Snippet explore to only show next/previous links

This avoids the costly total count query, needed to
compute links to the last page.

app/controllers/explore/snippets_controller.rb

 # frozen_string_literal: true
 
 class Explore::SnippetsController < Explore::ApplicationController
-  include PaginatedCollection
   include Gitlab::NoteableMetadata
 
   def index
     @snippets = SnippetsFinder.new(current_user, explore: true)
       .execute
       .page(params[:page])
+      .without_count
       .inc_author
 
-    return if redirect_out_of_range(@snippets)
-
     @noteable_meta_data = noteable_meta_data(@snippets, 'Snippet')
   end
 end

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

@@ -8,4 +8,4 @@
     %ul.content-list
       = render partial: 'shared/snippets/snippet', collection: @snippets, locals: { link_project: link_project }
 
-    = paginate @snippets, theme: 'gitlab', remote: remote
+    = paginate_collection @snippets, remote: remote

changelogs/unreleased/34420-optimize-pagination-on-explore-snippets.yml

+---
+title: Showing only "Next" button for snippet explore page.
+merge_request: 25404
+author:
+type: changed

spec/controllers/explore/snippets_controller_spec.rb

@@ -4,12 +4,33 @@ require 'spec_helper'
 
 describe Explore::SnippetsController do
   describe 'GET #index' do
-    it_behaves_like 'paginated collection' do
-      let(:collection) { Snippet.all }
+    let!(:project_snippet) { create_list(:project_snippet, 3, :public) }
+    let!(:personal_snippet) { create_list(:personal_snippet, 3, :public) }
 
-      before do
-        create(:personal_snippet, :public)
-      end
+    before do
+      allow(Kaminari.config).to receive(:default_per_page).and_return(2)
+    end
+
+    it 'renders' do
+      get :index
+
+      snippets = assigns(:snippets)
+
+      expect(snippets).to be_a(::Kaminari::PaginatableWithoutCount)
+      expect(snippets.size).to eq(2)
+      expect(snippets).to all(be_a(PersonalSnippet))
+      expect(response).to have_gitlab_http_status(:ok)
+    end
+
+    it 'renders pagination' do
+      get :index, params: { page: 2 }
+
+      snippets = assigns(:snippets)
+
+      expect(snippets).to be_a(::Kaminari::PaginatableWithoutCount)
+      expect(snippets.size).to eq(1)
+      expect(assigns(:snippets)).to all(be_a(PersonalSnippet))
+      expect(response).to have_gitlab_http_status(:ok)
     end
   end
 end