Original implementation to allow users to subscribe to labels

1. Allow subscribing (the current user) to a label

- Refactor the `Subscription` coffeescript class
  - The main change is that it accepts a container, and conducts all
    DOM queries within its scope. We need this because the labels
    page has multiple instances of `Subscription` on the same page.

2. Creating an issue or MR with labels notifies users subscribed to those labels

- Label `has_many` subscribers through subscriptions.

3. Adding a label to an issue or MR notifies users subscribed to those labels

- This only applies to subscribers of the label that has just been
  added, not all labels for the issue.

31 files changed, 458 insertions, 64 deletions

diff --git a/CHANGELOG b/CHANGELOG
index 015efa05c6a..fb9500e68a0 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -174,6 +174,8 @@ v 8.5.0
 
 v 8.4.5
   - No CE-specific changes
+  - Allow user subscription to a label; get notified for issues/merge requests related to that label.
+  - Allow user subscription to a label; get notified for issues/merge requests related to that label. (Timothy Andrew)
 
 v 8.4.4
   - Update omniauth-saml gem to 1.4.2
diff --git a/app/assets/javascripts/subscription.js.coffee b/app/assets/javascripts/subscription.js.coffee
index 7f41616d4e7..afc17338b26 100644
--- a/app/assets/javascripts/subscription.js.coffee
+++ b/app/assets/javascripts/subscription.js.coffee
@@ -1,17 +1,19 @@
 class @Subscription
-  constructor: (url) ->
-    $(".subscribe-button").unbind("click").click (event)=>
-      btn = $(event.currentTarget)
-      action = btn.find("span").text()
-      current_status = $(".subscription-status").attr("data-status")
-      btn.prop("disabled", true)
-      
-      $.post url, =>
-        btn.prop("disabled", false)
-        status = if current_status == "subscribed" then "unsubscribed" else "subscribed"
-        $(".subscription-status").attr("data-status", status)
-        action = if status == "subscribed" then "Unsubscribe" else "Subscribe"
-        btn.find("span").text(action)
-        $(".subscription-status>div").toggleClass("hidden")
+  constructor: (@url, container) ->
+    @subscribe_button = $(container).find(".subscribe-button")
+    @subscription_status = $(container).find(".subscription-status")
+    @subscribe_button.unbind("click").click(@toggleSubscription)
 
-    
+  toggleSubscription: (event) =>
+    btn = $(event.currentTarget)
+    action = btn.find("span").text()
+    current_status = @subscription_status.attr("data-status")
+    btn.prop("disabled", true)
+
+    $.post @url, =>
+      btn.prop("disabled", false)
+      status = if current_status == "subscribed" then "unsubscribed" else "subscribed"
+      @subscription_status.attr("data-status", status)
+      action = if status == "subscribed" then "Unsubscribe" else "Subscribe"
+      btn.find("span").text(action)
+      @subscription_status.find(">div").toggleClass("hidden")
diff --git a/app/assets/stylesheets/pages/labels.scss b/app/assets/stylesheets/pages/labels.scss
index 5ec0966194c..1791ba9fbd8 100644
--- a/app/assets/stylesheets/pages/labels.scss
+++ b/app/assets/stylesheets/pages/labels.scss
@@ -41,3 +41,7 @@
 .color-label {
   padding: 3px 4px;
 }
+
+.label-subscription {
+    display: inline-block;
+}
\ No newline at end of file
diff --git a/app/controllers/projects/labels_controller.rb b/app/controllers/projects/labels_controller.rb
index ecac3c395ec..d0334c37b67 100644
--- a/app/controllers/projects/labels_controller.rb
+++ b/app/controllers/projects/labels_controller.rb
@@ -1,8 +1,8 @@
 class Projects::LabelsController < Projects::ApplicationController
   before_action :module_enabled
-  before_action :label, only: [:edit, :update, :destroy]
+  before_action :label, only: [:edit, :update, :destroy, :toggle_subscription]
   before_action :authorize_read_label!
-  before_action :authorize_admin_labels!, except: [:index]
+  before_action :authorize_admin_labels!, except: [:index, :toggle_subscription]
 
   respond_to :js, :html
 
@@ -60,6 +60,11 @@ class Projects::LabelsController < Projects::ApplicationController
     end
   end
 
+  def toggle_subscription
+    @label.toggle_subscription(current_user)
+    render nothing: true
+  end
+
   protected
 
   def module_enabled
diff --git a/app/mailers/emails/issues.rb b/app/mailers/emails/issues.rb
index 4a88cb61132..2838baa1b4e 100644
--- a/app/mailers/emails/issues.rb
+++ b/app/mailers/emails/issues.rb
@@ -16,7 +16,14 @@ module Emails
     def closed_issue_email(recipient_id, issue_id, updated_by_user_id)
       setup_issue_mail(issue_id, recipient_id)
 
-      @updated_by = User.find updated_by_user_id
+      @updated_by = User.find(updated_by_user_id)
+      mail_answer_thread(@issue, issue_thread_options(updated_by_user_id, recipient_id))
+    end
+
+    def relabeled_issue_email(recipient_id, issue_id, updated_by_user_id, label_names)
+      setup_issue_mail(issue_id, recipient_id)
+      @label_names = label_names
+      @updated_by = User.find(updated_by_user_id)
       mail_answer_thread(@issue, issue_thread_options(updated_by_user_id, recipient_id))
     end
 
@@ -24,7 +31,7 @@ module Emails
       setup_issue_mail(issue_id, recipient_id)
 
       @issue_status = status
-      @updated_by = User.find updated_by_user_id
+      @updated_by = User.find(updated_by_user_id)
       mail_answer_thread(@issue, issue_thread_options(updated_by_user_id, recipient_id))
     end
 
diff --git a/app/mailers/emails/merge_requests.rb b/app/mailers/emails/merge_requests.rb
index 325996e2e16..680ce975c79 100644
--- a/app/mailers/emails/merge_requests.rb
+++ b/app/mailers/emails/merge_requests.rb
@@ -19,10 +19,20 @@ module Emails
                          subject: subject("#{@merge_request.title} (##{@merge_request.iid})"))
     end
 
+    def relabeled_merge_request_email(recipient_id, merge_request_id, updated_by_user_id, label_names)
+      setup_merge_request_mail(merge_request_id, recipient_id)
+      @label_names = label_names
+      @updated_by = User.find(updated_by_user_id)
+      mail_answer_thread(@merge_request,
+                      from: sender(@merge_request.author_id),
+                      to: recipient(recipient_id),
+                      subject: subject("#{@merge_request.title} (##{@merge_request.iid})"))
+    end
+
     def closed_merge_request_email(recipient_id, merge_request_id, updated_by_user_id)
       setup_merge_request_mail(merge_request_id, recipient_id)
 
-      @updated_by = User.find updated_by_user_id
+      @updated_by = User.find(updated_by_user_id)
       mail_answer_thread(@merge_request,
                          from: sender(updated_by_user_id),
                          to: recipient(recipient_id),
@@ -42,7 +52,7 @@ module Emails
       setup_merge_request_mail(merge_request_id, recipient_id)
 
       @mr_status = status
-      @updated_by = User.find updated_by_user_id
+      @updated_by = User.find(updated_by_user_id)
       mail_answer_thread(@merge_request,
                          from: sender(updated_by_user_id),
                          to: recipient(recipient_id),
diff --git a/app/models/concerns/issuable.rb b/app/models/concerns/issuable.rb
index 3c42f582937..affc4a842a7 100644
--- a/app/models/concerns/issuable.rb
+++ b/app/models/concerns/issuable.rb
@@ -8,6 +8,7 @@ module Issuable
   extend ActiveSupport::Concern
   include Participable
   include Mentionable
+  include Subscribable
   include StripAttribute
 
   included do
@@ -18,7 +19,6 @@ module Issuable
     has_many :notes, as: :noteable, dependent: :destroy
     has_many :label_links, as: :target, dependent: :destroy
     has_many :labels, through: :label_links
-    has_many :subscriptions, dependent: :destroy, as: :subscribable
 
     validates :author, presence: true
     validates :title, presence: true, length: { within: 0..255 }
@@ -149,28 +149,6 @@ module Issuable
     notes.awards.where(note: "thumbsup").count
   end
 
-  def subscribed?(user)
-    subscription = subscriptions.find_by_user_id(user.id)
-
-    if subscription
-      return subscription.subscribed
-    end
-
-    participants(user).include?(user)
-  end
-
-  def toggle_subscription(user)
-    subscriptions.
-      find_or_initialize_by(user_id: user.id).
-      update(subscribed: !subscribed?(user))
-  end
-
-  def unsubscribe(user)
-    subscriptions.
-      find_or_initialize_by(user_id: user.id).
-      update(subscribed: false)
-  end
-
   def to_hook_data(user)
     hook_data = {
       object_kind: self.class.name.underscore,
@@ -201,6 +179,12 @@ module Issuable
     end
   end
 
+  # Labels that are currently applied to this object
+  # that are not present in `old_labels`
+  def added_labels(old_labels)
+    self.labels - old_labels
+  end
+
   # Convert this Issuable class name to a format usable by Ability definitions
   #
   # Examples:
diff --git a/app/models/concerns/subscribable.rb b/app/models/concerns/subscribable.rb
new file mode 100644
index 00000000000..cab9241ac3d
--- /dev/null
+++ b/app/models/concerns/subscribable.rb
@@ -0,0 +1,43 @@
+# == Subscribable concern
+#
+# Users can subscribe to these models.
+#
+# Used by Issue, MergeRequest, Label
+#
+
+module Subscribable
+  extend ActiveSupport::Concern
+
+  included do
+    has_many :subscriptions, dependent: :destroy, as: :subscribable
+  end
+
+  def subscribed?(user)
+    subscription = subscriptions.find_by_user_id(user.id)
+
+    if subscription
+      return subscription.subscribed
+    end
+
+    # FIXME
+    # Issue/MergeRequest has participants, but Label doesn't.
+    # Ideally, subscriptions should be separate from participations,
+    # but that seems like a larger change with farther-reaching
+    # consequences, so this is a compromise for the time being.
+    if respond_to?(:participants)
+      participants(user).include?(user)
+    end
+  end
+
+  def toggle_subscription(user)
+    subscriptions.
+      find_or_initialize_by(user_id: user.id).
+      update(subscribed: !subscribed?(user))
+  end
+
+  def unsubscribe(user)
+    subscriptions.
+      find_or_initialize_by(user_id: user.id).
+      update(subscribed: false)
+  end
+end
diff --git a/app/models/label.rb b/app/models/label.rb
index 5ff644b8426..f7ffc0b7f36 100644
--- a/app/models/label.rb
+++ b/app/models/label.rb
@@ -14,6 +14,8 @@
 
 class Label < ActiveRecord::Base
   include Referable
+  include Subscribable
+
   # Represents a "No Label" state used for filtering Issues and Merge
   # Requests that have no label assigned.
   LabelStruct = Struct.new(:title, :name)
diff --git a/app/services/issuable_base_service.rb b/app/services/issuable_base_service.rb
index ca87dca4a70..971c074882e 100644
--- a/app/services/issuable_base_service.rb
+++ b/app/services/issuable_base_service.rb
@@ -95,7 +95,7 @@ class IssuableBaseService < BaseService
 
     old_labels = options[:old_labels]
     if old_labels && (issuable.labels != old_labels)
-      create_labels_note(issuable, issuable.labels - old_labels, old_labels - issuable.labels)
+      create_labels_note(issuable, issuable.added_labels(old_labels), old_labels - issuable.labels)
     end
   end
 end
diff --git a/app/services/issues/update_service.rb b/app/services/issues/update_service.rb
index 51ef9dfe610..b2e63a4e1af 100644
--- a/app/services/issues/update_service.rb
+++ b/app/services/issues/update_service.rb
@@ -4,7 +4,7 @@ module Issues
       update(issue)
     end
 
-    def handle_changes(issue, options = {})
+    def handle_changes(issue, old_labels: [], new_labels: [])
       if has_changes?(issue, options)
         todo_service.mark_pending_todos_as_done(issue, current_user)
       end
@@ -23,6 +23,11 @@ module Issues
         notification_service.reassigned_issue(issue, current_user)
         todo_service.reassigned_issue(issue, current_user)
       end
+
+      new_labels = issue.added_labels(old_labels)
+      if new_labels.present?
+        notification_service.relabeled_issue(issue, new_labels, current_user)
+      end
     end
 
     def reopen_service
diff --git a/app/services/merge_requests/update_service.rb b/app/services/merge_requests/update_service.rb
index 6319ad805b6..6fd569dc302 100644
--- a/app/services/merge_requests/update_service.rb
+++ b/app/services/merge_requests/update_service.rb
@@ -14,7 +14,7 @@ module MergeRequests
       update(merge_request)
     end
 
-    def handle_changes(merge_request, options = {})
+    def handle_changes(issue, old_labels: [], new_labels: [])
       if has_changes?(merge_request, options)
         todo_service.mark_pending_todos_as_done(merge_request, current_user)
       end
@@ -44,6 +44,11 @@ module MergeRequests
           merge_request.previous_changes.include?('source_branch')
         merge_request.mark_as_unchecked
       end
+
+      new_labels = merge_request.added_labels(old_labels)
+      if new_labels.present?
+        notification_service.relabeled_merge_request(merge_request, new_labels, current_user)
+      end
     end
 
     def reopen_service
diff --git a/app/services/notification_service.rb b/app/services/notification_service.rb
index ca8a41d93b8..e9955cd3e2d 100644
--- a/app/services/notification_service.rb
+++ b/app/services/notification_service.rb
@@ -52,6 +52,14 @@ class NotificationService
     reassign_resource_email(issue, issue.project, current_user, 'reassigned_issue_email')
   end
 
+  # When we change labels on an issue we should send emails.
+  #
+  # We pass in the labels, here, because we only want the labels that
+  # have been *added* during this relabel, not all of them.
+  def relabeled_issue(issue, labels, current_user)
+    relabel_resource_email(issue, issue.project, labels, current_user, 'relabeled_issue_email')
+  end
+
 
   # When create a merge request we should send next emails:
   #
@@ -70,6 +78,14 @@ class NotificationService
     reassign_resource_email(merge_request, merge_request.target_project, current_user, 'reassigned_merge_request_email')
   end
 
+  # When we change labels on a merge request we should send emails.
+  #
+  # We pass in the labels, here, because we only want the labels that
+  # have been *added* during this relabel, not all of them.
+  def relabeled_merge_request(merge_request, labels, current_user)
+    relabel_resource_email(merge_request, merge_request.project, labels, current_user, 'relabeled_merge_request_email')
+  end
+
   def close_mr(merge_request, current_user)
     close_resource_email(merge_request, merge_request.target_project, current_user, 'closed_merge_request_email')
   end
@@ -142,6 +158,7 @@ class NotificationService
     recipients = reject_muted_users(recipients, note.project)
 
     recipients = add_subscribed_users(recipients, note.noteable)
+    recipients = add_label_subscriptions(recipients, note.noteable)
     recipients = reject_unsubscribed_users(recipients, note.noteable)
 
     recipients.delete(note.author)
@@ -359,6 +376,16 @@ class NotificationService
     end
   end
 
+  def add_label_subscriptions(recipients, target)
+    return recipients unless target.respond_to? :labels
+
+    target.labels.each do |label|
+      recipients += label.subscriptions.where(subscribed: true).map(&:user)
+    end
+
+    recipients
+  end
+
   def new_resource_email(target, project, method)
     recipients = build_recipients(target, project, target.author)
 
@@ -392,6 +419,15 @@ class NotificationService
     end
   end
 
+  def relabel_resource_email(target, project, labels, current_user, method)
+    recipients = build_relabel_recipients(target, project, labels, current_user)
+    label_names = labels.map(&:name)
+
+    recipients.each do |recipient|
+      mailer.send(method, recipient.id, target.id, current_user.id, label_names).deliver_later
+    end
+  end
+
   def reopen_resource_email(target, project, current_user, method, status)
     recipients = build_recipients(target, project, current_user)
 
@@ -416,6 +452,7 @@ class NotificationService
 
     recipients = reject_muted_users(recipients, project)
     recipients = add_subscribed_users(recipients, target)
+    recipients = add_label_subscriptions(recipients, target)
     recipients = reject_unsubscribed_users(recipients, target)
 
     recipients.delete(current_user)
@@ -423,6 +460,13 @@ class NotificationService
     recipients.uniq
   end
 
+  def build_relabel_recipients(target, project, labels, current_user)
+    recipients = add_label_subscriptions([], target)
+    recipients = reject_unsubscribed_users(recipients, target)
+    recipients.delete(current_user)
+    recipients.uniq
+  end
+
   def mailer
     Notify
   end
diff --git a/app/views/notify/_relabeled_issuable_email.html.haml b/app/views/notify/_relabeled_issuable_email.html.haml
new file mode 100644
index 00000000000..a41ff07c306
--- /dev/null
+++ b/app/views/notify/_relabeled_issuable_email.html.haml
@@ -0,0 +1,5 @@
+%p
+  #{@updated_by.name} added the
+  %em= @label_names.to_sentence
+  #{"label".pluralize(@label_names.count)} to #{issuable.class.model_name.human} #{issuable.iid}.
+
diff --git a/app/views/notify/_relabeled_issuable_email.text.erb b/app/views/notify/_relabeled_issuable_email.text.erb
new file mode 100644
index 00000000000..1a28d7fd352
--- /dev/null
+++ b/app/views/notify/_relabeled_issuable_email.text.erb
@@ -0,0 +1,5 @@
+<%= issuable.class.model_name.human.titleize %> <%= issuable.iid %> was relabeled.
+
+Issue <%= issuable.iid %>: <%= url_for(namespace_project_issue_url(issuable.project.namespace, issuable.project, issuable)) %>
+Author: <%= issuable.author_name %>
+New Labels: <%= @label_names.to_sentence %>
diff --git a/app/views/notify/relabeled_issue_email.html.haml b/app/views/notify/relabeled_issue_email.html.haml
new file mode 100644
index 00000000000..a3e094e86eb
--- /dev/null
+++ b/app/views/notify/relabeled_issue_email.html.haml
@@ -0,0 +1 @@
+= render "relabeled_issuable_email", issuable: @issue
diff --git a/app/views/notify/relabeled_issue_email.text.erb b/app/views/notify/relabeled_issue_email.text.erb
new file mode 100644
index 00000000000..de7f04a323a
--- /dev/null
+++ b/app/views/notify/relabeled_issue_email.text.erb
@@ -0,0 +1 @@
+<%= render "relabeled_issuable_email", issuable: @issue %>
diff --git a/app/views/notify/relabeled_merge_request_email.html.haml b/app/views/notify/relabeled_merge_request_email.html.haml
new file mode 100644
index 00000000000..3937b449a37
--- /dev/null
+++ b/app/views/notify/relabeled_merge_request_email.html.haml
@@ -0,0 +1 @@
+= render "relabeled_issuable_email", issuable: @merge_request
diff --git a/app/views/notify/relabeled_merge_request_email.text.erb b/app/views/notify/relabeled_merge_request_email.text.erb
new file mode 100644
index 00000000000..5c4d86e4dc2
--- /dev/null
+++ b/app/views/notify/relabeled_merge_request_email.text.erb
@@ -0,0 +1 @@
+<%= render "relabeled_issuable_email", issuable: @merge_request %>
diff --git a/app/views/projects/labels/_label.html.haml b/app/views/projects/labels/_label.html.haml
index f7ddd30c5a9..3b14a925c46 100644
--- a/app/views/projects/labels/_label.html.haml
+++ b/app/views/projects/labels/_label.html.haml
@@ -10,6 +10,18 @@
       = link_to_label(label) do
         = pluralize label.open_issues_count, 'open issue'
 
+    - if current_user
+      %div{class: "label-subscription", data: {id: label.id}}
+        - subscribed = label.subscribed?(current_user)
+        - subscription_status = subscribed ? 'subscribed' : 'unsubscribed'
+        .subscription-status{data: {status: subscription_status}}
+        %button.btn.btn-sm.btn-info.subscribe-button{:type => 'button'}
+          %span= subscribed ? 'Unsubscribe' : 'Subscribe'
+
     - if can? current_user, :admin_label, @project
       = link_to 'Edit', edit_namespace_project_label_path(@project.namespace, @project, label), class: 'btn btn-sm'
       = link_to 'Delete', namespace_project_label_path(@project.namespace, @project, label), class: 'btn btn-sm btn-remove remove-row', method: :delete, remote: true, data: {confirm: "Remove this label? Are you sure?"}
+
+:javascript
+  new Subscription("#{toggle_subscription_namespace_project_label_path(@project.namespace, @project, label)}",
+                   ".label-subscription[data-id='#{label.id}']");
diff --git a/app/views/shared/issuable/_sidebar.html.haml b/app/views/shared/issuable/_sidebar.html.haml
index 9020a1330a3..b44086d4205 100644
--- a/app/views/shared/issuable/_sidebar.html.haml
+++ b/app/views/shared/issuable/_sidebar.html.haml
@@ -98,7 +98,7 @@
       %hr
       - if current_user
         - subscribed = issuable.subscribed?(current_user)
-        .block.light
+        .block.light.subscription
           .sidebar-collapsed-icon
             = icon('rss')
           .title.hide-collapsed
@@ -124,5 +124,5 @@
           = clipboard_button(clipboard_text: project_ref)
 
     :javascript
-      new Subscription("#{toggle_subscription_path(issuable)}");
+      new Subscription("#{toggle_subscription_path(issuable)}", ".subscription");
       new IssuableContext();
diff --git a/config/routes.rb b/config/routes.rb
index 780ad757c5b..2ae282f48a6 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -675,6 +675,10 @@ Rails.application.routes.draw do
           collection do
             post :generate
           end
+
+          member do
+            post :toggle_subscription
+          end
         end
 
         resources :issues, constraints: { id: /\d+/ }, except: [:destroy] do
diff --git a/features/project/labels.feature b/features/project/labels.feature
new file mode 100644
index 00000000000..cd3f3a789f0
--- /dev/null
+++ b/features/project/labels.feature
@@ -0,0 +1,16 @@
+@labels
+Feature: Labels
+  Background:
+    Given I sign in as a user
+    And I own project "Shop"
+    And I visit project "Shop" issues page
+    And project "Shop" has labels: "bug", "feature", "enhancement"
+
+  @javascript
+  Scenario: I can subscribe to a label
+    When I visit project "Shop" labels page
+    Then I should see that I am unsubscribed
+    When I click button "Subscribe"
+    Then I should see that I am subscribed
+    When I click button "Unsubscribe"
+    Then I should see that I am unsubscribed
diff --git a/features/steps/project/labels.rb b/features/steps/project/labels.rb
new file mode 100644
index 00000000000..3f800a10594
--- /dev/null
+++ b/features/steps/project/labels.rb
@@ -0,0 +1,34 @@
+class Spinach::Features::Labels < Spinach::FeatureSteps
+  include SharedAuthentication
+  include SharedIssuable
+  include SharedProject
+  include SharedNote
+  include SharedPaths
+  include SharedMarkdown
+
+  step 'And I visit project "Shop" labels page' do
+    visit namespace_project_labels_path(project.namespace, project)
+  end
+
+  step 'I should see that I am subscribed' do
+    expect(subscribe_button).to have_content 'Unsubscribe'
+  end
+
+  step 'I should see that I am unsubscribed' do
+    expect(subscribe_button).to have_content 'Subscribe'
+  end
+
+  step 'I click button "Unsubscribe"' do
+    subscribe_button.click
+  end
+
+  step 'I click button "Subscribe"' do
+    subscribe_button.click
+  end
+
+  private
+
+  def subscribe_button
+    first('.subscribe-button span')
+  end
+end
diff --git a/spec/factories/labels.rb b/spec/factories/labels.rb
index 6e70af10af3..91a7400afa1 100644
--- a/spec/factories/labels.rb
+++ b/spec/factories/labels.rb
@@ -13,7 +13,7 @@
 
 FactoryGirl.define do
   factory :label do
-    title "Bug"
+    title { FFaker::Color.name }
     color "#990000"
     project
   end
diff --git a/spec/models/concerns/subscribable_spec.rb b/spec/models/concerns/subscribable_spec.rb
new file mode 100644
index 00000000000..9ee60426a5d
--- /dev/null
+++ b/spec/models/concerns/subscribable_spec.rb
@@ -0,0 +1,16 @@
+require "spec_helper"
+
+describe Subscribable, "Subscribable" do
+  let(:resource) { create(:issue) }
+  let(:user) { create(:user) }
+
+  describe "#subscribed?" do
+    it do
+      expect(resource.subscribed?(user)).to be_falsey
+      resource.toggle_subscription(user)
+      expect(resource.subscribed?(user)).to be_truthy
+      resource.toggle_subscription(user)
+      expect(resource.subscribed?(user)).to be_falsey
+    end
+  end
+end
diff --git a/spec/services/issues/update_service_spec.rb b/spec/services/issues/update_service_spec.rb
index e579e49dfa7..dc9d8329751 100644
--- a/spec/services/issues/update_service_spec.rb
+++ b/spec/services/issues/update_service_spec.rb
@@ -48,7 +48,7 @@ describe Issues::UpdateService, services: true do
       it { expect(@issue.assignee).to eq(user2) }
       it { expect(@issue).to be_closed }
       it { expect(@issue.labels.count).to eq(1) }
-      it { expect(@issue.labels.first.title).to eq('Bug') }
+      it { expect(@issue.labels.first.title).to eq(label.name) }
 
       it 'should send email to user2 about assign of new issue and email to user3 about issue unassignment' do
         deliveries = ActionMailer::Base.deliveries
@@ -148,6 +148,60 @@ describe Issues::UpdateService, services: true do
       end
     end
 
+    context "when the issue is relabeled" do
+      it "sends notifications for subscribers of newly added labels" do
+        subscriber, non_subscriber = create_list(:user, 2)
+        label.toggle_subscription(subscriber)
+        2.times { label.toggle_subscription(non_subscriber) }
+
+        opts = { label_ids: [label.id] }
+
+        perform_enqueued_jobs do
+          @issue = Issues::UpdateService.new(project, user, opts).execute(issue)
+        end
+
+        @issue.reload
+        should_email(subscriber)
+        should_not_email(non_subscriber)
+      end
+
+      it "does send notifications for existing labels" do
+        second_label = create(:label)
+        issue.labels << label
+        subscriber, non_subscriber = create_list(:user, 2)
+        label.toggle_subscription(subscriber)
+        2.times { label.toggle_subscription(non_subscriber) }
+
+        opts = { label_ids: [label.id, second_label.id] }
+
+        perform_enqueued_jobs do
+          @issue = Issues::UpdateService.new(project, user, opts).execute(issue)
+        end
+
+        @issue.reload
+        should_email(subscriber)
+        should_not_email(non_subscriber)
+      end
+
+      it "does not send notifications for removed labels" do
+        second_label = create(:label)
+        issue.labels << label
+        subscriber, non_subscriber = create_list(:user, 2)
+        label.toggle_subscription(subscriber)
+        2.times { label.toggle_subscription(non_subscriber) }
+
+        opts = { label_ids: [second_label.id] }
+
+        perform_enqueued_jobs do
+          @issue = Issues::UpdateService.new(project, user, opts).execute(issue)
+        end
+
+        @issue.reload
+        should_not_email(subscriber)
+        should_not_email(non_subscriber)
+      end
+    end
+
     context 'when Issue has tasks' do
       before { update_issue({ description: "- [ ] Task 1\n- [ ] Task 2" }) }
 
diff --git a/spec/services/merge_requests/update_service_spec.rb b/spec/services/merge_requests/update_service_spec.rb
index 99703c7a8ec..104e63ccfee 100644
--- a/spec/services/merge_requests/update_service_spec.rb
+++ b/spec/services/merge_requests/update_service_spec.rb
@@ -53,7 +53,7 @@ describe MergeRequests::UpdateService, services: true do
       it { expect(@merge_request.assignee).to eq(user2) }
       it { expect(@merge_request).to be_closed }
       it { expect(@merge_request.labels.count).to eq(1) }
-      it { expect(@merge_request.labels.first.title).to eq('Bug') }
+      it { expect(@merge_request.labels.first.title).to eq(label.name) }
       it { expect(@merge_request.target_branch).to eq('target') }
 
       it 'should execute hooks with update action' do
@@ -176,6 +176,60 @@ describe MergeRequests::UpdateService, services: true do
       end
     end
 
+    context "when the merge request is relabeled" do
+      it "sends notifications for subscribers of newly added labels" do
+        subscriber, non_subscriber = create_list(:user, 2)
+        label.toggle_subscription(subscriber)
+        2.times { label.toggle_subscription(non_subscriber) }
+
+        opts = { label_ids: [label.id] }
+
+        perform_enqueued_jobs do
+          @merge_request = MergeRequests::UpdateService.new(project, user, opts).execute(merge_request)
+        end
+
+        @merge_request.reload
+        should_email(subscriber)
+        should_not_email(non_subscriber)
+      end
+
+      it "does send notifications for existing labels" do
+        second_label = create(:label)
+        merge_request.labels << label
+        subscriber, non_subscriber = create_list(:user, 2)
+        label.toggle_subscription(subscriber)
+        2.times { label.toggle_subscription(non_subscriber) }
+
+        opts = { label_ids: [label.id, second_label.id] }
+
+        perform_enqueued_jobs do
+          @merge_request = MergeRequests::UpdateService.new(project, user, opts).execute(merge_request)
+        end
+
+        @merge_request.reload
+        should_email(subscriber)
+        should_not_email(non_subscriber)
+      end
+
+      it "does not send notifications for removed labels" do
+        second_label = create(:label)
+        merge_request.labels << label
+        subscriber, non_subscriber = create_list(:user, 2)
+        label.toggle_subscription(subscriber)
+        2.times { label.toggle_subscription(non_subscriber) }
+
+        opts = { label_ids: [second_label.id] }
+
+        perform_enqueued_jobs do
+          @merge_request = MergeRequests::UpdateService.new(project, user, opts).execute(merge_request)
+        end
+
+        @merge_request.reload
+        should_not_email(subscriber)
+        should_not_email(non_subscriber)
+      end
+    end
+
     context 'when MergeRequest has tasks' do
       before { update_merge_request({ description: "- [ ] Task 1\n- [ ] Task 2" }) }
 
diff --git a/spec/services/notification_service_spec.rb b/spec/services/notification_service_spec.rb
index 2d0b5df4224..35afa768057 100644
--- a/spec/services/notification_service_spec.rb
+++ b/spec/services/notification_service_spec.rb
@@ -224,6 +224,16 @@ describe NotificationService, services: true do
 
         should_not_email(issue.assignee)
       end
+
+      it "should email subscribers of the issue's labels" do
+        subscriber, non_subscriber = create_list(:user, 2)
+        label = create(:label, issues: [issue])
+        label.toggle_subscription(subscriber)
+        2.times { label.toggle_subscription(non_subscriber) }
+        notification.new_issue(issue, @u_disabled)
+        should_email(subscriber)
+        should_not_email(non_subscriber)
+      end
     end
 
     describe :reassigned_issue do
@@ -326,6 +336,32 @@ describe NotificationService, services: true do
         should_not_email(@u_participating)
       end
     end
+
+    describe :relabel_issue do
+      it "sends email to subscribers of the given labels" do
+        subscriber, non_subscriber = create_list(:user, 2)
+        label = create(:label, issues: [issue])
+        label.toggle_subscription(subscriber)
+        2.times { label.toggle_subscription(non_subscriber) }
+        notification.relabeled_issue(issue, [label], @u_disabled)
+        should_email(subscriber)
+        should_not_email(non_subscriber)
+      end
+
+      it "doesn't send email to anyone but subscribers of the given labels" do
+        label = create(:label, issues: [issue])
+        notification.relabeled_issue(issue, [label], @u_disabled)
+
+        should_not_email(issue.assignee)
+        should_not_email(issue.author)
+        should_not_email(@u_watcher)
+        should_not_email(@u_participant_mentioned)
+        should_not_email(@subscriber)
+        should_not_email(@watcher_and_subscriber)
+        should_not_email(@unsubscriber)
+        should_not_email(@u_participating)
+      end
+    end
   end
 
   describe 'Merge Requests' do
@@ -349,6 +385,17 @@ describe NotificationService, services: true do
         should_not_email(@u_participating)
         should_not_email(@u_disabled)
       end
+
+      it "should email subscribers of the MR's labels" do
+        subscriber, non_subscriber = create_list(:user, 2)
+        label = create(:label)
+        merge_request.labels << label
+        label.toggle_subscription(subscriber)
+        2.times { label.toggle_subscription(non_subscriber) }
+        notification.new_merge_request(merge_request, @u_disabled)
+        should_email(subscriber)
+        should_not_email(non_subscriber)
+      end
     end
 
     describe :reassigned_merge_request do
@@ -410,6 +457,34 @@ describe NotificationService, services: true do
         should_not_email(@u_disabled)
       end
     end
+
+    describe :relabel_merge_request do
+      it "sends email to subscribers of the given labels" do
+        subscriber, non_subscriber = create_list(:user, 2)
+        label = create(:label)
+        merge_request.labels << label
+        label.toggle_subscription(subscriber)
+        2.times { label.toggle_subscription(non_subscriber) }
+        notification.relabeled_merge_request(merge_request, [label], @u_disabled)
+        should_email(subscriber)
+        should_not_email(non_subscriber)
+      end
+
+      it "doesn't send email to anyone but subscribers of the given labels" do
+        label = create(:label)
+        merge_request.labels << label
+        notification.relabeled_merge_request(merge_request, [label], @u_disabled)
+
+        should_not_email(merge_request.assignee)
+        should_not_email(merge_request.author)
+        should_not_email(@u_watcher)
+        should_not_email(@u_participant_mentioned)
+        should_not_email(@subscriber)
+        should_not_email(@watcher_and_subscriber)
+        should_not_email(@unsubscriber)
+        should_not_email(@u_participating)
+      end
+    end
   end
 
   describe 'Projects' do
@@ -467,16 +542,4 @@ describe NotificationService, services: true do
     # Make the watcher a subscriber to detect dupes
     issuable.subscriptions.create(user: @watcher_and_subscriber, subscribed: true)
   end
-
-  def sent_to_user?(user)
-    ActionMailer::Base.deliveries.map(&:to).flatten.count(user.email) == 1
-  end
-
-  def should_email(user)
-    expect(sent_to_user?(user)).to be_truthy
-  end
-
-  def should_not_email(user)
-    expect(sent_to_user?(user)).to be_falsey
-  end
 end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 7d939ca7509..596d607f2a1 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -32,6 +32,7 @@ RSpec.configure do |config|
   config.include LoginHelpers,        type: :feature
   config.include LoginHelpers,        type: :request
   config.include StubConfiguration
+  config.include EmailHelpers
   config.include RelativeUrl,         type: feature
   config.include TestEnv
   config.include ActiveJob::TestHelper
diff --git a/spec/support/email_helpers.rb b/spec/support/email_helpers.rb
new file mode 100644
index 00000000000..a85ab22ce36
--- /dev/null
+++ b/spec/support/email_helpers.rb
@@ -0,0 +1,13 @@
+module EmailHelpers
+  def sent_to_user?(user)
+    ActionMailer::Base.deliveries.map(&:to).flatten.count(user.email) == 1
+  end
+
+  def should_email(user)
+    expect(sent_to_user?(user)).to be_truthy
+  end
+
+  def should_not_email(user)
+    expect(sent_to_user?(user)).to be_falsey
+  end
+end