Custom Rails Generators in RubyEvents (WNB.rb Edition)

Transcript

1. Custom Rails Generators in RubyEvents Rachael Wright-Munn (@ChaelCodes)
2. Marco Roth Adrien Poly Hans Schnedlitz Rachael (Me) 󰎤 󰏃 󰎈 󰑔 RubyEvents Team
3. We index Events
4. Using Yaml!
5. Inherited architectural decision Why do you use yaml? Allows us to review events Allows any developer to update events Historical Record
6. Data changes require commits.
7. I needed a tool that would take unstructured data and turn it into commits.
8. GitHub Copilot
9. Spoiler Alert - This will work!
10. Invented Keys Problem: Used old/deprecated format AI is super-smart, but it doesn't know our system. Useful keys like `canceled` or `original_title` neglected No # TODO comments Spends lots of tokens understanding examples
11. This is true of contributors too!
12. 175+ Contributors!
13. Invented Typo Keys Problem: Used old/deprecated format Contributors are super-smart, but they don't know our system. Useful keys like `canceled` or `original_title` neglected No # TODO comments Spends lots of tokens time understanding examples
14. How do I teach them about RubyEvents?
15. How to teach them about RubyEvents? MCP Skill + CLI AI-native SDK that fetches context for a model Markdown documentation discoverable by AI paired with a normal CLI Preferred by AI Usable without tokens Context consumed in describing MCP tool Documentation and Context in Skill Context = Tokens ($) Validations in Skill
16. SKILL + CLI!
17. Why Generators? Familiar pattern for Rails devs Arguments and options Templating and file generation Documentation Testing File conflicts
18. I want to make a generator!
19. Generate a Generator
20. cfp_generator
21. USAGE
22. cfp_generator_test
23. How does it name things?
24. cfp_generator
25. application_name = rubyevents class_name = CFP edit_helper = edit_cfp_url(@cfp) NamedBase Requires one argument file_path = cfp fixture_file_name = cfps human_name = CFP i18n_scope = cfp index_helper = cfps
26. NamedBase Requires one argument
27. model_resource_name = cfp new_helper = new_cfp_url plural_file_name = cfps NamedBase Requires one argument plural_name = cfps plural_route_name = cfps plural_table_name = cfps redirect_resource_name = @cfp show_helper = cfp_url(@cfp)
28. NamedBase Requires one argument
29. singular_name = cfp singular_route_name = cfp singular_table_name = cfp NamedBase Requires one argument table_name = cfps
30. Let's throw all of that away. :)
31. Rails::Generators::Base
32. Arguments and Options
33. arguments argument :event, type: :string, desc: "event slug" required or default dependent on order bin/rails g cfp rails-world-2026
34. options class_option :event, type: :string, desc: "event-slug" Required, default, or optional Order independent bin/rails g cfp --event rails-world-2026
35. class_option
36. bin/rails g cfp --help
37. Help Documentation
38. Help Documentation
39. Option documentation
40. Help Documentation
41. USAGE
42. USAGE files are great for injecting context.
43. USAGE
44. Humans struggle with reading documentation too…
45. But I didn't even know this existed.
46. Generating Files
47. data/rails-world/rails-world-2026/cfp.yml
48. lib/generators/cfp/templates/cfp.yml.tt
49. lib/generators/cfp/templates/cfp.yml.tt
50. You can customize templates for the default generators.
51. cfp_generator.rb
52. source, destination create_cfp_file
53. cfp_generator.rb
54. cfp_generator.rb
55. cfp_generator.rb
56. cfp_generator.rb
57. Let's run it!
58. bin/rails g cfp
59. We have a working generator!!
60. I mentioned the ongoing meetup CFPs?
61. bin/rails g cfp
62. bin/rails g cfp
63. bin/rails g cfp
64. bin/rails g cfp
65. We trimmed whitespace using <%-
66. We need a test.
67. cfp_generator_test
68. cfp_generator_test
69. bundle exec rails test test/lib/generators/cfp_generator_test.rb
70. cfp_generator_test
71. bundle exec rails test test/lib/generators/cfp_generator_test.rb
72. cfp_generator_test
73. bundle exec rails test test/lib/generators/cfp_generator_test.rb
74. Green dots don't inspire much confidence.
75. tmp/generators/data/rails-world/rails-world-2025/cfp.yml
76. Wait. If it persists, why doesn't it conflict?
77. cfp_generator_test
78. cfp_generator_test
79. cfp_generator.rb
80. cfp_generator_test
81. railties/lib/rails/generators/testing/behavior.rb
82. Wouldn't this break if I had parallel test cases?
83. YEAH. IT'S A TRAP.
84. cfp_generator_test
85. Use Ruby's temp directories and cleanup in teardown.
86. But now I can't see the file.
87. Add a binding.irb
88. tmp/cfp_generator20260824-68187-24qeok/data/rails-world/rails-world-2025/cfp.yml
89. bundle exec rails test test/lib/generators/cfp_generator_test.rb
90. ctrl+c?? quit?
91. < THIS IS A TRAP cfp_generator_test
92. < THIS IS A TRAP cfp_generator_test
93. RAILS_LOG_TO_STDOUT=true bundle exec rails test test/lib/generators/cfp_generator_test.rb
94. RAILS_LOG_TO_STDOUT=true bin/rails test test/lib/generators
95. Testing Generators The generated test is a TRAP Use RAILS_LOG_TO_STDOUT=true to see output Replace destination_root with a tmp directory Don't prepare_destination
96. I have now taught you enough about generators to be dangerous.
97. What about the SKILL?
98. .agents/skills/event-data/SKILL.md
99. .agents/skills/event-data/SKILL.md
100. .agents/skills/event-data/SKILL.md
101. .agents/skills/event-data/SKILL.md
102. How to teach them about RubyEvents? MCP Skill + CLI AI-native SDK that fetches context for a model Markdown documentation discoverable by AI paired with a normal CLI Preferred by AI Usable without tokens Context consumed in describing MCP tool Documentation and Context in Skill Context = Tokens ($) Validations in Skill
103. I said… or MCP, but…
104. What if it were AND MCP?
105. AND MCP
106. The Full Story
107. IT'S A CLI AND MCP!
108. Generator changes are reflected in MCP tools
109. I can test SKILL+CLI vs MCP
110. How'd it go? Method AI - no g AI - g SKILL + CLI MCP Tokens Mistakes
111. GPT 5.4 - No Skill, No Generator, No MCP "Add Rails World 2026, which is described in @ai-test/RAILS_WORLD.md" Use deprecated event_name field (Mistake) Added invalid schedule.yml (Error) Keys in the wrong order (Error) No TODOs (Mistake)
112. How'd it go? Method Tokens Mistakes AI - no g 127,452 ($1.68) 2 Errors, 2 Mistakes AI - g SKILL + CLI MCP
113. GPT 5.4 - No Skill, Generators "Using custom rails generators - add Rails World 2026, which is described in @ai-test/RAILS_WORLD.md" Didn't call validations - missing custom colors (Error) Missing TODOs (Mistake)
114. How'd it go? Method Tokens Mistakes AI - no g 127,452 ($1.68) 2 Errors, 2 Mistakes AI - g 77,246 ($0.84) 1 Error, 1 Mistake SKILL + CLI MCP
115. GPT 5.4 - SKILL, Generators "Using /event-data - add Rails World 2026, which is described in @ai-test/RAILS_WORLD.md" Ran my generator once and then copied and pasted Ran the validations Added deprecated event_name (Mistake) Deleted my TODOs (Mistake)
116. How'd it go? Method Tokens Mistakes AI - no g 127,452 ($1.68) 2 Errors, 2 Mistakes AI - g 77,246 ($0.84) 1 Error, 1 Mistake SKILL + CLI 109,852 ($1.24) 2 Mistakes MCP
117. GPT 5.4 "Using rubyevents MCP tools - add Rails World 2026, which is described in @ai-test/RAILS_WORLD.md" Didn't call validations - missing custom colors (Error) Tweaked everyone's descriptions (Error) Deleted my TODOs (Mistake)
118. How'd it go? Method Tokens Mistakes AI - no g 127,452 ($1.68) 2 Errors, 2 Mistakes AI - g 77,246 ($0.84) 1 Error, 1 Mistake SKILL + CLI 109,852 ($1.24) 2 Mistakes MCP 88,324 ($1.88) 2 Errors, 1 Mistake
119. Fewer tokens - more expensive?
120. GPT 5.4-mini
121. How'd it go? Method Tokens Mistakes AI - no g 95,532 ($0.31) 3 Errors, 1 Mistake AI - g 98,440 ($0.31) 1 Failed Attempt, Forgot to generate talks SKILL + CLI 123,958 ($0.49) 0 MCP 55,707 ($0.18) 0
122. Smaller models with better tools outperformed larger models.
123. rubyonrails.org/ai
124. GPT 5.6 - Luna
125. How'd it go? Method Tokens Mistakes AI - no g 47,073 ($0.03) 0 Errors/Mistakes AI - g 82,601 ($0.10) 0 Errors/Mistakes SKILL + CLI 54,935 ($0.04) 0 Errors/Mistakes MCP 43,278 ($0.03) 0 Errors/Mistakes
126. Build a custom generator! Takeaways Remind your robots to use Rails generators. Use a small model with better tools. Customize existing generator templates! Build for humans too.
127. Humans and AI need help understanding our codebases. Let's build tools for both!
128. Thank you! Chael or Rachael (she/her) @ChaelCodes https://chael.codes/links hello@chael.codes Twitch/YouTube: Sundays at 18:00 UTC