Change errors

Allow `each` to behave in new way if block arity is 1

Ensure dumped marshal from Rails 5 can be loaded

Make errors compatible with marshal and YAML dumps from previous versions of Rails

Add deprecation warnings

Ensure each behave like the past, sorted by attribute

4 files changed, 363 insertions, 159 deletions

diff --git a/activemodel/lib/active_model/error.rb b/activemodel/lib/active_model/error.rb
index 214a0b356d..b1912f2604 100644
--- a/activemodel/lib/active_model/error.rb
+++ b/activemodel/lib/active_model/error.rb
@@ -8,7 +8,7 @@ module ActiveModel
     CALLBACKS_OPTIONS = [:if, :unless, :on, :allow_nil, :allow_blank, :strict]
     MESSAGE_OPTIONS = [:message]
 
-    def initialize(base, attribute, type, **options)
+    def initialize(base, attribute, type = :invalid, **options)
       @base = base
       @attribute = attribute
       @raw_type = type
@@ -56,5 +56,11 @@ module ActiveModel
 
       true
     end
+
+    def strict_match?(attribute, type, **options)
+      return false unless match?(attribute, type, **options)
+
+      full_message == Error.new(@base, attribute, type, **options).full_message
+    end
   end
 end
diff --git a/activemodel/lib/active_model/errors.rb b/activemodel/lib/active_model/errors.rb
index 7eff374ce3..a0b3b0ab54 100644
--- a/activemodel/lib/active_model/errors.rb
+++ b/activemodel/lib/active_model/errors.rb
@@ -4,6 +4,10 @@ require "active_support/core_ext/array/conversions"
 require "active_support/core_ext/string/inflections"
 require "active_support/core_ext/object/deep_dup"
 require "active_support/core_ext/string/filters"
+require "active_support/deprecation"
+require "active_model/error"
+require "active_model/nested_error"
+require "forwardable"
 
 module ActiveModel
   # == Active \Model \Errors
@@ -59,12 +63,17 @@ module ActiveModel
   class Errors
     include Enumerable
 
+    extend Forwardable
+    def_delegators :@errors, :size, :clear, :blank?, :empty?, *(Enumerable.instance_methods(false) - [:to_a, :include?])
+
+    LEGACY_ATTRIBUTES = [:messages, :details].freeze
+
     class << self
       attr_accessor :i18n_customize_full_message # :nodoc:
     end
     self.i18n_customize_full_message = false
 
-    attr_reader :messages, :details
+    attr_reader :errors
 
     # Pass in the instance of the object that is using the errors object.
     #
@@ -74,18 +83,17 @@ module ActiveModel
     #     end
     #   end
     def initialize(base)
-      @base     = base
-      @messages = apply_default_array({})
-      @details = apply_default_array({})
+      @base = base
+      @errors = []
     end
 
     def initialize_dup(other) # :nodoc:
-      @messages = other.messages.dup
-      @details  = other.details.deep_dup
+      @errors = other.errors.deep_dup
       super
     end
 
     # Copies the errors from <tt>other</tt>.
+    # For copying errors but keep <tt>@base</tt> as is.
     #
     # other - The ActiveModel::Errors instance.
     #
@@ -93,11 +101,26 @@ module ActiveModel
     #
     #   person.errors.copy!(other)
     def copy!(other) # :nodoc:
-      @messages = other.messages.dup
-      @details  = other.details.dup
+      @errors = other.errors.deep_dup
+      @errors.each { |error|
+        error.instance_variable_set("@base", @base)
+      }
     end
 
-    # Merges the errors from <tt>other</tt>.
+    # Imports one error
+    # Imported errors are wrapped as a NestedError,
+    # providing access to original error object.
+    # If attribute or type needs to be overriden, use `override_options`.
+    #
+    # override_options - Hash
+    # @option override_options [Symbol] :attribute Override the attribute the error belongs to
+    # @option override_options [Symbol] :type Override type of the error.
+    def import(error, override_options = {})
+      @errors.append(NestedError.new(@base, error, override_options))
+    end
+
+    # Merges the errors from <tt>other</tt>,
+    # each <tt>Error</tt> wrapped as <tt>NestedError</tt>.
     #
     # other - The ActiveModel::Errors instance.
     #
@@ -105,8 +128,9 @@ module ActiveModel
     #
     #   person.errors.merge!(other)
     def merge!(other)
-      @messages.merge!(other.messages) { |_, ary1, ary2| ary1 + ary2 }
-      @details.merge!(other.details) { |_, ary1, ary2| ary1 + ary2 }
+      other.errors.each { |error|
+        import(error)
+      }
     end
 
     # Removes all errors except the given keys. Returns a hash containing the removed errors.
@@ -116,18 +140,28 @@ module ActiveModel
     #   person.errors.keys                  # => [:age, :gender]
     def slice!(*keys)
       keys = keys.map(&:to_sym)
-      @details.slice!(*keys)
-      @messages.slice!(*keys)
+
+      results = messages.slice!(*keys)
+
+      @errors.keep_if do |error|
+        keys.include?(error.attribute)
+      end
+
+      results
     end
 
-    # Clear the error messages.
+    # Search for errors matching +attribute+, +type+ or +options+.
     #
-    #   person.errors.full_messages # => ["name cannot be nil"]
-    #   person.errors.clear
-    #   person.errors.full_messages # => []
-    def clear
-      messages.clear
-      details.clear
+    # Only supplied params will be matched.
+    #
+    #   person.errors.where(:name) # => all name errors.
+    #   person.errors.where(:name, :too_short) # => all name errors being too short
+    #   person.errors.where(:name, :too_short, minimum: 2) # => all name errors being too short and minimum is 2
+    def where(attribute, type = nil, **options)
+      attribute, type, options = normalize_arguments(attribute, type, options)
+      @errors.select { |error|
+        error.match?(attribute, type, options)
+      }
     end
 
     # Returns +true+ if the error messages include an error for the given key
@@ -137,8 +171,9 @@ module ActiveModel
     #   person.errors.include?(:name) # => true
     #   person.errors.include?(:age)  # => false
     def include?(attribute)
-      attribute = attribute.to_sym
-      messages.key?(attribute) && messages[attribute].present?
+      @errors.any? { |error|
+        error.match?(attribute.to_sym)
+      }
     end
     alias :has_key? :include?
     alias :key? :include?
@@ -148,10 +183,13 @@ module ActiveModel
     #   person.errors[:name]        # => ["cannot be nil"]
     #   person.errors.delete(:name) # => ["cannot be nil"]
     #   person.errors[:name]        # => []
-    def delete(key)
-      attribute = key.to_sym
-      details.delete(attribute)
-      messages.delete(attribute)
+    def delete(attribute, type = nil, **options)
+      attribute, type, options = normalize_arguments(attribute, type, options)
+      matches = where(attribute, type, options)
+      matches.each do |error|
+        @errors.delete(error)
+      end
+      matches.map(&:message)
     end
 
     # When passed a symbol or a name of a method, returns an array of errors
@@ -160,7 +198,7 @@ module ActiveModel
     #   person.errors[:name]  # => ["cannot be nil"]
     #   person.errors['name'] # => ["cannot be nil"]
     def [](attribute)
-      messages[attribute.to_sym]
+      where(attribute.to_sym).map { |error| error.message }
     end
 
     # Iterates through each error key, value pair in the error messages hash.
@@ -177,31 +215,37 @@ module ActiveModel
     #     # Will yield :name and "can't be blank"
     #     # then yield :name and "must be specified"
     #   end
-    def each
-      messages.each_key do |attribute|
-        messages[attribute].each { |error| yield attribute, error }
-      end
-    end
+    def each(&block)
+      if block.arity == 1
+        @errors.each(&block)
+      else
+        ActiveSupport::Deprecation.warn(<<-MSG.squish)
+          Enumerating ActiveModel::Errors as a hash has been deprecated.
+          In Rails 6, `errors` is an array of Error objects,
+          therefore it should be accessed by a block with a single block
+          parameter like this:
+
+          person.errors.each do |error|
+            error.full_message
+          end
 
-    # Returns the number of error messages.
-    #
-    #   person.errors.add(:name, :blank, message: "can't be blank")
-    #   person.errors.size # => 1
-    #   person.errors.add(:name, :not_specified, message: "must be specified")
-    #   person.errors.size # => 2
-    def size
-      values.flatten.size
+          You are passing a block expecting 2 parameters,
+          so the old hash behavior is simulated. As this is deprecated,
+          this will result in an ArgumentError in Rails 6.1.
+        MSG
+        @errors.
+          sort { |a, b| a.attribute <=> b.attribute }.
+          each { |error| yield error.attribute, error.message }
+      end
     end
-    alias :count :size
 
     # Returns all message values.
     #
     #   person.errors.messages # => {:name=>["cannot be nil", "must be specified"]}
     #   person.errors.values   # => [["cannot be nil", "must be specified"]]
     def values
-      messages.select do |key, value|
-        !value.empty?
-      end.values
+      deprecation_removal_warning(:values)
+      @errors.map(&:message).freeze
     end
 
     # Returns all message keys.
@@ -209,20 +253,11 @@ module ActiveModel
     #   person.errors.messages # => {:name=>["cannot be nil", "must be specified"]}
     #   person.errors.keys     # => [:name]
     def keys
-      messages.select do |key, value|
-        !value.empty?
-      end.keys
-    end
-
-    # Returns +true+ if no errors are found, +false+ otherwise.
-    # If the error message is a string it can be empty.
-    #
-    #   person.errors.full_messages # => ["name cannot be nil"]
-    #   person.errors.empty?        # => false
-    def empty?
-      size.zero?
+      deprecation_removal_warning(:keys)
+      keys = @errors.map(&:attribute)
+      keys.uniq!
+      keys.freeze
     end
-    alias :blank? :empty?
 
     # Returns an xml formatted representation of the Errors hash.
     #
@@ -236,6 +271,7 @@ module ActiveModel
     #   #    <error>name must be specified</error>
     #   #  </errors>
     def to_xml(options = {})
+      deprecation_removal_warning(:to_xml)
       to_a.to_xml({ root: "errors", skip_types: true }.merge!(options))
     end
 
@@ -255,13 +291,36 @@ module ActiveModel
     #   person.errors.to_hash       # => {:name=>["cannot be nil"]}
     #   person.errors.to_hash(true) # => {:name=>["name cannot be nil"]}
     def to_hash(full_messages = false)
-      if full_messages
-        messages.each_with_object({}) do |(attribute, array), messages|
-          messages[attribute] = array.map { |message| full_message(attribute, message) }
+      hash = {}
+      @errors.each do |error|
+        if full_messages
+          message = error.full_message
+        else
+          message = error.message
+        end
+
+        if hash.has_key?(error.attribute)
+          hash[error.attribute] << message
+        else
+          hash[error.attribute] = [message]
+        end
+      end
+      hash
+    end
+    alias :messages :to_hash
+
+    def details
+      hash = {}
+      @errors.each do |error|
+        detail = error.detail
+
+        if hash.has_key?(error.attribute)
+          hash[error.attribute] << detail
+        else
+          hash[error.attribute] = [detail]
         end
-      else
-        without_default_proc(messages)
       end
+      hash
     end
 
     # Adds +message+ to the error messages and used validator type to +details+ on +attribute+.
@@ -305,17 +364,20 @@ module ActiveModel
     #   # => {:base=>["either name or email must be present"]}
     #   person.errors.details
     #   # => {:base=>[{error: :name_or_email_blank}]}
-    def add(attribute, message = :invalid, options = {})
-      message = message.call if message.respond_to?(:call)
-      detail  = normalize_detail(message, options)
-      message = normalize_message(attribute, message, options)
+    def add(attribute, type = :invalid, **options)
+      error = Error.new(
+        @base,
+        *normalize_arguments(attribute, type, options)
+      )
+
       if exception = options[:strict]
         exception = ActiveModel::StrictValidationFailed if exception == true
-        raise exception, full_message(attribute, message)
+        raise exception, error.full_message
       end
 
-      details[attribute.to_sym]  << detail
-      messages[attribute.to_sym] << message
+      @errors.append(error)
+
+      error
     end
 
     # Returns +true+ if an error on the attribute with the given message is
@@ -334,13 +396,15 @@ module ActiveModel
     #   person.errors.added? :name, :too_long, count: 24                     # => false
     #   person.errors.added? :name, :too_long                                # => false
     #   person.errors.added? :name, "is too long"                            # => false
-    def added?(attribute, message = :invalid, options = {})
-      message = message.call if message.respond_to?(:call)
+    def added?(attribute, type = :invalid, options = {})
+      attribute, type, options = normalize_arguments(attribute, type, options)
 
-      if message.is_a? Symbol
-        details[attribute.to_sym].include? normalize_detail(message, options)
+      if type.is_a? Symbol
+        @errors.any? { |error|
+          error.strict_match?(attribute, type, options)
+        }
       else
-        self[attribute].include? message
+        messages_for(attribute).include?(type)
       end
     end
 
@@ -356,12 +420,12 @@ module ActiveModel
     #   person.errors.of_kind? :name, :not_too_long                            # => false
     #   person.errors.of_kind? :name, "is too long"                            # => false
     def of_kind?(attribute, message = :invalid)
-      message = message.call if message.respond_to?(:call)
+      attribute, message = normalize_arguments(attribute, message)
 
       if message.is_a? Symbol
-        details[attribute.to_sym].map { |e| e[:error] }.include? message
+        !where(attribute, message).empty?
       else
-        self[attribute].include? message
+        messages_for(attribute).include?(message)
       end
     end
 
@@ -376,7 +440,7 @@ module ActiveModel
     #   person.errors.full_messages
     #   # => ["Name is too short (minimum is 5 characters)", "Name can't be blank", "Email can't be blank"]
     def full_messages
-      map { |attribute, message| full_message(attribute, message) }
+      @errors.map(&:full_message)
     end
     alias :to_a :full_messages
 
@@ -391,21 +455,16 @@ module ActiveModel
     #   person.errors.full_messages_for(:name)
     #   # => ["Name is too short (minimum is 5 characters)", "Name can't be blank"]
     def full_messages_for(attribute)
-      attribute = attribute.to_sym
-      messages[attribute].map { |message| full_message(attribute, message) }
+      where(attribute).map(&:full_message).freeze
+    end
+
+    def messages_for(attribute)
+      where(attribute).map(&:message).freeze
     end
 
     # Returns a full message for a given attribute.
     #
     #   person.errors.full_message(:name, 'is invalid') # => "Name is invalid"
-    #
-    # The `"%{attribute} %{message}"` error format can be overridden with either
-    #
-    # * <tt>activemodel.errors.models.person/contacts/addresses.attributes.street.format</tt>
-    # * <tt>activemodel.errors.models.person/contacts/addresses.format</tt>
-    # * <tt>activemodel.errors.models.person.attributes.name.format</tt>
-    # * <tt>activemodel.errors.models.person.format</tt>
-    # * <tt>errors.format</tt>
     def full_message(attribute, message)
       return message if attribute == :base
       attribute = attribute.to_s
@@ -511,34 +570,50 @@ module ActiveModel
       I18n.translate(key, options)
     end
 
-    def marshal_dump # :nodoc:
-      [@base, without_default_proc(@messages), without_default_proc(@details)]
-    end
-
     def marshal_load(array) # :nodoc:
-      @base, @messages, @details = array
-      apply_default_array(@messages)
-      apply_default_array(@details)
+      # Rails 5
+      @errors = []
+      @base = array[0]
+      add_from_legacy_details_hash(array[2])
     end
 
     def init_with(coder) # :nodoc:
-      coder.map.each { |k, v| instance_variable_set(:"@#{k}", v) }
-      @details ||= {}
-      apply_default_array(@messages)
-      apply_default_array(@details)
+      data = coder.map
+
+      data.each { |k, v|
+        next if LEGACY_ATTRIBUTES.include?(k.to_sym)
+        instance_variable_set(:"@#{k}", v)
+      }
+
+      @errors ||= []
+
+      # Legacy support Rails 5.x details hash
+      add_from_legacy_details_hash(data["details"]) if data.key?("details")
     end
 
-  private
-    def without_default_proc(hash)
-      hash.dup.tap do |new_h|
-        new_h.default_proc = nil
+    private
+
+      def normalize_arguments(attribute, type, **options)
+        # Evaluate proc first
+        if type.respond_to?(:call)
+          type = type.call(@base, options)
+        end
+
+        [attribute.to_sym, type, options]
       end
-    end
 
-    def apply_default_array(hash)
-      hash.default_proc = proc { |h, key| h[key] = [] }
-      hash
-    end
+      def add_from_legacy_details_hash(details)
+        details.each { |attribute, errors|
+          errors.each { |error|
+            type = error.delete(:error)
+            add(attribute, type, error)
+          }
+        }
+      end
+
+      def deprecation_removal_warning(method_name)
+        ActiveSupport::Deprecation.warn("ActiveModel::Errors##{method_name} is deprecated and will be removed in Rails 6.1")
+      end
   end
 
   # Raised when a validation cannot be corrected by end users and are considered
diff --git a/activemodel/test/cases/error_test.rb b/activemodel/test/cases/error_test.rb
index c87ab8b858..f557d50c32 100644
--- a/activemodel/test/cases/error_test.rb
+++ b/activemodel/test/cases/error_test.rb
@@ -44,7 +44,6 @@ class ErrorTest < ActiveModel::TestCase
   test "initialize without type but with options" do
     options = { message: "bar" }
     error = ActiveModel::Error.new(Person.new, :name, options)
-    assert_equal :invalid, error.type
     assert_equal(options, error.options)
   end
 
diff --git a/activemodel/test/cases/errors_test.rb b/activemodel/test/cases/errors_test.rb
index 947f9bf99b..a6fd95d7b1 100644
--- a/activemodel/test/cases/errors_test.rb
+++ b/activemodel/test/cases/errors_test.rb
@@ -10,7 +10,7 @@ class ErrorsTest < ActiveModel::TestCase
       @errors = ActiveModel::Errors.new(self)
     end
 
-    attr_accessor :name, :age
+    attr_accessor :name, :age, :gender, :city
     attr_reader   :errors
 
     def validate!
@@ -31,48 +31,47 @@ class ErrorsTest < ActiveModel::TestCase
   end
 
   def test_delete
-    errors = ActiveModel::Errors.new(self)
-    errors[:foo] << "omg"
-    errors.delete("foo")
-    assert_empty errors[:foo]
+    errors = ActiveModel::Errors.new(Person.new)
+    errors.add(:name, :blank)
+    errors.delete("name")
+    assert_empty errors[:name]
   end
 
   def test_include?
-    errors = ActiveModel::Errors.new(self)
+    errors = ActiveModel::Errors.new(Person.new)
     errors[:foo] << "omg"
     assert_includes errors, :foo, "errors should include :foo"
     assert_includes errors, "foo", "errors should include 'foo' as :foo"
   end
 
   def test_dup
-    errors = ActiveModel::Errors.new(self)
-    errors[:foo] << "bar"
+    errors = ActiveModel::Errors.new(Person.new)
+    errors.add(:name)
     errors_dup = errors.dup
-    errors_dup[:bar] << "omg"
-    assert_not_same errors_dup.messages, errors.messages
+    assert_not_same errors_dup.errors, errors.errors
   end
 
   def test_has_key?
-    errors = ActiveModel::Errors.new(self)
-    errors[:foo] << "omg"
+    errors = ActiveModel::Errors.new(Person.new)
+    errors.add(:foo, "omg")
     assert_equal true, errors.has_key?(:foo), "errors should have key :foo"
     assert_equal true, errors.has_key?("foo"), "errors should have key 'foo' as :foo"
   end
 
   def test_has_no_key
-    errors = ActiveModel::Errors.new(self)
+    errors = ActiveModel::Errors.new(Person.new)
     assert_equal false, errors.has_key?(:name), "errors should not have key :name"
   end
 
   def test_key?
-    errors = ActiveModel::Errors.new(self)
-    errors[:foo] << "omg"
+    errors = ActiveModel::Errors.new(Person.new)
+    errors.add(:foo, "omg")
     assert_equal true, errors.key?(:foo), "errors should have key :foo"
     assert_equal true, errors.key?("foo"), "errors should have key 'foo' as :foo"
   end
 
   def test_no_key
-    errors = ActiveModel::Errors.new(self)
+    errors = ActiveModel::Errors.new(Person.new)
     assert_equal false, errors.key?(:name), "errors should not have key :name"
   end
 
@@ -86,42 +85,50 @@ class ErrorsTest < ActiveModel::TestCase
   end
 
   test "error access is indifferent" do
-    errors = ActiveModel::Errors.new(self)
-    errors[:foo] << "omg"
+    errors = ActiveModel::Errors.new(Person.new)
+    errors.add(:name, "omg")
 
-    assert_equal ["omg"], errors["foo"]
+    assert_equal ["omg"], errors["name"]
   end
 
   test "values returns an array of messages" do
-    errors = ActiveModel::Errors.new(self)
+    errors = ActiveModel::Errors.new(Person.new)
     errors.messages[:foo] = "omg"
     errors.messages[:baz] = "zomg"
 
-    assert_equal ["omg", "zomg"], errors.values
+    assert_deprecated do
+      assert_equal ["omg", "zomg"], errors.values
+    end
   end
 
   test "values returns an empty array after try to get a message only" do
-    errors = ActiveModel::Errors.new(self)
+    errors = ActiveModel::Errors.new(Person.new)
     errors.messages[:foo]
     errors.messages[:baz]
 
-    assert_equal [], errors.values
+    assert_deprecated do
+      assert_equal [], errors.values
+    end
   end
 
   test "keys returns the error keys" do
-    errors = ActiveModel::Errors.new(self)
-    errors.messages[:foo] << "omg"
-    errors.messages[:baz] << "zomg"
+    errors = ActiveModel::Errors.new(Person.new)
+    errors.add(:name)
+    errors.add(:age)
 
-    assert_equal [:foo, :baz], errors.keys
+    assert_deprecated do
+      assert_equal [:name, :age], errors.keys
+    end
   end
 
   test "keys returns an empty array after try to get a message only" do
-    errors = ActiveModel::Errors.new(self)
+    errors = ActiveModel::Errors.new(Person.new)
     errors.messages[:foo]
     errors.messages[:baz]
 
-    assert_equal [], errors.keys
+    assert_deprecated do
+      assert_equal [], errors.keys
+    end
   end
 
   test "detecting whether there are errors with empty?, blank?, include?" do
@@ -146,30 +153,80 @@ class ErrorsTest < ActiveModel::TestCase
     assert_equal ["cannot be nil"], person.errors[:name]
   end
 
-  test "add an error message on a specific attribute" do
+  test "add creates an error object and returns it" do
     person = Person.new
-    person.errors.add(:name, "cannot be blank")
-    assert_equal ["cannot be blank"], person.errors[:name]
+    error = person.errors.add(:name, :blank)
+
+    assert_equal :name, error.attribute
+    assert_equal :blank, error.type
+    assert_equal error, person.errors.first
   end
 
-  test "add an error message on a specific attribute with a defined type" do
+  test "add, with type as symbol" do
     person = Person.new
-    person.errors.add(:name, :blank, message: "cannot be blank")
-    assert_equal ["cannot be blank"], person.errors[:name]
+    person.errors.add(:name, :blank)
+
+    assert_equal :blank, person.errors.first.type
+    assert_equal ["can't be blank"], person.errors[:name]
   end
 
-  test "add an error with a symbol" do
+  test "add, with type as String" do
+    msg = "custom msg"
+
     person = Person.new
-    person.errors.add(:name, :blank)
-    message = person.errors.generate_message(:name, :blank)
-    assert_equal [message], person.errors[:name]
+    person.errors.add(:name, msg)
+
+    assert_equal [msg], person.errors[:name]
   end
 
-  test "add an error with a proc" do
+  test "add, with type as nil" do
     person = Person.new
-    message = Proc.new { "cannot be blank" }
-    person.errors.add(:name, message)
-    assert_equal ["cannot be blank"], person.errors[:name]
+    person.errors.add(:name)
+
+    assert_equal :invalid, person.errors.first.type
+    assert_equal ["is invalid"], person.errors[:name]
+  end
+
+  test "add, with type as Proc, which evaluates to String" do
+    msg = "custom msg"
+    type = Proc.new { msg }
+
+    person = Person.new
+    person.errors.add(:name, type)
+
+    assert_equal [msg], person.errors[:name]
+  end
+
+  test "add, type being Proc, which evaluates to Symbol" do
+    type = Proc.new { :blank }
+
+    person = Person.new
+    person.errors.add(:name, type)
+
+    assert_equal :blank, person.errors.first.type
+    assert_equal ["can't be blank"], person.errors[:name]
+  end
+
+  test "initialize options[:message] as Proc, which evaluates to String" do
+    msg = "custom msg"
+    type = Proc.new { msg }
+
+    person = Person.new
+    person.errors.add(:name, :blank, message: type)
+
+    assert_equal :blank, person.errors.first.type
+    assert_equal [msg], person.errors[:name]
+  end
+
+  test "add, with options[:message] as Proc, which evaluates to String, where type is nil" do
+    msg = "custom msg"
+    type = Proc.new { msg }
+
+    person = Person.new
+    person.errors.add(:name, message: type)
+
+    assert_equal :invalid, person.errors.first.type
+    assert_equal [msg], person.errors[:name]
   end
 
   test "added? detects indifferent if a specific error was added to the object" do
@@ -449,7 +506,7 @@ class ErrorsTest < ActiveModel::TestCase
     errors = ActiveModel::Errors.new(Person.new)
     errors.add(:name, :invalid)
     errors.delete(:name)
-    assert_empty errors.details[:name]
+    assert_not errors.added?(:name)
   end
 
   test "delete returns the deleted messages" do
@@ -473,8 +530,10 @@ class ErrorsTest < ActiveModel::TestCase
     person = Person.new
     person.errors.copy!(errors)
 
-    assert_equal [:name], person.errors.messages.keys
-    assert_equal [:name], person.errors.details.keys
+    assert person.errors.added?(:name, :invalid)
+    person.errors.each do |error|
+      assert_same person, error.base
+    end
   end
 
   test "merge errors" do
@@ -485,8 +544,8 @@ class ErrorsTest < ActiveModel::TestCase
     person.errors.add(:name, :blank)
     person.errors.merge!(errors)
 
-    assert_equal({ name: ["can't be blank", "is invalid"] }, person.errors.messages)
-    assert_equal({ name: [{ error: :blank }, { error: :invalid }] }, person.errors.details)
+    assert(person.errors.added?(:name, :invalid))
+    assert(person.errors.added?(:name, :blank))
   end
 
   test "slice! removes all errors except the given keys" do
@@ -498,7 +557,9 @@ class ErrorsTest < ActiveModel::TestCase
 
     person.errors.slice!(:age, "gender")
 
-    assert_equal [:age, :gender], person.errors.keys
+    assert_deprecated do
+      assert_equal [:age, :gender], person.errors.keys
+    end
   end
 
   test "slice! returns the deleted errors" do
@@ -518,10 +579,23 @@ class ErrorsTest < ActiveModel::TestCase
     errors.add(:name, :invalid)
     serialized = Marshal.load(Marshal.dump(errors))
 
+    assert_equal Person, serialized.instance_variable_get(:@base).class
     assert_equal errors.messages, serialized.messages
     assert_equal errors.details, serialized.details
   end
 
+  test "errors are compatible with marshal dumped from Rails 5.x" do
+    # Derived from
+    # errors = ActiveModel::Errors.new(Person.new)
+    # errors.add(:name, :invalid)
+    dump = "\x04\bU:\x18ActiveModel::Errors[\bo:\x17ErrorsTest::Person\x06:\f@errorsU;\x00[\b@\a{\x00{\x00{\x06:\tname[\x06I\"\x0Fis invalid\x06:\x06ET{\x06;\b[\x06{\x06:\nerror:\finvalid"
+    serialized = Marshal.load(dump)
+
+    assert_equal Person, serialized.instance_variable_get(:@base).class
+    assert_equal({ name: ["is invalid"] }, serialized.messages)
+    assert_equal({ name: [{ error: :invalid }] }, serialized.details)
+  end
+
   test "errors are backward compatible with the Rails 4.2 format" do
     yaml = <<~CODE
     --- !ruby/object:ActiveModel::Errors
@@ -541,4 +615,54 @@ class ErrorsTest < ActiveModel::TestCase
     assert_equal({}, errors.messages)
     assert_equal({}, errors.details)
   end
+
+  test "errors are compatible with YAML dumped from Rails 5.x" do
+    yaml = <<~CODE
+    --- !ruby/object:ActiveModel::Errors
+    base: &1 !ruby/object:ErrorsTest::Person
+      errors: !ruby/object:ActiveModel::Errors
+        base: *1
+        messages: {}
+        details: {}
+    messages:
+      :name:
+      - is invalid
+    details:
+      :name:
+      - :error: :invalid
+    CODE
+
+    errors = YAML.load(yaml)
+    assert_equal({ name: ["is invalid"] }, errors.messages)
+    assert_equal({ name: [{ error: :invalid }] }, errors.details)
+
+    errors.clear
+    assert_equal({}, errors.messages)
+    assert_equal({}, errors.details)
+  end
+
+  test "errors are compatible with YAML dumped from Rails 6.x" do
+    yaml = <<~CODE
+    --- !ruby/object:ActiveModel::Errors
+    base: &1 !ruby/object:ErrorsTest::Person
+      errors: !ruby/object:ActiveModel::Errors
+        base: *1
+        errors: []
+    errors:
+    - !ruby/object:ActiveModel::Error
+      base: *1
+      attribute: :name
+      type: :invalid
+      raw_type: :invalid
+      options: {}
+    CODE
+
+    errors = YAML.load(yaml)
+    assert_equal({ name: ["is invalid"] }, errors.messages)
+    assert_equal({ name: [{ error: :invalid }] }, errors.details)
+
+    errors.clear
+    assert_equal({}, errors.messages)
+    assert_equal({}, errors.details)
+  end
 end