add pr build check for pelican

.github/workflows/pelican-gh-pages.yml

@@ -3,48 +3,107 @@ name: Deploy to GitHub Pages
 on:
   push:
     branches: [master]
+  pull_request:
+    branches: [master]
   workflow_dispatch:
 
 concurrency:
-  group: pages
+  group: pages-${{ github.head_ref || github.ref }}
   cancel-in-progress: true
 
 permissions:
   contents: read
-  pages: write
-  id-token: write
 
 env:
   PYTHON_VERSION: '3.11'
 
 jobs:
   build:
     runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      pull-requests: write
     steps:
       - uses: actions/checkout@v5
       - name: Set up Python
         uses: actions/setup-python@v6
         with:
           python-version: ${{ env.PYTHON_VERSION }}
+      - name: Cache pip
+        uses: actions/cache@v4
+        with:
+          path: ~/.cache/pip
+          key: ${{ runner.os }}-pip-${{ hashFiles('requirements.txt') }}
+          restore-keys: |
+            ${{ runner.os }}-pip-
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
           python -m pip install -r requirements.txt
       - name: Build site for production
         run: |
           make prod
+      - name: Remove custom domain for PR previews
+        if: github.event_name == 'pull_request'
+        run: rm -f output/CNAME
+      - name: Upload preview artifact
+        if: github.event_name == 'pull_request'
+        uses: actions/upload-artifact@v4
+        with:
+          name: site-preview
+          path: output
+      - name: Comment preview link
+        if: github.event_name == 'pull_request'
+        uses: actions/github-script@v7
+        env:
+          RUN_URL: ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}
+        with:
+          script: |
+            const body = `Preview build ready: [download site-preview artifact](${process.env.RUN_URL})`;
+            await github.rest.issues.createComment({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: context.issue.number,
+              body
+            });
       - name: Upload Pages artifact
-        uses: actions/upload-pages-artifact@v3
+        uses: actions/upload-pages-artifact@v4
         with:
           path: output
 
   deploy:
     needs: build
+    if: github.event_name == 'push' && github.ref == 'refs/heads/master'
     runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      pages: write
+      id-token: write
     environment:
       name: github-pages
       url: ${{ steps.deployment.outputs.page_url }}
     steps:
       - name: Deploy to GitHub Pages
         id: deployment
         uses: actions/deploy-pages@v4
+
+  deploy_preview:
+    needs: build
+    if: github.event_name == 'pull_request' && github.event.pull_request.head.repo.fork == false
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      pages: write
+      id-token: write
+    environment:
+      name: pr-${{ github.event.number }}
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - name: Deploy PR preview to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4
+        with:
+          preview: true
+      - name: Publish preview URL
+        run: |
+          echo "Preview URL: ${{ steps.deployment.outputs.page_url }}" >> $GITHUB_STEP_SUMMARY