Merge pull request #1006 from airblade/warn_when_pt_cannot_load

Print warning when PT cannot be loaded ..

CHANGELOG.md

@@ -16,7 +16,8 @@ recommendations of [keepachangelog.com](http://keepachangelog.com/).
 
 ### Fixed
 
-- None
+- [#1003](https://github.com/airblade/paper_trail/pull/1003) - Warn when PT
+  cannot be loaded because rails is not loaded yet.
 
 ## 8.0.0 (2017-10-04)
 

lib/paper_trail.rb

@@ -14,6 +14,12 @@ require "paper_trail/serializers/yaml"
 # An ActiveRecord extension that tracks changes to your models, for auditing or
 # versioning.
 module PaperTrail
+  E_RAILS_NOT_LOADED = <<-EOS.squish.freeze
+    PaperTrail has been loaded too early, before rails is loaded. This can
+    happen when another gem defines the ::Rails namespace, then PT is loaded,
+    all before rails is loaded. You may want to reorder your Gemfile, or defer
+    the loading of PT by using `require: false` and a manual require elsewhere.
+  EOS
   E_TIMESTAMP_FIELD_CONFIG = <<-EOS.squish.freeze
     PaperTrail.timestamp_field= has been removed, without replacement. It is no
     longer configurable. The timestamp field in the versions table must now be
@@ -190,8 +196,14 @@ ActiveSupport.on_load(:active_record) do
 end
 
 # Require frameworks
-if defined?(::Rails) && ActiveRecord::VERSION::STRING >= "3.2"
-  require "paper_trail/frameworks/rails"
+if defined?(::Rails)
+  # Rails module is sometimes defined by gems like rails-html-sanitizer
+  # so we check for presence of Rails.application.
+  if defined?(::Rails.application)
+    require "paper_trail/frameworks/rails"
+  else
+    ::Kernel.warn(::PaperTrail::E_RAILS_NOT_LOADED)
+  end
 else
   require "paper_trail/frameworks/active_record"
 end