How do you apply new lint rules to the legacy project with active development? Have you added standard gem recently, and now you are required to change a lot of files but could not apply them at once.

I got the same problem, and we could not add a massive amount of the small changes because it would require regular rebasing while this PR is on review, or even some safe changes could cause annoying problems.

Most common solution

Ask developers to add cosmetic changes for all changed files in the PR in separate commits. Which adds some problems for Code Reviewer in finding business logic changes.

PRs Authors and Code Reviewers without big enthusiasm will follow this.

So, I decided to delegate this annoying problem to the machine!

Photo by Thierry K

Approach

I added a simple periodical job on Continuous Integration (GitHub Actions):

Checkout repository,
Select several random files,
Run safe lint auto-corrections,
Create PR with new changes

Open PR with auto-corrections changes

#!/usr/bin/env bash

set -e

echo "-----Create and switch to new branch-----"

current_date=$(date +"%Y%m%d%H%M")
new_branch_name="auto-fix-lint-${current_date}"
git checkout -b "$new_branch_name"

git config user.name "jt-bot"
git config user.email "bot@jetthoughts.com"

echo "-----Run Rubocop-----"

# shellcheck disable=SC2046
bin/rubocop --no-server --fail-level "E" -a $(bin/rubocop --no-server -L **/*.rb | sort -R | head -n 5 | tr "\n" " ")

echo "-----Commit Updates-----"

git add .

commit_message="Auto-fix lint warnings ${current_date}"

git commit -am "$commit_message" ||
  (bin/rubocop -aF --fail-level "A" && exit 1) ||
  git commit -am "$commit_message" ||  exit 1

if [[ -z "${GITHUB_TOKEN}" ]]; then
  echo "No Pull Request, because no GITHUB_TOKEN passed!"
  exit 1
else
  git push "https://${GITHUB_TOKEN}@github.com/${GITHUB_USERNAME}/${GITHUB_REPONAME}.git" -f

  curl -X POST \
    -H "Authorization: token ${GITHUB_TOKEN}" \
    -d '{"title":"'"$commit_message"'","base":"develop","head":"'"$GITHUB_USERNAME"':'"$new_branch_name"'"}' \
    "https://api.github.com/repos/${GITHUB_USERNAME}/${GITHUB_REPONAME}/pulls"
fi

By Lines

current_date=$(date +"%Y%m%d%H%M")
new_branch_name="auto-fix-lint-${current_date}"
git checkout -b "$new_branch_name"

Create a unique branch to store our changes.

git config user.name "jt-bot"
git config user.email "bot@jetthoughts.com"

Set up Git to make commits.

bin/rubocop --no-server --fail-level "E" -a $(bin/rubocop --no-server -L **/*.rb | sort -R | head -n 5 | tr "\n" " ")

This line finds all supported by Rubocop files, shuffle and take top 5 (you can update it).

git commit -am "$commit_message" ||
  (bin/rubocop -aF --fail-level "A" && exit 1) ||
  git commit -am "$commit_message" ||  exit 1

If there are no changes from the previous step, we try to find the first file with changes.

git push "https://${GITHUB_TOKEN}@github.com/${GITHUB_USERNAME}/${GITHUB_REPONAME}.git" -f

  curl -X POST \
    -H "Authorization: token ${GITHUB_TOKEN}" \
    -d '{"title":"'"$commit_message"'","base":"develop","head":"'"$GITHUB_USERNAME"':'"$new_branch_name"'"}' \
    "https://api.github.com/repos/${GITHUB_USERNAME}/${GITHUB_REPONAME}/pulls"

Pushes and creates PR with changes.

2. GitHub Action Flow with Scheduler

Need to use Personal Tokens only for GitHub to get it you should use GitHub Docs: Creating a personal access token. And more details why we need to use Personal Tokens: GitHub Docs: Triggering a workflow from a workflow

---
name: Auto-fix

on:
  schedule:
    # * is a special character in YAML so you have to quote this string
    - cron: '0 0 * * 1,3' # Each Monday and Wednesday

env:
  CI: true
  RAILS_ENV: test

concurrency:
  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
  cancel-in-progress: true

jobs:
  rubocop:
    runs-on: ubuntu-latest
    env:
      GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
      GITHUB_USERNAME: jetthoughts
      GITHUB_REPONAME: jt_tools

    steps:
      - uses: actions/checkout@v3
        with:
          fetch-depth: 1

      - name: Set up Ruby
        uses: ruby/setup-ruby@v1
        with:
          bundler-cache: true

      - name: Create Pull Request with RuboCop fixes (3 retries)
        continue-on-error: true
        run: |
          bin/ci-generates-lint-fix || bin/ci-generates-lint-fix || bin/ci-generates-lint-fix

Bonus: mark PR to be auto-merged and request code review

---
name: Enable auto-merge for bots' PRs

on: pull_request

permissions:
  pull-requests: write
  statuses: write
  contents: write

jobs:
  select_for_auto_merge:
    runs-on: ubuntu-latest
    if: ${{ github.actor == 'github-actions[bot]' ||  startsWith(github.head_ref, 'auto-') }}
    steps:
      - name: Enable auto-merge for bots' PRs
        run: |
          gh pr merge --auto --rebase "$PR_URL"
          gh pr edit "$PR_URL" --add-reviewer "@jetthoughts/developers" --add-label "Need to review"
        env:
          PR_URL: ${{github.event.pull_request.html_url}}
          GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}

And we got "Atomic Habit."

After several weeks you will get cleaned code, and there was no harm to Code Reviewers or Developers ;)

Paul Keen is an Open Source Contributor and a Chief Technology Officer at JetThoughts. Follow him on LinkedIn or GitHub.

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Incremental lint fixes by GitHub Actions