Raise more helpful error message on missing gem

Tell people to install `activerecord-session_store` gem when it's not
installed instead ofraising `NameError` on missing
`ActionDispatch::Session::ActiveRecordStore`.

2 files changed, 26 insertions, 0 deletions

diff --git a/railties/lib/rails/application/configuration.rb b/railties/lib/rails/application/configuration.rb
index f8ddeeb99e..0202e86f32 100644
--- a/railties/lib/rails/application/configuration.rb
+++ b/railties/lib/rails/application/configuration.rb
@@ -125,6 +125,13 @@ module Rails
           case @session_store
           when :disabled
             nil
+          when :active_record_store
+            begin
+              ActionDispatch::Session::ActiveRecordStore
+            rescue NameError
+              raise "`ActiveRecord::SessionStore` is extracted out of Rails into a gem. " \
+                "Please add `activerecord-session_store` to your Gemfile to use it."
+            end
           when Symbol
             ActionDispatch::Session.const_get(@session_store.to_s.camelize)
           else
diff --git a/railties/test/application/configuration_test.rb b/railties/test/application/configuration_test.rb
index ebdbbaee8b..039b08c723 100644
--- a/railties/test/application/configuration_test.rb
+++ b/railties/test/application/configuration_test.rb
@@ -630,5 +630,24 @@ module ApplicationTests
       ActiveRecord::Base
       assert defined?(FooObserver)
     end
+
+    test "config.session_store with :active_record_store with activerecord-session_store gem" do
+      begin
+        make_basic_app do |app|
+          ActionDispatch::Session::ActiveRecordStore = Class.new(ActionDispatch::Session::CookieStore)
+          app.config.session_store :active_record_store
+        end
+      ensure
+        ActionDispatch::Session.send :remove_const, :ActiveRecordStore
+      end
+    end
+
+    test "config.session_store with :active_record_store without activerecord-session_store gem" do
+      assert_raise RuntimeError, /activerecord-session_store/ do
+        make_basic_app do |app|
+          app.config.session_store :active_record_store
+        end
+      end
+    end
   end
 end