Use Prev/Next pagination for exploring projects

This changes the pagination of the "Explore" pages so they use a simpler
pagination system that only shows "Prev" and "Next" buttons. This
removes the need for getting the total number of rows to display, a
process that can easily take up to 2 seconds when browsing through a
large list of projects.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/27390

Gemfile

@@ -84,7 +84,7 @@ gem 'rack-cors', '~> 0.4.0', require: 'rack/cors'
 gem 'hashie-forbidden_attributes'
 # Pagination
-gem 'kaminari', '~> 0.17.0'
+gem 'kaminari', '~> 1.0'
 # HAML
 gem 'hamlit', '~> 2.6.1'

Gemfile.lock

@@ -419,9 +419,18 @@ GEM
     json-schema (2.6.2)
       addressable (~> 2.3.8)
     jwt (1.5.6)
-    kaminari (0.17.0)
-      actionpack (>= 3.0.0)
-      activesupport (>= 3.0.0)
+    kaminari (1.0.1)
+      activesupport (>= 4.1.0)
+      kaminari-actionview (= 1.0.1)
+      kaminari-activerecord (= 1.0.1)
+      kaminari-core (= 1.0.1)
+    kaminari-actionview (1.0.1)
+      actionview
+      kaminari-core (= 1.0.1)
+    kaminari-activerecord (1.0.1)
+      activerecord
+      kaminari-core (= 1.0.1)
+    kaminari-core (1.0.1)
     kgio (2.10.0)
     knapsack (1.11.0)
       rake
@@ -1011,7 +1020,7 @@ DEPENDENCIES
   jquery-rails (~> 4.1.0)
   json-schema (~> 2.6.2)
   jwt (~> 1.5.6)
-  kaminari (~> 0.17.0)
+  kaminari (~> 1.0)
   knapsack (~> 1.11.0)
   kubeclient (~> 2.2.0)
   letter_opener_web (~> 1.3.0)

app/controllers/explore/projects_controller.rb

@@ -6,7 +6,7 @@ class Explore::ProjectsController < Explore::ApplicationController
   def index
     params[:sort] ||= 'latest_activity_desc'
     @sort = params[:sort]
-    @projects = load_projects.page(params[:page])
+    @projects = load_projects
     respond_to do |format|
       format.html
@@ -21,7 +21,7 @@ class Explore::ProjectsController < Explore::ApplicationController
   def trending
     params[:trending] = true
     @sort = params[:sort]
-    @projects = load_projects.page(params[:page])
+    @projects = load_projects
     respond_to do |format|
       format.html
@@ -34,7 +34,7 @@ class Explore::ProjectsController < Explore::ApplicationController
   end
   def starred
-    @projects = load_projects.reorder('star_count DESC').page(params[:page])
+    @projects = load_projects.reorder('star_count DESC')
     respond_to do |format|
       format.html
@@ -50,6 +50,9 @@ class Explore::ProjectsController < Explore::ApplicationController
   def load_projects
     ProjectsFinder.new(current_user: current_user, params: params)
-      .execute.includes(:route, namespace: :route)
+      .execute
+      .includes(:route, namespace: :route)
+      .page(params[:page])
+      .without_count
   end
 end

app/helpers/pagination_helper.rb

+module PaginationHelper
+  def paginate_collection(collection, remote: nil)
+    if collection.is_a?(Kaminari::PaginatableWithoutCount)
+      paginate_without_count(collection)
+    elsif collection.respond_to?(:total_pages)
+      paginate_with_count(collection, remote: remote)
+    end
+  end
+
+  def paginate_without_count(collection)
+    render(
+      'kaminari/gitlab/without_count',
+      previous_path: path_to_prev_page(collection),
+      next_path: path_to_next_page(collection)
+    )
+  end
+
+  def paginate_with_count(collection, remote: nil)
+    paginate(collection, remote: remote, theme: 'gitlab')
+  end
+end

app/views/kaminari/gitlab/_without_count.html.haml

+.gl-pagination
+  %ul.pagination.clearfix
+    - if previous_path
+      %li.prev
+        = link_to(t('views.pagination.previous'), previous_path, rel: 'prev')
+    - if next_path
+      %li.next
+        = link_to(t('views.pagination.next'), next_path, rel: 'next')

app/views/shared/projects/_list.html.haml

@@ -23,6 +23,6 @@
           = icon('lock fw', base: 'circle', class: 'fa-lg private-fork-icon')
           %strong= pluralize(@private_forks_count, 'private fork')
           %span  you have no access to.
-    = paginate(projects, remote: remote, theme: "gitlab") if projects.respond_to? :total_pages
+    = paginate_collection(projects, remote: remote)
   - else
     .nothing-here-block No projects found

changelogs/unreleased/pagination-projects-explore.yml

+---
+title: Use Prev/Next pagination for exploring projects
+merge_request:
+author:

spec/helpers/pagination_helper_spec.rb

+require 'spec_helper'
+
+describe PaginationHelper do
+  describe '#paginate_collection' do
+    let(:collection) { User.all.page(1) }
+
+    it 'paginates a collection without using a COUNT' do
+      without_count = collection.without_count
+
+      expect(helper).to receive(:paginate_without_count)
+        .with(without_count)
+        .and_call_original
+
+      helper.paginate_collection(without_count)
+    end
+
+    it 'paginates a collection using a COUNT' do
+      expect(helper).to receive(:paginate_with_count).and_call_original
+
+      helper.paginate_collection(collection)
+    end
+  end
+end