From e1ed7a4717768bc5795f75e384e6f842417d3616 Mon Sep 17 00:00:00 2001
From: Robert Mosolgo <rdmosolgo@gmail.com>
Date: Fri, 26 Jan 2018 08:59:33 -0500
Subject: [PATCH 1/2] Add failing test for infinite loop when unloading
 autoloaded modules when an error occured during the load.

---
 activesupport/test/dependencies_test.rb | 55 +++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/activesupport/test/dependencies_test.rb b/activesupport/test/dependencies_test.rb
index d636da46d2..513ce181d3 100644
--- a/activesupport/test/dependencies_test.rb
+++ b/activesupport/test/dependencies_test.rb
@@ -185,6 +185,61 @@ def test_require_dependency_interaction_with_autoloading
     end
   end
 
+  # Regression see https://github.com/rails/rails/issues/31694
+  def test_included_constant_that_changes_to_have_exception_then_back_does_not_loop_forever
+    # This constant references a nested constant whose namespace will be auto-generated
+    parent_constant = <<-RUBY
+      class ConstantReloadError
+        AnotherConstant::ReloadError
+      end
+    RUBY
+
+    # This constant's namespace will be auto-generated,
+    # also, we'll edit it to contain an error at load-time
+    child_constant = <<-RUBY
+      class AnotherConstant::ReloadError
+        # no_such_method_as_this
+      end
+    RUBY
+
+    # Create a version which contains an error during loading
+    child_constant_with_error = child_constant.sub("# no_such_method_as_this", "no_such_method_as_this")
+
+    fixtures_path = File.join(__dir__, "autoloading_fixtures")
+    Dir.mktmpdir(nil, fixtures_path) do |tmpdir|
+      # Set up the file structure where constants will be loaded from
+      child_constant_path = "#{tmpdir}/another_constant/reload_error.rb"
+      File.write("#{tmpdir}/constant_reload_error.rb", parent_constant)
+      Dir.mkdir("#{tmpdir}/another_constant")
+      File.write(child_constant_path, child_constant_with_error)
+
+      tmpdir_name = tmpdir.split("/").last
+      with_loading("autoloading_fixtures/#{tmpdir_name}") do
+        # Load the file, with the error:
+        assert_raises(NameError) {
+          ConstantReloadError
+        }
+
+        Timeout.timeout(0.1) do
+          # Remove the constant, as if Rails development middleware is reloading changed files:
+          ActiveSupport::Dependencies.remove_unloadable_constants!
+          refute defined?(AnotherConstant::ReloadError)
+        end
+
+        # Change the file, so that it is **correct** this time:
+        File.write(child_constant_path, child_constant)
+
+        # Again: Remove the constant, as if Rails development middleware is reloading changed files:
+        ActiveSupport::Dependencies.remove_unloadable_constants!
+        refute defined?(AnotherConstant::ReloadError)
+
+        # Now, reload the _fixed_ constant:
+        assert ConstantReloadError
+        assert AnotherConstant::ReloadError
+      end
+    end
+  end
+
   def test_module_loading
     with_autoloading_fixtures do
       assert_kind_of Module, A

From d92fb27885ddcb0a92ac67f69bf0eb8c912f4dc7 Mon Sep 17 00:00:00 2001
From: Robert Mosolgo <rdmosolgo@gmail.com>
Date: Fri, 26 Jan 2018 09:41:27 -0500
Subject: [PATCH 2/2] Remove duplicates after autoloading modules

---
 activesupport/lib/active_support/dependencies.rb | 1 +
 1 file changed, 1 insertion(+)

diff --git a/activesupport/lib/active_support/dependencies.rb b/activesupport/lib/active_support/dependencies.rb
index abc648e0c6..0f59558bb5 100644
--- a/activesupport/lib/active_support/dependencies.rb
+++ b/activesupport/lib/active_support/dependencies.rb
@@ -447,6 +447,7 @@ def autoload_module!(into, const_name, qualified_name, path_suffix)
       mod = Module.new
       into.const_set const_name, mod
       autoloaded_constants << qualified_name unless autoload_once_paths.include?(base_path)
+      autoloaded_constants.uniq!
       mod
     end