Check for the existence of PHPStan source after extraction.

Fix namespace error in the class property of composer.json.

Author: ianef

composer.json

@@ -22,7 +22,7 @@
         }
     ],
     "extra": {
-        "class": "Xact\\PHPStan\\Plugin"
+        "class": "Xact\\PHPStan\\Dev\\Plugin"
     },
     "require-dev": {
         "composer/composer": "^2.5"

src/Plugin.php

@@ -51,5 +51,9 @@ public function extractPHPStan(): void
             $phar = new Phar($pharPath);
             $phar->extractTo($extractPath);
         }
+
+        if (!file_exists($extractPath) || !file_exists("{$extractPath}/src")) {
+            throw new Exception("Could not find phpstan/src after extracting the .phar file.");
+        }
     }
 }