Update the download data via a GitHub workflow

This workflow has a `workflow_dispatch` trigger to allow for manually
starting this workflow directly after, say, a Git for Windows version
was released.

Signed-off-by: Johannes Schindelin <[email protected]>

.github/workflows/update-download-data.yml

@@ -0,0 +1,87 @@
+name: Update download data
+
+on:
+  workflow_dispatch:
+  schedule:
+    # check daily for updates
+    - cron: '31 13 * * *'
+  push:
+    branches:
+      - main
+      - hugo
+
+permissions:
+  contents: write # need to be able to push
+
+jobs:
+  update-download-data:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          sparse-checkout: |
+            _sync_state
+            script
+      - name: ruby setup
+        uses: ruby/setup-ruby@v1
+        with:
+          bundler-cache: true
+      - name: update download data
+        id: update
+        run: |
+          # this seems to be needed to let `bundle exec` see `vendor/bundle/`
+          { bundle check || bundle install --frozen; } &&
+
+          # update download data
+          bundle exec ruby ./update-download-data.rb &&
+
+          # commit changes (if any)
+          if git diff-files --quiet --ignore-submodules --
+          then
+            what="$(git diff hugo.yml |
+              sed -n 's/^+ *filename: Git-\([.0-9]*\)-.*\.exe$/Git for Windows v\1/p')"
+            mac="$(git diff hugo.yml |
+              sed -n 's/^+ *filename: git-\([.0-9]*\)-.*\.dmg$/Git for macOS v\1/p')"
+            test -z "$mac" || what="$what${what:+, }$mac"
+            commit_message="Update download data ${what:+ ($what)}"
+            echo "result=$commit_message" >>$GITHUB_OUTPUT
+
+            git \
+              -c user.name=${{ github.actor }} \
+              -c user.email=${{ github.actor }}@noreply.github.com \
+              commit -m "$commit_message" &&
+
+            git bundle create download-data.bundle ${{ github.sha }}..${{ github.ref }} &&
+            git push origin HEAD
+      - name: upload bundle
+        if: steps.update.output.result != ''
+        uses: actions/upload-artifact@v3
+        with:
+          name: bundle
+          path: download-data.bundle
+    outputs:
+      commit-message: ${{ steps.update.outputs.result }}
+  push-updates:
+    needs: [update-download-data]
+    if: needs.check-for-updates.outputs.matrix != '[""]'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/download-artifact@v3
+      - name: apply updates
+        id: apply
+        shell: bash
+        run: |
+          langs=
+          for bundle in bundle-*/*.bundle
+          do
+            git -c core.editor=: \
+              -c user.name=${{ github.actor }} \
+              -c user.email=${{ github.actor }}@noreply.github.com \
+              pull --no-rebase $bundle ${{ github.ref }} ||
+            exit 1
+          done
+      - name: update gh-pages
+        uses: ./.github/actions/update-gh-pages
+        with:
+          commit-message: ${{ needs.update-download-data.outputs.commit-message }}