Allow the SearchState implementation to be configurable

app/controllers/concerns/blacklight/controller.rb

@@ -26,6 +26,11 @@ module Blacklight::Controller
     helper_method :search_action_url, :search_action_path, :search_facet_url, :search_facet_path
     helper_method :search_state
 
+    # Specify which class to use for the search state. You can subclass SearchState if you
+    # want to override any of the methods (e.g. SearchState#url_for_document)
+    class_attribute :search_state_class
+    self.search_state_class = Blacklight::SearchState
+
     # This callback runs when a user first logs in
 
     define_callbacks :logging_in_user
@@ -64,7 +69,7 @@ def render_saved_searches?
 
     # @return [Blacklight::SearchState] a memoized instance of the parameter state.
     def search_state
-      @search_state ||= Blacklight::SearchState.new(params, blacklight_config)
+      @search_state ||= search_state_class.new(params, blacklight_config)
     end
 
     # Default route to the search action (used e.g. in global partials). Override this method

app/helpers/blacklight/render_constraints_helper_behavior.rb

@@ -65,7 +65,7 @@ def remove_constraint_url(localized_params)
   # @return [String]
   def render_constraints_filters(localized_params = params)
      return "".html_safe unless localized_params[:f]
-     path = Blacklight::SearchState.new(localized_params, blacklight_config)
+     path = controller.search_state_class.new(localized_params, blacklight_config)
      content = []
      localized_params[:f].each_pair do |facet, values|
        content << render_filter_element(facet, values, path)

app/helpers/blacklight/url_helper_behavior.rb

@@ -2,10 +2,6 @@
 ##
 # URL helper methods
 module Blacklight::UrlHelperBehavior
-  ##
-  # Extension point for downstream applications
-  # to provide more interesting routing to
-  # documents
   def url_for_document(doc, options = {})
     search_state.url_for_document(doc, options)
   end

lib/blacklight/search_state.rb

@@ -32,9 +32,13 @@ def to_hash
     alias to_h to_hash
 
     def reset
-      Blacklight::SearchState.new(ActionController::Parameters.new, blacklight_config)
+      self.class.new(ActionController::Parameters.new, blacklight_config)
     end
 
+    ##
+    # Extension point for downstream applications
+    # to provide more interesting routing to
+    # documents
     def url_for_document(doc, options = {})
       if respond_to?(:blacklight_config) &&
           blacklight_config.show.route &&
@@ -116,7 +120,7 @@ def remove_facet_params(field, item)
     # @yield [params] The merged parameters hash before being sanitized
     def params_for_search(params_to_merge = {})
       # params hash we'll return
-      my_params = params.dup.merge(Blacklight::SearchState.new(params_to_merge, blacklight_config))
+      my_params = params.dup.merge(self.class.new(params_to_merge, blacklight_config))
 
       if block_given?
         yield my_params

spec/helpers/blacklight/render_constraints_helper_behavior_spec.rb

@@ -69,6 +69,7 @@
     let(:params) { ActionController::Parameters.new f: { 'type' => [''] } }
     before do
       allow(helper).to receive(:blacklight_config).and_return(config)
+      allow(controller).to receive(:search_state_class).and_return(Blacklight::SearchState)
     end
     subject { helper.render_constraints_filters(params) }