Add phpstan

Author: barryvdh

composer.json

@@ -17,7 +17,8 @@
     },
     "require-dev": {
         "phpunit/phpunit": "^7|^9",
-        "squizlabs/php_codesniffer": "^3.5"
+        "squizlabs/php_codesniffer": "^3.5",
+        "phpstan/phpstan": "^1.4"
     },
     "autoload": {
         "psr-4": {
@@ -31,6 +32,7 @@
     },
     "scripts": {
         "test": "phpunit",
+        "analyse": "vendor/bin/phpstan analyse src tests --level=4",
         "check-style": "phpcs -p --standard=PSR12 --exclude=Generic.Files.LineLength --runtime-set ignore_errors_on_exit 1 --runtime-set ignore_warnings_on_exit 1 src tests",
         "fix-style": "phpcbf -p --standard=PSR12 --exclude=Generic.Files.LineLength --runtime-set ignore_errors_on_exit 1 --runtime-set ignore_warnings_on_exit 1 src tests"
     },