added preview workflow (#83)

Author: shravanngoswamii

.github/workflows/preview.yml

@@ -0,0 +1,70 @@
+name: PR Preview Workflow
+
+on:
+  pull_request_target:
+    types: [opened, synchronize, closed]
+
+jobs:
+  build-and-preview:
+    if: github.event.action == 'opened' || github.event.action == 'synchronize'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      
+      - name: Set up Quarto
+        uses: quarto-dev/quarto-actions/setup@v2
+      
+      - run: quarto --version
+
+      - name: Render Quarto site
+        run: quarto render
+
+      - name: Deploy to GitHub Pages
+        uses: JamesIves/github-pages-deploy-action@v4
+        with:
+          branch: gh-pages
+          folder: _site
+          target-folder: pr-previews/${{ github.event.pull_request.number }}
+          clean: false
+          commit-message: Deploy preview for PR ${{ github.event.pull_request.number }}
+          token: ${{ secrets.GITHUB_TOKEN }}
+
+  comment-preview-url:
+    needs: build-and-preview
+    if: needs.build-and-preview.result == 'success'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Comment Preview URL
+        uses: thollander/actions-comment-pull-request@v2
+        with:
+          message: |
+            <!-- preview-url-comment -->
+            Preview the changes: https://turinglang.org/pr-previews/${{ github.event.pull_request.number }}
+            Please avoid using the search feature and navigation bar in PR previews!
+          comment_tag: preview-url-comment
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+  delete-preview-directory:
+    if: github.event.action == 'closed' || github.event.pull_request.merged == true
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout gh-pages branch
+        uses: actions/checkout@v4
+        with:
+          ref: gh-pages
+
+      - name: Remove PR Preview Directory
+        run: |
+          PR_NUMBER=${{ github.event.pull_request.number }}
+          PREVIEW_DIR="pr-previews/${PR_NUMBER}"
+          git config --global user.name "github-actions[bot]"
+          git config --global user.email "github-actions[bot]@users.noreply.github.com"
+          git pull origin gh-pages
+          rm -rf ${PREVIEW_DIR}
+          git add .
+          git commit -m "Remove preview for merged PR #${PR_NUMBER}"
+          git push
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}