lock-sync-gate.yml

# SPDX-License-Identifier: MPL-2.0
name: Lock Sync Gate

# Fails any pull request whose .github/workflows/actions.lock has drifted from
# the workflow YAML. That drift is not cosmetic: GitHub refuses such a run at
# startup, creating ZERO jobs, and reports only "This run likely failed because
# of a workflow file issue." A single grouped Dependabot bump can take out most
# of a repository's CI that way, because Dependabot rewrites `uses:` refs in the
# YAML and cannot touch the lockfile. Measured across 200 repositories on
# 2026-09-22: 39 had silently dead CI from exactly this cause.
# See hyperpolymath/standards#968.
#
# This workflow deliberately carries NO `uses:` of its own. It checks out by
# calling git in a `run:` step instead of using actions/checkout, so it has no
# lockfile entry to go stale and is structurally immune to the very failure it
# detects. Do not add a `uses:` to this file.
#
# There is also no `paths:` filter, on purpose: a filtered workflow never
# reports on pull requests that miss the filter, which deadlocks any branch
# ruleset that requires this check.

on:
  pull_request:
  push:
    branches: [main]

permissions:
  contents: read

concurrency:
  group: lock-sync-gate-${{ github.ref }}
  cancel-in-progress: true

jobs:
  lock-sync:
    name: actions.lock is in sync with the workflow YAML
    runs-on: ubuntu-latest
    timeout-minutes: 5
    steps:
      - name: Check out without actions/checkout
        env:
          REPO: ${{ github.repository }}
          SHA: ${{ github.event.pull_request.head.sha || github.sha }}
          TOKEN: ${{ github.token }}
        run: |
          set -euo pipefail
          # Authenticate the fetch. An anonymous clone works only for public
          # repositories; this gate must also run on private ones. The header
          # form is used rather than a token in the remote URL so the
          # credential is never written into .git/config.
          AUTH="AUTHORIZATION: basic $(printf 'x-access-token:%s' "${TOKEN}" | base64 -w0)"
          git init -q .
          git remote add origin "https://github.com/${REPO}.git"
          git -c http.extraheader="${AUTH}" fetch -q --depth 1 origin "${SHA}"
          git checkout -q FETCH_HEAD
          echo "checked out ${SHA}"

      - name: Verify lockfile synchronisation
        run: |
          set -euo pipefail
          test -x scripts/check-lock-sync.sh \
            || { echo "::error::scripts/check-lock-sync.sh missing or not executable"; exit 1; }
          ./scripts/check-lock-sync.sh