shims for running rails 2 with a rails 3 cache

* cache entries are wrapped in rails 3
 * serialized attributes are handled differently
 * stub out a bunch of classes that will just be ignored
   on the returned object

Change-Id: Iff15a0f5c39cd7ceae25144585539acbfc7a62ad
Reviewed-on: https://gerrit.instructure.com/31717
Reviewed-by: James Williams  <jamesw@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>

config/initializers/active_record.rb

@@ -1861,7 +1861,91 @@ ActiveRecord::ConnectionAdapters::SchemaStatements.class_eval do
 end
 
 # shims so that AR objects serialized under rails 2 function under rail s3
-unless CANVAS_RAILS2
+if CANVAS_RAILS2
+  class ActiveSupport::Cache::Entry
+    def value
+      Marshal.load(@compressed ? Zlib::Inflate.inflate(@value) : @value) if @value
+    end
+  end
+
+  ActiveSupport::Cache::Store.subclasses.map(&:constantize).each do |subclass|
+    subclass.class_eval do
+      def read_with_rails3_shim(*args)
+        result = read_without_rails3_shim(*args)
+        result = result.value if ActiveSupport::Cache::Entry === result
+        result
+      end
+      alias_method_chain :read, :rails3_shim
+    end
+  end
+
+  module ActiveRecord::AttributeMethods::Serialization; end
+
+  class ActiveRecord::AttributeMethods::Serialization::Attribute < Struct.new(:coder, :value, :state)
+    def unserialize
+      return nil if self.value.nil?
+      self.value = self.coder.load(self.value)
+    end
+  end
+
+  module ActiveRecord::Coders; end
+  class ActiveRecord::Coders::YAMLColumn
+    def load(yaml)
+      return @object_class.new if @object_class != Object && yaml.nil?
+      return yaml unless yaml.is_a?(String) && yaml =~ /^---/
+      begin
+        obj = YAML.load(yaml)
+
+        unless obj.is_a?(@object_class) || obj.nil?
+          raise SerializationTypeMismatch,
+                "Attribute was supposed to be a #{object_class}, but was a #{obj.class}"
+        end
+        obj ||= @object_class.new if @object_class != Object
+
+        obj
+      rescue ArgumentError
+        yaml
+      end
+    end
+  end
+
+  class ActiveRecord::Base
+    def unserialize_attribute_with_rails3_shim(attr_name)
+      @attributes[attr_name] = @attributes[attr_name].unserialize if ActiveRecord::AttributeMethods::Serialization::Attribute === @attributes[attr_name]
+      unserialize_attribute_without_rails3_shim(attr_name)
+    end
+    alias_method_chain :unserialize_attribute, :rails3_shim
+  end
+
+  class ActiveRecord::Relation
+
+  end
+
+  module Arel; end
+  class Arel::TreeManager; end
+  class Arel::SelectManager < Arel::TreeManager; end
+  class Arel::Table; end
+  module Arel::Attributes; end
+  class Arel::Attributes::Attribute < Struct.new :relation, :name; end
+  module Arel::Nodes; end
+  class Arel::Nodes::Node; end
+  class Arel::Nodes::And < Arel::Nodes::Node; end
+  class Arel::Nodes::Binary < Arel::Nodes::Node; end
+  class Arel::Nodes::Equality < Arel::Nodes::Binary; end
+  class Arel::Nodes::JoinSource < Arel::Nodes::Binary; end
+  class Arel::Nodes::SelectCore < Arel::Nodes::Node; end
+  class Arel::Nodes::SelectStatement < Arel::Nodes::Node; end
+  class Arel::Nodes::SqlLiteral < String; end
+
+
+  module Switchman; end
+  class Switchman::Shard < ActiveRecord::Base
+    attr_accessible
+    def self._load(str)
+      Shard.lookup(str.to_i)
+    end
+  end
+else
   ActiveRecord::AttributeMethods::Serialization::ClassMethods.class_eval do
     def attribute_cast_code(attr_name)
       if serialized_attributes.include?(attr_name)

lib/stubs/shard.rb

@@ -46,6 +46,10 @@ class Shard
     default
   end
 
+  def self.lookup(id)
+    default
+  end
+
   def self.partition_by_shard(array, partition_proc = nil)
     return [] if array.empty?
     Array(yield array)