Auto-merge workflow

.github/workflows/dependabot-auto-merge.yaml

@@ -0,0 +1,119 @@
+name: Dependabot auto-merge
+"on":
+  # Use pull_request_target instead of pull_request to get elevated permissions
+  # This is safe for Dependabot PRs because:
+  # 1. We verify the PR author is dependabot[bot]
+  # 2. We don't check out or run code from the PR
+  # 3. We only enable auto-merge, which requires branch protection to pass
+  pull_request_target:
+    types: [opened, reopened, synchronize]
+  pull_request_review:
+    types: [submitted]
+  check_suite:
+    types: [completed]
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  dependabot:
+    runs-on: ubuntu-latest
+    if: >-
+      (github.event_name == 'pull_request_target' && github.event.pull_request.user.login == 'dependabot[bot]' &&
+      github.event.pull_request.base.ref == 'main') || (github.event_name == 'pull_request_review' &&
+      github.event.pull_request.user.login == 'dependabot[bot]' && github.event.pull_request.base.ref == 'main') ||
+      (github.event_name == 'check_suite' && github.event.check_suite.pull_requests[0] != null &&
+      startsWith(github.event.check_suite.head_branch, 'dependabot/'))
+    steps:
+      - name: Get PR details
+        id: pr
+        # jq's // empty alternative operator returns an empty string instead of
+        # the literal "null" when a key is absent or null in the event payload.
+        # This ensures the downstream empty/null/numeric checks work correctly.
+        run: |
+          if [ "${GITHUB_EVENT_NAME}" = "check_suite" ]; then
+            PR_NUMBER="$(jq -r '.check_suite.pull_requests[0].number // empty' "${GITHUB_EVENT_PATH}")"
+            if [ -z "$PR_NUMBER" ] || [ "$PR_NUMBER" = "null" ] || ! [[ "$PR_NUMBER" =~ ^[0-9]+$ ]]; then
+              echo "No valid PR number found in check_suite event (got: $PR_NUMBER)"
+              exit 1
+            fi
+            PR_JSON=$(gh pr view "$PR_NUMBER" --repo "$GITHUB_REPOSITORY" --json author,baseRefName)
+            AUTHOR=$(echo "$PR_JSON" | jq -r '.author.login')
+            BASE_REF=$(echo "$PR_JSON" | jq -r '.baseRefName')
+
+            {
+              echo "author=$AUTHOR"
+              echo "base_ref=$BASE_REF"
+              echo "number=$PR_NUMBER"
+            } >> "$GITHUB_OUTPUT"
+          else
+            # For pull_request_target and pull_request_review, use event data
+            {
+              echo "author=$(jq -r '.pull_request.user.login // empty' "${GITHUB_EVENT_PATH}")"
+              echo "base_ref=$(jq -r '.pull_request.base.ref // empty' "${GITHUB_EVENT_PATH}")"
+              echo "number=$(jq -r '.pull_request.number // empty' "${GITHUB_EVENT_PATH}")"
+            } >> "$GITHUB_OUTPUT"
+          fi
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Enable auto-merge for Dependabot PRs
+        if: steps.pr.outputs.author == 'dependabot[bot]' && steps.pr.outputs.base_ref == 'main'
+        shell: bash
+        env:
+          PR_NUMBER: ${{ steps.pr.outputs.number }}
+          GH_TOKEN: ${{ secrets.WORKFLOW_PAT }}
+        # yamllint disable rule:line-length
+        run: |
+          set -o pipefail
+
+          attempt_merge() {
+            gh pr merge --auto --rebase "${PR_NUMBER}" --repo "$GITHUB_REPOSITORY" 2>&1 | tee /tmp/gh-output.txt
+          }
+
+          if attempt_merge; then
+            exit 0
+          fi
+
+          # Not a real failure: requirements not yet met, or auto-merge already enabled.
+          if grep -qE "auto-merge is already enabled|[Rr]equired.*status.*check|[Rr]equired approving review|[Rr]equired.*review" /tmp/gh-output.txt; then
+            echo "Auto-merge not enabled yet - this is expected when requirements are not met or already enabled"
+            exit 0
+          fi
+
+          # The repository-level "Allow auto-merge" setting is off. Re-enable it and retry once.
+          # This can happen if the setting is accidentally toggled in the repository admin UI.
+          if grep -qF "Auto merge is not allowed for this repository" /tmp/gh-output.txt; then
+            echo "Repository Allow auto-merge is disabled; attempting to re-enable..."
+            if ! gh api "repos/${GITHUB_REPOSITORY}" --method PATCH --field allow_auto_merge=true > /dev/null; then
+              echo "Could not re-enable Allow auto-merge on the repository. Manual intervention required."
+              exit 1
+            fi
+            echo "Repository setting re-enabled; retrying..."
+            if ! attempt_merge; then
+              echo "Auto-merge still failed after re-enabling repository setting:"
+              cat /tmp/gh-output.txt
+              exit 1
+            fi
+            exit 0
+          fi
+
+          # Concurrent merge race: another PR merged while this one was being processed,
+          # moving the base branch. Request a Dependabot rebase to update this branch;
+          # this workflow re-triggers naturally via check_suite:completed when the rebased
+          # branch passes checks. With N concurrent Dependabot PRs, this converges in N-1
+          # rounds: each round merges one PR, and any PRs that fall behind again each get
+          # a fresh rebase request on the next trigger.
+          if grep -qF "Base branch was modified" /tmp/gh-output.txt; then
+            echo "Base branch was modified by a concurrent merge. Requesting Dependabot rebase..."
+            gh pr comment "${PR_NUMBER}" --repo "$GITHUB_REPOSITORY" --body "@dependabot rebase" || true
+            echo "Rebase requested; workflow will re-trigger when the rebased branch passes checks."
+            exit 0
+          fi
+
+          # Unexpected error.
+          echo "Unexpected error enabling auto-merge:"
+          cat /tmp/gh-output.txt
+          exit 1
+        # yamllint enable