Fix /explore sorting (trending)

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/27044

app/controllers/explore/projects_controller.rb

@@ -22,6 +22,7 @@ class Explore::ProjectsController < Explore::ApplicationController
 
   def trending
     @projects = filter_projects(Project.trending)
+    @projects = @projects.sort(@sort = params[:sort])
     @projects = @projects.page(params[:page])
 
     respond_to do |format|

changelogs/unreleased/27044-fix-explore-sorting-on-trending.yml

+---
+title: Fix /explore sorting
+merge_request:
+author:

spec/controllers/explore/projects_controller_spec.rb

+require 'spec_helper'
+
+describe Explore::ProjectsController do
+  let(:user) { create(:user) }
+  let(:visibility) { :public }
+
+  describe 'GET #trending' do
+    let!(:project_1) { create(:project, visibility, ci_id: 1) }
+    let!(:project_2) { create(:project, visibility, ci_id: 2) }
+
+    let!(:trending_project_1) { create(:trending_project, project: project_1) }
+    let!(:trending_project_2) { create(:trending_project, project: project_2) }
+
+    before do
+      sign_in(user)
+    end
+
+    context 'sorting by update date' do
+      it 'sorts by last updated' do
+        get :trending, sort: 'updated_desc'
+        expect(assigns(:projects)).to eq [project_2, project_1]
+      end
+
+      it 'sorts by oldest updated' do
+        get :trending, sort: 'updated_asc'
+        expect(assigns(:projects)).to eq [project_1, project_2]
+      end
+    end
+  end
+end

spec/factories/trending_project.rb

+FactoryGirl.define do
+  # TrendingProject
+  factory :trending_project, class: 'TrendingProject' do
+    project
+  end
+end