explains why these requires are in an unusual place

1 files changed, 8 insertions, 0 deletions

diff --git a/activesupport/lib/active_support/deprecation.rb b/activesupport/lib/active_support/deprecation.rb
index b732c17e0f..6c15fffc0f 100644
--- a/activesupport/lib/active_support/deprecation.rb
+++ b/activesupport/lib/active_support/deprecation.rb
@@ -4,6 +4,14 @@ module ActiveSupport
   # \Deprecation specifies the API used by Rails to deprecate methods, instance
   # variables, objects and constants.
   class Deprecation
+    # active_support.rb sets an autoload for ActiveSupport::Deprecation.
+    #
+    # If these requires were at the top of the file the constant would not be
+    # defined by the time their files were loaded. Since some of them reopen
+    # ActiveSupport::Deprecation its autoload would be triggered, resulting in
+    # a circular require warning for active_support/deprecation.rb.
+    #
+    # So, we define the constant first, and load dependencies later.
     require 'active_support/deprecation/instance_delegator'
     require 'active_support/deprecation/behaviors'
     require 'active_support/deprecation/reporting'