Add a workflow to help with BCD updates

This attempts to automate many of the existing manual steps:
* Checks out the branch
* Checks for removed BCD keys
* Checks for features with an empty definition
* Checks for baseline status changes

Where possible it automatically updates to removed BCD keys. So far it
doesn't attempt to figure out the correct replacement for removed
keys.

It is designed to output a GitHub comment indicating the changes, to
speed up human review.

Author: jgraham

.github/workflows/bcd_upgrade.yml

@@ -0,0 +1,90 @@
+name: BCD upgrade automation
+
+on:
+  pull_request:
+    types: [opened]
+
+jobs:
+  check-metadata:
+    name: Check if BCD upgrade
+    runs-on: ubuntu-latest
+    if: github.event.pull_request.user.login == 'dependabot[bot]'
+    outputs:
+      is-bcd-upgrade: ${{ steps.metadata.outputs.is-bcd-upgrade }}
+    steps:
+      - name: Fetch Dependabot metadata
+        id: fetch-metadata
+        continue-on-error: true
+        uses: dependabot/fetch-metadata@08eff52bf64351f401fb50d4972fa95b9f2c2d1b #v2.4.0
+
+      - id: metadata
+        run: echo "is-bcd-upgrade=${{ contains(steps.fetch-metadata.outputs.dependency-names, '@mdn/browser-compat-data') }}" >> "$GITHUB_OUTPUT"
+
+  automate:
+    name: Automate BCD upgrade
+    needs: check-metadata
+    if: needs.check-metadata.outputs.is-bcd-upgrade == 'true'
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      pull-requests: write
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
+          token: ${{ secrets.GITHUB_TOKEN }}
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version-file: .nvmrc
+          cache: npm
+
+      - run: |
+          git config user.name "github-actions[bot]"
+          git config user.email "github-actions[bot]@users.noreply.github.com"
+          npm install
+
+      - name: Remove deleted BCD keys and snapshot baseline
+        id: pre-dist
+        run: |
+          npx tsx scripts/bcd-upgrade.ts pre-dist --state-path bcd-update-state.json
+
+      - name: Commit key removals
+        run: |
+          if ! git diff --quiet features/; then
+            git add features/
+            git commit -m "Remove deleted BCD keys from web-features definitions"
+          fi
+
+      - name: Rebuild dist files
+        if: steps.pre-dist.outcome == 'success'
+        run: npm run dist
+
+      - name: Commit dist changes
+        if: steps.pre-dist.outcome == 'success'
+        run: |
+          if ! git diff --quiet features/; then
+            git add features/
+            git commit -m "Refresh dist"
+          fi
+
+      - name: Push changes
+        run: git push origin ${{ github.head_ref }}
+
+      - name: Format PR comment
+        id: comment
+        run: |
+          BODY=$(npx tsx scripts/bcd-upgrade.ts post-dist \
+            --state-path bcd-update-state.json)
+          {
+            echo 'body<<EOF'
+            echo "$BODY"
+            echo 'EOF'
+          } >> "$GITHUB_OUTPUT"
+
+      - name: Post PR comment
+        if: steps.comment.outputs.body != ''
+        uses: peter-evans/create-or-update-comment@71345be0265236311c031f5c7866368bd1eff043 #v4.0.0
+        with:
+          issue-number: ${{ github.event.number }}
+          body: ${{ steps.comment.outputs.body }}

package.json

@@ -17,6 +17,7 @@
   },
   "scripts": {
     "audit-consumers": "tsx scripts/audit-consumers.ts",
+    "bcd-upgrade": "tsx scripts/bcd-upgrade.ts",
     "build": "tsx scripts/build.ts package",
     "dist": "tsx scripts/dist.ts",
     "undist": "tsx scripts/undist.ts",