Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

This cop identifies possible cases where Active Record save! or related should be used instead of save because the model might have failed to save and an exception is better than unhandled failure.

This will allow: - update or save calls, assigned to a variable, or used as a condition in an if/unless/case statement. - create calls, assigned to a variable that then has a call to persisted?. - calls if the result is explicitly returned from methods and blocks, or provided as arguments. - calls whose signature doesn't look like an ActiveRecord persistence method.

By default it will also allow implicit returns from methods and blocks. that behavior can be turned off with AllowImplicitReturn: false.

You can permit receivers that are giving false positives with AllowedReceivers: []

Example:

# bad
user.save
user.update(name: 'Joe')
user.find_or_create_by(name: 'Joe')
user.destroy

# good
unless user.save
  # ...
end
user.save!
user.update!(name: 'Joe')
user.find_or_create_by!(name: 'Joe')
user.destroy!

user = User.find_or_create_by(name: 'Joe')
unless user.persisted?
  # ...
end

def save_user
  return user.save
end

Example: AllowImplicitReturn: true (default)

# good
users.each { |u| u.save }

def save_user
  user.save
end

Example: AllowImplicitReturn: false

# bad
users.each { |u| u.save }
def save_user
  user.save
end

# good
users.each { |u| u.save! }

def save_user
  user.save!
end

def save_user
  return user.save
end

Example: AllowedReceivers: ['merchant.customers', 'Service::Mailer']

# bad
merchant.create
customers.builder.save
Mailer.create

module Service::Mailer
  self.create
end

# good
merchant.customers.create
MerchantService.merchant.customers.destroy
Service::Mailer.update(message: 'Message')
::Service::Mailer.update
Services::Service::Mailer.update(message: 'Message')
Service::Mailer::update

This cop identifies possible cases where Active Record save! or related should be used instead of save because the model might have failed to save and an exception is better than unhandled failure.

This will allow: - update or save calls, assigned to a variable, or used as a condition in an if/unless/case statement. - create calls, assigned to a variable that then has a call to persisted?. - calls if the result is explicitly returned from methods and blocks, or provided as arguments. - calls whose signature doesn't look like an ActiveRecord persistence method.

By default it will also allow implicit returns from methods and blocks. that behavior can be turned off with AllowImplicitReturn: false.

You can permit receivers that are giving false positives with AllowedReceivers: []

Example:

# bad
user.save
user.update(name: 'Joe')
user.find_or_create_by(name: 'Joe')
user.destroy

# good
unless user.save
  # ...
end
user.save!
user.update!(name: 'Joe')
user.find_or_create_by!(name: 'Joe')
user.destroy!

user = User.find_or_create_by(name: 'Joe')
unless user.persisted?
  # ...
end

def save_user
  return user.save
end

Example: AllowImplicitReturn: true (default)

# good
users.each { |u| u.save }

def save_user
  user.save
end

Example: AllowImplicitReturn: false

# bad
users.each { |u| u.save }
def save_user
  user.save
end

# good
users.each { |u| u.save! }

def save_user
  user.save!
end

def save_user
  return user.save
end

Example: AllowedReceivers: ['merchant.customers', 'Service::Mailer']

# bad
merchant.create
customers.builder.save
Mailer.create

module Service::Mailer
  self.create
end

# good
merchant.customers.create
MerchantService.merchant.customers.destroy
Service::Mailer.update(message: 'Message')
::Service::Mailer.update
Services::Service::Mailer.update(message: 'Message')
Service::Mailer::update

This cop checks for the use of methods which skip validations which are listed in https://guides.rubyonrails.org/active_record_validations.html#skipping-validations

Methods may be ignored from this rule by configuring a Whitelist.

Example:

# bad
Article.first.decrement!(:view_count)
DiscussionBoard.decrement_counter(:post_count, 5)
Article.first.increment!(:view_count)
DiscussionBoard.increment_counter(:post_count, 5)
person.toggle :active
product.touch
Billing.update_all("category = 'authorized', author = 'David'")
user.update_attribute(:website, 'example.com')
user.update_columns(last_request_at: Time.current)
Post.update_counters 5, comment_count: -1, action_count: 1

# good
user.update(website: 'example.com')
FileUtils.touch('file')

Example: Whitelist: ["touch"]

# bad
DiscussionBoard.decrement_counter(:post_count, 5)
DiscussionBoard.increment_counter(:post_count, 5)
person.toggle :active

# good
user.touch