MONGOID-5836 Don't repeat callbacks for embedded grandchildren.

lib/mongoid/interceptable.rb

@@ -235,9 +235,6 @@ def _mongoid_run_child_before_callbacks(kind, children: [], callback_list: [])
         return false if env.halted
         env.value = !env.halted
         callback_list << [next_sequence, env]
-        if (grandchildren = child.send(:cascadable_children, kind))
-          _mongoid_run_child_before_callbacks(kind, children: grandchildren, callback_list: callback_list)
-        end
       end
       callback_list
     end

spec/mongoid/interceptable_spec.rb

@@ -389,6 +389,25 @@ class TestClass
         end
       end
     end
+
+    context 'with embedded grandchildren' do
+      DCFCG = DuplicateCallbacksForCascadableGrandchildren
+
+      let(:parent) do
+        parent = DCFCG::Parent.new
+        child = DCFCG::Child.new
+        grandchild = DCFCG::Child.new
+
+        child.children = [ grandchild ]
+        parent.children = [ child ]
+
+        parent.tap(&:save)
+      end
+
+      it 'should not repeat any before callbacks' do
+        expect { parent }.not_to raise_exception(DCFCG::DuplicateCallbackDetected)
+      end
+    end
   end
 
   describe ".before_destroy" do

spec/mongoid/interceptable_spec_models.rb

@@ -318,3 +318,30 @@ def break_mongoid
   end
 end
 
+module DuplicateCallbacksForCascadableGrandchildren
+  class DuplicateCallbackDetected < RuntimeError
+  end
+
+  class Parent
+    include Mongoid::Document
+
+    embeds_many :children, cascade_callbacks: true, as: :parent
+  end
+
+  class Child
+    include Mongoid::Document
+
+    embedded_in :parent, polymorphic: true
+    embeds_many :children, cascade_callbacks: true, as: :parent
+
+    before_save :check_for_duplicate_callback
+
+    private
+
+    def check_for_duplicate_callback
+      raise DuplicateCallbackDetected if @callback_invoked
+      @callback_invoked = true
+    end
+  end
+end
+