detect circular constant autoloading

Nowadays circular autoloads do not work, but the user gets a NameError
that says some constant is undefined. That's puzzling, because he is
normally trying to autoload a constant he knows can be autoloaded.
With this check we can give a better error message.

3 files changed, 16 insertions, 0 deletions

diff --git a/activesupport/test/autoloading_fixtures/circular1.rb b/activesupport/test/autoloading_fixtures/circular1.rb
new file mode 100644
index 0000000000..a45761f066
--- /dev/null
+++ b/activesupport/test/autoloading_fixtures/circular1.rb
@@ -0,0 +1,6 @@
+silence_warnings do
+  Circular2
+end
+
+class Circular1
+end
diff --git a/activesupport/test/autoloading_fixtures/circular2.rb b/activesupport/test/autoloading_fixtures/circular2.rb
new file mode 100644
index 0000000000..c847fa5001
--- /dev/null
+++ b/activesupport/test/autoloading_fixtures/circular2.rb
@@ -0,0 +1,4 @@
+Circular1
+
+class Circular2
+end
diff --git a/activesupport/test/dependencies_test.rb b/activesupport/test/dependencies_test.rb
index f1da6378a7..e5bc806397 100644
--- a/activesupport/test/dependencies_test.rb
+++ b/activesupport/test/dependencies_test.rb
@@ -145,6 +145,12 @@ class DependenciesTest < ActiveSupport::TestCase
     end
   end
 
+  def test_circular_autoloading_detection
+    with_autoloading_fixtures do
+      assert_raise(RuntimeError, "Circular dependency detected while autoloading constant Circular1") { Circular1 }
+    end
+  end
+
   def test_module_loading
     with_autoloading_fixtures do
       assert_kind_of Module, A