Fix nested blank search params not being stripped from searches.

From https://danbooru.donmai.us/forum_topics/9127?page=258#forum_post_151308:

    When you do a user search (from https://danbooru.donmai.us/users/search)
    the results only include those with someone in the inviter field.

The bug was that nested blank search params (/users?search[inviter][name_matches]=)
didn't get stripped from the search.

app/controllers/application_controller.rb

@@ -199,15 +199,17 @@ class ApplicationController < ActionController::Base
   # /tags?search[name]=touhou&search[category]=&search[order]=
   # => /tags?search[name]=touhou
   def normalize_search
-    if request.get?
-      if params[:search].blank?
-        params[:search] = ActionController::Parameters.new
-      end
+    return unless request.get?
+    params[:search] ||= ActionController::Parameters.new
 
-      if params[:search].is_a?(ActionController::Parameters) && params[:search].values.any?(&:blank?)
-        params[:search].reject! {|k,v| v.blank?}
-        redirect_to url_for(params: params.except(:controller, :action, :index).permit!)
-      end
+    deep_reject_blank = lambda do |hash|
+      hash.reject { |k, v| v.blank? || (v.is_a?(Hash) && deep_reject_blank.call(v).blank?) }
+    end
+    nonblank_search_params = deep_reject_blank.call(params[:search])
+
+    if nonblank_search_params != params[:search]
+      params[:search] = nonblank_search_params
+      redirect_to url_for(params: params.except(:controller, :action, :index).permit!)
     end
   end
 

test/functional/users_controller_test.rb

@@ -26,6 +26,11 @@ class UsersControllerTest < ActionDispatch::IntegrationTest
         get users_path, params: {:search => {:name_matches => @user.name}}
         assert_response :success
       end
+
+      should "list all users (with blank search parameters)" do
+        get users_path, params: { search: { inviter: { name_matches: "" }, level: "", name: "test" } }
+        assert_redirected_to users_path(search: { name: "test" })
+      end
     end
 
     context "show action" do