Add support for Rails 5.1

This updates the code to work with Rails 5.1.0.alpha, as of commit
rails/rails@1bdc395.

The biggest change was to call the new methods provided by
`ActiveRecord::Dirty` when needed. In the next version of Rails after
5.1, dirty will be "cleared" before after_save callbacks are run. This
means that code in an after_save callback will behave the same as if it
was run after calling `.save`.

Since the concept of "changed" is fairly nebulous, two new method sets
were introduced with names that specify whether they're operating on
changes from what we think is in the database to what's in memory, or
the changes that were just persisted. Paper trail will now use the
latter set of methods if available and called from an after_ callback.

There were a few other unrelated changes required to get this working on
master. The first was the change from `appear_as_new_record` to
`appear_as_unpersisted`. This was due to a single test that broke as a
result of
rails/rails@c546a2b
where reifying a version with a nil has_one association was persisting the
change to the foreign key. I am actually unsure how that commit caused
the problem (or more specifically, I'm unsure how it was passing
before). However, as best as I can tell, the purpose of
`appear_as_new_record` was to attempt to prevent the callbacks in
`AutosaveAssociation` (which is the module responsible for persisting
foreign key changes earlier than most people want most of the time
because backwards compatibility or the maintainer hates himself or
something) from running. By also stubbing out `persisted?` we can
actually prevent those. A more stable option might be to use `suppress`
instead, similar to the other branch in `reify_has_one`.

The remaining breakage was due to the `Song` model relying on internals
that have changed from underneath it. From Rails 5 onwards there is a
public API available to do what it wants, so we can just use that
instead.

This commit is not expected to pass on Rails 3, as paper-trail-gem#898 makes it sound
like support might be dropped. If this needs to be ammended to support
Rails 3, I will do so, but I will also grumble very loudly about it.

lib/paper_trail/record_trail.rb

@@ -3,24 +3,33 @@ module PaperTrail
   class RecordTrail
     def initialize(record)
       @record = record
+      @in_after_callback = false
     end
 
     # Utility method for reifying. Anything executed inside the block will
     # appear like a new record.
-    def appear_as_new_record
+    def appear_as_unpersisted
       @record.instance_eval {
         alias :old_new_record? :new_record?
         alias :new_record? :present?
+        alias :old_persisted? :persisted?
+        alias :persisted? :nil?
       }
       yield
-      @record.instance_eval { alias :new_record? :old_new_record? }
+      @record.instance_eval {
+        alias :new_record? :old_new_record?
+        alias :persisted? :old_persisted?
+      }
     end
 
     def attributes_before_change
-      changed = @record.changed_attributes.select { |k, _v|
-        @record.class.column_names.include?(k)
-      }
-      @record.attributes.merge(changed)
+      @record.attributes.map do |k, v|
+        if @record.class.column_names.include?(k)
+          [k, attribute_in_previous_version(k)]
+        else
+          [k, v]
+        end
+      end.to_h
     end
 
     def changed_and_not_ignored
@@ -34,7 +43,7 @@ def changed_and_not_ignored
           }
       end
       skip = @record.paper_trail_options[:skip]
-      @record.changed - ignore - skip
+      changed_in_latest_version - ignore - skip
     end
 
     # Invoked after rollbacks to ensure versions records are not created for
@@ -65,7 +74,7 @@ def changed_notably?
 
     # @api private
     def changes
-      notable_changes = @record.changes.delete_if { |k, _v|
+      notable_changes = changes_in_latest_version.delete_if { |k, _v|
         !notably_changed.include?(k)
       }
       AttributeSerializers::ObjectChangesAttribute.
@@ -87,7 +96,7 @@ def enabled_for_model?
     # changed.
     def ignored_attr_has_changed?
       ignored = @record.paper_trail_options[:ignore] + @record.paper_trail_options[:skip]
-      ignored.any? && (@record.changed & ignored).any?
+      ignored.any? && (changed_in_latest_version & ignored).any?
     end
 
     # Returns true if this instance is the current, live one;
@@ -107,9 +116,9 @@ def merge_metadata(data)
             # If it is an attribute that is changing in an existing object,
             # be sure to grab the current version.
             if @record.has_attribute?(v) &&
-                @record.send("#{v}_changed?".to_sym) &&
+                attribute_changed_in_latest_version?(v) &&
                 data[:event] != "create"
-              @record.send("#{v}_was".to_sym)
+              attribute_in_previous_version(v)
             else
               @record.send(v)
             end
@@ -164,11 +173,14 @@ def previous_version
     end
 
     def record_create
+      @in_after_callback = true
       return unless enabled?
       versions_assoc = @record.send(@record.class.versions_association_name)
       version = versions_assoc.create! data_for_create
       update_transaction_id(version)
       save_associations(version)
+    ensure
+      @in_after_callback = false
     end
 
     # Returns data for record create
@@ -225,6 +237,7 @@ def record_object_changes?
     end
 
     def record_update(force)
+      @in_after_callback = true
       if enabled? && (force || changed_notably?)
         versions_assoc = @record.send(@record.class.versions_association_name)
         version = versions_assoc.create(data_for_update)
@@ -235,6 +248,8 @@ def record_update(force)
           save_associations(version)
         end
       end
+    ensure
+      @in_after_callback = false
     end
 
     # Returns data for record update
@@ -474,5 +489,41 @@ def version
     def versions
       @record.public_send(@record.class.versions_association_name)
     end
+
+    def attribute_in_previous_version(attr_name)
+      if @in_after_callback && rails_51?
+        @record.attribute_before_last_save(attr_name.to_s)
+      else
+        @record.attribute_was(attr_name.to_s)
+      end
+    end
+
+    def changed_in_latest_version
+      if @in_after_callback && rails_51?
+        @record.saved_changes.keys
+      else
+        @record.changed
+      end
+    end
+
+    def changes_in_latest_version
+      if @in_after_callback && rails_51?
+        @record.saved_changes
+      else
+        @record.changes
+      end
+    end
+
+    def attribute_changed_in_latest_version?(attr_name)
+      if @in_after_callback && rails_51?
+        @record.saved_change_to_attribute?(attr_name.to_s)
+      else
+        @record.attribute_changed?(attr_name.to_s)
+      end
+    end
+
+    def rails_51?
+      ActiveRecord::VERSION::MAJOR >= 5 && ActiveRecord::VERSION::MINOR >= 1
+    end
   end
 end

lib/paper_trail/reifier.rb

@@ -264,7 +264,7 @@ def reify_has_ones(transaction_id, model, options = {})
             if options[:mark_for_destruction]
               model.send(assoc.name).mark_for_destruction if model.send(assoc.name, true)
             else
-              model.paper_trail.appear_as_new_record do
+              model.paper_trail.appear_as_unpersisted do
                 model.send "#{assoc.name}=", nil
               end
             end
@@ -277,7 +277,7 @@ def reify_has_ones(transaction_id, model, options = {})
                 has_and_belongs_to_many: false
               )
             )
-            model.paper_trail.appear_as_new_record do
+            model.paper_trail.appear_as_unpersisted do
               without_persisting(child) do
                 model.send "#{assoc.name}=", child
               end

test/dummy/app/models/song.rb

@@ -1,7 +1,6 @@
 # Example from 'Overwriting default accessors' in ActiveRecord::Base.
 class Song < ActiveRecord::Base
   has_paper_trail
-  attr_accessor :name
 
   # Uses an integer of seconds to hold the length of the song
   def length=(minutes)
@@ -12,30 +11,36 @@ def length
     read_attribute(:length) / 60
   end
 
-  # override attributes hashes like some libraries do
-  def attributes_with_name
-    if name
-      attributes_without_name.merge(name: name)
-    else
-      attributes_without_name
+  if ActiveRecord::VERSION::MAJOR >= 5
+    attribute :name
+  else
+    attr_accessor :name
+
+    # override attributes hashes like some libraries do
+    def attributes_with_name
+      if name
+        attributes_without_name.merge(name: name)
+      else
+        attributes_without_name
+      end
     end
-  end
 
-  # `alias_method_chain` is deprecated in rails 5, but we cannot use the
-  # suggested replacement, `Module#prepend`, because we still support ruby 1.9.
-  alias attributes_without_name attributes
-  alias attributes attributes_with_name
+    # `alias_method_chain` is deprecated in rails 5, but we cannot use the
+    # suggested replacement, `Module#prepend`, because we still support ruby 1.9.
+    alias attributes_without_name attributes
+    alias attributes attributes_with_name
 
-  def changed_attributes_with_name
-    if name
-      changed_attributes_without_name.merge(name: name)
-    else
-      changed_attributes_without_name
+    def changed_attributes_with_name
+      if name
+        changed_attributes_without_name.merge(name: name)
+      else
+        changed_attributes_without_name
+      end
     end
-  end
 
-  # `alias_method_chain` is deprecated in rails 5, but we cannot use the
-  # suggested replacement, `Module#prepend`, because we still support ruby 1.9.
-  alias changed_attributes_without_name changed_attributes
-  alias changed_attributes changed_attributes_with_name
+    # `alias_method_chain` is deprecated in rails 5, but we cannot use the
+    # suggested replacement, `Module#prepend`, because we still support ruby 1.9.
+    alias changed_attributes_without_name changed_attributes
+    alias changed_attributes changed_attributes_with_name
+  end
 end