fix infinite loop by parent attr

lib/reform/form/active_model/validations.rb

@@ -177,7 +177,10 @@ def full_messages
           private
 
           def full_messages_for_nested_fields(form_fields)
-            form_fields.map { |field| full_messages_for_twin(field[1]) }
+            form_fields
+              .to_a
+              .reject { |field| field[0] == "parent" }
+              .map { |field| full_messages_for_twin(field[1]) }
           end
 
           def full_messages_for_twin(object)

test/parent_test.rb

@@ -0,0 +1,43 @@
+require 'test_helper'
+require 'disposable/twin/parent'
+
+class ParentTest < BaseTest
+
+  class AlbumForm < Reform::Form
+
+    feature Disposable::Twin::Parent
+
+    property :band
+    validates :band, presence: true
+
+    collection :songs, virtual: true, default: [], populator: :populate_songs! do
+      property :name
+      validate :unique_name
+
+      def unique_name
+        if name == parent.band
+          errors.add(:name, "Song name shouldn't be the same as #{parent.band}")
+        end
+      end
+    end
+
+    def populate_songs!(fragment:, **)
+      existed_song = songs.find { |song| song.name == fragment[:name] }
+      return existed_song if existed_song
+      songs.append(OpenStruct.new(name: fragment[:name]))
+    end
+
+  end
+
+  let (:form) {
+    AlbumForm.new(OpenStruct.new(
+      :band => "Killer Queen"
+    ))
+  }
+
+  it "allows nested collection validation messages to be shown" do
+    form.validate(songs: [{ name: "Killer Queen" }])
+    _(form.errors.full_messages).must_equal(["Name Song name shouldn't be the same as Killer Queen"])
+  end
+
+end