RuboCop for Code Review

Code Review Meetup #1 https://connpass.com/event/75567/
https://docs.google.com/presentation/d/e/2PACX-1vQRTU7twM5Yv32YNvlEHeAb1JAhuJx2oZPrX6_aqXe0fEUooVEi64HFxFKXGbfR3DjtUUYSRmLX562z/pub?start=false&loop=false&delayms=3000

Transcript

1. RuboCop for Code Review Code Review Meetup #1 Jan. 19, 2018
2. User.find(name: "pocke").inspect • Masataka Kuwabara • Engineer at Actcat, Inc. / SideCI ◦ Rubyist, Gopher and Vimmer. • RuboCop's core developer. ◦ Today, I'll talk about RuboCop.
3. Goal • Improve code review with RuboCop. • RuboCop is not a “Silver Bullet”. ◦ When RuboCop reviews your code, you should review RuboCop's warnings.
4. Note • I’ll talk about Ruby today, but we can apply the practices to projects that is written in other languages.
5. Agenda • What's RuboCop? • The internal of RuboCop • RuboCop for Code Review
6. Questions
7. Questions • Are you Rubyist? • Do you know RuboCop?
8. What's RuboCop?
9. What's RuboCop? • A static analyzer for Ruby. • It has 3 type checks. ◦ Style ◦ Lint ◦ Metrics
10. Style Check coding style
11. Style: check coding style • White spaces ◦ Indentation width ◦ White spaces around brackets • Syntax vs Method call ◦ alias vs alias_method ◦ for vs each
12. Style checks based on one of the style guides. • https://github.com/bbatsov/ruby- style-gudie ◦ If your coding style has differences, you can configure RuboCop.
13. Style: example # Use `def foo(arr)` def foo arr for x in arr # Use each bar # Bad indentation end end
14. Lint Check bugs
15. Lint: check bugs • Unreachable code • Debug code • Unused variables • etc...
16. Lint: example def foo binding.irb # debug code return true # It’s never executed. puts 'hi' end
17. Metrics Check complexity
18. Metrics: check complexity • ABC size ◦ Assignment, Branches, Conditional • Line length • Class length • etc...
19. The internal of RuboCop
20. How does RuboCop check code? • RuboCop analyzes each file individually. • RuboCop does not execute code. See “Writing Lint for Ruby” in RubyKaigi 2017.
21. Analyzing each file individually
22. Analyzing each file individually • RuboCop does not check relations between files. ◦ e.g. db/schema.rb and models. • For simplicity and performance. ◦ RuboCop can analyze parallelly.
23. Do not execute code
24. Do not execute code • RuboCop doesn’t execute your code. ◦ Pros: If your code has system('rm -rf /'), it does not remove. ◦ Cons: RuboCop cannot understand application completely. ▪ e.g. eval, method call
25. RuboCop for Code Review
26. RuboCop for Code Review • What does “RuboCop for Code Review” mean? • Advantage of RuboCop in Code Review. • Action for RuboCop Review
27. What does “RuboCop for Code Review” mean?
28. What does “RuboCop for Code Review” mean? • RuboCop also reviews your code. ◦ Human Review + RuboCop Review
29. How does RuboCop review • rubocop $(git diff --name-only) before human review. • I recommend using CI to run RuboCop. ◦ e.g. SideCI, CodeClimate and Reviewdog.
30. Advantages of RuboCop in review
31. Advantages of RuboCop in review • Reduce human reviews. • Enhancement reviews.
32. Reduce human reviews • Layout and style reviews by human are no longer necessary. ◦ e.g. “Remove the spaces”, “Use each method instead of for”. ◦ It’s a RuboCop job, not a human job.
33. Enhancement reviews • RuboCop can find bugs that human will overlook. ◦ Duplicate method definitions. ◦ binding.irb(debug code)
34. Action for RuboCop Review
35. Action for RuboCop Review • You should review “RuboCop Review”.
36. Action for RuboCop Review For Style Reviews
37. Action for Style Review • Check your coding style. ◦ If the review does not match with your coding style, you should configure or ignore the review. ◦ http://rubocop.readthedocs.io/en/stabl e/
38. Action for RuboCop Review For Lint Reviews
39. Action for Lint Review • Lint reviews has false positives. ◦ In other words, Lint review has a mistake sometimes. ◦ Because RuboCop does not know your application completely. ▪ See the slides above. • It is not a bug, it is a restriction.
40. How to start and/or continue to use RuboCop?
41. Start and/or continue to use RuboCop • You can get knowledges from WEB+DB PRESS vol.102. ◦ “RuboCopできれいで安全なコード” written by me. ◦ http://amzn.asia/fZ9cgZO
42. Conclusion
43. Conclusion • RuboCop is not a “Silver Bullet”. ◦ In many cases, the default coding style doesn't match your coding style. ◦ RuboCop has false positives. ◦ So when RuboCop reviews your code, you should review RuboCop Review.