add psalm

.github/workflows/php.yml

@@ -21,4 +21,34 @@ jobs:
         run: composer install --no-progress
 
       - name: Run test suite
-        run: vendor/bin/pest --fail-on-warning
+        run: vendor/bin/pest --fail-on-warning
+  static-analysis:
+    runs-on: ubuntu-latest
+    name: Psalm
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: '8.1'
+          coverage: none
+
+      - name: Validate composer.json and composer.lock
+        run: composer validate
+
+      - name: Cache Composer packages
+        id: composer-cache
+        uses: actions/cache@v2
+        with:
+          path: vendor
+          key: ${{ runner.os }}-php-8.1-${{ hashFiles('**/composer.json') }}
+          restore-keys: |
+            ${{ runner.os }}-php-8.1
+
+      - name: Install dependencies
+        if: steps.composer-cache.outputs.cache-hit != 'true'
+        run: composer install --no-progress --no-ansi
+
+      - name: Run Psalm
+        run: vendor/bin/psalm