[Rails] Introduction of Rubocop by beginners


Rubocop is a Ruby static code analysis tool. ruby-style-guide will point out the corrections and improvements in the source code.

Indentation deviations, unnecessary spaces, line breaks, etc. are automatically corrected by typing a specific command, so you can format the code so that it is easy for you to read as well as for others. can.



gem 'rubocop', require: false


bundle install

Try using


bundle exec rubocop

When run, you will get output similar to the following: スクリーンショット 2020-07-10 8.06.47.png

These are the fixes detected by Rubocop. However, if you follow all the default rules, you'll have too much to worry about when writing code, so you can set the rules you and your team allow.

Customize settings

In the application directory Create a file called .rubocop.yml and write the settings in it.


  #Set directories to exclude. For example, schema and migration files are rarely rewritten, so they are not detected.
    - bin/*
    - db/schema.rb
    - node_modules/**/*
    - db/migrate/*
    - vendor/**/*
  #Check for Rails
    enabled: true

# "Missing top-level class documentation comment."Disable
  Enabled: false

# "Prefer single-quoted strings when you don't need string interpolation or special symbols."Disable
  Enabled: false

# "Line is too long"Disable
  Enabled: false

#'frozen_string_literal: true'Disable
  Enabled: false

Various settings such as are possible. I will play around with it by referring to Default settings.

After setting, again


bundle exec rubocop
スクリーンショット 2020-07-10 8.29.43.png Then, you can see that 72files is 56files, which is less than before.

To fix


bundle exec rubocop --auto-gen-config

A file called .rubocop.todo.yml is automatically generated. As a result, all corrections will be temporarily invalidated. If you run rubocop here, there will be no corrections.


# Offense count: 1
# Cop supports --auto-correct.
# Configuration parameters: TreatCommentsAsGroupSeparators, ConsiderPunctuation, Include.
# Include: **/*.gemfile, **/Gemfile, **/gems.rb
    - 'Gemfile'

As an example, there is the above description. If you delete this description, the invalidated corrections of the relevant part will be restored. I will fix it immediately, but

Cop supports --auto-correct.

 If there is a description, Rubocop will automatically correct it with the following command.

#### **`Terminal`**

bundle exec rubocop -a

This time, the gem description in the Gemfile is not in alphabetical order, but it is rearranged in the correct order.


  1. Install gem and customize the settings to `` `.rubocop.yml```
  2. Execute `bundle exec rubocop --auto-gen-config``` and Generate `.rubocop.todo.yml```.
  3. Delete and correct one description in .rubocop.todo.yml Repeat 4.3.

In the actual field, it is automated and it seems that you will not fix it yourself, I'm still a beginner, so I'll improve each one and check the rules. I try to be an engineer who can write easy-to-read code from the beginning.

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