Make pagination optional for issuables

On epics roadmap page we list all epics in the given time frame
without pagination (at least for the first iteration), in this
case it would be nice to use the existing issuables index logic
except pagination (see MR gitlab-ee!4281). For this reason this
patch allows to easily disable pagination.

Related gitlab-ee!4281

app/controllers/concerns/issuable_collections.rb

@@ -12,11 +12,9 @@ module IssuableCollections
 
   # rubocop:disable Gitlab/ModuleWithInstanceVariables
   def set_issuables_index
-    @issuables          = issuables_collection
-    @issuables          = @issuables.page(params[:page])
-    @issuable_meta_data = issuable_meta_data(@issuables, collection_type)
-    @total_pages        = issuable_page_count
+    @issuables = issuables_collection
 
+    set_pagination
     return if redirect_out_of_range(@total_pages)
 
     if params[:label_name].present?
@@ -35,14 +33,26 @@ module IssuableCollections
       @users.push(author) if author
     end
   end
+
+  def set_pagination
+    return if pagination_disabled?
+
+    @issuables          = @issuables.page(params[:page])
+    @issuable_meta_data = issuable_meta_data(@issuables, collection_type)
+    @total_pages        = issuable_page_count
+  end
   # rubocop:enable Gitlab/ModuleWithInstanceVariables
 
+  def pagination_disabled?
+    false
+  end
+
   def issuables_collection
     finder.execute.preload(preload_for_collection)
   end
 
   def redirect_out_of_range(total_pages)
-    return false if total_pages.zero?
+    return false if total_pages.nil? || total_pages.zero?
 
     out_of_range = @issuables.current_page > total_pages # rubocop:disable Gitlab/ModuleWithInstanceVariables
 

spec/controllers/projects/issues_controller_spec.rb

@@ -102,6 +102,18 @@ describe Projects::IssuesController do
 
         expect(response).to redirect_to(namespace_project_issues_path(page: last_page, state: controller.params[:state], scope: controller.params[:scope]))
       end
+
+      it 'does not use pagination if disabled' do
+        allow(controller).to receive(:pagination_disabled?).and_return(true)
+
+        get :index,
+          namespace_id: project.namespace.to_param,
+          project_id: project,
+          page: (last_page + 1).to_param
+
+        expect(response).to have_gitlab_http_status(200)
+        expect(assigns(:issues).size).to eq(2)
+      end
     end
   end