[Fix rubocop#4153] Add a new cop Lint/ReturnInVoidContext

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 * [#4448](https://github.com/bbatsov/rubocop/pull/4448): Add new `TapFormatter`. ([@cyberdelia][])
 * Add new `Style/HeredocDelimiters` cop. ([@drenmi][])
+* [#4153](https://github.com/bbatsov/rubocop/issues/4153): New cop `Lint/ReturnInVoidContext` checks for the use of a return with a value in a context where it will be ignored. ([@harold-s][])
 
 ### Bug fixes
 
@@ -2827,3 +2828,4 @@
 [@yhirano55]: https://github.com/yhirano55
 [@hoshinotsuyoshi]: https://github.com/hoshinotsuyoshi
 [@timrogers]: https://github.com/timrogers
+[@harold-s]: https://github.com/harold-s

config/enabled.yml

@@ -1387,6 +1387,10 @@ Lint/UselessElseWithoutRescue:
   Description: 'Checks for useless `else` in `begin..end` without `rescue`.'
   Enabled: true
 
+Lint/ReturnInVoidContext:
+  Description: 'Checks for return in void context'
+  Enabled: true
+
 Lint/UselessSetterCall:
   Description: 'Checks for useless setter call to a local variable.'
   Enabled: true

lib/rubocop.rb

@@ -245,6 +245,7 @@
 require 'rubocop/cop/lint/require_parentheses'
 require 'rubocop/cop/lint/rescue_exception'
 require 'rubocop/cop/lint/rescue_type'
+require 'rubocop/cop/lint/return_in_void_context'
 require 'rubocop/cop/lint/safe_navigation_chain'
 require 'rubocop/cop/lint/script_permission'
 require 'rubocop/cop/lint/shadowed_exception'

lib/rubocop/cop/lint/return_in_void_context.rb

@@ -0,0 +1,62 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Lint
+      # This cop checks for the use of a return with a value in a context
+      # where it the value will be ignored. (initialize and setter methods)
+      #
+      # @example
+      #
+      #   # 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
+      #
+      class ReturnInVoidContext < Cop
+        MSG = 'Do not return a value in `%s`.'.freeze
+        def on_return(return_node)
+          method_name = method_name(return_node)
+          return unless method_name && return_node.descendants.any? &&
+                        useless_return_method?(method_name)
+
+          add_offense(return_node, :keyword, format(message, method_name))
+        end
+
+        private
+
+        def method_name(return_node)
+          method_node = return_node.each_ancestor(:block, :def, :defs).first
+          return nil unless method_node.type == :def
+          method_node.children.first
+        end
+
+        def method_setter?(method_name)
+          method_name.to_s.end_with?('=') &&
+            !%i[!= == === >= <=].include?(method_name)
+        end
+
+        def useless_return_method?(method_name)
+          method_name == :initialize || method_setter?(method_name)
+        end
+      end
+    end
+  end
+end

manual/cops.md

@@ -204,6 +204,7 @@ In the following section you find all available cops:
 * [Lint/RequireParentheses](cops_lint.md#lintrequireparentheses)
 * [Lint/RescueException](cops_lint.md#lintrescueexception)
 * [Lint/RescueType](cops_lint.md#lintrescuetype)
+* [Lint/ReturnInVoidContext](cops_lint.md#lintreturninvoidcontext)
 * [Lint/SafeNavigationChain](cops_lint.md#lintsafenavigationchain)
 * [Lint/ScriptPermission](cops_lint.md#lintscriptpermission)
 * [Lint/ShadowedException](cops_lint.md#lintshadowedexception)

manual/cops_lint.md

@@ -1479,6 +1479,41 @@ rescue NameError
 end
 ```
 
+## Lint/ReturnInVoidContext
+
+Enabled by default | Supports autocorrection
+--- | ---
+Enabled | No
+
+This cop checks for the use of a return with a value in a context
+where it the value will be ignored. (initialize and setter methods)
+
+ # good
+  def initialize
+    foo
+    return if bar?
+    baz
+  end
+
+  def foo=(bar)
+    return
+  end
+
+### Example
+
+```ruby
+# bad
+def initialize
+  foo
+  return :qux if bar?
+  baz
+end
+
+def foo=(bar)
+  return 42
+end
+```
+
 ## Lint/SafeNavigationChain
 
 Enabled by default | Supports autocorrection

spec/rubocop/cop/lint/return_in_void_context_spec.rb

@@ -0,0 +1,96 @@
+# frozen_string_literal: true
+
+describe RuboCop::Cop::Lint::ReturnInVoidContext do
+  subject(:cop) { described_class.new }
+
+  shared_examples 'registers an offense' do |message|
+    it 'registers an offense' do
+      inspect_source(cop, source)
+
+      expect(cop.offenses.size).to eq(1)
+      expect(cop.messages).to eq([message])
+    end
+  end
+
+  shared_examples 'does not registers an offense' do
+    it 'does not registers an offense' do
+      inspect_source(cop, source)
+      expect(cop.offenses.size).to eq(0)
+    end
+  end
+
+  context 'with an initialize method containing a return with a value' do
+    let(:source) do
+      ['class A',
+       '  def initialize',
+       '    return :qux if bar?',
+       '  end',
+       'end']
+    end
+    it_behaves_like 'registers an offense',
+                    'Do not return a value in `initialize`.'
+  end
+
+  context 'with an initialize method containing a return without a value' do
+    let(:source) do
+      ['class A',
+       '  def initialize',
+       '    return if bar?',
+       '  end',
+       'end']
+    end
+
+    it_behaves_like 'does not registers an offense'
+  end
+
+  context 'with a setter method containing a return with a value' do
+    let(:source) do
+      ['class A',
+       '  def foo=(bar)',
+       '    return 42',
+       '  end',
+       'end']
+    end
+
+    it_behaves_like 'registers an offense',
+                    'Do not return a value in `foo=`.'
+  end
+
+  context 'with a setter method containing a return without a value' do
+    let(:source) do
+      ['class A',
+       '  def foo=(bar)',
+       '    return',
+       '  end',
+       'end']
+    end
+
+    it_behaves_like 'does not registers an offense'
+  end
+
+  context 'with a non initialize method containing a return' do
+    let(:source) do
+      ['class A',
+       '  def bar',
+       '    foo',
+       '    return :qux if bar?',
+       '    foo',
+       '  end',
+       'end']
+    end
+    it_behaves_like 'does not registers an offense'
+  end
+
+  context 'with a class method called initialize containing a return' do
+    let(:source) do
+      ['class A',
+       '  def self.initialize',
+       '    foo',
+       '    return :qux if bar?',
+       '    foo',
+       '  end',
+       'end']
+    end
+    it_behaves_like 'does not registers an offense'
+  end
+end