Cop ideas

[pocke]

Feel free to comment cop ideas with type.

• Prefer find_each over each
  • We already have Rails/FindEach
• Check method executes SQL usage in view.
  • AR::Base.where is not allowed in view
  • Detect method call that returns AR::Relation
• Check bool type argument receives type that is always truthy or falsy.
  • e.g. after_update :foo, if: -> { 1 + 1 }
  • The if's block requires bool type, but 1 + 1 is always truthy.
• Prefer Hash#dig over Hash#[]
  • New cop for Hash#dig rubocop/rubocop#5332
• Improve Rails/SaveBang
• find_by with bang or conditional https://github.com/rubocop-hq/rubocop-rails/issues/167
• Detect unreachable code with bot type
• Rails/DynamicFindBy without false positives
• truthy type in conditional
• Replacement of Style/BracesAroundHashParameters
  • ref: [Fix #7641] Remove Style/BracesAroundHashParameters cop rubocop/rubocop#7643
  • Maybe we can provide a cop for methods that receive both of keyword arguments and a hash.
• Method aliases
  • find vs detect, map vs collect, etc...
• Replace String#first and comparison with String#start_with?.
  • Cop ideas #2 (comment)
  • It is faster.
  • String#frist is added by ActiveSupport
• AR::Relation#pluck vs AR::Relation#select for sub-query
  • rel.where(id: rel2.pluck(:id))
  • We may be able to reduce query with replacing pluck with select, but it depends on context.
• send with public method name
  • foo.send(:foo_public_method) should be foo.foo_public_method
• str[/substr/]should be str['substr']
  • Maybe typing is overkill?
• Style/HashTransformValues with not-hash iteration
  • Model.pluck(:id, :val).map { |id, val| [id, foo(val)] }.to_h

---

I already search the following sources to find cop ideas.

• Pull Request comments from a Rails application in our company.
• rubocop-rails's issues
• Reading real-world Rails application's pull requests.
  • https://pocke.hatenablog.com/entry/2020/02/05/195545
• Read OSS Rails Application
  • GitLab, Redmine, etc

[koic]

This comment is inspired by the following commit in the rails/rails repository.
rails/rails@051e349

Performance/StartWith cop would be extended with the following example if RuboCop can detect a receiver type is the String type.

# bad
receiver.first == 'str'

# good
receiver.start_with?('str')

https://github.com/rubocop-hq/rubocop-performance/blob/master/lib/rubocop/cop/performance/start_with.rb

[pocke]

Thanks for your comment, @koic !

I'll add your idea to the checklist.

By the way, I guess your example code does not work well because String#first returns the first character, but it compares with 'str' in your example.
Probably it should be receiver.first == 's'.

And I confirmed String#first is added by ActiveSupport.

Thanks!

[yahonda]

Let me follow up rubocop/rubocop-minitest#68 (comment) here.

_ method is only defined by Minitest::Spec::DSL::InstanceMethods but rubocop-minitest is not able to handle the class of this method. I'm wondering if RuboCop knows the type it can skip auto-corrections.

cc @koic

[koic]

I think Style/HashEachMethods cop can be strictly detected depending on the receiver type.
rubocop/rubocop#7832

values.each { |k, v| do_something(k, v) }

[koic]

It would be useful to be able to know a full qualified class name that omit the namespace as follows:

module Gem
  def self.foo
    raise Exception
  end
end

Gem.foo #=> Gem::Exception

cf. rubocop/rubocop#7846

[koic]

Performance/AncestorsInclude cop.
rubocop/rubocop-performance#149

[koic]

It seems possible to detect without false positive by using receiver type (AR mode or not).
rubocop/rubocop-rails#149

[yahonda]

I'm wondering if warnings via ruby/ruby#4070 can be detected by RuboCop or RuboCop with type.

# frozen_string_literal: true

# bad
Struct.new(:a).new(a: 1)

foo = Struct.new(:x)
foo.new(x: 1)

# good
Struct.new(:b).new({ b: 1 })

bar = Struct.new(:y)
bar.new({ y: 1 })

[koic]

Type information is required to determine whether the receiver has to_time method.
rubocop/rubocop-rails#288