2 files changed, 30 insertions, 1 deletions
diff --git a/activemodel/lib/active_model/errors.rb b/activemodel/lib/active_model/errors.rb
index 22839bd9fb..42c004ce31 100644
--- a/activemodel/lib/active_model/errors.rb
+++ b/activemodel/lib/active_model/errors.rb
@@ -220,7 +220,7 @@ module ActiveModel
     #     # then yield :name and "must be specified"
     #   end
     def each(&block)
-      if block.arity == 1
+      if block.arity <= 1
         @errors.each(&block)
       else
         ActiveSupport::Deprecation.warn(<<~MSG)
@@ -303,6 +303,16 @@ module ActiveModel
       hash
     end
 
+    def to_h
+      ActiveSupport::Deprecation.warn(<<~EOM)
+        ActiveModel::Errors#to_h is deprecated and will be removed in Rails 6.2
+        Please use `ActiveModel::Errors.to_hash` instead. The values in the hash
+        returned by `ActiveModel::Errors.to_hash` is an array of error messages.
+      EOM
+
+      to_hash.transform_values { |values| values.last }
+    end
+
     def messages
       DeprecationHandlingMessageHash.new(self)
     end
diff --git a/activemodel/test/cases/errors_test.rb b/activemodel/test/cases/errors_test.rb
index d66d6ceff0..a6cd1da717 100644
--- a/activemodel/test/cases/errors_test.rb
+++ b/activemodel/test/cases/errors_test.rb
@@ -44,6 +44,14 @@ class ErrorsTest < ActiveModel::TestCase
     assert_includes errors, "foo", "errors should include 'foo' as :foo"
   end
 
+  def test_each_when_arity_is_negative
+    errors = ActiveModel::Errors.new(Person.new)
+    errors.add(:name, :blank)
+    errors.add(:gender, :blank)
+
+    assert_equal([:name, :gender], errors.map(&:attribute))
+  end
+
   def test_any?
     errors = ActiveModel::Errors.new(Person.new)
     errors.add(:name)
@@ -466,6 +474,17 @@ class ErrorsTest < ActiveModel::TestCase
     assert_equal ["name cannot be blank", "name cannot be nil"], person.errors.to_a
   end
 
+  test "to_h is deprecated" do
+    person = Person.new
+    person.errors.add(:name, "cannot be blank")
+    person.errors.add(:name, "too long")
+
+    expected_deprecation = "ActiveModel::Errors#to_h is deprecated"
+    assert_deprecated(expected_deprecation) do
+      assert_equal({ name: "too long" }, person.errors.to_h)
+    end
+  end
+
   test "to_hash returns the error messages hash" do
     person = Person.new
     person.errors.add(:name, "cannot be blank")