`ActiveRecord::Base#becomes` should copy the errors

2 files changed, 22 insertions, 0 deletions

diff --git a/activemodel/lib/active_model/errors.rb b/activemodel/lib/active_model/errors.rb
index 4726a68f69..ef6141a51d 100644
--- a/activemodel/lib/active_model/errors.rb
+++ b/activemodel/lib/active_model/errors.rb
@@ -81,6 +81,18 @@ module ActiveModel
       super
     end
 
+    # Copies the errors from <tt>other</tt>.
+    #
+    # other - The ActiveModel::Errors instance.
+    #
+    # Examples
+    #
+    #   person.errors.copy!(other)
+    def copy!(other) # :nodoc:
+      @messages = other.messages.dup
+      @details  = other.details.dup
+    end
+
     # Clear the error messages.
     #
     #   person.errors.full_messages # => ["name cannot be nil"]
diff --git a/activemodel/test/cases/errors_test.rb b/activemodel/test/cases/errors_test.rb
index f6d171bec6..a5ac055033 100644
--- a/activemodel/test/cases/errors_test.rb
+++ b/activemodel/test/cases/errors_test.rb
@@ -410,4 +410,14 @@ class ErrorsTest < ActiveModel::TestCase
     person.errors.clear
     assert person.errors.details.empty?
   end
+
+  test "copy errors" do
+    errors = ActiveModel::Errors.new(Person.new)
+    errors.add(:name, :invalid)
+    person = Person.new
+    person.errors.copy!(errors)
+
+    assert_equal [:name], person.errors.messages.keys
+    assert_equal [:name], person.errors.details.keys
+  end
 end