Add basic run of PHPStan (ref squizlabs#2201)

.travis.yml

@@ -21,6 +21,7 @@ matrix:
     - php: 7.2
     - php: 7.3
     - php: nightly
+      env: PHPSTAN=1
 
   allow_failures:
     - php: nightly
@@ -56,3 +57,5 @@ script:
   - if [[ $XMLLINT == "1" ]]; then diff -B ./src/Standards/PSR12/ruleset.xml <(xmllint --format "./src/Standards/PSR12/ruleset.xml"); fi
   - if [[ $XMLLINT == "1" ]]; then diff -B ./src/Standards/Squiz/ruleset.xml <(xmllint --format "./src/Standards/Squiz/ruleset.xml"); fi
   - if [[ $XMLLINT == "1" ]]; then diff -B ./src/Standards/Zend/ruleset.xml <(xmllint --format "./src/Standards/Zend/ruleset.xml"); fi
+  # Run PHPStan
+  - if [[ $PHPSTAN == "1" ]]; then composer require --dev phpstan/phpstan && php vendor/bin/phpstan analyse src --level=0 --configuration=phpstan.neon --autoload-file=tests/bootstrap.php; fi

phpstan.neon

@@ -0,0 +1,13 @@
+parameters:
+    ignoreErrors:
+        -
+            message: '~^Undefined variable: \$phpCodeSnifferConfig$~'
+            path: %currentWorkingDirectory%/src/Config.php
+
+    dynamicConstantNames:
+        - PHP_CODESNIFFER_IN_TESTS
+        - PHP_CODESNIFFER_CBF
+        - PHP_CODESNIFFER_VERBOSITY
+
+    excludes_analyse:
+        - */Tests/*