Linting Legacy Code

Linters are great tools that help to prevent accidental bugs, automate code reviews, and enforce a style guide. But even with all the benefits, linters are still not as widely adopted as they should be. For legacy codebases, a gigantic patch will be needed to fix existing warnings. One approach to mitigate some of these concerns is to introduce linting incrementally. I will talk about adding lint rules one at a time, linting on new changes only, and reporting warnings unobtrusively.

Transcript

1. LINTING LEGACY CODE INTEGRATING LINTERS INTO OUR WORKFLOW Ivan Tse, Paperless Post Twitter: @ivan_tse GitHub: @ivantsepp
2. OUTLINE What are linters? Why should we use them? The challenges Possible approaches
3. A linter is a tool that analyzes code to flag suspicious behavior
5. WHY SHOULD WE USE LINTERS Can catch bugs or mistakes Enforceable style guides
6. “Programs are meant to be read by humans and only incidentally for computers to execute.” — H. Abelson and G. Sussman
9. “Any styleguide will become more valuable as more of its enforcement becomes more automated.” http://davidtheclark.com/scss-lint-styleguide/
10. LINTERS ARE AUTOMATED CODE REVIEWS
12. AVAILABLE LINTERS: Ruby: Rubocop (there are rules for Rails and even Rspec) Haml: haml-lint Scss: Scss-lint Javascript: JSLint, JSHint, ESLint React: ESLint-plugin-React Chef: Foodcritic
13. CHALLENGES FOR INTRODUCING LINTERS Legacy codebase False positives Very opinionated Integration
14. HOUND Hound comments on style violations in GitHub pull requests, allowing you and your team to better review and maintain a clean codebase.
15. CODE CLIMATE The Code Climate Platform is the first open, extensible platform for all types of static analysis.
16. THE "LEGACY CODEBASE" PROBLEM LINT INCREMENTALLY
17. HOW TO LINT CHANGES
20. Run the linter on the file before and after the changes. Report any new warnings
22. File is eventually left in an inconsistent state
26. THE "VERY OPINIONATED" PROBLEM STYLE GUIDE REPOSITORY
28. THE "INTEGRATION" PROBLEM Run multiple linters including custom rules (ex. `named_scope`) Pass/Fail CI builds
29. THE "FALSE POSITIVE" PROBLEM Ignore rules
30. RESULTS
32. Missing semicolon. (semi) `0px` should be written without units as `0` Properties should be ordered ...
36. FINAL THOUGHTS
37. THANK YOU