[PHP] Add pow to exp Rector [ref #638]

config/level/php/php56.yml

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+services:
+    Rector\Php\Rector\PowToExpRector: ~

packages/Php/src/Rector/PowToExpRector.php

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+<?php declare(strict_types=1);
+
+namespace Rector\Php\Rector;
+
+use PhpParser\Node;
+use PhpParser\Node\Expr\BinaryOp\Pow;
+use PhpParser\Node\Expr\FuncCall;
+use Rector\Rector\AbstractRector;
+use Rector\RectorDefinition\CodeSample;
+use Rector\RectorDefinition\RectorDefinition;
+
+final class PowToExpRector extends AbstractRector
+{
+    public function getDefinition(): RectorDefinition
+    {
+        return new RectorDefinition(
+            'Changes pow(val, val2) to ** (exp) parameter',
+            [new CodeSample('pow(1, 2);', '1**2;')]
+        );
+    }
+
+    /**
+     * @return string[]
+     */
+    public function getNodeTypes(): array
+    {
+        return [FuncCall::class];
+    }
+
+    /**
+     * @param FuncCall $funcCallNode
+     */
+    public function refactor(Node $funcCallNode): ?Node
+    {
+        if ((string) $funcCallNode->name !== 'pow') {
+            return $funcCallNode;
+        }
+
+        if (count($funcCallNode->args) !== 2) {
+            return $funcCallNode;
+        }
+
+        $firstArgument = $funcCallNode->args[0]->value;
+        $secondArgument = $funcCallNode->args[1]->value;
+
+        return new Pow($firstArgument, $secondArgument);
+    }
+}

packages/Php/tests/Rector/PowToExpRector/Correct/correct.php.inc

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+<?php declare(strict_types=1);
+
+$result = 1 ** 2;
+
+$result = 1.2 ** 2.3;
+
+echo (-2) ** 3;
+
+($a--) ** (++$b);
+
+\a\pow(5,6);7 ** 8;
+
+(9 ** 10) ** 11 ** 12;
+
+(1 + 2) ** (3 * 4);
+
+($b = 4) ** 3;
+
+13 ** 14;
+
+$$a ** $$b;

packages/Php/tests/Rector/PowToExpRector/PowToExpRectorTest.php

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+<?php declare(strict_types=1);
+
+namespace Rector\Php\Tests\Rector\PowToExpRector;
+
+use Iterator;
+use Rector\Testing\PHPUnit\AbstractRectorTestCase;
+
+/**
+ * @covers \Rector\Php\Rector\PowToExpRector
+ *
+ * Few tests copied from https://github.com/FriendsOfPHP/PHP-CS-Fixer/commit/14660432d9d0b66bf65135d793b52872cc6eccbc#diff-b412676c923661ef450f4a0903c5442a
+ */
+final class PowToExpRectorTest extends AbstractRectorTestCase
+{
+    /**
+     * @dataProvider provideWrongToFixedFiles()
+     */
+    public function test(string $wrong, string $fixed): void
+    {
+        $this->doTestFileMatchesExpectedContent($wrong, $fixed);
+    }
+
+    public function provideWrongToFixedFiles(): Iterator
+    {
+        yield [__DIR__ . '/Wrong/wrong.php.inc', __DIR__ . '/Correct/correct.php.inc'];
+    }
+
+    protected function provideConfig(): string
+    {
+        return __DIR__ . '/config.yml';
+    }
+}

packages/Php/tests/Rector/PowToExpRector/Wrong/wrong.php.inc

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+<?php declare(strict_types=1);
+
+$result = pow(1, 2);
+
+$result = pow(1.2, 2.3);
+
+echo pow(-2, 3);
+
+pow($a--,++$b);
+
+\a\pow(5,6);pow(7,8);
+
+pow(pow(9,10),pow(11,12));
+
+pow(1 + 2, 3 * 4);
+
+pow($b = 4, 3);
+
+\pow(13,14);
+
+pow($$a, $$b);

packages/Php/tests/Rector/PowToExpRector/config.yml

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+services:
+    Rector\Php\Rector\PowToExpRector: ~