Adopting Sorbet at Scale

Presented at RubyConf 2019

Transcript

2. 2 Seatbelts
3. 3 Seatbelts save lives
4. Benefits 50% Reduction in serious injury 45% Reduction in risk of death 4 https://www.cdc.gov/motorvehiclesafety/seatbeltbrief/index.html
5. Yet... 4% of Canadian drivers 13% of US drivers 54% of Turkish drivers 5 drive without a seatbelt https://en.wikipedia.org/wiki/Seat_belt_use_rates_by_country
6. Why? 6 01 02 03 04 Find them uncomfortable Over 65s find them restricting Do not think they ever need them Think they’re less likely to have an accident https://www.bbc.com/news/blogs-magazine-monitor-29416372
7. “But cars are safe. We test them!” 7
8. - Costs too much ⏱ and - Cannot test every situation (Crash) Testing 8
9. The higher the stakes, the safer the car 9
10. 10 Ufuk Kayserilioğlu Rails and Ruby Infrastructure Team
11. Shopify Scale Commerce 1M Merchants 8000 orders/min (peak) 12B USD sales/year 11 135B USD total sales
12. Shopify Scale Engineering 1500 RnD Employees ~21K Ruby files ~150K tests 12 ~40 deploys daily
13. 13 There is too much at stake here. We need seatbelts!
14. Adopting Sorbet at Scale
15. 15 Sorbet 01
16. Sorbet ﹘ fast ﹘ expressive ﹘ static ﹘ gradual type checker for Ruby 16
17. 17 def foo(opts) opts.fetch("bar") end foo(bar: 1) foo.rb
18. 18 # typed: true extend(T::Sig) sig do params(opts: T::Hash[Symbol, Integer]) .returns(Integer) end def foo(opts) opts.fetch("bar") end foo(bar: 1) foo.rb
19. 19 foo.rb:9: Expected Symbol but found String("bar") for argument arg0 https://srb.help/7002 10 | opts.fetch("bar") ^^^^^^^^^^^^^^^^^ hash.rbi#L517: Method Hash#fetch has specified arg0 as Symbol 517 | arg0: K, ^^^^ Got String("bar") originating from: foo.rb:9: 10 | opts.fetch("bar") ^^^^^ Errors: 1 srb tc foo.rb
20. 20 # typed: true require "view_gem" View.render foo.rb
21. view.rbi 21 # typed: true require "view_gem" View.render foo.rb # typed: true class View def self.render(file) end end
22. view.rbi 22 # typed: true require "view_gem" View.render # ^ error: Not enough arguments provided for method View.render. Expected: 1, got: 0 foo.rb # typed: true class View def self.render(file) end end
23. 23 Our Journey 02
24. 24 Sorbet is mandatory in CI May 2019 Sorbet over all files Mar 2019 Sorbet is open-sourced Jun 2019 Shopify gets access to Sorbet Jul 2018 Sorbet introduced in Core Oct 2018 Timeline
25. We paid the early adopter price 25
26. 26 Built a runtime component No runtime component Problem ﹘ Initial version built in-house (waffle-cone) ﹘ Shared our work with the Sorbet team ﹘ Later on switched to sorbet-runtime
27. 27 Built a gem RBI generator All constants must resolve Problem ﹘ Initial version built on YARD ﹘ Decided that structure of constants more important ﹘ Built a runtime reflection based tool ﹘ Open sourced as tapioca
28. 28 Built Rubocop rules Some Ruby constructs are not supported Problem ﹘ Initial rules bundled with waffle-cone ﹘ Extracted out to rubocop-sorbet ﹘ Open sourced
29. 29 Built DSL plugins for Sorbet Metaprogramming Problem ﹘ Based on simple class method name matching ﹘ Can run Ruby scripts to generate interface ﹘ Contributed to Sorbet, documented ﹘ Slow and error-prone
30. 30 RBI generator for models Rails support Problem ﹘ Rake task to generate RBI files for AR models ﹘ Based on sorbet-rails ﹘ Planning switch to sorbet-rails
31. 31 Results 03
32. Strictness levels of non-test files 32
33. Percentage of checked calls 33
34. Developer invocations of type check 34
35. Evolution of method signatures 35
36. Testimonials Likes 36 “We get quicker feedback than tests or CI”
37. Testimonials Likes 37 “Allowed us to write less tests”
38. Testimonials Likes 38 “Both static and runtime type checkers caught errors not caught by tests alone”
39. Testimonials Likes 39 “Improves code quality, encourages better code design”
40. Testimonials Likes 40 “Evergreen documentation, makes onboarding easier”
41. Testimonials Dislikes 41 “Syntax is verbose, it is not DRY”
42. Testimonials Dislikes 42 “Hard to add types to existing code”
43. Testimonials Dislikes 43 “Rails and metaprogramming support is not complete yet”
44. 44 Pitfalls 04
45. 45 Metaprogramming support ﹘ If you use a lot of DSLs, you will need to generate RBI files for them. ﹘ Limited ability to extend Sorbet to understand more syntax. DSL plugins too slow. Pitfall 1
46. 46 Some missing stdlib signatures ﹘ Stdlib/core method signatures are maintained by the Sorbet team. ﹘ No full coverage, so you might get some errors for perfectly valid Ruby code. ﹘ Contribute missing signatures back to Sorbet. Pitfall 2
47. 47 No constants via inheritance class Foo Bar = 42 end class Baz < Foo end Baz::Bar # error: Unable to resolve constant Bar Foo::Bar # ok Pitfall 3
48. 48 No dynamic superclass/mixin def superclass Class.new end def mixin Module.new end class Baz < superclass # error: ^ Superclasses must only contain constant literals include mixin # error: ^ include must only contain constant literals end Pitfall 4
49. 49 Runtime type checking overhead ﹘ Checking types at runtime adds ~7% overhead. ﹘ Not a problem for dev and test. ﹘ Might not want it for production. Pitfall 5
50. 50 How to get started 05
51. 51 Sorbet Playground ﹘ Play around at https://sorbet.run to get familiar ﹘ Read the docs at https://sorbet.org/docs/ Step 1
52. 52 Add Sorbet to your project ﹘ Add sorbet, sorbet-runtime to your Gemfile ﹘ Run bundle exec srb init Step 2
53. 53 Add Sorbet to your project ﹘ Add sorbet, sorbet-runtime and tapioca to your Gemfile ﹘ Run bundle exec tapioca init ﹘ Run bundle exec tapioca sync Step 2 (alt)
54. 54 Start by typing new code ﹘ Easier to type when adding new code. ﹘ Add types to existing code when it is easy and convenient. ﹘ Use rubocop-sorbet to add template signatures to existing code in bulk Step 3
55. 55 Lean on gradual typing ﹘ You can type as much or as little as you want. ﹘ Start small, increase coverage slowly. ﹘ Don’t break other people’s workflows. Step 4
56. 56 Don’t overtype ﹘ It is OK to use simpler signatures ﹘ There is no harm in using T.untyped when needed. ﹘ Your colleagues should not need a PhD in type theory to make code changes. Step 5
57. 57 Track your progress ﹘ Sorbet metrics via --metrics-file flag ﹘ Easy to parse JSON format ﹘ Set up a nightly task and dashboard to track progress Step 6
58. Thank you Don’t forget to fasten your seatbelts! Reach out to me Twitter: @paracycle Github: @paracycle Join us at the Shopify booth!