Allow errors to remove duplicates, and ensure cyclic associations w/ autosave duplicate errors can be removed

See SHA 7550f0a016

activemodel/lib/active_model/error.rb

@@ -62,5 +62,20 @@ module ActiveModel
 
       full_message == Error.new(@base, attribute, type, **options).full_message
     end
+
+    def ==(other)
+      attributes_for_hash == other.attributes_for_hash
+    end
+    alias eql? ==
+
+    def hash
+      attributes_for_hash.hash
+    end
+
+    protected
+
+      def attributes_for_hash
+        [@base, @attribute, @raw_type, @options]
+      end
   end
 end

activemodel/lib/active_model/errors.rb

@@ -64,7 +64,7 @@ module ActiveModel
     include Enumerable
 
     extend Forwardable
-    def_delegators :@errors, :size, :clear, :blank?, :empty?
+    def_delegators :@errors, :size, :clear, :blank?, :empty?, :uniq!
     # TODO: forward all enumerable methods after `each` deprecation is removed.
     def_delegators :@errors, :count
 

activemodel/test/cases/error_test.rb

@@ -170,4 +170,24 @@ class ErrorTest < ActiveModel::TestCase
       assert_equal "name can't be blank", error.full_message
     }
   end
+
+  test "equality by base attribute, type and options" do
+    person = Person.new
+
+    e1 = ActiveModel::Error.new(person, :name, foo: :bar)
+    e2 = ActiveModel::Error.new(person, :name, foo: :bar)
+    e2.instance_variable_set(:@_humanized_attribute, "Name")
+
+    assert_equal(e1, e2)
+  end
+
+  test "inequality" do
+    person = Person.new
+    error = ActiveModel::Error.new(person, :name, foo: :bar)
+
+    assert error != ActiveModel::Error.new(person, :name, foo: :baz)
+    assert error != ActiveModel::Error.new(person, :name)
+    assert error != ActiveModel::Error.new(person, :title, foo: :bar)
+    assert error != ActiveModel::Error.new(Person.new, :name, foo: :bar)
+  end
 end

activerecord/lib/active_record/autosave_association.rb

@@ -491,9 +491,7 @@ module ActiveRecord
       end
 
       def _ensure_no_duplicate_errors
-        errors.messages.each_key do |attribute|
-          errors[attribute].uniq!
-        end
+        errors.uniq!
       end
   end
 end