Merge pull request rails#43738 from zokioki/zp-active-model-errors-self-merge-43737

Allow ActiveModel::Error#merge! to handle merging of an instance to itself

Author: rafaelfranca

activemodel/lib/active_model/errors.rb

@@ -140,6 +140,8 @@ def import(error, override_options = {})
     #
     #   person.errors.merge!(other)
     def merge!(other)
+      return errors if equal?(other)
+
       other.errors.each { |error|
         import(error)
       }

activemodel/test/cases/errors_test.rb

@@ -657,6 +657,16 @@ def call
     assert(person.errors.added?(:name, :blank))
   end
 
+  test "merge does not import errors when merging with self" do
+    errors = ActiveModel::Errors.new(Person.new)
+    errors.add(:name, :invalid)
+    errors_before_merge = errors.dup
+
+    errors.merge!(errors)
+
+    assert(errors.errors.eql?(errors_before_merge.errors))
+  end
+
   test "errors are marshalable" do
     errors = ActiveModel::Errors.new(Person.new)
     errors.add(:name, :invalid)