Reintroduce and deprecate whitelisted_params config

This allows people to switch to the new config without
breaking their applications or requiring a new release
for libraries using this gem.

lib/canonical-rails.rb

@@ -1,4 +1,5 @@
 require "canonical-rails/engine"
+require "canonical-rails/deprecation"
 
 module CanonicalRails
 
@@ -23,6 +24,10 @@ def self.setup
   mattr_accessor :collection_actions
   @@collection_actions = [:index]
 
+  # @deprecated: use config.allowed_parameters instead
+  mattr_accessor :whitelisted_parameters
+  @@whitelisted_parameters = []
+
   mattr_accessor :allowed_parameters
   @@allowed_parameters = []
 
@@ -34,6 +39,11 @@ def self.sym_collection_actions
   end
 
   def self.sym_allowed_parameters
-    @@sym_allowed_parameters ||= self.allowed_parameters.map(&:to_sym)
+    @@sym_allowed_parameters ||= if self.whitelisted_parameters.empty?
+      self.allowed_parameters.map(&:to_sym)
+    else
+      CanonicalRails::Deprecation.warn('config.whitelisted_parameters is deprecated, please use config.allowed_parameters instead.')
+      self.whitelisted_parameters.map(&:to_sym)
+    end
   end
 end

lib/canonical-rails/deprecation.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+require 'active_support/deprecation'
+
+module CanonicalRails
+  Deprecation = ActiveSupport::Deprecation.new('1.0', 'CanonicalRails')
+end

spec/helpers/canonical_rails/tag_helper_spec.rb

@@ -210,6 +210,26 @@
         end
       end
     end
+
+    describe 'with the old config.whitelisted_parameters' do
+      before do
+        CanonicalRails.whitelisted_parameters = ['page']
+        allow_any_instance_of(controller.class)
+          .to receive(:params)
+          .and_return(ActionController::Parameters.new('i-will' => 'kill-your-seo', 'page' => '5'))
+        controller.request.path_parameters = { controller: 'our_resources', action: 'index' }
+      end
+
+      after do
+        CanonicalRails.class_variable_set(:@@sym_whitelisted_parameters, nil)
+      end
+
+      it 'emits a deprecation warning and keeps working' do
+        expect(CanonicalRails::Deprecation).to receive(:warn).once
+        expect(helper.allowed_params['page']).to eq(5)
+        expect(helper.allowed_params['i-will']).to eq(5)
+      end
+    end
   end
 
   describe 'when host is specified' do