Add tooling to verify the composer file

.github/workflows/composer-json-lint.yml

@@ -0,0 +1,67 @@
+name: "Lint composer.json"
+
+on:
+  pull_request:
+  push:
+
+jobs:
+  coding-standards:
+    name: "Lint composer.json"
+
+    runs-on: ${{ matrix.operating-system }}
+
+    strategy:
+      matrix:
+        dependencies:
+          - "highest"
+        php-version:
+          - "8.0"
+        operating-system:
+          - "ubuntu-latest"
+
+    steps:
+      - name: "Checkout"
+        uses: "actions/checkout@v2"
+
+      - name: "Install PHP"
+        uses: "shivammathur/setup-php@v2"
+        with:
+          coverage: "none"
+          php-version: "${{ matrix.php-version }}"
+          ini-values: memory_limit=-1
+          tools: composer:v2, composer-normalize, composer-require-checker, composer-unused
+
+      - name: Get composer cache directory
+        id: composer-cache
+        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+
+      - name: "Cache dependencies"
+        uses: "actions/cache@v2"
+        with:
+          path: ${{ steps.composer-cache.outputs.dir }}
+          key: "php-${{ matrix.php-version }}-composer-${{ matrix.dependencies }}-${{ hashFiles('**/composer.lock') }}"
+          restore-keys: "php-${{ matrix.php-version }}-composer-${{ matrix.dependencies }}-"
+
+      - name: "Install lowest dependencies"
+        if: ${{ matrix.dependencies == 'lowest' }}
+        run: "composer update --prefer-lowest --no-interaction --no-progress"
+
+      - name: "Install highest dependencies"
+        if: ${{ matrix.dependencies == 'highest' }}
+        run: "composer update --no-interaction --no-progress"
+
+      - name: "Install locked dependencies"
+        if: ${{ matrix.dependencies == 'locked' }}
+        run: "composer install --no-interaction --no-progress"
+
+      - name: "Validate composer.json"
+        run: "composer validate --strict"
+
+      - name: "Normalize composer.json"
+        run: "composer-normalize --dry-run"
+
+      - name: "Check composer.json explicit dependencies"
+        run: "composer-require-checker check"
+
+      - name: "Check composer.json unused dependencies"
+        run: "composer-unused"