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

Checks for a newline after the final magic comment.

Example:

# good
# frozen_string_literal: true

# Some documentation for Person
class Person
  # Some code
end

# bad
# frozen_string_literal: true
# Some documentation for Person
class Person
  # Some code
end

This cop checks for spaces between -> and opening parameter brace in lambda literals.

Example: EnforcedStyle: requirenospace (default)

# bad
  a = -> (x, y) { x + y }

  # good
  a = ->(x, y) { x + y }

Example: EnforcedStyle: require_space

# bad
  a = ->(x, y) { x + y }

  # good
  a = -> (x, y) { x + y }

Checks for a newline after the final magic comment.

Example:

# good
# frozen_string_literal: true

# Some documentation for Person
class Person
  # Some code
end

# bad
# frozen_string_literal: true
# Some documentation for Person
class Person
  # Some code
end

Checks that required_ruby_version of gemspec and TargetRubyVersion of .rubocop.yml are equal. Thereby, RuboCop to perform static analysis working on the version required by gemspec.

Example:

# When `TargetRubyVersion` of .rubocop.yml is `2.3`.

# bad
Gem::Specification.new do |spec|
  spec.required_ruby_version = '>= 2.2.0'
end

# bad
Gem::Specification.new do |spec|
  spec.required_ruby_version = '>= 2.4.0'
end

# good
Gem::Specification.new do |spec|
  spec.required_ruby_version = '>= 2.3.0'
end

# good
Gem::Specification.new do |spec|
  spec.required_ruby_version = '>= 2.3'
end

# good
Gem::Specification.new do |spec|
  spec.required_ruby_version = ['>= 2.3.0', '< 2.5.0']
end

This cop checks that your heredocs are using meaningful delimiters. By default it disallows END and EO*, and can be configured through blacklisting additional delimiters.

Example:

# good
<<-SQL
  SELECT * FROM foo
SQL

# bad
<<-END
  SELECT * FROM foo
END

# bad
<<-EOS
  SELECT * FROM foo
EOS

Dependencies in the gemspec should be alphabetically sorted.

Example:

# bad
spec.add_dependency 'rubocop'
spec.add_dependency 'rspec'

# good
spec.add_dependency 'rspec'
spec.add_dependency 'rubocop'

# good
spec.add_dependency 'rubocop'

spec.add_dependency 'rspec'

# bad
spec.add_development_dependency 'rubocop'
spec.add_development_dependency 'rspec'

# good
spec.add_development_dependency 'rspec'
spec.add_development_dependency 'rubocop'

# good
spec.add_development_dependency 'rubocop'

spec.add_development_dependency 'rspec'

# bad
spec.add_runtime_dependency 'rubocop'
spec.add_runtime_dependency 'rspec'

# good
spec.add_runtime_dependency 'rspec'
spec.add_runtime_dependency 'rubocop'

# good
spec.add_runtime_dependency 'rubocop'

spec.add_runtime_dependency 'rspec'

# good only if TreatCommentsAsGroupSeparators is true
# For code quality
spec.add_dependency 'rubocop'
# For tests
spec.add_dependency 'rspec'

Checks for a newline after the final magic comment.

Example:

# good
# frozen_string_literal: true

# Some documentation for Person
class Person
  # Some code
end

# bad
# frozen_string_literal: true
# Some documentation for Person
class Person
  # Some code
end

Checks for a newline after the final magic comment.

Example:

# good
# frozen_string_literal: true

# Some documentation for Person
class Person
  # Some code
end

# bad
# frozen_string_literal: true
# Some documentation for Person
class Person
  # Some code
end

This cop checks for rescuing StandardError. There are two supported styles implicit and explicit. This cop will not register an offense if any error other than StandardError is specified.

Example: EnforcedStyle: implicit

# `implicit` will enforce using `rescue` instead of
# `rescue StandardError`.

# bad
begin
  foo
rescue StandardError
  bar
end

# good
begin
  foo
rescue
  bar
end

# good
begin
  foo
rescue OtherError
  bar
end

# good
begin
  foo
rescue StandardError, SecurityError
  bar
end

Example: EnforcedStyle: explicit (default)

# `explicit` will enforce using `rescue StandardError`
# instead of `rescue`.

# bad
begin
  foo
rescue
  bar
end

# good
begin
  foo
rescue StandardError
  bar
end

# good
begin
  foo
rescue OtherError
  bar
end

# good
begin
  foo
rescue StandardError, SecurityError
  bar
end

Checks for a newline after the final magic comment.

Example:

# good
# frozen_string_literal: true

# Some documentation for Person
class Person
  # Some code
end

# bad
# frozen_string_literal: true
# Some documentation for Person
class Person
  # Some code
end

Dependencies in the gemspec should be alphabetically sorted.

Example:

# bad
spec.add_dependency 'rubocop'
spec.add_dependency 'rspec'

# good
spec.add_dependency 'rspec'
spec.add_dependency 'rubocop'

# good
spec.add_dependency 'rubocop'

spec.add_dependency 'rspec'

# bad
spec.add_development_dependency 'rubocop'
spec.add_development_dependency 'rspec'

# good
spec.add_development_dependency 'rspec'
spec.add_development_dependency 'rubocop'

# good
spec.add_development_dependency 'rubocop'

spec.add_development_dependency 'rspec'

# bad
spec.add_runtime_dependency 'rubocop'
spec.add_runtime_dependency 'rspec'

# good
spec.add_runtime_dependency 'rspec'
spec.add_runtime_dependency 'rubocop'

# good
spec.add_runtime_dependency 'rubocop'

spec.add_runtime_dependency 'rspec'

# good only if TreatCommentsAsGroupSeparators is true
# For code quality
spec.add_dependency 'rubocop'
# For tests
spec.add_dependency 'rspec'