PR build: try to push to temporary branch when being called from forks

This might not work due to permissions.

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

Author: dscho

.github/workflows/pr.yml

@@ -19,14 +19,23 @@ jobs:
           git add -A \*.html &&
           git diff-index --cached --exit-code HEAD -- ||
           echo "need-to-commit=yes" >>$GITHUB_OUTPUT
-      - name: commit & push
+      - name: commit
         if: steps.check.outputs.need-to-commit == 'yes'
         run: |
           git config user.name "${{github.actor}}" &&
           git config user.email "${{github.actor}}@users.noreply.github.com" &&
           git commit -m 'Convert Markdown to HTML' -- \*.html &&
           git update-index --refresh &&
           git diff-files --exit-code &&
-          git diff-index --cached --exit-code HEAD -- &&
-          git push
-
+          git diff-index --cached --exit-code HEAD --
+      - name: commit
+        if: steps.check.outputs.need-to-commit == 'yes' && github.event.pull_request.head.repo.full_name == github.event.pull_request.base.repo.full_name
+        run: git push
+      - name: publish temporary branch and add instructions how to fetch
+        if: steps.check.outputs.need-to-commit == 'yes' && github.event.pull_request.head.repo.full_name != github.event.pull_request.base.repo.full_name
+        run: |
+          auth="$(printf 'PAT:%s' '${{ secrets.GITHUB_TOKEN }}' | base64 -w 0)" &&
+          echo "::add-mask::$auth" &&
+          git -c http.extraHeader="Authorization: Basic $auth" push "${{ github.event.pull_request.base.repo.clone_url }}" HEAD:refs/tmp/pr-${{ github.event.number }} &&
+          echo '::error::HTML pages are out of date. Please call `git pull --ff-only ${{ github.event.pull_request.base.repo.clone_url }}" refs/tmp/pr-${{ github.event.number }}` and push to the PR branch' >&2
+          exit 1