Support custom phpstan rules

Allow core and contrib to run phpstan how ever it likes.

src/DrupalCI/Plugin/BuildTask/BuildStep/CodebaseValidate/Phpstan.php

@@ -83,16 +83,20 @@ class Phpstan extends BuildTaskBase implements BuildStepInterface, BuildTaskInte
       return 0;
     }
 
-    $this->addPhpstanNeon();
-
     // Run phpstan.
     $source_dir = $this->environment->getExecContainerSourceDir();
     $project_dir = $this->codebase->getProjectConfigDirectory(FALSE);
     $work_dir = $this->environment->getContainerWorkDir();
     $this->io->writeln('<info>Running PHPStan at ' . $source_dir);
 
+    // If phpstan file is missing, provide some basic deprecation checks.
+    if (!file_exists($work_dir . '/phpstan.neon') || !file_exists($work_dir . '/phpstan.neon.dist')) {
+      $this->addPhpstanNeon();
+      $neon = '-c ' . $work_dir . '/' . $this->pluginDir . '/phpstan.neon';
+    }
+
     $result = $this->execEnvironmentCommands([
-      'cd ' . $project_dir . ' && sudo -u www-data ' . $source_dir . static::$phpstanExecutable . ' analyse --error-format checkstyle -c ' . $work_dir . '/' . $this->pluginDir . '/phpstan.neon . > ' . $work_dir . '/' . $this->pluginDir . '/phpstan_results.xml',
+      'cd ' . $project_dir . ' && sudo -u www-data ' . $source_dir . static::$phpstanExecutable . ' analyse --error-format checkstyle ' . $neon . ' > ' . $work_dir . '/' . $this->pluginDir . '/phpstan_results.xml',
     ]);
 
     // Save phpstan results for later examination.