Add link check

.github/workflows/build.yml

@@ -21,16 +21,20 @@ jobs:
       matrix:
         node-version: [16]
     steps:
+      # Checkout doc repo and its dependencies
       - name: Checkout
-        uses: actions/checkout@v1
-      - name: Use Node.js ${{ matrix.node-version }}
+        uses: actions/checkout@v2
+      # Setup Node
+      - name: Setup (Node.js ${{ matrix.node-version }})
         uses: actions/setup-node@v1
         with:
           node-version: ${{ matrix.node-version }}
+      # Install and build
       - name: Install
         run: npm ci
       - name: Build
         run: npm run prod
+      # Deploy, limited to the master branch
       - name: Deploy
         if: success() && github.ref == 'refs/heads/master'
         uses: peaceiris/actions-gh-pages@v3
@@ -40,3 +44,6 @@ jobs:
           cname: einundzwanzig.space
           user_name: 'github-actions[bot]'
           user_email: 'github-actions[bot]@users.noreply.github.com'
+      # Run linkcheck, propagate linkcheck failure through grep pipe
+      - name: Linkcheck
+        run: set -o pipefail; npm run linkcheck 2>/dev/null | grep "Getting links from\|BROKEN"