Lint

# bad
some_method a { |val| puts val }

# good
# With parentheses, there's no ambiguity.
some_method(a { |val| puts val })
# or (different meaning)
some_method(a) { |val| puts val }

# good
# Operator methods require no disambiguation
foo == bar { |b| b.baz }

# good
# Lambda arguments require no disambiguation
foo = ->(bar) { bar.baz }

# bad

# The `*` is interpreted as a splat operator but it could possibly be
# a `*` method invocation (i.e. `do_something.*(some_array)`).
do_something *some_array

# good

# With parentheses, there's no ambiguity.
do_something(*some_array)

# bad

# This is interpreted as a method invocation with a regexp literal,
# but it could possibly be `/` method invocations.
# (i.e. `do_something./(pattern)./(i)`)
do_something /pattern/i

# good

# With parentheses, there's no ambiguity.
do_something(/pattern/i)

# bad
if some_var = true
  do_something
end

# good
if some_var == true
  do_something
end

# bad
BigDecimal.new(123.456, 3)

# good
BigDecimal(123.456, 3)

# bad
x.top >= x.top

if a.x != 0 && a.x != 0
  do_something
end

def childs?
  left_child || left_child
end

# bad
:true

# good
true

# bad
:false

# good
false

# bad

def bake(pie: pie)
  pie.heat_up
end

# good

def bake(pie:)
  pie.refrigerate
end

# good

def bake(pie: self.pie)
  pie.feed_to(user)
end

# bad

def cook(dry_ingredients = dry_ingredients)
  dry_ingredients.reduce(&:+)
end

# good

def cook(dry_ingredients = self.dry_ingredients)
  dry_ingredients.combine
end

# bad
task :lint do
  FILES_TO_LINT = Dir['lib/*.rb']
end

# bad
describe 'making a request' do
  class TestRequest; end
end

# bad
module M
  extend ActiveSupport::Concern
  included do
    LIST = []
  end
end

# good
task :lint do
  files_to_lint = Dir['lib/*.rb']
end

# good
describe 'making a request' do
  let(:test_request) { Class.new }
  # see also `stub_const` for RSpec
end

# good
module M
  extend ActiveSupport::Concern
  included do
    const_set(:LIST, [])
  end
end

# By default checks every constant

# bad
User

# bad
User::Login

# good
::User

# good
::User::Login

# bad (ok during development)

# using pry
def some_method
  binding.pry
  do_something
end

# bad (ok during development)

# using byebug
def some_method
  byebug
  do_something
end

# good

def some_method
  do_something
end

# bad

File.exists?(some_path)
Dir.exists?(some_path)
iterator?

# good

File.exist?(some_path)
Dir.exist?(some_path)
block_given?

# Example for OpenSSL::Cipher instantiation.

# bad
OpenSSL::Cipher::AES.new(128, :GCM)

# good
OpenSSL::Cipher.new('aes-128-gcm')

# Example for OpenSSL::Digest instantiation.

# bad
OpenSSL::Digest::SHA256.new

# good
OpenSSL::Digest.new('SHA256')

# Example for ::Digest inherited class methods.

# bad
OpenSSL::Digest::SHA256.digest('foo')

# good
OpenSSL::Digest.digest('SHA256', 'foo')

# bad
def initialize
  @x ||= 1
end

# good
def initialize
  @x = 1
end

# bad

case x
when 'first'
  do_something
when 'first'
  do_something_else
end

# good

case x
when 'first'
  do_something
when 'second'
  do_something_else
end

# bad
if x == 1
  do_something
elsif x == 1
  do_something_else
end

# good
if x == 1
  do_something
elsif x == 2
  do_something_else
end

# bad

hash = { food: 'apple', food: 'orange' }

# good

hash = { food: 'apple', other_food: 'orange' }

# bad

def foo
  1
end

def foo
  2
end

# bad

def foo
  1
end

alias foo bar

# good

def foo
  1
end

def bar
  2
end

# good

def foo
  1
end

alias bar foo

# bad
require 'foo'
require 'bar'
require 'foo'

# good
require 'foo'
require 'bar'

# good
require 'foo'
require_relative 'foo'

# bad
begin
  something
rescue FirstException
  handle_exception
rescue FirstException
  handle_other_exception
end

# good
begin
  something
rescue FirstException
  handle_exception
rescue SecondException
  handle_other_exception
end

# bad

sum = numbers.each_with_object(0) { |e, a| a += e }

# good

num = 0
sum = numbers.each_with_object(num) { |e, a| a += e }

# bad

if something
  # ...
else do_this
  do_that
end

# good

if something
  # ...
else
  do_this
  do_that
end

# bad
if condition
end

# bad
unless condition
end

# bad
if condition
  do_something
elsif other_condition
end

# good
if condition
  do_something
end

# good
unless condition
  do_something
end

# good
if condition
  do_something
elsif other_condition
  do_something_else
end

# bad

def some_method
  do_something
ensure
end

# bad

begin
  do_something
ensure
end

# good

def some_method
  do_something
ensure
  do_something_else
end

# good

begin
  do_something
ensure
  do_something_else
end

# bad

foo = ()
if ()
  bar
end

# good

foo = (some_expression)
if (some_expression)
  bar
end

# bad
# Empty file

# good
# File containing non commented source lines

# bad

"result is #{}"

# good

"result is #{some_result}"

# bad
case foo
when bar
  do_something
when baz
end

# good
case condition
when foo
  do_something
when bar
  nil
end

# bad

def foo
  do_something
ensure
  cleanup
  return self
end

# good

def foo
  do_something
  self
ensure
  cleanup
end

# also good

def foo
  begin
    do_something
  rescue SomeException
    # Let's ignore this exception
  end
  self
ensure
  cleanup
end

# Target codes supports Ruby 2.6 and higher only
# bad
ERB.new(str, nil, '-', '@output_buffer')

# good
ERB.new(str, trim_mode: '-', eoutvar: '@output_buffer')

# Target codes supports Ruby 2.5 and lower only
# good
ERB.new(str, nil, '-', '@output_buffer')

# Target codes supports Ruby 2.6, 2.5 and lower
# bad
ERB.new(str, nil, '-', '@output_buffer')

# good
# Ruby standard library style
# https://github.com/ruby/ruby/commit/3406c5d
if ERB.instance_method(:initialize).parameters.assoc(:key) # Ruby 2.6+
  ERB.new(str, trim_mode: '-', eoutvar: '@output_buffer')
else
  ERB.new(str, nil, '-', '@output_buffer')
end

# good
# Use `RUBY_VERSION` style
if RUBY_VERSION >= '2.6'
  ERB.new(str, trim_mode: '-', eoutvar: '@output_buffer')
else
  ERB.new(str, nil, '-', '@output_buffer')
end

# bad
(1..20).each do |x|
  puts x if (x == 5) .. (x == 10)
end

# good
(1..20).each do |x|
  puts x if (x >= 5) && (x <= 10)
end

# bad
x == 0.1
x != 0.1

# good - using BigDecimal
x.to_d == 0.1.to_d

# good
(x - 0.1).abs < Float::EPSILON

# good
tolerance = 0.0001
(x - 0.1).abs < tolerance

# Or some other epsilon based type of comparison:
# https://www.embeddeduse.com/2019/08/26/qt-compare-two-floats/

# bad

float = 3.0e400

# good

float = 42.9

# bad

format('A value: %s and another: %i', a_value)

# good

format('A value: %s and another: %i', a_value, another)

# bad

format('Unnumbered format: %s and numbered: %2$s', a_value, another)

# good

format('Numbered format: %1$s and numbered %2$s', a_value, another)

# bad
hash = {}
hash[foo.object_id] = :bar
hash.key?(baz.object_id)

# good
hash = {}.compare_by_identity
hash[foo] = :bar
hash.key?(baz)

# bad

   <<-SQL
     bar
   SQL
   .strip_indent

   <<-SQL
     bar
   SQL
   .strip_indent
   .trim

# good

   <<~SQL
     bar
   SQL

   <<~SQL.trim
     bar
   SQL

# bad
foo.object_id == bar.object_id

# good
foo.equal?(bar)

# bad

array = ['Item 1' 'Item 2']

# good

array = ['Item 1Item 2']
array = ['Item 1' + 'Item 2']
array = [
  'Item 1' \
  'Item 2'
]

# bad

class C
  private

  def self.method
    puts 'hi'
  end
end

# good

class C
  def self.method
    puts 'hi'
  end

  private_class_method :method
end

# good

class C
  class << self
    private

    def method
      puts 'hi'
    end
  end
end

# bad

foo = 'something with #{interpolation} inside'

# good

foo = "something with #{interpolation} inside"

# bad
if 20
  do_something
end

# bad
if some_var && true
  do_something
end

# good
if some_var && some_condition
  do_something
end

# good
# When using a boolean value for an infinite loop.
while true
  break if condition
end

# bad

"result is #{10}"

# good

"result is 10"

# bad

# using while
begin
  do_something
end while some_condition

# bad

# using until
begin
  do_something
end until some_condition

# good

# while replacement
loop do
  do_something
  break unless some_condition
end

# good

# until replacement
loop do
  do_something
  break if some_condition
end

# Lint/MissingCopEnableDirective:
#   MaximumRangeSize: .inf

# good
# rubocop:disable Layout/SpaceAroundOperators
x= 0
# rubocop:enable Layout/SpaceAroundOperators
# y = 1
# EOF

# bad
# rubocop:disable Layout/SpaceAroundOperators
x= 0
# EOF

# Lint/MissingCopEnableDirective:
#   MaximumRangeSize: 2

# good
# rubocop:disable Layout/SpaceAroundOperators
x= 0
# With the previous, there are 2 lines on which cop is disabled.
# rubocop:enable Layout/SpaceAroundOperators

# bad
# rubocop:disable Layout/SpaceAroundOperators
x= 0
x += 1
# Including this, that's 3 lines on which the cop is disabled.
# rubocop:enable Layout/SpaceAroundOperators

# bad
class Employee < Person
  def initialize(name, salary)
    @salary = salary
  end
end

# good
class Employee < Person
  def initialize(name, salary)
    super(name)
    @salary = salary
  end
end

# bad
class Parent
  def self.inherited(base)
    do_something
  end
end

# good
class Parent
  def self.inherited(base)
    super
    do_something
  end
end

# bad

x < y < z
10 <= x <= 20

# good

x < y && y < z
10 <= x && x <= 20

# bad

# `bar` definition actually produces methods in the same scope
# as the outer `foo` method. Furthermore, the `bar` method
# will be redefined every time `foo` is invoked.
def foo
  def bar
  end
end

# good

def foo
  bar = -> { puts 'hello' }
  bar.call
end

# good

def foo
  self.class.class_eval do
    def bar
    end
  end
end

def foo
  self.class.module_exec do
    def bar
    end
  end
end

# good

def foo
  class << self
    def bar
    end
  end
end

# bad

# The percent literal for nested_attributes is parsed as four tokens,
# yielding the array [:name, :content, :"%i[incorrectly", :"nested]"].
attributes = {
  valid_attributes: %i[name content],
  nested_attributes: %i[name content %i[incorrectly nested]]
}

# bad

result = (1..4).reduce(0) do |acc, i|
  next if i.odd?
  acc + i
end

# good

result = (1..4).reduce(0) do |acc, i|
  next acc if i.odd?
  acc + i
end

# bad
Dir["./lib/**/*.rb"].each do |file|
  require file
end

# good
Dir["./lib/**/*.rb"].sort.each do |file|
  require file
end

# bad
Dir.glob(Rails.root.join(__dir__, 'test', '*.rb')) do |file|
  require file
end

# good
Dir.glob(Rails.root.join(__dir__, 'test', '*.rb')).sort.each do |file|
  require file
end

# bad
Dir['./lib/**/*.rb'].each(&method(:require))

# good
Dir['./lib/**/*.rb'].sort.each(&method(:require))

# bad
Dir.glob(Rails.root.join('test', '*.rb'), &method(:require))

# good
Dir.glob(Rails.root.join('test', '*.rb')).sort.each(&method(:require))

class ItemApi
  rescue_from ValidationError do |e| # non-iteration block with arg
    return { message: 'validation error' } unless e.errors # allowed
    error_array = e.errors.map do |error| # block with method chain
      return if error.suppress? # warned
      return "#{error.param}: invalid" unless error.message # allowed
      "#{error.param}: #{error.message}"
    end
    { message: 'validation error', errors: error_array }
  end

  def update_items
    transaction do # block without arguments
      return unless update_necessary? # allowed
      find_each do |item| # block without method chain
        return if item.stock == 0 # false-negative...
        item.update!(foobar: true)
      end
    end
  end
end

# bad

'10'.to_i
'10.2'.to_f
'10'.to_c

# good

Integer('10', 10)
Float('10.2')
Complex('10')

# bad

# frozen_string_literal: true
# encoding: ascii
p [''.frozen?, ''.encoding] #=> [true, #<Encoding:UTF-8>]

# good

# encoding: ascii
# frozen_string_literal: true
p [''.frozen?, ''.encoding] #=> [true, #<Encoding:US-ASCII>]

# good

#!/usr/bin/env ruby
# encoding: ascii
# frozen_string_literal: true
p [''.frozen?, ''.encoding] #=> [true, #<Encoding:US-ASCII>]

/(foo)bar/ =~ 'foobar'

# bad - always returns nil

puts $2 # => nil

# good

puts $1 # => foo

# bad
do_something (foo)

# good
do_something(foo)
do_something (2 + 3) * 4
do_something (foo * bar).baz

# bad

%w('foo', "bar")

# good

%w(foo bar)

# bad

%i(:foo, :bar)

# good

%i(foo bar)

# bad
raise Exception, 'Error message here'

# good
raise StandardError, 'Error message here'

# bad

rand 1
Kernel.rand(-1)
rand 1.0
rand(-1.0)

# good

0 # just use 0 instead

# bad
# rubocop:disable Layout/LineLength
x += 1
# rubocop:enable Layout/LineLength

# good
x += 1

# bad
foo = 1
# rubocop:enable Layout/LineLength

# good
foo = 1

# bad
# rubocop:disable Style/StringLiterals
foo = "1"
# rubocop:enable Style/StringLiterals
baz
# rubocop:enable all

# good
# rubocop:disable Style/StringLiterals
foo = "1"
# rubocop:enable all
baz

# bad
require 'unloaded_feature'
require 'thread'

# good
require 'unloaded_feature'

# bad
do_something if attrs&.respond_to?(:[])

# good
do_something if attrs.respond_to?(:[])

# bad
while node&.is_a?(BeginNode)
  node = node.parent
end

# good
while node.is_a?(BeginNode)
  node = node.parent
end

# good - without `&.` this will always return `true`
foo&.respond_to?(:to_a)

# bad

a = *[1, 2, 3]
a = *'a'
a = *1

begin
  foo
rescue *[StandardError, ApplicationError]
  bar
end

case foo
when *[1, 2, 3]
  bar
else
  baz
end

# good

c = [1, 2, 3]
a = *c
a, b = *c
a, *b = *c
a = *1..10
a = ['a']

begin
  foo
rescue StandardError, ApplicationError
  bar
end

case foo
when 1, 2, 3
  bar
else
  baz
end

# bad

"result is #{something.to_s}"

# good

"result is #{something}"

# bad
ary.each_with_index do |v|
  v
end

# good
ary.each do |v|
  v
end

# bad
ary.each.with_index do |v|
  v
end

# good
ary.each do |v|
  v
end

# bad
ary.each_with_object([]) do |v|
  v
end

# good
ary.each do |v|
  v
end

# bad
ary.each.with_object([]) do |v|
  v
end

# good
ary.each do |v|
  v
end

# bad
if /foo/
  do_something
end

# good
if /foo/ =~ $_
  do_something
end

# bad

if day.is? :tuesday && month == :jan
  # ...
end

# good

if day.is?(:tuesday) && month == :jan
  # ...
end

# bad

begin
  do_something
rescue Exception
  handle_exception
end

# good

begin
  do_something
rescue ArgumentError
  handle_exception
end

# bad
begin
  bar
rescue nil
  baz
end

# bad
def foo
  bar
rescue 1, 'a', "#{b}", 0.0, [], {}
  baz
end

# good
begin
  bar
rescue
  baz
end

# good
def foo
  bar
rescue NameError
  baz
end

# bad
def initialize
  foo
  return :qux if bar?
  baz
end

def foo=(bar)
  return 42
end

# good
def initialize
  foo
  return if bar?
  baz
end

def foo=(bar)
  return
end

# bad

x&.foo.bar
x&.foo + bar
x&.foo[bar]

# good

x&.foo&.bar
x&.foo || bar

# bad
foo&.bar && foo.baz

# bad
foo.bar || foo&.baz

# bad
foo&.bar && (foobar.baz || foo.baz)

# good
foo.bar && foo.baz

# good
foo&.bar || foo&.baz

# good
foo&.bar && (foobar.baz || foo&.baz)

# bad
return if foo&.empty?
return unless foo&.empty?

# good
return if foo && foo.empty?
return unless foo && foo.empty?

# bad

# A file which has a shebang line as its first line is not
# granted execute permission.

#!/usr/bin/env ruby
puts 'hello, world'

# good

# A file which has a shebang line as its first line is
# granted execute permission.

#!/usr/bin/env ruby
puts 'hello, world'

# good

# A file which has not a shebang line as its first line is not
# granted execute permission.

puts 'hello, world'

# bad
foo = foo
foo, bar = foo, bar
Foo = Foo

# good
foo = bar
foo, bar = bar, foo
Foo = Bar

# bad
Foo.send(:include, Bar)
Foo.send(:prepend, Bar)
Foo.send(:extend, Bar)

# bad
Foo.public_send(:include, Bar)
Foo.public_send(:prepend, Bar)
Foo.public_send(:extend, Bar)

# bad
Foo.__send__(:include, Bar)
Foo.__send__(:prepend, Bar)
Foo.__send__(:extend, Bar)

# good
Foo.include Bar
Foo.prepend Bar
Foo.extend Bar

# bad
do_something do |foo|
  foo = 42
  puts foo
end

def do_something(foo)
  foo = 42
  puts foo
end

# good
do_something do |foo|
  foo = foo + 42
  puts foo
end

def do_something(foo)
  foo = foo + 42
  puts foo
end

def do_something(foo)
  puts foo
end

# bad

begin
  something
rescue Exception
  handle_exception
rescue StandardError
  handle_standard_error
end

# good

begin
  something
rescue StandardError
  handle_standard_error
rescue Exception
  handle_exception
end

# good, however depending on runtime environment.
#
# This is a special case for system call errors.
# System dependent error code depends on runtime environment.
# For example, whether `Errno::EAGAIN` and `Errno::EWOULDBLOCK` are
# the same error code or different error code depends on environment.
# This good case is for `Errno::EAGAIN` and `Errno::EWOULDBLOCK` with
# the same error code.
begin
  something
rescue Errno::EAGAIN, Errno::EWOULDBLOCK
  handle_standard_error
end

# bad

def some_method
  foo = 1

  2.times do |foo| # shadowing outer `foo`
    do_something(foo)
  end
end

# good

def some_method
  foo = 1

  2.times do |bar|
    do_something(bar)
  end
end

# bad
Bad = Struct.new(:members, :clone, :count)
b = Bad.new([], true, 1)
b.members #=> [] (overriding `Struct#members`)
b.clone #=> true (overriding `Object#clone`)
b.count #=> 1 (overriding `Enumerable#count`)

# good
Good = Struct.new(:id, :name)
g = Good.new(1, "foo")
g.members #=> [:id, :name]
g.clone #=> #<struct Good id=1, name="foo">
g.count #=> 2

# bad
def some_method
  do_something
rescue
end

# bad
begin
  do_something
rescue
end

# good
def some_method
  do_something
rescue
  handle_exception
end

# good
begin
  do_something
rescue
  handle_exception
end

class Point
  attr_reader :x, :y

  # bad, incorrect arity
  def to_json
    JSON.generate([x, y])
  end

  # good, preserving args
  def to_json(*args)
    JSON.generate([x, y], *args)
  end

  # good, discarding args
  def to_json(*_args)
    JSON.generate([x, y])
  end
end

# Detected since Ruby 2.7
return 1 # 1 is always ignored.

# bad
class Foo
  attr_reader :foo,

  def bar
    puts "Unreachable."
  end
end

# good
class Foo
  attr_reader :foo

  def bar
    puts "No problem!"
  end
end

# bad

1.is_a?(Fixnum)
1.is_a?(Bignum)

# good

1.is_a?(Integer)

# bad

def some_method
  return
  do_something
end

# bad

def some_method
  if cond
    return
  else
    return
  end
  do_something
end

# good

def some_method
  do_something
end

# bad
while node
  do_something(node)
  node = node.parent
  break
end

# good
while node
  do_something(node)
  node = node.parent
end

# bad
def verify_list(head)
  item = head
  begin
    if verify(item)
      return true
    else
      return false
    end
  end while(item)
end

# good
def verify_list(head)
  item = head
  begin
    if verify(item)
      item = item.next
    else
      return false
    end
  end while(item)

  true
end

# bad
def find_something(items)
  items.each do |item|
    if something?(item)
      return item
    else
      raise NotFoundError
    end
  end
end

# good
def find_something(items)
  items.each do |item|
    if something?(item)
      return item
    end
  end
  raise NotFoundError
end

# bad
do_something do |used, unused|
  puts used
end

do_something do |bar|
  puts :foo
end

define_method(:foo) do |bar|
  puts :baz
end

# good
do_something do |used, _unused|
  puts used
end

do_something do
  puts :foo
end

define_method(:foo) do |_bar|
  puts :baz
end

# bad
def some_method(used, unused, _unused_but_allowed)
  puts used
end

# good
def some_method(used, _unused, _unused_but_allowed)
  puts used
end

# bad
URI.escape('http://example.com')
URI.encode('http://example.com')

# good
CGI.escape('http://example.com')
URI.encode_www_form([['example', 'param'], ['lang', 'en']])
URI.encode_www_form(page: 10, locale: 'en')
URI.encode_www_form_component('http://example.com')

# bad
URI.unescape(enc_uri)
URI.decode(enc_uri)

# good
CGI.unescape(enc_uri)
URI.decode_www_form(enc_uri)
URI.decode_www_form_component(enc_uri)

# bad
URI.regexp('http://example.com')

# good
URI::DEFAULT_PARSER.make_regexp('http://example.com')

# bad
class Foo
  public # this is redundant (default access is public)

  def method
  end
end

# bad
class Foo
  # The following is redundant (methods defined on the class'
  # singleton class are not affected by the public modifier)
  public

  def self.method3
  end
end

# bad
class Foo
  protected

  define_method(:method2) do
  end

  protected # this is redundant (repeated from previous modifier)

  [1,2,3].each do |i|
    define_method("foo#{i}") do
    end
  end
end

# bad
class Foo
  private # this is redundant (no following methods are defined)
end

# good
class Foo
  private # this is not redundant (a method is defined)

  def method2
  end
end

# good
class Foo
  # The following is not redundant (conditionally defined methods are
  # considered as always defining a method)
  private

  if condition?
    def method
    end
  end
end

# good
class Foo
  protected # this is not redundant (a method is defined)

  define_method(:method2) do
  end
end

# bad

def some_method
  some_var = 1
  do_something
end

# good

def some_method
  some_var = 1
  do_something(some_var)
end

# bad

begin
  do_something
else
  do_something_else # This will never be run.
end

# good

begin
  do_something
rescue
  handle_errors
else
  do_something_else
end

# bad
def initialize
  super
end

def method
  super
end

# good - with default arguments
def initialize(x = Object.new)
  super
end

# good
def initialize
  super
  initialize_internals
end

def method(*args)
  super(:extra_arg, *args)
end

# bad

def something
  x = Something.new
  x.attr = 5
end

# good

def something
  x = Something.new
  x.attr = 5
  x
end

# bad
-5.times { do_something }
0.times { do_something }
1.times { do_something  }
1.times { |i| do_something(i) }

# good
do_something
do_something(1)