\User;
+  
+- $className = User::className();
++ $className = User::class;
+```

src/Fixer/LanguageConstruct/RemoveClassNameMethodUsagesFixer.php

@@ -0,0 +1,123 @@
+<?php
+declare(strict_types=1);
+
+namespace Ely\CS\Fixer\LanguageConstruct;
+
+use Ely\CS\Fixer\AbstractFixer;
+use PhpCsFixer\FixerDefinition\CodeSample;
+use PhpCsFixer\FixerDefinition\FixerDefinition;
+use PhpCsFixer\Tokenizer\CT;
+use PhpCsFixer\Tokenizer\Token;
+use PhpCsFixer\Tokenizer\Tokens;
+use SplFileInfo;
+
+/**
+ * Replaces Yii2 BaseObject::className() usages with native ::class keyword, introduced in PHP 5.5.
+ *
+ * @author ErickSkrauch <erickskrauch@ely.by>
+ */
+final class RemoveClassNameMethodUsagesFixer extends AbstractFixer {
+
+    /**
+     * @inheritdoc
+     */
+    public function getDefinition() {
+        return new FixerDefinition(
+            'Converts Yii2 `BaseObject::className()` method usage into `::class` keyword.',
+            [
+                new CodeSample(
+                    '<?php
+
+use Foo\Bar\Baz;
+
+$className = Baz::className();
+'
+                ),
+            ]
+        );
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function isCandidate(Tokens $tokens) {
+        return $tokens->isTokenKindFound(T_STRING);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function isRisky() {
+        return true;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function applyFix(SplFileInfo $file, Tokens $tokens) {
+        for ($index = $tokens->count() - 4; $index > 0; --$index) {
+            $candidate = $this->getReplaceCandidate($tokens, $index);
+            if ($candidate === null) {
+                continue;
+            }
+
+            $this->fixClassNameMethodUsage(
+                $tokens,
+                $index,
+                $candidate[0], // brace open
+                $candidate[1]  // brace close
+            );
+        }
+    }
+
+    /**
+     * @param Tokens $tokens
+     * @param int    $index
+     *
+     * @return null|array
+     */
+    private function getReplaceCandidate(Tokens $tokens, $index) {
+        if (!$tokens[$index]->isGivenKind(T_STRING)) {
+            return null;
+        }
+
+        $braceOpenIndex = $tokens->getNextMeaningfulToken($index);
+        if (!$tokens[$braceOpenIndex]->equals('(')) {
+            return null;
+        }
+
+        $braceCloseIndex = $tokens->getNextMeaningfulToken($braceOpenIndex);
+        if (!$tokens[$braceCloseIndex]->equals(')')) {
+            return null;
+        }
+
+        $doubleColon = $tokens->getPrevMeaningfulToken($index);
+        if (!$tokens[$doubleColon]->isGivenKind([T_DOUBLE_COLON])) {
+            return null;
+        }
+
+        $methodName = $tokens[$index]->getContent();
+        if ($methodName !== 'className') {
+            return null;
+        }
+
+        return [
+            $braceOpenIndex,
+            $braceCloseIndex,
+        ];
+    }
+
+    /**
+     * @param Tokens  $tokens
+     * @param int     $index
+     * @param int     $braceOpenIndex
+     * @param int     $braceCloseIndex
+     */
+    private function fixClassNameMethodUsage(Tokens $tokens, int $index, int $braceOpenIndex, int $braceCloseIndex) {
+        $tokens->clearTokenAndMergeSurroundingWhitespace($braceCloseIndex);
+        $tokens->clearTokenAndMergeSurroundingWhitespace($braceOpenIndex);
+        $tokens->clearAt($index);
+        $tokens->insertAt($index, new Token([CT::T_CLASS_CONSTANT, 'class']));
+    }
+
+}

src/Rules.php

@@ -65,6 +65,7 @@ class Rules {
         'Ely/new_with_braces' => [
             'remove_for_anonymous_classes' => true,
         ],
+        'Ely/remove_class_name_method_usages' => true,
     ];
 
     public static function create(array $overwrittenRules = []): array {

tests/Fixer/LanguageConstruct/RemoveClassNameMethodUsagesFixerTest.php

@@ -0,0 +1,67 @@
+<?php
+declare(strict_types=1);
+
+namespace Ely\CS\Test\Fixer\Operator;
+
+use Ely\CS\Fixer\LanguageConstruct\RemoveClassNameMethodUsagesFixer;
+use PhpCsFixer\Tests\Test\AbstractFixerTestCase;
+
+/**
+ * @covers \Ely\CS\Fixer\LanguageConstruct\RemoveClassNameMethodUsagesFixer
+ */
+class RemoveClassNameMethodUsagesFixerTest extends AbstractFixerTestCase {
+
+    /**
+     * @param string      $expected
+     * @param null|string $input
+     *
+     * @dataProvider provideFixCases
+     */
+    public function testFix($expected, $input = null) {
+        $this->doTest($expected, $input);
+    }
+
+    public function provideFixCases() {
+        return [
+            [
+                '<?php echo className();',
+            ],
+            [
+                '<?php
+use Foo\Bar\Baz;
+
+$exceptionString = Baz::classname();
+',
+            ],
+            [
+                '<?php
+use Foo\Bar\Baz;
+
+$className = Baz::class;
+',
+                '<?php
+use Foo\Bar\Baz;
+
+$className = Baz::className();
+',
+            ],
+            [
+                '<?php
+use Foo\Bar\Baz;
+
+$exceptionString = "The class should be instance of " . Baz::class . " and nothing else";
+',
+                '<?php
+use Foo\Bar\Baz;
+
+$exceptionString = "The class should be instance of " . Baz::className() . " and nothing else";
+',
+            ],
+        ];
+    }
+
+    protected function createFixer() {
+        return new RemoveClassNameMethodUsagesFixer();
+    }
+
+}