DEV: Add support for Rails 6

Minor fixes to add Rails 6 support to Discourse, we now will boot
with RAILS_MASTER=1, all specs pass

Only one tiny deprecation left

Largest change was the way ActiveModel:Errors changed interface a
bit but there is a simple backwards compat way of working it

lib/freedom_patches/active_record_attribute_methods.rb

@@ -10,9 +10,19 @@
 module ActiveRecord
   module AttributeMethods
     module ClassMethods
+      # this is for Rails 5
       def enforce_raw_sql_whitelist(*args)
         return
       end
+
+      BLANK_ARRAY = [].freeze
+
+      # this patch just allows everyting in Rails 6
+      def disallow_raw_sql!(args, permit: nil)
+        # we may consider moving to https://github.com/rails/rails/pull/33330
+        # once all frozen string hints are in place
+        return BLANK_ARRAY
+      end
     end
   end
 end

lib/freedom_patches/rails6.rb

@@ -0,0 +1,9 @@
+# this is a quick backport of a new method introduced in Rails 6
+# to be removed after we upgrade to Rails 6
+if ! defined? ActionView::Base.with_view_paths
+  class ActionView::Base
+    class << self
+      alias with_view_paths new
+    end
+  end
+end