All About RuboCop (RubyKaigi 2018)

Slide deck from my talk at RubyKaigi 2018 in Sendai.

Transcript

1. Hello!
   

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2. Божидар
   

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4. Bozhidar
   

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5. Божo
   

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6. Bozho
   cool
   

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7. Bozo
   not
   cool
   

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8. Bozho is not a bozo!
   

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9. Bozho is not a bozo!
   (at least he claims so)
   

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10. Bug
    cool
    

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11. (The RuboCop Guy)
    

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12. Sofia, Bulgaria
    Sofia, Bulgaria
    

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14. Grigor Dimitrov vs Kei Nishikori
    

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16. Lukanka
    

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17. Bulgarian Cheese
    

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18. Rakia
    Connecting People
    

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19. Shopska Salad
    (use only with Rakia)
    

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21. bbatsov
    

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22. Ruby & Rails
    style guides
    

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27. First time in Japan!!!
    

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34. All
    About
    RuboCop
    by Bozhidar Batsov
    (a.k.a. bug)
    

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35. Writing Lint
    for
    Ruby
    by Masataka Kuwabara
    (a.k.a. Pocke)
    http://rubykaigi.org/2017/presentations/p_ck_.html
    

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36. Improve Ruby
    coding style
    rules and Lint
    by Koichi Ito
    http://rubykaigi.org/2018/presentations/koic.html#jun01
    

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37. Something
    About
    RuboCop
    by Bozhidar Batsov
    (a.k.a. bug)
    

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38. RuboCop in a
    Nutshell
    

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39. A Ruby static code analysis
    tool aimed to enforce the
    Ruby Community Style Guide
    

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40. In other words…
    

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41. It keeps your
    codebase consistent
    

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42. It saves you time
    

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43. It advances the Ruby
    language forward
    

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45. 32,608,128
    

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46. Provides an efficient
    way for codebases to be
    updated
    

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47. Disclaimer
    

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48. Lint tools are not a
    replacement for
    common sense
    

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49. Why an entire talk about
    a mere lint tool?
    

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52. Notable Japanese
    Contributors
    • Yuji Nakayama (@yujinakayama)
    
    • Masataka Kuwabara (@pocke)
    
    • Koichi Ito (@koic)
    
    • Yukihiro "Matz" Matsumoto (@matz) ;-)
    

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54. https://github.com/rubocop-jp/issues
    

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55. https://github.com/fortissimo1997/ruby-style-guide
    

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56. 314 open issues
    

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57. 100 volunteers
    

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58. 3.14 issues/person
    

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59. Coincidence?
    

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60. Or providence?
    

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61. A Brief History of Time
    

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62. A Brief History of
    RuboCop
    

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63. 2011
    The Ruby Style Guide
    

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65. May, 2012
    RuboCop 0.0.0
    

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66. May, 2012
    RuboCop 0.0.0
    

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68. Static code analysis
    with regular
    expressions …
    

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70. Nov, 2012
    Along Came Jonas
    

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73. Spring, 2013
    Return of the Jedi
    

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74. Using a proper
    parser!
    

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76. Struggles with Ripper
    

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77. Ripper supported
    only MRI
    

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78. I wanted to build a
    cross-platform tool
    

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79. Ripper had (has?)
    almost no
    documentation
    

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80. Ripper is tied to the
    underlying Ruby
    runtime
    

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81. …which means you can’t
    parse code as Ruby 2.3
    while running Ruby 2.5
    

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82. Ripper has a very hard
    to work with AST
    representation
    

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83. pry(main)> Ripper.sexp('alias :some :test')
    => [:program,
    [[:alias,
    [:symbol_literal, [:symbol, [:@ident, "some", [1, 7]]]],
    [:symbol_literal, [:symbol, [:@ident, "test", [1, 13]]]]]]]
    

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84. each(:method_add_arg, sexp) do |s|
    next if s[1][0] != :call
    receiver = s[1][1][1]
    method_name = s[1][3][1]
    if receiver && receiver[1] == 'Array' &&
    method_name == 'new' && s[2] == [:arg_paren, nil]
    offences.delete(Offence.new(:convention,
    receiver[2].lineno,
    ERROR_MESSAGE))
    add_offence(:convention,
    receiver[2].lineno,
    ERROR_MESSAGE)
    end
    end
    

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85. And many quirks…
    

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86. pry(main)> Ripper.lex(':one')
    => [[[1, 0], :on_symbeg, ":"], [[1, 1], :on_ident,
    "one"]]
    pry(main)> Ripper.lex(':alias')
    => [[[1, 0], :on_symbeg, ":"], [[1, 1], :on_kw,
    "alias"]]
    

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87. pry(main)> Ripper.lex('def alias(arg)')

    => [[[1, 0], :on_kw, "def"],

    [[1, 3], :on_sp, " "],

    [[1, 4], :on_kw, "alias"],

    [[1, 9], :on_lparen, "("],

    [[1, 10], :on_ident, “arg"],

    [[1, 13], :on_rparen, ")"]]
    pry(main)> Ripper.lex('def aliass(arg)')

    => [[[1, 0], :on_kw, "def"],

    [[1, 3], :on_sp, " "],

    [[1, 4], :on_ident, "aliass"],

    [[1, 10], :on_lparen, "("],

    [[1, 11], :on_ident, "arg"],

    [[1, 14], :on_rparen, ")"]]
    

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88. Which no one really
    considered
    problematic…
    

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91. Parser: A New Hope
    

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92. parser is
    cross-platform
    

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93. well documented
    

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94. supports multiple
    parsing targets
    (Ruby 1.9 - 2.5)
    

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96. easy to work with ast
    format
    https://github.com/whitequark/ast
    

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97. p Parser::CurrentRuby.parse("2 + 2")
    # (send
    # (int 2) :+
    # (int 2))
    

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98. AST node source
    location mappings
    

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99. p Parser::CurrentRuby.parse("2 + 2").loc
    # ## @dot=nil,
    # @begin=nil,
    # @end=nil,
    # @selector=#,
    # @expression=#>
    p Parser::CurrentRuby.parse("2 + 2").loc.selector.source
    # "+"
    

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100. $ ruby-parse -L -e "2+2"
     (send
     (int 2) :+
     (int 2))
     2+2
     ~ selector
     ~~~ expression
     (int 2)
     2+2
     ~ expression
     (int 2)
     2+2
     ~ expression
     

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101. powerful code
     rewriting capabilities
     

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103. Struggles with Parser
     

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104. Parser was brand
     new
     

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105. Had no real users
     

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106. And had plenty of
     bugs…
     

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108. Peter Zotov
     (@whitequark)
     

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109. 28th May, 2013
     State of Unity
     

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110. RuboCop 0.8
     

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111. 1st July, 2013
     RuboCop 0.9
     

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112. Formatters
     

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113. Auto-correct
     

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115. Commissioner
     (single parsing run triggers all cops)
     

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116. Results caching
     (rubocop —-cache)
     

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117. Parallel Checks
     (rubocop —-parallel)
     

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118. Pattern Matching
     (regex-style matching for ast nodes)
     

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119. def on_send(node)
     receiver_node, method_name, *arg_nodes = *node
     return unless receiver_node && receiver_node.array_type? &&
     method_name == :* && arg_nodes.first.str_type?
     add_offense(node, location: :selector)
     end
     Style/ArrayJoin (before)
     

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120. Style/ArrayJoin (now)
     def_node_matcher :join_candidate?, '(send $array :* $str)'
     def on_send(node)
     join_candidate?(node) { add_offense(node, location: :selector) }
     end
     

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121. RuboCop Today
     

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122. Started out with no
     configuration at all…
     

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123. Today things are
     infinitely configurable
     

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124. Metrics/LineLength:
     Enabled: false
     

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125. Metrics/LineLength:
     Max: 100
     

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126. Style/StringLiterals:
     Enabled: false
     

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127. Style/StringLiterals:
     EnforcedStyle: double_quotes
     

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128. You can set a target
     Ruby/Rails version
     

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129. You can limit cops to
     certain folders with
     Exclude/Include directives
     

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130. You can have different
     settings for the same cops
     in different directories
     

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131. You can inherit
     between configuration
     files
     

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132. You can auto-generate
     an initial configuration
     for your project
     

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133. rubocop —-auto-gen-config
     

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134. And you can read
     about all of this in
     RuboCop’s manual…
     

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135. rubocop.readthedocs.io
     

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136. gry is a smarter
     alternative to the
     built-in command
     https://github.com/pocke/gry
     

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137. RuboCop started as a
     code style checker
     

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138. •Style
     •Lint
     •Layout
     •Naming
     •Security
     •Performance
     •Performance
     •Rails
     •Bundler
     •Metric
     •Gemspec
     

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139. RuboCop is a great
     code formatter
     

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140. rubocop —-only Layout -a
     

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141. RuboCop does some
     linting better than
     ruby -w
     

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142. rubocop —-lint
     

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143. You can extend
     RuboCop with your
     own cops
     

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144. Granite
     (business actions architecture for Rails applications)
     https://toptal.github.io/granite/
     

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145. $ bundle exec rake new_cop[Department/Name]
     

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146. https://rubocop.readthedocs.io/
     en/latest/development/
     

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147. class SimplifyNotEmptyWithAny < Cop
     MSG = 'Use `.any?` and remove the negation part.'.freeze
     def_node_matcher :not_empty_call?, <(send (send (...) :empty?) :!)
     PATTERN
     def on_send(node)
     return unless not_empty_call?(node)
     add_offense(node)
     end
     end
     

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148. RuboCop has a rich
     ecosystem of
     extensions
     

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151. 189!!!
     

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152. Notable Extensions
     • rubocop-rspec
     • guard-rubocop
     • rubocop-sequel
     • rubocop-cask
     

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153. Integration with code
     quality services
     •Code Climate
     •HoundCI
     •SideCI
     •Codacy
     

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154. RuboCop has
     integrations with
     many editors and IDEs
     

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155. Emacs 26.1 is out
     and it’s amazing!
     

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156. (spacemacs)
     

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157. The Road to
     RuboCop 1.0
     

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158. #1 question I get
     asked about RuboCop?
     

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159. When is RuboCop 1.0
     coming?
     

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160. Remove Rails
     (and maybe Performance)
     cops from RuboCop’s core
     

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161. Provide a proper (and
     stable) API for writing
     RuboCop extensions
     

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162. Introducing the brand
     new RuboCop HQ!
     

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163. https://github.com/bbatsov/rubocop
     

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164. https://github.com/rubocop-hq/rubocop
     

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165. RuboCop HQ
     •RuboCop
     •RuboCop JP
     •RuboCop RSpec/Rails/Performance
     •guard-rubocop, etc
     •Ruby & Rails Style Guides
     •Libraries extracted from RuboCop (e.g. node
     extensions, node pattern matching, etc)
     

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166. Review the config of all
     cops and come up with
     the best defaults
     

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167. Ideally each default
     should be backed by
     solid data/rationale
     

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168. Adjust the list of
     enabled by default cops
     

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169. Come up with a less painful
     process for dealing with new
     cops and configuration changes
     

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170. mry makes RuboCop
     upgrades less painful
     https://github.com/pocke/mry
     

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171. Agree on what’s going to
     be constituting breaking
     changes down the road
     

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172. Breaking changes
     •Cop API changes
     •Extension API changes
     •Dropping support for Ruby versions
     •Renaming/removing cops
     •Renaming/changing/removing config values
     

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173. Cop status “New” in
     minor releases
     

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174. Cop status gets changed
     to Enabled/Disabled in
     major releases
     

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175. Extra Cop metadata
     •Version added
     •Version default config changed
     •Version deprecated
     

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176. eslint.org-grade
     manual/website
     

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177. RuboCop.org
     •Easy to navigate & mobile-friendly
     •Published using MkDocs (or similar)
     •Separate User and Developer manual
     •Getter getting started resources (e.g. video tutorials)
     •Improved cop documentation
     

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179. That’s a lot of work!
     

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180. Apes Together Strong!
     

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181. Rubyists Together Strong!
     

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182. Felina
     

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183. Thanks!
     twitter: @bbatsov
     github: @bbatsov
     http//batsov.com
     http://emacsredux.com
     RubyKaigi
     Sendai,
     Japan
     31.05.2018
     

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