[Fix #5388] Add new Style/UnlessMultipleConditions cop

.rubocop.yml

@@ -29,6 +29,12 @@ Style/FormatStringToken:
   Exclude:
     - spec/**/*
 
+Style/UnlessMultipleConditions:
+  # Because RuboCop currently supports Ruby 2.1.
+  # In Ruby 2.1 not implementing `Hash#dig`, the following code is useful.
+  # `unless hash[:a] && hash[:a][:b]`
+  Enabled: false
+
 Layout/EndOfLine:
   EnforcedStyle: lf
 

CHANGELOG.md

@@ -13,6 +13,7 @@
 * [#5319](https://github.com/bbatsov/rubocop/pull/5319): Add new `Security/Open` cop. ([@mame][])
 * Add `EnforcedStyleForEmptyBrackets` configuration to `Layout/SpaceInsideReferenceBrackets`.([@garettarrowood][])
 * [#5358](https://github.com/bbatsov/rubocop/pull/5358):  `--no-auto-gen-timestamp` CLI option suppresses the inclusion of the date and time it was generated in auto-generated config. ([@dominicsayers][])
+* [#5388](https://github.com/bbatsov/rubocop/issues/5388): Add new `Style/UnlessMultipleConditions` cop. ([@wata727][])
 
 ### Bug fixes
 

config/enabled.yml

@@ -1969,6 +1969,10 @@ Style/UnlessElse:
   StyleGuide: '#no-else-with-unless'
   Enabled: true
 
+Style/UnlessMultipleConditions:
+  Description: 'Do not use `unless` with multiple conditions.'
+  Enabled: true
+
 Style/UnneededCapitalW:
   Description: 'Checks for %W when interpolation is not needed.'
   Enabled: true

lib/rubocop.rb

@@ -508,6 +508,7 @@
 require_relative 'rubocop/cop/style/trailing_underscore_variable'
 require_relative 'rubocop/cop/style/trivial_accessors'
 require_relative 'rubocop/cop/style/unless_else'
+require_relative 'rubocop/cop/style/unless_multiple_conditions'
 require_relative 'rubocop/cop/style/unneeded_capital_w'
 require_relative 'rubocop/cop/style/unneeded_interpolation'
 require_relative 'rubocop/cop/style/unneeded_percent_q'

lib/rubocop/cop/style/unless_multiple_conditions.rb

@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Style
+      # This cop checks that `unless` is not used with multiple conditions.
+      # In general, using multiple conditions with `unless` reduces readability.
+      #
+      # @example
+      #   # bad
+      #   unless foo && bar
+      #     something
+      #   end
+      #
+      #   # bad
+      #   unless foo || bar
+      #     something
+      #   end
+      #
+      #   # good
+      #   if !foo || !bar
+      #     something
+      #   end
+      #
+      #   # good
+      #   if !foo && !bar
+      #     something
+      #   end
+      class UnlessMultipleConditions < Cop
+        MSG = 'Avoid using `unless` with multiple conditions.'.freeze
+
+        def on_if(node)
+          return unless node.unless?
+
+          add_offense(node.condition) if node.condition.and_type? ||
+                                         node.condition.or_type?
+        end
+      end
+    end
+  end
+end

manual/cops.md

@@ -511,6 +511,7 @@ In the following section you find all available cops:
 * [Style/TrailingUnderscoreVariable](cops_style.md#styletrailingunderscorevariable)
 * [Style/TrivialAccessors](cops_style.md#styletrivialaccessors)
 * [Style/UnlessElse](cops_style.md#styleunlesselse)
+* [Style/UnlessMultipleConditions](cops_style.md#styleunlessmultipleconditions)
 * [Style/UnneededCapitalW](cops_style.md#styleunneededcapitalw)
 * [Style/UnneededInterpolation](cops_style.md#styleunneededinterpolation)
 * [Style/UnneededPercentQ](cops_style.md#styleunneededpercentq)

manual/cops_style.md

@@ -5659,6 +5659,39 @@ end
 
 * [https://github.com/bbatsov/ruby-style-guide#no-else-with-unless](https://github.com/bbatsov/ruby-style-guide#no-else-with-unless)
 
+## Style/UnlessMultipleConditions
+
+Enabled by default | Supports autocorrection
+--- | ---
+Enabled | No
+
+This cop checks that `unless` is not used with multiple conditions.
+In general, using multiple conditions with `unless` reduces readability.
+
+### Examples
+
+```ruby
+# bad
+unless foo && bar
+  something
+end
+
+# bad
+unless foo || bar
+  something
+end
+
+# good
+if !foo || !bar
+  something
+end
+
+# good
+if !foo && !bar
+  something
+end
+```
+
 ## Style/UnneededCapitalW
 
 Enabled by default | Supports autocorrection

spec/rubocop/cop/style/unless_multiple_conditions_spec.rb

@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Style::UnlessMultipleConditions do
+  subject(:cop) { described_class.new(config) }
+
+  let(:config) { RuboCop::Config.new }
+
+  it 'registers an offense when using `unless`' \
+     'with multiple `and` conditions' do
+    expect_offense(<<-RUBY.strip_indent)
+      unless foo && bar
+             ^^^^^^^^^^ Avoid using `unless` with multiple conditions.
+        something
+      end
+    RUBY
+  end
+
+  it 'registers an offense when using `unless` with multiple `or` conditions' do
+    expect_offense(<<-RUBY.strip_indent)
+      unless foo || bar
+             ^^^^^^^^^^ Avoid using `unless` with multiple conditions.
+        something
+      end
+    RUBY
+  end
+
+  it 'does not register an offense when using `if`' \
+     'with multiple `and` conditions' do
+    expect_no_offenses(<<-RUBY.strip_indent)
+      if !foo && !bar
+        something
+      end
+    RUBY
+  end
+
+  it 'does not register an offense when using `if`' \
+     'with multiple `or` conditions' do
+    expect_no_offenses(<<-RUBY.strip_indent)
+      if !foo || !bar
+        something
+      end
+    RUBY
+  end
+
+  it 'does not register an offense when using `unless` with single condition' do
+    expect_no_offenses(<<-RUBY.strip_indent)
+      unless foo
+        something
+      end
+    RUBY
+  end
+end