Add linting to prevent embarassing errors (#5209)

* Added linting to prevent embarassing errors

Refs vimeo/psalm#5201

* Ignore unused requirements

.github/workflows/ci.yml

@@ -2,6 +2,41 @@ name: Run unit tests
 
 on: [push, pull_request]
 jobs:
+  lint:
+    name: Check PHP syntax
+    runs-on: ubuntu-latest
+    steps:
+      - name: Set up PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: '7.1'
+          tools: composer:v2
+
+      - uses: actions/checkout@v2
+
+      - name: Get Composer Cache Directories
+        id: composer-cache
+        run: |
+          echo "::set-output name=files_cache::$(composer config cache-files-dir)"
+          echo "::set-output name=vcs_cache::$(composer config cache-vcs-dir)"
+
+      - name: Cache composer cache
+        uses: actions/cache@v2
+        with:
+          path: |
+            ${{ steps.composer-cache.outputs.files_cache }}
+            ${{ steps.composer-cache.outputs.vcs_cache }}
+          key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-composer-
+
+      - name: Run composer install
+        run: composer install -o --ignore-platform-reqs
+        env:
+          COMPOSER_ROOT_VERSION: dev-master
+
+      - run: |
+          vendor/bin/parallel-lint src
   chunk-matrix:
     name: Generate Chunk Matrix
 

composer.json

@@ -44,6 +44,7 @@
         "amphp/amp": "^2.4.2",
         "bamarni/composer-bin-plugin": "^1.2",
         "brianium/paratest": "^4.0||^6.0",
+        "php-parallel-lint/php-parallel-lint": "^1.2",
         "phpdocumentor/reflection-docblock": "^5",
         "phpmyadmin/sql-parser": "5.1.0||dev-master",
         "phpspec/prophecy": ">=1.9.0",