Add the `method_source` gem to the default Gemfile

Fixes #18473

railties/CHANGELOG.md

+*   Add the `method_source` gem to the default Gemfile for apps
+
+    *Sean Griffin*
+
 *   Drop old test locations from `rake stats`
     - test/functional
     - test/unit

railties/lib/rails/generators/rails/app/templates/Gemfile

@@ -36,6 +36,10 @@ group :development, :test do
   # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
   gem 'spring'
 <% end -%>
+
+  # Adds `Method#source` and `Method#comment` to get the source code of a
+  # method from the console
+  gem 'method_source'
 <% end -%>
 end
 

railties/test/generators/app_generator_test.rb

@@ -409,6 +409,13 @@ def test_inclusion_of_a_debugger
     end
   end
 
+  def test_inclusion_of_method_source
+    run_generator
+    assert_file "Gemfile" do |content|
+      assert_gem 'method_source'
+    end
+  end
+
   def test_inclusion_of_doc
     run_generator
     assert_file 'Gemfile', /gem 'sdoc',\s+'~> 0.4.0',\s+group: :doc/