fixes circularity check in dependencies

The check for circular loading should depend on a stack of files being
loaded at the moment, rather than the collection of loaded files.

This showed up indirectly in #16468, where a misspelled helper would
incorrectly result in a circularity error message.

References #16468

3 files changed, 28 insertions, 0 deletions

diff --git a/activesupport/test/autoloading_fixtures/typo.rb b/activesupport/test/autoloading_fixtures/typo.rb
new file mode 100644
index 0000000000..8e047f5fd4
--- /dev/null
+++ b/activesupport/test/autoloading_fixtures/typo.rb
@@ -0,0 +1,2 @@
+TypO = 1
+
diff --git a/activesupport/test/dependencies_test.rb b/activesupport/test/dependencies_test.rb
index 899bb75eae..f2f60167c4 100644
--- a/activesupport/test/dependencies_test.rb
+++ b/activesupport/test/dependencies_test.rb
@@ -157,6 +157,31 @@ class DependenciesTest < ActiveSupport::TestCase
     end
   end
 
+  def test_ensures_the_expected_constant_is_defined
+    with_autoloading_fixtures do
+      e = assert_raise(LoadError) { Typo }
+      assert_match %r{Unable to autoload constant Typo, expected .*activesupport/test/autoloading_fixtures/typo.rb to define it}, e.message
+    end
+  end
+
+  def test_require_dependency_does_not_assume_any_particular_constant_is_defined
+    with_autoloading_fixtures do
+      require_dependency 'typo'
+      assert_equal 1, TypO
+    end
+  end
+
+  # Regression, see https://github.com/rails/rails/issues/16468.
+  def test_require_dependency_interaction_with_autoloading
+    with_autoloading_fixtures do
+      require_dependency 'typo'
+      assert_equal 1, TypO
+
+      e = assert_raise(LoadError) { Typo }
+      assert_match %r{Unable to autoload constant Typo, expected .*activesupport/test/autoloading_fixtures/typo.rb to define it}, e.message
+    end
+  end
+
   def test_module_loading
     with_autoloading_fixtures do
       assert_kind_of Module, A
diff --git a/activesupport/test/dependencies_test_helpers.rb b/activesupport/test/dependencies_test_helpers.rb
index 9268512a97..e4d5197112 100644
--- a/activesupport/test/dependencies_test_helpers.rb
+++ b/activesupport/test/dependencies_test_helpers.rb
@@ -13,6 +13,7 @@ module DependenciesTestHelpers
     ActiveSupport::Dependencies.autoload_paths = prior_autoload_paths
     ActiveSupport::Dependencies.mechanism = old_mechanism
     ActiveSupport::Dependencies.explicitly_unloadable_constants = []
+    ActiveSupport::Dependencies.clear
   end
 
   def with_autoloading_fixtures(&block)