Add new Lint/EmptyBlock cop

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## master (unreleased)
 
+### New features
+
+* [#8895](https://github.com/rubocop-hq/rubocop/pull/8895): Add new `Lint/EmptyBlock` cop. ([@fatkodima][])
+
 ## 1.0.0 (2020-10-21)
 
 ### New features

config/default.yml

@@ -1474,6 +1474,12 @@ Lint/ElseLayout:
   Enabled: true
   VersionAdded: '0.17'
 
+Lint/EmptyBlock:
+  Description: 'This cop checks for blocks without a body.'
+  Enabled: pending
+  VersionAdded: '1.1'
+  AllowComments: true
+
 Lint/EmptyConditionalBody:
   Description: 'This cop checks for the presence of `if`, `elsif` and `unless` branches without a body.'
   Enabled: true

docs/modules/ROOT/pages/cops.adoc

@@ -204,6 +204,7 @@ 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#lintemptyblock[Lint/EmptyBlock]
 * xref:cops_lint.adoc#lintemptyconditionalbody[Lint/EmptyConditionalBody]
 * xref:cops_lint.adoc#lintemptyensure[Lint/EmptyEnsure]
 * xref:cops_lint.adoc#lintemptyexpression[Lint/EmptyExpression]

docs/modules/ROOT/pages/cops_lint.adoc

@@ -994,6 +994,67 @@ else
 end
 ----
 
+== Lint/EmptyBlock
+
+|===
+| Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+
+| Pending
+| Yes
+| No
+| 1.1
+| -
+|===
+
+This cop checks for blocks without a body.
+Such empty blocks are typically an oversight or we should provide a comment
+be clearer what we're aiming for.
+
+=== Examples
+
+[source,ruby]
+----
+# bad
+items.each { |item| }
+
+# good
+items.each { |item| puts item }
+----
+
+==== AllowComments: true (default)
+
+[source,ruby]
+----
+# good
+items.each do |item|
+  # TODO: implement later (inner comment)
+end
+
+items.each { |item| } # TODO: implement later (inline comment)
+----
+
+==== AllowComments: false
+
+[source,ruby]
+----
+# bad
+items.each do |item|
+  # TODO: implement later (inner comment)
+end
+
+items.each { |item| } # TODO: implement later (inline comment)
+----
+
+=== Configurable attributes
+
+|===
+| Name | Default value | Configurable values
+
+| AllowComments
+| `true`
+| Boolean
+|===
+
 == Lint/EmptyConditionalBody
 
 |===

lib/rubocop.rb

@@ -266,6 +266,7 @@
 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_block'
 require_relative 'rubocop/cop/lint/empty_conditional_body'
 require_relative 'rubocop/cop/lint/empty_ensure'
 require_relative 'rubocop/cop/lint/empty_expression'

lib/rubocop/cli/command/auto_genenerate_config.rb

@@ -90,7 +90,7 @@ def run_all_cops(line_length_contents)
         def reset_config_and_auto_gen_file
           @config_store = ConfigStore.new
           @config_store.options_config = @options[:config] if @options[:config]
-          File.open(AUTO_GENERATED_FILE, 'w') {}
+          File.open(AUTO_GENERATED_FILE, 'w') {} # create or truncate if exists
           add_inheritance_from_auto_generated_file(@options[:config])
         end
 

lib/rubocop/cop/corrector.rb

@@ -23,7 +23,7 @@ def initialize(source)
         )
 
         # Don't print warnings to stderr if corrections conflict with each other
-        diagnostics.consumer = ->(diagnostic) {}
+        diagnostics.consumer = ->(diagnostic) {} # noop
       end
 
       alias rewrite process # Legacy

lib/rubocop/cop/lint/empty_block.rb

@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Lint
+      # This cop checks for blocks without a body.
+      # Such empty blocks are typically an oversight or we should provide a comment
+      # be clearer what we're aiming for.
+      #
+      # @example
+      #   # bad
+      #   items.each { |item| }
+      #
+      #   # good
+      #   items.each { |item| puts item }
+      #
+      # @example AllowComments: true (default)
+      #   # good
+      #   items.each do |item|
+      #     # TODO: implement later (inner comment)
+      #   end
+      #
+      #   items.each { |item| } # TODO: implement later (inline comment)
+      #
+      # @example AllowComments: false
+      #   # bad
+      #   items.each do |item|
+      #     # TODO: implement later (inner comment)
+      #   end
+      #
+      #   items.each { |item| } # TODO: implement later (inline comment)
+      #
+      class EmptyBlock < Base
+        MSG = 'Empty block detected.'
+
+        def on_block(node)
+          return if node.body
+          return if cop_config['AllowComments'] &&
+                    processed_source.contains_comment?(node.source_range)
+
+          add_offense(node)
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/lint/empty_block_spec.rb

@@ -0,0 +1,63 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Lint::EmptyBlock, :config do
+  let(:cop_config) do
+    { 'AllowComments' => true }
+  end
+
+  it 'registers an offense for empty block within method call' do
+    expect_offense(<<~RUBY)
+      items.each { |item| }
+      ^^^^^^^^^^^^^^^^^^^^^ Empty block detected.
+    RUBY
+  end
+
+  it 'registers an offense for empty block within lambda' do
+    expect_offense(<<~RUBY)
+      lambda { |item| }
+      ^^^^^^^^^^^^^^^^^ Empty block detected.
+    RUBY
+  end
+
+  it 'does not register an offense for empty block with inner comments' do
+    expect_no_offenses(<<~RUBY)
+      items.each do |item|
+        # TODO: implement later
+      end
+    RUBY
+  end
+
+  it 'does not register an offense for empty block with inline comments' do
+    expect_no_offenses(<<~RUBY)
+      items.each { |item| } # TODO: implement later
+    RUBY
+  end
+
+  it 'does not register an offense when block is not empty' do
+    expect_no_offenses(<<~RUBY)
+      items.each { |item| puts item }
+    RUBY
+  end
+
+  context 'when AllowComments is false' do
+    let(:cop_config) do
+      { 'AllowComments' => false }
+    end
+
+    it 'registers an offense for empty block with inner comments' do
+      expect_offense(<<~RUBY)
+        items.each do |item|
+        ^^^^^^^^^^^^^^^^^^^^ Empty block detected.
+          # TODO: implement later
+        end
+      RUBY
+    end
+
+    it 'registers an offense for empty block with inline comments' do
+      expect_offense(<<~RUBY)
+        items.each { |item| } # TODO: implement later
+        ^^^^^^^^^^^^^^^^^^^^^ Empty block detected.
+      RUBY
+    end
+  end
+end