Allow user to filter by Issues/Merge Requests without a Milestone

app/finders/issuable_finder.rb

@@ -76,7 +76,7 @@ class IssuableFinder
     return @milestones if defined?(@milestones)
 
     @milestones =
-      if milestones? && params[:milestone_title] != NONE
+      if milestones? && params[:milestone_title] != NoMilestone.title
         Milestone.where(title: params[:milestone_title])
       else
         nil
@@ -183,7 +183,12 @@ class IssuableFinder
 
   def by_milestone(items)
     if milestones?
-      items = items.where(milestone_id: milestones.try(:pluck, :id))
+      # `milestone_title` will still be present when "No Milestone" is selected
+      if params[:milestone_title] != NoMilestone.title
+        items = items.where(milestone_id: milestones.try(:pluck, :id))
+      else
+        items = items.where(milestone_id: NoMilestone.id)
+      end
     end
 
     items

app/helpers/milestones_helper.rb

@@ -29,6 +29,8 @@ module MilestonesHelper
       end.active
 
     grouped_milestones = Milestones::GroupService.new(milestones).execute
+    grouped_milestones.unshift(NoMilestone)
+
     options_from_collection_for_select(grouped_milestones, 'title', 'title', params[:milestone_title])
   end
 end

app/models/no_milestone.rb

@@ -0,0 +1,13 @@
+# NoMilestone
+#
+# Represents a "No Milestone" state used for filtering Issues and Merge Requests
+# that have no milestone assigned.
+class NoMilestone
+  def self.id
+    nil
+  end
+
+  def self.title
+    'No Milestone'
+  end
+end

app/views/shared/issuable/_filter.html.haml

@@ -43,11 +43,15 @@
             placeholder: 'Author', class: 'trigger-submit', any_user: true, first_user: true)
 
         .filter-item.inline.milestone-filter
-          = select_tag('milestone_title', projects_milestones_options, class: "select2 trigger-submit", prompt: 'Milestone')
+          = select_tag('milestone_title', projects_milestones_options,
+            class: 'select2 trigger-submit', include_blank: true,
+            data: {placeholder: 'Milestone'})
 
         - if @project
           .filter-item.inline.labels-filter
-            = select_tag('label_name', project_labels_options(@project), class: "select2 trigger-submit", prompt: 'Label')
+            = select_tag('label_name', project_labels_options(@project),
+              class: 'select2 trigger-submit', include_blank: true,
+              data: {placeholder: 'Label'})
 
         .pull-right
           = render 'shared/sort_dropdown'

spec/features/issues/filter_by_milestone_spec.rb

@@ -0,0 +1,38 @@
+require 'spec_helper'
+
+feature 'Issue filtering by Milestone' do
+  include Select2Helper
+
+  let(:project) { create(:empty_project) }
+
+  before do
+    login_as(:admin)
+  end
+
+  scenario 'User filters by Issues without a Milestone', js: true do
+    create(:issue, project: project)
+
+    visit_issues
+    filter_by_milestone(NoMilestone.title)
+
+    expect(page).to have_css('.issue-title', count: 1)
+  end
+
+  scenario 'User filters by Issues with a specific Milestone', js: true do
+    milestone = create(:milestone, project: project)
+    create(:issue, project: project, milestone: milestone)
+
+    visit_issues
+    filter_by_milestone(milestone.title)
+
+    expect(page).to have_css('.issue-title', count: 1)
+  end
+
+  def visit_issues
+    visit namespace_project_issues_path(project.namespace, project)
+  end
+
+  def filter_by_milestone(title)
+    select2(title, from: '#milestone_title')
+  end
+end

spec/features/merge_requests/filter_by_milestone_spec.rb

@@ -0,0 +1,38 @@
+require 'spec_helper'
+
+feature 'Merge Request filtering by Milestone' do
+  include Select2Helper
+
+  let(:project) { create(:project) }
+
+  before do
+    login_as(:admin)
+  end
+
+  scenario 'User filters by Merge Requests without a Milestone', js: true do
+    create(:merge_request, :simple, source_project: project)
+
+    visit_merge_requests
+    filter_by_milestone(NoMilestone.title)
+
+    expect(page).to have_css('.merge-request-title', count: 1)
+  end
+
+  scenario 'User filters by Merge Requests with a specific Milestone', js: true do
+    milestone = create(:milestone, project: project)
+    create(:merge_request, :simple, source_project: project, milestone: milestone)
+
+    visit_merge_requests
+    filter_by_milestone(milestone.title)
+
+    expect(page).to have_css('.merge-request-title', count: 1)
+  end
+
+  def visit_merge_requests
+    visit namespace_project_merge_requests_path(project.namespace, project)
+  end
+
+  def filter_by_milestone(title)
+    select2(title, from: '#milestone_title')
+  end
+end