Sort root files in withRootFiles() to keep cache hash stable

src/Configuration/RectorConfigBuilder.php

@@ -405,6 +405,8 @@ public function withRootFiles(): self
             // this file cannot be interpreted as PHP file
             // https://www.jetbrains.com/help/phpstorm/ide-advanced-metadata.html#expected-arguments
             ->notName('.phpstorm.meta.php')
+            // the paths are part of the cache hash, so the filesystem order must not leak into it
+            ->sortByName()
         ;
 
         foreach ($rootPhpFilesFinder as $rootPhpFileFinder) {

tests/Configuration/RectorConfigBuilderRootFilesTest.php

@@ -0,0 +1,79 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Rector\Tests\Configuration;
+
+use Nette\Utils\FileSystem;
+use PHPUnit\Framework\TestCase;
+use Rector\Config\RectorConfig;
+use Rector\Configuration\RectorConfigBuilder;
+use ReflectionProperty;
+use Webmozart\Assert\Assert;
+
+final class RectorConfigBuilderRootFilesTest extends TestCase
+{
+    /**
+     * Deliberately not in name order: the filesystem returns entries in an order of its own,
+     * which differs between machines, e.g. between two CI runner images.
+     *
+     * @var string[]
+     */
+    private const array ROOT_FILE_NAMES = ['rector.php', 'ecs.php', '.php-cs-fixer.dist.php', 'deploy.php'];
+
+    private string $originalWorkingDirectory;
+
+    private string $projectDirectory;
+
+    protected function setUp(): void
+    {
+        $workingDirectory = getcwd();
+        Assert::string($workingDirectory);
+        $this->originalWorkingDirectory = $workingDirectory;
+
+        $temporaryDirectory = realpath(sys_get_temp_dir());
+        Assert::string($temporaryDirectory);
+
+        $this->projectDirectory = $temporaryDirectory . '/' . uniqid('rector_root_files_');
+        foreach (self::ROOT_FILE_NAMES as $rootFileName) {
+            FileSystem::write($this->projectDirectory . '/' . $rootFileName, '<?php' . PHP_EOL, null);
+        }
+
+        chdir($this->projectDirectory);
+    }
+
+    protected function tearDown(): void
+    {
+        chdir($this->originalWorkingDirectory);
+
+        FileSystem::delete($this->projectDirectory);
+    }
+
+    public function testRootFilesAreSortedByName(): void
+    {
+        $rectorConfigBuilder = RectorConfig::configure()->withRootFiles();
+
+        // the paths are part of the cache invalidation hash, so their order has to be stable across machines
+        $expectedPaths = [
+            $this->projectDirectory . '/.php-cs-fixer.dist.php',
+            $this->projectDirectory . '/deploy.php',
+            $this->projectDirectory . '/ecs.php',
+            $this->projectDirectory . '/rector.php',
+        ];
+
+        $this->assertSame($expectedPaths, $this->resolvePaths($rectorConfigBuilder));
+    }
+
+    /**
+     * @return string[]
+     */
+    private function resolvePaths(RectorConfigBuilder $rectorConfigBuilder): array
+    {
+        $pathsReflectionProperty = new ReflectionProperty(RectorConfigBuilder::class, 'paths');
+
+        /** @var string[] $paths */
+        $paths = $pathsReflectionProperty->getValue($rectorConfigBuilder);
+
+        return $paths;
+    }
+}