[ WIP ] Delay removal to docs to post validation.

First part of solving #2367 although we still have broken other specs
now with the first part of the fix.

.travis.yml

@@ -24,6 +24,8 @@ matrix:
     - rvm: jruby-head
       jdk: openjdk7
       env: JRUBY_OPTS="-Xcompile.invokedynamic=false"
-
+branches:
+  except:
+    - nested-destroy-validation-fail
 services:
   - mongodb

lib/mongoid/atomic.rb

@@ -114,6 +114,7 @@ def atomic_array_add_to_sets
     #
     # @since 2.1.0
     def atomic_updates
+      process_flagged_destroys
       mods = Modifiers.new
       generate_atomic_updates(mods, self)
       _children.each do |child|
@@ -302,6 +303,19 @@ def flag_as_destroyed
       atomic_path
     end
 
+    def flagged_destroys
+      @flagged_destroys ||= []
+    end
+
+    def process_flagged_destroys
+      _assigning do
+        flagged_destroys.each do |block|
+          block.call
+        end
+      end
+      flagged_destroys.clear
+    end
+
     private
 
     # Get the atomic paths utility for this document.

lib/mongoid/persistence/modification.rb

@@ -20,6 +20,7 @@ module Modification
       # @since 2.1.0
       def prepare(&block)
         return false if validating? && document.invalid?(:update)
+        document.process_flagged_destroys
         result = document.run_callbacks(:save) do
           document.run_callbacks(:update) do
             yield(document); true

lib/mongoid/relations/builders/nested_attributes/many.rb

@@ -103,8 +103,11 @@ def process_attributes(parent, attrs, options)
               converted = first ? convert_id(first.class, id) : id
               doc = existing.find(converted)
               if destroyable?(attrs)
-                existing.delete(doc)
-                doc.destroy unless doc.embedded? || doc.destroyed?
+                doc.flagged_for_destroy = true
+                parent.flagged_destroys.push(->{
+                  existing.delete(doc)
+                  doc.destroy unless doc.embedded? || doc.destroyed?
+                })
               else
                 attrs.delete_id
                 if metadata.embedded?

spec/mongoid/nested_attributes_spec.rb

@@ -1258,6 +1258,50 @@
 
               context "when allow_destroy is true" do
 
+                context "when the parent validation failed" do
+
+                  before(:all) do
+                    Band.validates_presence_of :name
+                    Band.accepts_nested_attributes_for :records, :allow_destroy => true
+                  end
+
+                  after(:all) do
+                    Band.send(:undef_method, :records_attributes=)
+                    Band.reset_callbacks(:validate)
+                  end
+
+                  let!(:band) do
+                    Band.create(name: "Depeche Mode")
+                  end
+
+                  let!(:record) do
+                    band.records.create
+                  end
+
+                  let(:attributes) do
+                    {
+                      name: nil,
+                      records_attributes: { "foo" => { "id" => record.id, "_destroy" => true }}
+                    }
+                  end
+
+                  before do
+                    band.update_attributes(attributes)
+                  end
+
+                  it "does not remove the child document" do
+                    band.records.should_not be_empty
+                  end
+
+                  it "keeps the child flagged for destruction" do
+                    record.should be_flagged_for_destroy
+                  end
+
+                  it "does not persist any change" do
+                    band.reload.records.should eq([ record ])
+                  end
+                end
+
                 context "when the child accesses the parent after destroy" do
 
                   before(:all) do