commit-messages.yml

# Copyright 2025 Budapest University of Technology and Economics
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# Every commit in this repository is a single subject line with no body and no
# trailers, authored by a real person rather than an AI identity. See
# README.md. This check is what makes that a rule rather than a preference.

name: Commits

on:
  pull_request:
  workflow_dispatch:

concurrency:
  # One run for each workflow, branch and event. A new run cancels the run that
  # it makes obsolete, so no job continues for a commit that is already old.
  group: ${{ github.workflow }}-${{ github.event_name }}-${{ github.ref }}
  cancel-in-progress: true

permissions:
  contents: read

jobs:
  check:
    name: Message and authorship
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          # Need both endpoints of the PR range to enumerate its commits.
          fetch-depth: 0

      - name: Check every commit in this pull request
        env:
          BASE_SHA: ${{ github.event.pull_request.base.sha }}
          HEAD_SHA: ${{ github.event.pull_request.head.sha }}
        run: |
          set -euo pipefail

          fail=0
          while read -r sha; do
            [ -n "$sha" ] || continue
            subject=$(git log -1 --format=%s "$sha")

            # Strip trailing blank lines before counting, so a message that just
            # ends with a newline is not mistaken for having a body.
            lines=$(git log -1 --format=%B "$sha" \
                    | sed -e :a -e '/^\n*$/{$d;N;ba' -e '}' | wc -l)

            if [ "$lines" -gt 1 ]; then
              echo "::error::${sha:0:8} has a multi-line message. Subject line only — see README.md."
              echo "         subject: $subject"
              fail=1
            fi

            if git log -1 --format=%B "$sha" | grep -qiE '^\s*(co-authored-by|claude-session|generated-by|signed-off-by-ai)\s*:'; then
              echo "::error::${sha:0:8} carries a trailer. Trailers are not used in this repository."
              echo "         subject: $subject"
              fail=1
            fi

            if git log -1 --format=%B "$sha" | grep -qiE 'claude|copilot|chatgpt|generated with'; then
              echo "::error::${sha:0:8} mentions an AI assistant. Commit messages do not carry AI attribution."
              echo "         subject: $subject"
              fail=1
            fi

            # Commits are attributed to the person responsible for the change,
            # never to an assistant that helped write it.
            ident=$(git log -1 --format='%an <%ae> / %cn <%ce>' "$sha")
            if printf '%s' "$ident" | grep -qiE 'anthropic\.com|noreply@openai|copilot@|@users\.noreply\.github\.com.*bot'; then
              echo "::error::${sha:0:8} is authored or committed by an AI identity: $ident"
              echo "         subject: $subject"
              fail=1
            fi
          done < <(git rev-list --no-merges "$BASE_SHA..$HEAD_SHA")

          if [ "$fail" -ne 0 ]; then
            {
              echo "## Commit message check failed"
              echo
              echo "Every commit in this repository is a **single subject line** —"
              echo "no body, no trailers, no AI attribution — and is authored by a"
              echo "real person. See the Contribute section of README.md."
              echo
              echo "To fix a branch:"
              echo '```bash'
              echo 'git rebase -i <base>   # reword the offending commits'
              echo '# or, to strip every body on the branch at once:'
              echo 'git filter-branch -f --msg-filter "head -n 1" <base>..HEAD'
              echo '# to fix authorship:'
              echo 'git config user.name "Your Name" && git config user.email you@example.com'
              echo 'git rebase --exec "git commit --amend --no-edit --reset-author" <base>'
              echo '```'
            } >> "$GITHUB_STEP_SUMMARY"
            exit 1
          fi

          echo "✅ All commits are a single subject line, authored by a person." >> "$GITHUB_STEP_SUMMARY"