1 files changed, 81 insertions, 0 deletions
diff --git a/activemodel/lib/active_model/error.rb b/activemodel/lib/active_model/error.rb
new file mode 100644
index 0000000000..5a1298e27f
--- /dev/null
+++ b/activemodel/lib/active_model/error.rb
@@ -0,0 +1,81 @@
+# frozen_string_literal: true
+
+module ActiveModel
+  # == Active \Model \Error
+  #
+  # Represents one single error
+  class Error
+    CALLBACKS_OPTIONS = [:if, :unless, :on, :allow_nil, :allow_blank, :strict]
+    MESSAGE_OPTIONS = [:message]
+
+    def initialize(base, attribute, type = :invalid, **options)
+      @base = base
+      @attribute = attribute
+      @raw_type = type
+      @type = type || :invalid
+      @options = options
+    end
+
+    def initialize_dup(other)
+      @attribute = @attribute.dup
+      @raw_type = @raw_type.dup
+      @type = @type.dup
+      @options = @options.deep_dup
+    end
+
+    attr_reader :base, :attribute, :type, :raw_type, :options
+
+    def message
+      case raw_type
+      when Symbol
+        base.errors.generate_message(attribute, raw_type, options.except(*CALLBACKS_OPTIONS))
+      else
+        raw_type
+      end
+    end
+
+    def detail
+      { error: raw_type }.merge(options.except(*CALLBACKS_OPTIONS + MESSAGE_OPTIONS))
+    end
+
+    def full_message
+      base.errors.full_message(attribute, message)
+    end
+
+    # See if error matches provided +attribute+, +type+ and +options+.
+    def match?(attribute, type = nil, **options)
+      if @attribute != attribute || (type && @type != type)
+        return false
+      end
+
+      options.each do |key, value|
+        if @options[key] != value
+          return false
+        end
+      end
+
+      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
+
+    def ==(other)
+      other.is_a?(self.class) && 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