Breaking Nil to Fix Bugs - An experimental approach

In Ruby, encountering `nil` is inevitable and often leads to frustrating bugs and NoMethodError exceptions. While `nil` is a crucial part of Ruby's design, it can be the source of elusive and hard-to-diagnose issues in your codebase. This talk explores an unconventional and experimental approach to debugging by "breaking" the nil object.
How will we debug bugs?
- extending the NilClass
- customizing method_missing
- creating methods dynamically with the previous options

This is probably the wrong solution. Don't try this in production. However, we'll find bugs and it will be fun!

Transcript

1. Breaking Nil to fix bugs An experimental approach Enrique Mogollan @mogox Software Engineer - Salesforce Trailhead 1
2. Breaking Nil to fix bugs An experimental approach Enrique Mogollan @mogox Software Engineer - Salesforce Trailhead 2
3. Breaking Nil to fix bugs An experimental approach Enrique Mogollan @mogox Software Engineer - Salesforce Trailhead 3 Do not use it in production!
4. Breaking Nil to fix bugs An experimental approach Enrique Mogollan @mogox Software Engineer - Salesforce Trailhead 4 Do not use it in production!
5. We have the & operator why talk about nil? 5
6. params = { id: 1234, lesson_id: 2024 } def mark_lesson_complete(params) user = User.find_by(params[:user_id]) user&.complete(params[:lesson_id]) end mark_lesson_complete(params) 6 Intro
7. What is the issue? 1. Code will raise error Id “not found” 2. Invalid parameters on User.find_by 3.Wrong implementation of `complete` method 7 Intro
8. What is the issue? 1. Code will raise error Id “not found” 2. Invalid parameters on User.find_by 3.Wrong implementation of `complete` method 8 Intro
9. 9 params = { id: 1234, lesson_id: 2024 } def mark_lesson_complete(params) user = User.find_by(params[:user_id]) user&.complete(params[:lesson_id]) end mark_lesson_complete(params) # Result: User with ID 1 was marked as complete (user<id: 1>).complete(lesson_id: 2024) Intro
10. 10 params[:user_id] = nil 🤦 Intro
11. 11 user = User.find_by(nil) == user = User.first 🤦 Intro
12. 12 Unexpected Consequences: • User.find_by(nil) returns a user • The false safety of & Intro
13. 13 Intro That’s why talk about nil!
14. Breaking Nil to fix bugs An experimental approach Enrique Mogollan @mogox Software Engineer - Salesforce Trailhead 14 Do not use it in production!
15. 15 About Enrique: • From San Miguel de Allende, in the ❤ of Mexico • CS in Mexico and MS CS in Valencia, Spain • Spanish is my first language, ruby is my favorite Intro
16. 16 • Programming Languages Vs Languages Section 1.
17. 17 Love is all you need - Words that express “love” in English: LOVE Section 1.
18. 18 Love is all you need - Words that express “love” in English: LOVE Section 1.
19. 19 In Spanish: we have more love - Amar - Querer - Encariñarse - Estimar - Apreciar - Cariño - Adorar Section 1.
20. 20 Love is all you need We use context to express meaning: - I love you as a friend. - I Love Rock n' Roll - Love Bites Section 1.
21. 21 Describe ideas with more context or create new concepts MINASWAN Section 1.
22. 22 Describe ideas with more context or create new concepts MINASWAN Section 1. Matz is nice and so we are nice We [the ruby community] are driven by love and passion - Matz during Rubyconf 2024
23. 23 params = { id: 1234, lesson_id: 2024 } def mark_lesson_complete(params) user = User.find_by(params[:user_id]) user&.complete(params[:lesson_id]) end mark_lesson_complete(params) What is the missing concept? Section 1.
24. 24 There is a description we need for nil parameters Let’s do a experiment Section 1.
25. 25 Experiment No. 1 Let’s do a experiment data = nil data.help # =====> Trying to call method `help` # from a nil instance” experiment_1.rb:28
26. 26 Experiment No. 1 Let’s do a experiment data = nil data.help(user_id: 123, lesson_id: 456) # =====> Trying to call method `help` # from a nil instance” experiment_1.rb:28
27. 27 Experiment No. 1 class NilClass def method_missing(method, *args, &block) error_message = "===> Trying to call method `#{method}`" puts error_message puts caller.take(5).join("\n") puts "=====> args: #{args}" if args&.size > 0 puts "=====> block: #{block.source}" if block puts "=====> NoMethodError not raised" end def respond_to_missing?(method_name, include_private) false end end
28. 28 Experiment No. 1 Let’s run the experiment Experiment 1
29. 29 Experiment No. 1 [1] pry(main)> ls nil NilClass#methods: & =~ inspect pretty_print_cycle to_a to_f to_i to_s === ^ nil? rationalize to_c to_h to_r | NilClass # nil is a singleton
30. 30 Experiment No. 1 Monkey Patched NilClass [1] pry(main)> ls nil NilClass#methods: & =~ inspect nil? rationalize to_ary to_f to_hash to_r | === ^ method_missing pretty_print_cycle to_a to_c to_h to_i to_s
31. 31 Experiment No. 1 We know a bit more about the context - Where are we calling nil - What parameters & block - Not configurable, always on - We probably bypass other nil
32. What can we break next? 32 Section 2
33. In languages there are words that mean completely different things but they are spelled the same In English they are called: Homographs 33 Section 2
34. An example is: I left my phone on the left side of the table 34 Section 2
35. Same word different meaning. In general this can happen: in the same language across countries, or across regions. 35 Section 2
36. 36 Homographs =~ Polymorphism Section 3
37. Caña - In Mexico = Sugarcane 37 Section 2
38. Caña - In Spain Sugarcane Or Beer 🍺 38 Section 2
39. Chat with my manager in Spain 39 Section 2
40. Chat with my manager in Spain 🍺 🍺 “A darle caña” 40 Section 2
41. “A darle caña” Beers for everyone?! 41 Section 2
42. Works in my local 42 Section 2
43. Doesn’t work in staging 43 Section 2
44. Doesn’t work in staging 44 undefined method `zero?’ for an instance of String (NoMethodError) Section 2
45. My code doesn’t work in staging But it’s kind of urgent, so I test with staging2 45 Section 2
46. My code doesn’t work in staging But it’s kind of urgent, so I test with staging2 And it works! 46 Section 2
47. They are the same kind of environments Same network Same code base 47 Section 2
48. Login, into staging (#1) run the code and see watch it fail 48 Section 2
49. Debug time: 49 class LoginHelper def login(organization_id, user_id, user_profile) profile = user_profile.login_data client.user_info(organization_id, user_id, profile) end def client @client ||= HttpHelper.new end end
50. Debug time (App code): 50 class Client::HttpHelper def user_info(organization_id, user_id, profile) params = { organization_id:, user_id:, profile: } request_auth(LOGIN_URL, timeout, ) end private def timeout if development? DEFAULT_TIMEOUT else ENV['TIMEOUT_SECONDS'].to_s end end def development? @host != PRODUCTION && @host != STAGING end def request_auth(url, timeout, params) uri = URI.parse(url) Net::HTTP.start(uri.hostname, uri.port, read_timeout: timeout, use_ssl: true) do |http| request = Net::HTTP::Post.new(uri.request_uri) request['authorization'] = "#{jwt}" http.request(request) # HERE IS THE ISSUE end rescue StandardError => re re.backtrace.join("\n") raise re end end
51. Debug time (Net::Http Code): 51 module Net class HTTP < Protocol def request(req, body = nil, &block) # :yield: +response+ unless started? start { req['connection'] ||= 'close' return request(req, body, &block) } end if proxy_user() req.proxy_basic_auth proxy_user(), proxy_pass() unless use_ssl? end req.set_body_internal body res = transport_request(req, &block) if sspi_auth?(res) sspi_auth(req) res = transport_request(req, &block) end res end def transport_request(req) begin begin_transport req res = catch(:response) { ... res = HTTPResponse.read_new(@socket) ... } rescue Net::OpenTimeout raise rescue Net::ReadTimeout, IOError, EOFError, .... end ... rescue => exception D "Conn close because of error #{exception}" @socket.close if @socket raise exception end end def begin_transport(req) if @socket.closed? connect ... end def connect D "opening connection to #{conn_addr}:#{conn_port}..." s = Timeout.timeout(@open_timeout, Net::OpenTimeout) { begin TCPSocket.open(conn_addr, conn_port, @local_host, @local_port) rescue => e raise e, "Failed to open TCP connection to “... end end end end class Timeout def timeout(sec, klass = nil, message = nil) return yield(sec) if sec == nil or sec.zero? ... end end
52. Let’s simplify the error: 52 Timeout.timeout(timeout, Timeout::Error, msg) do # more code end
53. Let’s simplify the error: 53 Timeout.timeout(timeout, Timeout::Error, msg) do # more code end `timeout': undefined method `zero?' for an instance of String (NoMethodError)
54. Let’s simplify the error: 54 def development? false # hostname == (“staging|prod”) end timeout = development? ? DEFAULT_TIMEOUT : ENV[‘TIMEOUT_SECONDS'].to_s
55. Let’s simplify the error: 55 def development? false # hostname == (“staging|prod”) end timeout = development? ? DEFAULT_TIMEOUT : ENV[‘TIMEOUT_SECONDS'].to_s ENV[‘TIMEOUT_SECONDS’] => nil timeout = “”
56. The focus of today 56 nil.to_s => ""
57. The focus of today 57 nil.to_s => "" "".zero? `timeout': undefined method `zero?' for an instance of String (NoMethodError)
58. App Code: • LoginHelper#login • HttpHelper#user_info 58 Net::HTTP •Net::HTTP#request • #transport request • #begin_transport • #connect • Timeout#timeout Section 2
59. App Code: • LoginHelper#login • HttpHelper#user_info • HttpHelper#timeout 59 Net::HTTP •Net::HTTP#request • #transport request • #begin_transport • #connect • Timeout#timeout Section 2
60. 60 Experiment No. 1 class NilClass # EXPERIMENT 1 def method_missing(method, *args, &block) error_message = "===> Trying to call method `#{method}`" puts error_message puts caller.take(5).join("\n") puts "=====> args: #{args}" if args&.size > 0 puts "=====> block: #{block.source}" if block puts "=====> NoMethodError not raised" end def respond_to_missing?(method_name, include_private) false end end
61. 61 Experiment No. 2 module NilTracker def method_missing(method, *args, &block) ... end def respond_to_missing?(method_name, false) false end end
62. 62 Experiment No. 2 module NilTracker def method_missing(method, *args, &block) ... end def respond_to_missing?(method_name, false) false end end nil.extend(NilTracker)
63. 63 Experiment No. 2 module NilTracker def method_missing(method, *args, &block) ... if raise_exception? puts "====> Raising NoMethodError <=====" raise NoMethodError.new(error_message) else puts "=====> NoMethodError ignored" puts "================================\n\n" end end def raise_exception? tracker_helper.raise_exception end end
64. 64 Experiment No. 2 class TrackerHelper include Singleton attr_accessor :raise_exception end
65. 65 Let’s run the experiment Experiment 2 Experiment No. 2
66. 66 Experiment No. 2 [1] pry(main)> ls nil NilTracker#methods: method_missing raise_exception= raise_exception? to_ary to_hash to_str tracker_helper NilClass#methods: & =~ inspect pretty_print_cycle to_a to_f to_i to_s === ^ nil? rationalize to_c to_h to_r |
67. 67 Language Evolution Section 3
68. 68 Language Evolution Section 3 Like English, Spanish, Italian
69. 69 For example: Section 3 • self-portrait • selfie
70. 70 For example: Section 3 • self-portrait • selfie In Spanish: • auto-retrato • selfie
71. 71 Ruby Language evolution Section 3 Ruby 1.9 (December 25, 2007) • Hash#fetch Ruby 2.3 (December 25, 2015) • & safe navigation operator • Hash#dig
72. 72 Story time - Slow week at work Section 3 - Rake task => development environment - Data Microservice => Web App - 10 minutes later
73. 73 10 min later Section 3 - I login, go to the /info page - It’s broken
74. 74 10 min later Section 3 - I login, go to the /info page - It’s broken “ActionView::Template::Error" "(undefined method `[]' for nil)"
75. 75 10 min later Section 3 My good old friend nil, we meet again. “ActionView::Template::Error" "(undefined method `[]' for nil)"
76. 76 What did I break? Section 3 - Localization task failed. - The tool to report the failure failed
77. 77 How is the web app broken because of tags? Section 3 # Inside a view %span= @tags[:level][:label] # Inside a controller @tags = data[:tags] @labels = data[:labels]
78. 78 How is the web app broken because of tags? Section 3 # Inside a view %span= @tags.dig(:level,:label) # Inside a controller @tags = data.fetch(:tags,{}) @labels = data.fetch(:labels,{})
79. 79 What can we do about this? Section 3 module NilTracker def method_missing(method, *args, &block) nil_tracker.log(method, caller.take(5), args, block) end end
80. 80 What can we do about this? Section 3 def log(method, caller_lines, *args, &block) error_message = "=====> Trying to call method ...” puts error_message puts "=====> Caller: (stacktrace)" puts caller.take(5).join("\n") puts "=====> args: #{args}" if args&.size > 0 puts "=====> block: #{block.source}" if block create_method(method, args, block) store_method_info(method, caller_lines, args, block) end
81. Let’s wrap all this in a Gem 81 What would be a good name for Gem that - The gem defeats nil by creating dynamically methods - It’s like a self healing super power for the Ruby apps
82. Let’s wrap all this in a Gem 82 What would be a good name for Gem that - The gem defeats nil by creating dynamically methods - It’s like a self healing super power for the Ruby apps Wolvernil
83. 83 Wolvernil Section 3 def create_method(method, *args, &block) return if methods_list[method] Wolvernil.define_method(method) do |*args, &block| Puts "---> Calling a method #{method} in the nil class" end end def store_method_info(method, caller_lines, *args, &block) methods_list[method] = { args:, block:, caller_lines:, timestamp: Time.now } end
84. 84 Experiment No. 3 Let’s run the experiment - Wolvernil Experiment 3
85. 85 Experiment No. 3 Let’s run the experiment - Wolvernil [1] pry(#<RubyConf>)> ls nil Wolvernil#methods: []= help1 help2 help3 ]permitted? raise_exception= call method_missing process_wait raise_exception? to_ary to_hash to_str NilClass#methods: & =~ inspect pretty_print_cycle to_a to_f to_i to_s === ^ nil? rationalize to_c to_h to_r |
86. Additional data: 86 { :help3 => { # method name :args => [ [0] [true], [1] #<Proc:0x000000011bd838f0 experiment_3.rb:121> ], :block => “{ puts \"Help is on the way\" }\n", :caller_lines => "experiment_3.rb:121:in `break_nil'\nexperiment_3.rb:129:in `<main>'", :timestamp => 2024-11-10 16:34:43.744649 -0800 } }
87. 87 Experiment No. 3 Wolvernil Creates methods in at the error level What if?
88. 88 Experiment No. 3 Wolvernil Instead of create methods We fix existing methods
89. 89 Experiment No. 3 Wolvernil With Magic!
90. 90 Experiment No. 3 Wolvernil With AI! (Claude -from Anthropic- for example)
91. params = { id: 1234, lesson_id: 2024 } def mark_lesson_complete(params) user = User.find_by(params[:user_id]) user&.complete(params[:lesson_id]) end mark_lesson_complete(params) 91 Intro
92. 92 Experiment No. 3 Wolvernil + AI def mark_lesson_complete(user_id:, lesson_id:) user = User.find_by(id: user_id) user&.complete(lesson_id) end # Called with: mark_lesson_complete( user_id: params[:user_id], lesson_id: params[:lesson_id] )
93. 93 Experiment No. 3 Wolvernil Don’t use it in production… Yet!
94. 94 Other tooling available | Production ready Section 3 Dry::Struct Sorbet
95. 95 Section 3 Dry::Struct require 'dry-struct' class User < Dry::Struct attribute :name, Types::String.optional attribute :age, Types::Coercible::Integer end user = User.new(name: nil, age: '21') user.name # nil user.age # 21
96. extend T::Sig sig {params(x: String).void} def must_be_given_string(x) puts "Got string: #{x}" end sig {params(x: T.nilable(String)).void} def foo(x) must_be_given_string(x) # error: Expected `String` but found `T.nilable(String)` for argument `x` if x must_be_given_string(x) # ok end end 96 Section 3 Sorbet
97. 97 Technical Summary: Summary • Monkey Patch on the NilClass • nil.extend(NilTracker)
98. 98 Technical Summary: Summary •Gem: Wolvernil •Tools to prevent nil errors in production
99. 99 Final Notes: Section 3 Missing concepts Polymorphism and Evolution
100. 100 Resources Section 3 1. Nothing is something: https://www.youtube.com/watch?v=OMPfEXIlTVE&ab_channel=Confreaks 2. The case of the missing method: https://www.youtube.com/watch?v=mn2D_k-X-es&ab_channel=Confreaks 3. Sorbet - https://sorbet.org/ 4. Dry::Struct - https://dry-rb.org/gems/dry-struct/1.0/recipes/ 5. Experimental approach: https://github.com/mogox/wolvernil 6. The rest of the code: https://github.com/mogox/talk_breaking_nil 7. Sugar cane picture (permission from the photographer granted for this presentation only): https://www.karemrodriguez.com/zafra-in-veracruz Contact info: @mogox
101. 101 Thank you!!!!! Gracias! Section 3
102. 102 Section 3
103. 103 Next in the story! Questions?! Wolverhash