ci: Add PHPStan

This should prevent whole swathes of bugs, especially once we increase the rule level.

.github/workflows/ci.yml

@@ -46,6 +46,9 @@ jobs:
       - name: Run unit tests
         run: composer test
 
+      - name: Run static analysis
+        run: composer phpstan -- --error-format=github
+
   test-compiled:
     runs-on: ubuntu-latest
 

composer.json

@@ -32,6 +32,7 @@
     "require-dev": {
         "friendsofphp/php-cs-fixer": "^2.19 || ^3.8",
         "mf2/mf2": "^0.5.0",
+        "phpstan/phpstan": "^1.10",
         "psr/simple-cache": "^1 || ^2 || ^3",
         "yoast/phpunit-polyfills": "^1.0.1"
     },
@@ -61,6 +62,7 @@
         "sort-packages": true
     },
     "scripts": {
+        "phpstan": "phpstan analyze --memory-limit 512M",
         "test": "phpunit"
     }
 }

phpstan.neon

@@ -0,0 +1,19 @@
+parameters:
+    level: 2
+
+    paths:
+        - src/
+        - tests/
+
+    ignoreErrors:
+        # Not used since https://github.com/simplepie/simplepie/commit/b2eb0134d53921e75f0fa70b1cf901ed82b988b1 but cannot be removed due to BC.
+        - '(Constructor of class SimplePie\\Enclosure has an unused parameter \$javascript\.)'
+
+        # Testing legacy dynamic property usage.
+        - '(Access to an undefined property SimplePie.IRI::\$nonexistant_prop\.)'
+
+        # PHPStan stubs bug https://github.com/phpstan/phpstan/issues/8629
+        -
+            message: '(^Access to an undefined property XMLReader::\$\w+\.$)'
+            # Only occurs on PHP ≥ 8.2
+            reportUnmatched: false