Add new Lint/EmptyConditionalBody cop

CHANGELOG.md

@@ -20,6 +20,7 @@
 * [#7425](https://github.com/rubocop-hq/rubocop/pull/7425): Add new `Lint/TopLevelReturnWithArgument` cop. ([@iamravitejag][])
 * [#8417](https://github.com/rubocop-hq/rubocop/pull/8417): Add new `Style/GlobalStdStream` cop. ([@fatkodima][])
 * [#7949](https://github.com/rubocop-hq/rubocop/issues/7949): Add new `Style/SingleArgumentDig` cop. ([@volfgox][])
+* [#8341](https://github.com/rubocop-hq/rubocop/pull/8341): Add new `Lint/EmptyConditionalBody` cop. ([@fatkodima][])
 
 ### Bug fixes
 

config/default.yml

@@ -1442,6 +1442,12 @@ Lint/ElseLayout:
   Enabled: true
   VersionAdded: '0.17'
 
+Lint/EmptyConditionalBody:
+  Description: 'This cop checks for the presence of `if`, `elsif` and `unless` branches without a body.'
+  Enabled: 'pending'
+  AllowComments: true
+  VersionAdded: '0.89'
+
 Lint/EmptyEnsure:
   Description: 'Checks for empty ensure block.'
   Enabled: true

docs/modules/ROOT/pages/cops.adoc

@@ -200,6 +200,7 @@ In the following section you find all available cops:
 * xref:cops_lint.adoc#lintduplicaterescueexception[Lint/DuplicateRescueException]
 * xref:cops_lint.adoc#linteachwithobjectargument[Lint/EachWithObjectArgument]
 * xref:cops_lint.adoc#lintelselayout[Lint/ElseLayout]
+* xref:cops_lint.adoc#lintemptyconditionalbody[Lint/EmptyConditionalBody]
 * xref:cops_lint.adoc#lintemptyensure[Lint/EmptyEnsure]
 * xref:cops_lint.adoc#lintemptyexpression[Lint/EmptyExpression]
 * xref:cops_lint.adoc#lintemptyinterpolation[Lint/EmptyInterpolation]

docs/modules/ROOT/pages/cops_lint.adoc

@@ -893,6 +893,90 @@ else
 end
 ----
 
+== Lint/EmptyConditionalBody
+
+|===
+| Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+
+| Pending
+| Yes
+| No
+| 0.89
+| -
+|===
+
+This cop checks for the presence of `if`, `elsif` and `unless` branches without a body.
+
+=== Examples
+
+[source,ruby]
+----
+# 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
+----
+
+==== AllowComments: true (default)
+
+[source,ruby]
+----
+# good
+if condition
+  do_something
+elsif other_condition
+  # noop
+end
+----
+
+==== AllowComments: false
+
+[source,ruby]
+----
+# bad
+if condition
+  do_something
+elsif other_condition
+  # noop
+end
+----
+
+=== Configurable attributes
+
+|===
+| Name | Default value | Configurable values
+
+| AllowComments
+| `true`
+| Boolean
+|===
+
 == Lint/EmptyEnsure
 
 |===

lib/rubocop.rb

@@ -258,6 +258,7 @@
 require_relative 'rubocop/cop/lint/duplicate_rescue_exception'
 require_relative 'rubocop/cop/lint/each_with_object_argument'
 require_relative 'rubocop/cop/lint/else_layout'
+require_relative 'rubocop/cop/lint/empty_conditional_body'
 require_relative 'rubocop/cop/lint/empty_ensure'
 require_relative 'rubocop/cop/lint/empty_expression'
 require_relative 'rubocop/cop/lint/empty_interpolation'

lib/rubocop/cop/lint/empty_conditional_body.rb

@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Lint
+      # This cop checks for the presence of `if`, `elsif` and `unless` branches without a body.
+      # @example
+      #   # 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
+      #
+      # @example AllowComments: true (default)
+      #   # good
+      #   if condition
+      #     do_something
+      #   elsif other_condition
+      #     # noop
+      #   end
+      #
+      # @example AllowComments: false
+      #   # bad
+      #   if condition
+      #     do_something
+      #   elsif other_condition
+      #     # noop
+      #   end
+      #
+      class EmptyConditionalBody < Base
+        MSG = 'Avoid `%<keyword>s` branches without a body.'
+
+        def on_if(node)
+          return if node.body
+          return if cop_config['AllowComments'] && comment_lines?(node)
+
+          add_offense(node, message: format(MSG, keyword: node.keyword))
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/lint/empty_conditional_body_spec.rb

@@ -0,0 +1,94 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Lint::EmptyConditionalBody, :config do
+  let(:cop_config) do
+    { 'AllowComments' => true }
+  end
+
+  it 'registers an offense for missing `if` body' do
+    expect_offense(<<~RUBY)
+      if condition
+      ^^^^^^^^^^^^ Avoid `if` branches without a body.
+      end
+    RUBY
+  end
+
+  it 'does not register an offense for missing `if` body with a comment' do
+    expect_no_offenses(<<~RUBY)
+      if condition
+        # noop
+      end
+    RUBY
+  end
+
+  it 'registers an offense for missing `elsif` body' do
+    expect_offense(<<~RUBY)
+      if condition
+        do_something
+      elsif other_condition
+      ^^^^^^^^^^^^^^^^^^^^^ Avoid `elsif` branches without a body.
+      end
+    RUBY
+  end
+
+  it 'does not register an offense for missing `elsif` body with a comment' do
+    expect_no_offenses(<<~RUBY)
+      if condition
+        do_something
+      elsif other_condition
+        # noop
+      end
+    RUBY
+  end
+
+  it 'registers an offense for missing `unless` body' do
+    expect_offense(<<~RUBY)
+      unless condition
+      ^^^^^^^^^^^^^^^^ Avoid `unless` branches without a body.
+      end
+    RUBY
+  end
+
+  it 'does not register an offense for missing `unless` body with a comment' do
+    expect_no_offenses(<<~RUBY)
+      unless condition
+        # noop
+      end
+    RUBY
+  end
+
+  context 'when AllowComments is false' do
+    let(:cop_config) do
+      { 'AllowComments' => false }
+    end
+
+    it 'registers an offense for missing `if` body with a comment' do
+      expect_offense(<<~RUBY)
+        if condition
+        ^^^^^^^^^^^^ Avoid `if` branches without a body.
+          # noop
+        end
+      RUBY
+    end
+
+    it 'registers an offense for missing `elsif` body with a comment' do
+      expect_offense(<<~RUBY)
+        if condition
+          do_something
+        elsif other_condition
+        ^^^^^^^^^^^^^^^^^^^^^ Avoid `elsif` branches without a body.
+          # noop
+        end
+      RUBY
+    end
+
+    it 'registers an offense for missing `unless` body with a comment' do
+      expect_offense(<<~RUBY)
+        unless condition
+        ^^^^^^^^^^^^^^^^ Avoid `unless` branches without a body.
+          # noop
+        end
+      RUBY
+    end
+  end
+end