ci: land the changelog as soothfast-bot via the broker

.github/workflows/changelog.yml

@@ -12,30 +12,23 @@ jobs:
   changelog:
     if: ${{ !endsWith(github.actor, '[bot]') }}
     runs-on: ubuntu-latest
-    permissions: {} # all repo access comes from the minted App token below
+    # Only the newest regeneration may land: an older one sees a stale tree.
+    # A cancel between mint and land leaves its one-hour token unrevoked.
+    concurrency:
+      group: changelog
+      cancel-in-progress: true
+    environment: soothfast-bot
+    permissions:
+      contents: read
+      id-token: write # soothfast-bot token via the broker, see bot/
     steps:
       - uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
         with:
           egress-policy: audit
-      - name: Mint a soothfast-bot token
-        id: app-token
-        uses: actions/create-github-app-token@bcd2ba49218906704ab6c1aa796996da409d3eb1 # v3.2.0
-        with:
-          client-id: ${{ vars.CHANGELOG_APP_CLIENT_ID }}
-          private-key: ${{ secrets.CHANGELOG_APP_PRIVATE_KEY }}
-          permission-contents: write
-          permission-pull-requests: write
-      - name: Get soothfast-bot user id
-        id: app-user
-        env:
-          GH_TOKEN: ${{ steps.app-token.outputs.token }}
-          APP_SLUG: ${{ steps.app-token.outputs.app-slug }}
-        run: echo "id=$(gh api "/users/${APP_SLUG}[bot]" --jq .id)" >> "$GITHUB_OUTPUT"
-      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0 # zizmor: ignore[artipacked]
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           fetch-depth: 0 # surface diff + previous-tag lookup need history
-          ref: ${{ github.ref_name }}
-          token: ${{ steps.app-token.outputs.token }}
+          persist-credentials: false
       - uses: dtolnay/rust-toolchain@6bed0761d98439e5a578e2877258200ad565ba87 # stable
         with:
           toolchain: stable
@@ -59,22 +52,16 @@ jobs:
           # shellcheck disable=SC2086 # both are deliberate flag lists
           cargo run --release -p cargo-soothfast -- \
             report changelog $PKGS --baseline self $AGAINST
-      - uses: peter-evans/create-pull-request@5f6978faf089d4d20b00c7766989d076bb2fc7f1 # v8.1.1
-        id: cpr
-        with:
-          token: ${{ steps.app-token.outputs.token }}
-          add-paths: CHANGELOG.md
-          commit-message: "docs: regenerate CHANGELOG.md"
-          title: "docs: regenerate CHANGELOG.md"
-          body: Automated CHANGELOG regeneration.
-          branch: bot/changelog-update
-          delete-branch: true
-          author: >-
-            ${{ steps.app-token.outputs.app-slug }}[bot]
-            <${{ steps.app-user.outputs.id }}+${{ steps.app-token.outputs.app-slug }}[bot]@users.noreply.github.com>
-      - name: Merge pull request
-        if: steps.cpr.outputs.pull-request-number
+      # Minted after the build so no step that compiles the tree holds it.
+      - name: Mint a soothfast-bot token
+        id: bot
+        run: action/bot-token.sh
+      - name: Land the regenerated changelog
         env:
-          GH_TOKEN: ${{ steps.app-token.outputs.token }}
-          PR_NUMBER: ${{ steps.cpr.outputs.pull-request-number }}
-        run: gh pr merge --auto --squash --delete-branch "$PR_NUMBER"
+          TOKEN: ${{ steps.bot.outputs.token }}
+          APP_SLUG: ${{ steps.bot.outputs.app_slug }}
+          BRANCH: bot/changelog-update
+          TITLE: "docs: regenerate CHANGELOG.md"
+          BODY: Automated CHANGELOG regeneration.
+          PATHS: CHANGELOG.md
+        run: action/land.sh

action/land.sh

@@ -0,0 +1,49 @@
+#!/usr/bin/env bash
+# Commit PATHS as APP_SLUG[bot], push them to BRANCH, open or refresh its
+# pull request against the default branch, and merge it: auto-merge when the
+# default branch has a rule that blocks merging, immediately otherwise. The
+# working tree keeps the regenerated files but HEAD is left where it was.
+# TOKEN is revoked on every exit path.
+# Inputs: TOKEN APP_SLUG BRANCH TITLE BODY PATHS (space separated pathspecs).
+set -euo pipefail
+
+: "${TOKEN:?}" "${APP_SLUG:?}" "${BRANCH:?}" "${TITLE:?}" "${PATHS:?}"
+export GH_TOKEN="$TOKEN"
+trap 'gh api -X DELETE /installation/token >/dev/null || true' EXIT
+
+read -ra paths <<<"$PATHS"
+git add -- "${paths[@]}"
+if git diff --cached --quiet; then
+  echo "land: nothing to commit"
+  exit 0
+fi
+
+bot_id=$(gh api "/users/${APP_SLUG}[bot]" --jq .id)
+head=$(git rev-parse HEAD)
+git -c "user.name=${APP_SLUG}[bot]" \
+  -c "user.email=${bot_id}+${APP_SLUG}[bot]@users.noreply.github.com" \
+  commit -q -m "$TITLE"
+# shellcheck disable=SC2016 # git expands $TOKEN when it runs the helper
+git -c credential.helper= \
+  -c credential.helper='!f() { echo "username=x-access-token"; echo "password=$TOKEN"; }; f' \
+  push --force "https://github.com/${GITHUB_REPOSITORY}" "HEAD:refs/heads/${BRANCH}"
+git reset -q --soft "$head"
+
+default=$(gh repo view --json defaultBranchRef --jq .defaultBranchRef.name)
+pr=$(gh pr list --head "$BRANCH" --base "$default" --state open --json number --jq '.[0].number // empty')
+if [ -z "$pr" ]; then
+  url=$(gh pr create --head "$BRANCH" --base "$default" --title "$TITLE" --body "${BODY:-}")
+  pr=${url##*/}
+else
+  gh pr edit "$pr" --title "$TITLE" --body "${BODY:-}" >/dev/null
+fi
+
+# History-only rules (deletion, linear history) leave the PR clean, and
+# --auto refuses a PR with nothing to wait for.
+blocking=$(gh api "repos/${GITHUB_REPOSITORY}/rules/branches/${default}" \
+  --jq '[.[] | select(.type == "required_status_checks" or .type == "pull_request" or .type == "merge_queue")] | length')
+if [ "$blocking" -gt 0 ]; then
+  gh pr merge --auto --squash --delete-branch "$pr"
+else
+  gh pr merge --squash --delete-branch "$pr"
+fi