This cop checks if the length of a method exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable.

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 if and unless statements that would fit on one line if written as a modifier if/unless. The maximum line length is configured in the Metrics/LineLength cop. The tab size is configured in the IndentationWidth of the Layout/Tab cop.

Example:

# bad
if condition
  do_stuff(bar)
end

unless qux.empty?
  Foo.do_something
end

# good
do_stuff(bar) if condition
Foo.do_something unless qux.empty?

This cop enforces empty line after guard clause

Example:

# bad
def foo
  return if need_return?
  bar
end

# good
def foo
  return if need_return?

  bar
end

# good
def foo
  return if something?
  return if something_different?

  bar
end

# also good
def foo
  if something?
    do_something
    return if need_return?
  end
end

This cop is designed to help upgrade to after Ruby 3.0. It will add the comment # frozen_string_literal: true to the top of files to enable frozen string literals. Frozen string literals may be default after Ruby 3.0. The comment will be added below a shebang and encoding comment. The frozen string literal comment is only valid in Ruby 2.3+.

Example: EnforcedStyle: always (default)

# The `always` style will always add the frozen string literal comment
# to a file, regardless of the Ruby version or if `freeze` or `<<` are
# called on a string literal.
# bad
module Bar
  # ...
end

# good
# frozen_string_literal: true

module Bar
  # ...
end

Example: EnforcedStyle: never

# The `never` will enforce that the frozen string literal comment does
# not exist in a file.
# bad
# frozen_string_literal: true

module Baz
  # ...
end

# good
module Baz
  # ...
end

This cop transforms usages of a method call safeguarded by a non nil check for the variable whose method is being called to safe navigation (&.). If there is a method chain, all of the methods in the chain need to be checked for safety, and all of the methods will need to be changed to use safe navigation. We have limited the cop to not register an offense for method chains that exceed 2 methods.

Configuration option: ConvertCodeThatCanStartToReturnNil The default for this is false. When configured to true, this will check for code in the format !foo.nil? && foo.bar. As it is written, the return of this code is limited to false and whatever the return of the method is. If this is converted to safe navigation, foo&.bar can start returning nil as well as what the method returns.

Example:

# bad
foo.bar if foo
foo.bar.baz if foo
foo.bar(param1, param2) if foo
foo.bar { |e| e.something } if foo
foo.bar(param) { |e| e.something } if foo

foo.bar if !foo.nil?
foo.bar unless !foo
foo.bar unless foo.nil?

foo && foo.bar
foo && foo.bar.baz
foo && foo.bar(param1, param2)
foo && foo.bar { |e| e.something }
foo && foo.bar(param) { |e| e.something }

# good
foo&.bar
foo&.bar&.baz
foo&.bar(param1, param2)
foo&.bar { |e| e.something }
foo&.bar(param) { |e| e.something }
foo && foo.bar.baz.qux # method chain with more than 2 methods
foo && foo.nil? # method that `nil` responds to

# Method calls that do not use `.`
foo && foo < bar
foo < bar if foo

# This could start returning `nil` as well as the return of the method
foo.nil? || foo.bar
!foo || foo.bar

# Methods that are used on assignment, arithmetic operation or
# comparison should not be converted to use safe navigation
foo.baz = bar if foo
foo.baz + bar if foo
foo.bar > 2 if foo

This cop checks how the whens of a case expression are indented in relation to its case or end keyword.

It will register a separate offense for each misaligned when.

Example:

# If Layout/EndAlignment is set to keyword style (default)
# *case* and *end* should always be aligned to same depth,
# and therefore *when* should always be aligned to both -
# regardless of configuration.

# bad for all styles
case n
  when 0
    x * 2
  else
    y / 3
end

# good for all styles
case n
when 0
  x * 2
else
  y / 3
end

Example: EnforcedStyle: case (default)

# if EndAlignment is set to other style such as
# start_of_line (as shown below), then *when* alignment
# configuration does have an effect.

# bad
a = case n
when 0
  x * 2
else
  y / 3
end

# good
a = case n
    when 0
      x * 2
    else
      y / 3
end

Example: EnforcedStyle: end

# bad
a = case n
    when 0
      x * 2
    else
      y / 3
end

# good
a = case n
when 0
  x * 2
else
  y / 3
end