Add inheritance hook creating subclasses if missing. Finn: #3416, Cockpit: #18043.

app/models/report.rb

@@ -1,6 +1,7 @@
 require 'forwardable'
 
 class Report < ActiveRecord::Base
+  InheritedNamespace.activate
   extend Forwardable
   include Enumerable
   #belongs_to :user

app/models/report/inherited_namespace.rb

@@ -0,0 +1,23 @@
+module Report::InheritedNamespace
+  def self.activate
+    [Report, Report::Validation, Report::Filter, Report::GroupBy, Report::Result].each do |klass|
+      extend_object klass
+    end
+  end
+
+  def const_missing(name, *)
+    super
+  rescue NameError => error
+    raise error unless respond_to? superclass and superclass != self
+    begin
+      zuper = superclass.const_get(name)
+      case zuper
+      when Class  then const_set name, Class.new(zuper).extend(InheritedNamespace)
+      when Module then const_set name, Module.new { include zuper }.extend(InheritedNamespace)
+      else const_set name, zuper
+      end
+    rescue NameError
+      raise error
+    end
+  end
+end