1 files changed, 49 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/core_ext/module/redefine_method.rb b/activesupport/lib/active_support/core_ext/module/redefine_method.rb
new file mode 100644
index 0000000000..a0a6622ca4
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/module/redefine_method.rb
@@ -0,0 +1,49 @@
+# frozen_string_literal: true
+
+class Module
+  if RUBY_VERSION >= "2.3"
+    # Marks the named method as intended to be redefined, if it exists.
+    # Suppresses the Ruby method redefinition warning. Prefer
+    # #redefine_method where possible.
+    def silence_redefinition_of_method(method)
+      if method_defined?(method) || private_method_defined?(method)
+        # This suppresses the "method redefined" warning; the self-alias
+        # looks odd, but means we don't need to generate a unique name
+        alias_method method, method
+      end
+    end
+  else
+    def silence_redefinition_of_method(method)
+      if method_defined?(method) || private_method_defined?(method)
+        alias_method :__rails_redefine, method
+        remove_method :__rails_redefine
+      end
+    end
+  end
+
+  # Replaces the existing method definition, if there is one, with the passed
+  # block as its body.
+  def redefine_method(method, &block)
+    visibility = method_visibility(method)
+    silence_redefinition_of_method(method)
+    define_method(method, &block)
+    send(visibility, method)
+  end
+
+  # Replaces the existing singleton method definition, if there is one, with
+  # the passed block as its body.
+  def redefine_singleton_method(method, &block)
+    singleton_class.redefine_method(method, &block)
+  end
+
+  def method_visibility(method) # :nodoc:
+    case
+    when private_method_defined?(method)
+      :private
+    when protected_method_defined?(method)
+      :protected
+    else
+      :public
+    end
+  end
+end