cherry-pick test and source doc from #20050

guides/source/generators.md

@@ -503,6 +503,14 @@ Adds a specified source to `Gemfile`:
 add_source "http://gems.github.com"
 ```
 
+This method also takes a block:
+
+```ruby
+add_source "http://gems.github.com" do
+  gem "rspec-rails"
+end
+```
+
 ### `inject_into_file`
 
 Injects a block of code into a defined position in your file.

railties/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   Adding support for passing a block to the `add_source` action of a custom generator
+
+    *Mike Dalton*, *Hirofumi Wakasugi*
+
 *   `assert_file` understands paths with special characters
     (eg. `v0.1.4~alpha+nightly`).
 

railties/test/generators/actions_test.rb

@@ -47,6 +47,14 @@ def test_add_source_adds_source_to_gemfile
     assert_file 'Gemfile', /source 'http:\/\/gems\.github\.com'/
   end
 
+  def test_add_source_with_block_adds_source_to_gemfile_with_gem
+    run_generator
+    action :add_source, 'http://gems.github.com' do
+      gem 'rspec-rails'
+    end
+    assert_file 'Gemfile', /source 'http:\/\/gems\.github\.com' do\n  gem 'rspec-rails'\nend/
+  end
+
   def test_gem_should_put_gem_dependency_in_gemfile
     run_generator
     action :gem, 'will-paginate'