Make it possible to get good polymorphic joins

Actually getting polymorphic joins to work correctly will require
either explicitly specifying the master branch of the `ransack`
project (commit c9cc20de9e0f or something with equivalent
functionality) in the project `Gemfile` or the `ransack` project
releasing a new 2.x (> 2.3.2) version with that functionality.

Addresses most of the Active Record 5.2.x (>= 5.2.1) problems in
rzane#97.  The only remaining issues are around inner
joins after left joins.

Gemfile

@@ -12,6 +12,19 @@ else
   gem 'activerecord', ENV['AR']
 end
 
+case ENV.fetch('RANSACK', 'latest')
+when 'latest'
+  gem 'ransack', require: false
+when 'master'
+  gem 'ransack', github: 'activerecord-hackery/ransack', require: false
+else
+  ENV['RANSACK'].split('#').tap do |repo, branch|
+    opts = {git: repo, require: false}
+    opts[:branch] = branch if branch
+    gem 'ransack', opts
+  end
+end
+
 gem 'bump'
 
 group :test do

baby_squeel.gemspec

@@ -20,7 +20,7 @@ Gem::Specification.new do |spec|
   spec.files = Dir.glob('{lib/**/*,*.{md,txt,gemspec}}')
 
   spec.add_dependency 'activerecord', '>= 4.2.0'
-  spec.add_dependency 'polyamorous', '~> 2.3.0'
+  spec.add_dependency 'ransack', '~> 2.3'
   spec.add_dependency 'join_dependency', '~> 0.1.4'
 
   spec.add_development_dependency 'bundler', '~> 2'

lib/baby_squeel.rb

@@ -1,6 +1,11 @@
 require 'active_record'
 require 'active_record/relation'
-require 'polyamorous'
+begin
+  require 'polyamorous'
+rescue LoadError
+  # Trying loading from 'ransack' as of commit c9cc20de9 (post v2.3.2)
+  require 'polyamorous/polyamorous'
+end
 require 'baby_squeel/version'
 require 'baby_squeel/errors'
 require 'baby_squeel/active_record/base'