Make Rake/Desc to not require description for the default task

.rubocop_todo.yml

@@ -1,14 +1,7 @@
 # This configuration was generated by
 # `rubocop --auto-gen-config`
-# on 2019-09-17 22:35:51 +0900 using RuboCop version 0.74.0.
+# on 2019-09-18 21:43:54 +0900 using RuboCop version 0.74.0.
 # The point is for the user to remove these configuration records
 # one by one as the offenses are removed from the code base.
 # Note that changes in the inspected code, or installation of new
 # versions of RuboCop, may require this file to be generated again.
-
-# Offense count: 1
-# Configuration parameters: Include.
-# Include: Rakefile, **/*.rake
-Rake/Desc:
-  Exclude:
-    - 'Rakefile'

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## master (unreleased)
 
+### Bug fixes
+
+* [#8](https://github.com/pocke/rubocop-rake/issues/8): Make Rake/Desc to not require description for the default task. ([@pocke][])
+
 <!--
 
 ### New features
@@ -16,7 +20,7 @@
 
 ### New features
 
-* [#5](https://github.com/pocke/rubocop-rake): Add `Rake/MethodDefinitionInTask`. ([@pocke][])
+* [#5](https://github.com/pocke/rubocop-rake/pull/5): Add `Rake/MethodDefinitionInTask`. ([@pocke][])
 
 ## 0.1.0 (2019-09-04)
 

lib/rubocop/cop/rake/desc.rb

@@ -7,6 +7,9 @@ module Rake
       # It is useful as a documentation of task. And Rake does not display
       # task that does not have `desc` by `rake -T`.
       #
+      # Note: This cop does not require description for the default task,
+      #       because the default task is executed with `rake` without command.
+      #
       # @example
       #   # bad
       #   task :do_something
@@ -34,6 +37,7 @@ class Desc < Cop
         def on_send(node)
           return unless task?(node)
           return if task_with_desc?(node)
+          return if task_name(node) == :default
 
           add_offense(node)
         end
@@ -49,6 +53,23 @@ def on_send(node)
           desc_candidate.send_type? && desc_candidate.method_name == :desc
         end
 
+        private def task_name(node)
+          first_arg = node.arguments[0]
+          case first_arg&.type
+          when :sym, :str
+            return first_arg.value.to_sym
+          when :hash
+            return nil if first_arg.children.size != 1
+
+            pair = first_arg.children.first
+            key = pair.children.first
+            case key.type
+            when :sym, :str
+              key.value.to_sym
+            end
+          end
+        end
+
         private def parent_and_task(task_node)
           parent = task_node.parent
           return nil, task_node unless parent

spec/rubocop/cop/rake/desc_spec.rb

@@ -44,4 +44,12 @@
       task :bar
     RUBY
   end
+
+  it 'do not register an offense for the default task' do
+    expect_no_offenses(<<~RUBY)
+      task default: :spec
+
+      task default: [:spec, :rubocop]
+    RUBY
+  end
 end