3 files changed, 17 insertions, 5 deletions
diff --git a/railties/lib/rails/api/task.rb b/railties/lib/rails/api/task.rb
index 3e7223f075..81d6dea792 100644
--- a/railties/lib/rails/api/task.rb
+++ b/railties/lib/rails/api/task.rb
@@ -69,12 +69,11 @@ module Rails
 
         options << '-m'  << api_main
         options << '-e'  << 'UTF-8'
-        options << '-f'  << 'sdoc'
-        options << '-T'  << 'rails'
 
         configure_rdoc_files
 
         before_running_rdoc do
+          load_and_configure_sdoc
           setup_horo_variables
         end
       end
@@ -84,6 +83,15 @@ module Rails
         # no-op
       end
 
+      def load_and_configure_sdoc
+        require 'sdoc'
+        options << '-f'  << 'sdoc'
+        options << '-T'  << 'rails'
+      rescue LoadError
+        $stderr.puts %(Unable to load SDoc, please add\n\n    gem 'sdoc', require: false\n\nto the Gemfile.)
+        exit 1
+      end
+
       def configure_rdoc_files
         rdoc_files.include(api_main)
 
@@ -111,9 +119,8 @@ module Rails
     end
 
     class RepoTask < Task
-      def initialize(name)
+      def load_and_configure_sdoc
         super
-
         options << '-g' # link to GitHub, SDoc flag
       end
 
diff --git a/railties/lib/rails/generators/rails/app/templates/Gemfile b/railties/lib/rails/generators/rails/app/templates/Gemfile
index b3883a94fc..07cf31dd83 100644
--- a/railties/lib/rails/generators/rails/app/templates/Gemfile
+++ b/railties/lib/rails/generators/rails/app/templates/Gemfile
@@ -11,7 +11,7 @@ source 'https://rubygems.org'
 
 group :doc do
   # bundle exec rake doc:rails generates the API under doc/api.
-  gem 'sdoc'
+  gem 'sdoc', require: false
 end
 
 # Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
diff --git a/railties/test/generators/app_generator_test.rb b/railties/test/generators/app_generator_test.rb
index b813a7f6bb..51e91656c0 100644
--- a/railties/test/generators/app_generator_test.rb
+++ b/railties/test/generators/app_generator_test.rb
@@ -303,6 +303,11 @@ class AppGeneratorTest < Rails::Generators::TestCase
     assert_file "Gemfile", /# gem 'debugger'/
   end
 
+  def test_inclusion_of_lazy_loaded_sdoc
+    run_generator
+    assert_file 'Gemfile', /gem 'sdoc', require: false/
+  end
+
   def test_template_from_dir_pwd
     FileUtils.cd(Rails.root)
     assert_match(/It works from file!/, run_generator([destination_root, "-m", "lib/template.rb"]))