Use ResourceLabelEvent for tracking label changes

app/assets/javascripts/notes/components/note_actions.vue

@@ -24,12 +24,13 @@ export default {
       required: true,
     },
     noteId: {
-      type: Number,
+      type: String,
       required: true,
     },
     noteUrl: {
       type: String,
-      required: true,
+      required: false,
+      default: '',
     },
     accessLevel: {
       type: String,
@@ -225,11 +226,11 @@ export default {
             Report as abuse
           </a>
         </li>
-        <li>
+        <li v-if="noteUrl">
           <button
             :data-clipboard-text="noteUrl"
             type="button"
-            css-class="btn-default btn-transparent"
+            class="btn-default btn-transparent js-btn-copy-note-link"
           >
             Copy link
           </button>

app/assets/javascripts/notes/components/note_awards_list.vue

@@ -25,7 +25,7 @@ export default {
       required: true,
     },
     noteId: {
-      type: Number,
+      type: String,
       required: true,
     },
     canAwardEmoji: {

app/assets/javascripts/notes/components/note_form.vue

@@ -20,9 +20,9 @@ export default {
       default: '',
     },
     noteId: {
-      type: Number,
+      type: String,
       required: false,
-      default: 0,
+      default: '',
     },
     markdownVersion: {
       type: Number,
@@ -67,7 +67,10 @@ export default {
       'getUserDataByProp',
     ]),
     noteHash() {
-      return `#note_${this.noteId}`;
+      if (this.noteId) {
+        return `#note_${this.noteId}`;
+      }
+      return '#';
     },
     markdownPreviewPath() {
       return this.getNoteableDataByProp('preview_note_path');

app/assets/javascripts/notes/components/note_header.vue

@@ -9,7 +9,8 @@ export default {
   props: {
     author: {
       type: Object,
-      required: true,
+      required: false,
+      default: () => ({}),
     },
     createdAt: {
       type: String,
@@ -21,7 +22,7 @@ export default {
       default: '',
     },
     noteId: {
-      type: Number,
+      type: String,
       required: true,
     },
     includeToggle: {
@@ -72,7 +73,10 @@ export default {
         {{ __('Toggle discussion') }}
       </button>
     </div>
-    <a :href="author.path">
+    <a
+      v-if="Object.keys(author).length"
+      :href="author.path"
+    >
       <span class="note-header-author-name">{{ author.name }}</span>
       <span
         v-if="author.status_tooltip_html"
@@ -81,6 +85,9 @@ export default {
         @{{ author.username }}
       </span>
     </a>
+    <span v-else>
+      {{ __('A deleted user') }}
+    </span>
     <span class="note-headline-light">
       <span class="note-headline-meta">
         <template v-if="actionText">

app/controllers/concerns/issuable_actions.rb

@@ -95,6 +95,7 @@ module IssuableActions
       .includes(:noteable)
       .fresh
 
+    notes = ResourceEvents::MergeIntoNotesService.new(issuable, current_user).execute(notes)
     notes = prepare_notes_for_rendering(notes)
     notes = notes.reject { |n| n.cross_reference_not_visible_for?(current_user) }
 

app/controllers/concerns/notes_actions.rb

@@ -18,6 +18,7 @@ module NotesActions
     notes = notes_finder.execute
       .inc_relations_for_view
 
+    notes = ResourceEvents::MergeIntoNotesService.new(noteable, current_user, last_fetched_at: current_fetched_at).execute(notes)
     notes = prepare_notes_for_rendering(notes)
     notes = notes.reject { |n| n.cross_reference_not_visible_for?(current_user) }
 

app/helpers/notes_helper.rb

@@ -108,7 +108,7 @@ module NotesHelper
   end
 
   def noteable_note_url(note)
-    Gitlab::UrlBuilder.build(note)
+    Gitlab::UrlBuilder.build(note) if note.id
   end
 
   def form_resources

app/models/concerns/issuable.rb

@@ -109,10 +109,6 @@ module Issuable
       false
     end
 
-    def etag_caching_enabled?
-      false
-    end
-
     def has_multiple_assignees?
       assignees.count > 1
     end

app/models/concerns/noteable.rb

@@ -82,4 +82,23 @@ module Noteable
   def lockable?
     [MergeRequest, Issue].include?(self.class)
   end
+
+  def etag_caching_enabled?
+    false
+  end
+
+  def expire_note_etag_cache
+    return unless discussions_rendered_on_frontend?
+    return unless etag_caching_enabled?
+
+    Gitlab::EtagCaching::Store.new.touch(note_etag_key)
+  end
+
+  def note_etag_key
+    Gitlab::Routing.url_helpers.project_noteable_notes_path(
+      project,
+      target_type: self.class.name.underscore,
+      target_id: id
+    )
+  end
 end

app/models/label_note.rb

+# frozen_string_literal: true
+
+class LabelNote < Note
+  attr_accessor :resource_parent
+  attr_reader :events
+
+  def self.from_events(events, resource: nil, resource_parent: nil)
+    resource ||= events.first.issuable
+
+    attrs = {
+      system: true,
+      author: events.first.user,
+      created_at: events.first.created_at,
+      discussion_id: events.first.discussion_id,
+      noteable: resource,
+      system_note_metadata: SystemNoteMetadata.new(action: 'label'),
+      events: events,
+      resource_parent: resource_parent
+    }
+
+    if resource_parent.is_a?(Project)
+      attrs[:project_id] = resource_parent.id
+    end
+
+    LabelNote.new(attrs)
+  end
+
+  def events=(events)
+    @events = events
+
+    update_outdated_markdown
+  end
+
+  def cached_html_up_to_date?(markdown_field)
+    true
+  end
+
+  def note
+    @note ||= note_text
+  end
+
+  def note_html
+    @note_html ||= "<p dir=\"auto\">#{note_text(html: true)}</p>"
+  end
+
+  def project
+    resource_parent if resource_parent.is_a?(Project)
+  end
+
+  def group
+    resource_parent if resource_parent.is_a?(Group)
+  end
+
+  private
+
+  def update_outdated_markdown
+    events.each do |event|
+      if event.outdated_markdown?
+        event.refresh_invalid_reference
+      end
+    end
+  end
+
+  def note_text(html: false)
+    added = labels_str('added', label_refs_by_action('add', html))
+    removed = labels_str('removed', label_refs_by_action('remove', html))
+
+    [added, removed].compact.join(' and ')
+  end
+
+  # returns string containing added/removed labels including
+  # count of deleted labels:
+  #
+  # added ~1 ~2 + 1 deleted label
+  # added 3 deleted labels
+  # added ~1 ~2 labels
+  def labels_str(prefix, label_refs)
+    existing_refs = label_refs.select { |ref| ref.present? }.sort
+    refs_str = existing_refs.empty? ? nil : existing_refs.join(' ')
+
+    deleted = label_refs.count - existing_refs.count
+    deleted_str = deleted == 0 ? nil : "#{deleted} deleted"
+
+    return nil unless refs_str || deleted_str
+
+    label_list_str = [refs_str, deleted_str].compact.join(' + ')
+    suffix = 'label'.pluralize(deleted > 0 ? deleted : existing_refs.count)
+
+    "#{prefix} #{label_list_str} #{suffix}"
+  end
+
+  def label_refs_by_action(action, html)
+    field = html ? :reference_html : :reference
+
+    events.select { |e| e.action == action }.map(&field)
+  end
+end

app/models/note.rb

@@ -389,18 +389,7 @@ class Note < ActiveRecord::Base
   end
 
   def expire_etag_cache
-    return unless noteable&.discussions_rendered_on_frontend?
-    return unless noteable&.etag_caching_enabled?
-
-    Gitlab::EtagCaching::Store.new.touch(etag_key)
-  end
-
-  def etag_key
-    Gitlab::Routing.url_helpers.project_noteable_notes_path(
-      project,
-      target_type: noteable_type.underscore,
-      target_id: noteable_id
-    )
+    noteable&.expire_note_etag_cache
   end
 
   def touch(*args)

app/models/resource_label_event.rb

@@ -3,33 +3,122 @@
 # This model is not used yet, it will be used for:
 # https://gitlab.com/gitlab-org/gitlab-ce/issues/48483
 class ResourceLabelEvent < ActiveRecord::Base
+  include Importable
+  include Gitlab::Utils::StrongMemoize
+  include CacheMarkdownField
+
+  cache_markdown_field :reference
+
   belongs_to :user
   belongs_to :issue
   belongs_to :merge_request
   belongs_to :label
 
-  validates :user, presence: true, on: :create
-  validates :label, presence: true, on: :create
+  scope :created_after, ->(time) { where('created_at > ?', time) }
+
+  validates :user, presence: { unless: :importing? }, on: :create
+  validates :label, presence: { unless: :importing? }, on: :create
   validate :exactly_one_issuable
 
+  after_save :expire_etag_cache
+  after_destroy :expire_etag_cache
+
   enum action: {
     add: 1,
     remove: 2
   }
 
-  def self.issuable_columns
-    %i(issue_id merge_request_id).freeze
+  def self.issuable_attrs
+    %i(issue merge_request).freeze
   end
 
   def issuable
     issue || merge_request
   end
 
+  # create same discussion id for all actions with the same user and time
+  def discussion_id(resource = nil)
+    strong_memoize(:discussion_id) do
+      Digest::SHA1.hexdigest([self.class.name, created_at, user_id].join("-"))
+    end
+  end
+
+  def project
+    issuable.project
+  end
+
+  def group
+    issuable.group if issuable.respond_to?(:group)
+  end
+
+  def outdated_markdown?
+    return true if label_id.nil? && reference.present?
+
+    reference.nil? || latest_cached_markdown_version != cached_markdown_version
+  end
+
+  def banzai_render_context(field)
+    super.merge(pipeline: 'label', only_path: true)
+  end
+
+  def refresh_invalid_reference
+    # label_id could be nullified on label delete
+    self.reference = '' if label_id.nil?
+
+    # reference is not set for events which were not rendered yet
+    self.reference ||= label_reference
+
+    if changed?
+      save
+    elsif invalidated_markdown_cache?
+      refresh_markdown_cache!
+    end
+  end
+
   private
 
+  def label_reference
+    if local_label?
+      label.to_reference(format: :id)
+    elsif label.is_a?(GroupLabel)
+      label.to_reference(label.group, target_project: resource_parent, format: :id)
+    else
+      label.to_reference(resource_parent, format: :id)
+    end
+  end
+
   def exactly_one_issuable
-    if self.class.issuable_columns.count { |attr| self[attr] } != 1
-      errors.add(:base, "Exactly one of #{self.class.issuable_columns.join(', ')} is required")
+    issuable_count = self.class.issuable_attrs.count { |attr| self["#{attr}_id"] }
+
+    return true if issuable_count == 1
+
+    # if none of issuable IDs is set, check explicitly if nested issuable
+    # object is set, this is used during project import
+    if issuable_count == 0 && importing?
+      issuable_count = self.class.issuable_attrs.count { |attr| self.public_send(attr) } # rubocop:disable GitlabSecurity/PublicSend
+
+      return true if issuable_count == 1
     end
+
+    errors.add(:base, "Exactly one of #{self.class.issuable_attrs.join(', ')} is required")
+  end
+
+  def expire_etag_cache
+    issuable.expire_note_etag_cache
+  end
+
+  def local_label?
+    params = { include_ancestor_groups: true }
+    if resource_parent.is_a?(Project)
+      params[:project_id] = resource_parent.id
+    else
+      params[:group_id] = resource_parent.id
+    end
+
+    LabelsFinder.new(nil, params).execute(skip_authorization: true).where(id: label.id).any?
+  end
+
+  def resource_parent
+    issuable.project || issuable.group
   end
 end

app/serializers/note_entity.rb

@@ -4,6 +4,12 @@ class NoteEntity < API::Entities::Note
   include RequestAwareEntity
   include NotesHelper
 
+  expose :id do |note|
+    # resource events are represented as notes too, but don't
+    # have ID, discussion ID is used for them instead
+    note.id ? note.id.to_s : note.discussion_id
+  end
+
   expose :type
 
   expose :author, using: NoteUserEntity
@@ -46,8 +52,8 @@ class NoteEntity < API::Entities::Note
   expose :emoji_awardable?, as: :emoji_awardable
   expose :award_emoji, if: -> (note, _) { note.emoji_awardable? }, using: AwardEmojiEntity
 
-  expose :report_abuse_path do |note|
-    new_abuse_report_path(user_id: note.author.id, ref_url: Gitlab::UrlBuilder.build(note))
+  expose :report_abuse_path, if: -> (note, _) { note.author_id } do |note|
+    new_abuse_report_path(user_id: note.author_id, ref_url: Gitlab::UrlBuilder.build(note))
   end
 
   expose :noteable_note_url do |note|

app/serializers/project_note_entity.rb

 # frozen_string_literal: true
 
 class ProjectNoteEntity < NoteEntity
-  expose :human_access do |note|
+  expose :human_access, if: -> (note, _) { note.project.present? } do |note|
     note.project.team.human_max_access(note.author_id)
   end
 
@@ -9,7 +9,7 @@ class ProjectNoteEntity < NoteEntity
     toggle_award_emoji_project_note_path(note.project, note.id)
   end
 
-  expose :path do |note|
+  expose :path, if: -> (note, _) { note.id } do |note|
     project_note_path(note.project, note)
   end
 

app/services/issuable/common_system_notes_service.rb

@@ -55,7 +55,9 @@ module Issuable
       added_labels = issuable.labels - old_labels
       removed_labels = old_labels - issuable.labels
 
-      SystemNoteService.change_label(issuable, issuable.project, current_user, added_labels, removed_labels)
+      ResourceEvents::ChangeLabelsService
+        .new(issuable, current_user)
+        .execute(added_labels: added_labels, removed_labels: removed_labels)
     end
 
     def create_title_change_note(old_title)

app/services/issues/move_service.rb

@@ -36,6 +36,7 @@ module Issues
 
     def update_new_issue
       rewrite_notes
+      copy_resource_label_events
       rewrite_issue_award_emoji
       add_note_moved_from
     end
@@ -96,6 +97,18 @@ module Issues
       end
     end
 
+    def copy_resource_label_events
+      @old_issue.resource_label_events.find_in_batches do |batch|
+        events = batch.map do |event|
+          event.attributes
+            .except('id', 'reference', 'reference_html')
+            .merge('issue_id' => @new_issue.id, 'created_at' => event.created_at)
+        end
+
+        Gitlab::Database.bulk_insert(ResourceLabelEvent.table_name, events)
+      end
+    end
+
     def rewrite_issue_award_emoji
       rewrite_award_emoji(@old_issue, @new_issue)
     end

app/services/labels/promote_service.rb

@@ -13,6 +13,7 @@ module Labels
 
         label_ids_for_merge(new_label).find_in_batches(batch_size: BATCH_SIZE) do |batched_ids|
           update_issuables(new_label, batched_ids)
+          update_resource_label_events(new_label, batched_ids)
           update_issue_board_lists(new_label, batched_ids)
           update_priorities(new_label, batched_ids)
           subscribe_users(new_label, batched_ids)
@@ -52,6 +53,12 @@ module Labels
         .update_all(label_id: new_label)
     end
 
+    def update_resource_label_events(new_label, label_ids)
+      ResourceLabelEvent
+        .where(label: label_ids)
+        .update_all(label_id: new_label)
+    end
+
     def update_issue_board_lists(new_label, label_ids)
       List
         .where(label: label_ids)

app/services/resource_events/change_labels_service.rb

 # frozen_string_literal: true
 
-# This service is not used yet, it will be used for:
-# https://gitlab.com/gitlab-org/gitlab-ce/issues/48483
 module ResourceEvents
   class ChangeLabelsService
     attr_reader :resource, :user
@@ -25,6 +23,7 @@ module ResourceEvents
       end
 
       Gitlab::Database.bulk_insert(ResourceLabelEvent.table_name, labels)
+      resource.expire_note_etag_cache
     end
 
     private

app/services/resource_events/merge_into_notes_service.rb

+# frozen_string_literal: true
+
+# We store events about issuable label changes in a separate table (not as
+# other system notes), but we still want to display notes about label changes
+# as classic system notes in UI.  This service generates "synthetic" notes for
+# label event changes and merges them with classic notes and sorts them by
+# creation time.
+
+module ResourceEvents
+  class MergeIntoNotesService
+    include Gitlab::Utils::StrongMemoize
+
+    attr_reader :resource, :current_user, :params
+
+    def initialize(resource, current_user, params = {})
+      @resource = resource
+      @current_user = current_user
+      @params = params
+    end
+
+    def execute(notes = [])
+      (notes + label_notes).sort_by { |n| n.created_at }
+    end
+
+    private
+
+    def label_notes
+      label_events_by_discussion_id.map do |discussion_id, events|
+        LabelNote.from_events(events, resource: resource, resource_parent: resource_parent)
+      end
+    end
+
+    def label_events_by_discussion_id
+      return [] unless resource.respond_to?(:resource_label_events)
+
+      events = resource.resource_label_events.includes(:label, :user)
+      events = since_fetch_at(events)
+
+      events.group_by { |event| event.discussion_id }
+    end
+
+    def since_fetch_at(events)
+      return events unless params[:last_fetched_at].present?
+
+      last_fetched_at = Time.at(params.fetch(:last_fetched_at).to_i)
+      events.created_after(last_fetched_at - NotesFinder::FETCH_OVERLAP)
+    end
+
+    def resource_parent
+      strong_memoize(:resource_parent) do
+        resource.project || resource.group
+      end
+    end
+  end
+end

app/services/system_note_service.rb

@@ -98,47 +98,6 @@ module SystemNoteService
     create_note(NoteSummary.new(issue, project, author, body, action: 'assignee'))
   end
 
-  # Called when one or more labels on a Noteable are added and/or removed
-  #
-  # noteable       - Noteable object
-  # project        - Project owning noteable
-  # author         - User performing the change
-  # added_labels   - Array of Labels added
-  # removed_labels - Array of Labels removed
-  #
-  # Example Note text:
-  #
-  #   "added ~1 and removed ~2 ~3 labels"
-  #
-  #   "added ~4 label"
-  #
-  #   "removed ~5 label"
-  #
-  # Returns the created Note object
-  def change_label(noteable, project, author, added_labels, removed_labels)
-    labels_count = added_labels.count + removed_labels.count
-
-    references     = ->(label) { label.to_reference(format: :id) }
-    added_labels   = added_labels.map(&references).join(' ')
-    removed_labels = removed_labels.map(&references).join(' ')
-
-    text_parts = []
-
-    if added_labels.present?
-      text_parts << "added #{added_labels}"
-      text_parts << 'and' if removed_labels.present?
-    end
-
-    if removed_labels.present?
-      text_parts << "removed #{removed_labels}"
-    end
-
-    text_parts << 'label'.pluralize(labels_count)
-    body = text_parts.join(' ')
-
-    create_note(NoteSummary.new(noteable, project, author, body, action: 'label'))
-  end
-
   # Called when the milestone of a Noteable is changed
   #
   # noteable  - Noteable object

changelogs/unreleased/label-event.yml

+---
+title: Use separate model for tracking resource label changes and render label system
+  notes based on data from this model.
+merge_request:
+author:
+type: added

db/migrate/20180901200537_add_resource_label_event_reference_fields.rb

+# frozen_string_literal: true
+
+class AddResourceLabelEventReferenceFields < ActiveRecord::Migration
+  DOWNTIME = false
+
+  def change
+    add_column :resource_label_events, :cached_markdown_version, :integer
+    add_column :resource_label_events, :reference, :text
+    add_column :resource_label_events, :reference_html, :text
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20180901171833) do
+ActiveRecord::Schema.define(version: 20180901200537) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -1841,6 +1841,9 @@ ActiveRecord::Schema.define(version: 20180901171833) do
     t.integer "label_id"
     t.integer "user_id"
     t.datetime_with_timezone "created_at", null: false
+    t.integer "cached_markdown_version"
+    t.text "reference"
+    t.text "reference_html"
   end
 
   add_index "resource_label_events", ["issue_id"], name: "index_resource_label_events_on_issue_id", using: :btree

doc/api/README.md

@@ -40,6 +40,7 @@ following locations:
 - [Namespaces](namespaces.md)
 - [Notes](notes.md) (comments)
 - [Discussions](discussions.md) (threaded comments)
+- [Resource Label Events](resource_label_events.md)
 - [Notification settings](notification_settings.md)
 - [Open source license templates](templates/licenses.md)
 - [Pages Domains](pages_domains.md)

doc/api/resource_label_events.md

+# Resource label events API
+
+Resource label events keep track about who, when, and which label was added or removed to an issuable.
+
+## Issues
+
+### List project issue label events
+
+Gets a list of all label events for a single issue.
+
+```
+GET /projects/:id/issues/:issue_iid/resource_label_events
+```
+
+| Attribute           | Type             | Required   | Description  |
+| ------------------- | ---------------- | ---------- | ------------ |
+| `id`                | integer/string   | yes        | The ID or [URL-encoded path of the project](README.md#namespaced-path-encoding) |
+| `issue_iid`         | integer          | yes        | The IID of an issue |
+
+```json
+[
+  {
+    "id": 142,
+    "user": {
+      "id": 1,
+      "name": "Administrator",
+      "username": "root",
+      "state": "active",
+      "avatar_url": "https://www.gravatar.com/avatar/e64c7d89f26bd1972efa854d13d7dd61?s=80&d=identicon",
+      "web_url": "http://gitlab.example.com/root"
+    },
+    "created_at": "2018-08-20T13:38:20.077Z",
+    "resource_type": "Issue",
+    "resource_id": 253,
+    "label": {
+      "id": 73,
+      "name": "a1",
+      "color": "#34495E",
+      "description": ""
+    },
+    "action": "add"
+  },
+  {
+    "id": 143,
+    "user": {
+      "id": 1,
+      "name": "Administrator",
+      "username": "root",
+      "state": "active",
+      "avatar_url": "https://www.gravatar.com/avatar/e64c7d89f26bd1972efa854d13d7dd61?s=80&d=identicon",
+      "web_url": "http://gitlab.example.com/root"
+    },
+    "created_at": "2018-08-20T13:38:20.077Z",
+    "resource_type": "Issue",
+    "resource_id": 253,
+    "label": {
+      "id": 74,
+      "name": "p1",
+      "color": "#0033CC",
+      "description": ""
+    },
+    "action": "remove"
+  }
+]
+```
+
+```bash
+curl --request GET --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v4/projects/5/issues/11/resource_label_events
+```
+
+### Get single issue label event
+
+Returns a single label event for a specific project issue
+
+```
+GET /projects/:id/issues/:issue_iid/resource_label_events/:resource_label_event_id
+```
+
+Parameters:
+
+| Attribute       | Type           | Required | Description |
+| --------------- | -------------- | -------- | ----------- |
+| `id`            | integer/string | yes      | The ID or [URL-encoded path of the project](README.md#namespaced-path-encoding) |
+| `issue_iid`     | integer        | yes      | The IID of an issue |
+| `resource_label_event_id` | integer        | yes      | The ID of a label event |
+
+```bash
+curl --request GET --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v4/projects/5/issues/11/resource_label_events/1
+```
+
+## Merge requests
+
+### List project merge request label events
+
+Gets a list of all label events for a single merge request.
+
+```
+GET /projects/:id/merge_requests/:merge_request_iid/resource_label_events
+```
+
+| Attribute           | Type             | Required   | Description  |
+| ------------------- | ---------------- | ---------- | ------------ |
+| `id`                | integer/string   | yes        | The ID or [URL-encoded path of the project](README.md#namespaced-path-encoding) |
+| `merge_request_iid` | integer          | yes        | The IID of a merge request |
+
+```json
+[
+  {
+    "id": 119,
+    "user": {
+      "id": 1,
+      "name": "Administrator",
+      "username": "root",
+      "state": "active",
+      "avatar_url": "https://www.gravatar.com/avatar/e64c7d89f26bd1972efa854d13d7dd61?s=80&d=identicon",
+      "web_url": "http://gitlab.example.com/root"
+    },
+    "created_at": "2018-08-20T06:17:28.394Z",
+    "resource_type": "MergeRequest",
+    "resource_id": 28,
+    "label": {
+      "id": 74,
+      "name": "p1",
+      "color": "#0033CC",
+      "description": ""
+    },
+    "action": "add"
+  },
+  {
+    "id": 120,
+    "user": {
+      "id": 1,
+      "name": "Administrator",
+      "username": "root",
+      "state": "active",
+      "avatar_url": "https://www.gravatar.com/avatar/e64c7d89f26bd1972efa854d13d7dd61?s=80&d=identicon",
+      "web_url": "http://gitlab.example.com/root"
+    },
+    "created_at": "2018-08-20T06:17:28.394Z",
+    "resource_type": "MergeRequest",
+    "resource_id": 28,
+    "label": {
+      "id": 41,
+      "name": "project",
+      "color": "#D1D100",
+      "description": ""
+    },
+    "action": "add"
+  }
+]
+```
+
+```bash
+curl --request GET --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v4/projects/5/merge_requests/11/resource_label_events
+```
+
+### Get single merge request label event
+
+Returns a single label event for a specific project merge request
+
+```
+GET /projects/:id/merge_requests/:merge_request_iid/resource_label_events/:resource_label_event_id
+```
+
+Parameters:
+
+| Attribute           | Type           | Required | Description |
+| ------------------- | -------------- | -------- | ----------- |
+| `id`                | integer/string | yes      | The ID or [URL-encoded path of the project](README.md#namespaced-path-encoding) |
+| `merge_request_iid` | integer        | yes      | The IID of a merge request |
+| `resource_label_event_id`     | integer        | yes      | The ID of a label event |
+
+```bash
+curl --request GET --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v4/projects/5/merge_requests/11/resource_label_events/120
+```

lib/api/api.rb

@@ -118,6 +118,7 @@ module API
     mount ::API::Namespaces
     mount ::API::Notes
     mount ::API::Discussions
+    mount ::API::ResourceLabelEvents
     mount ::API::NotificationSettings
     mount ::API::PagesDomains
     mount ::API::Pipelines

lib/api/entities.rb

@@ -1437,5 +1437,19 @@ module API
         badge.type == 'ProjectBadge' ? 'project' : 'group'
       end
     end
+
+    class ResourceLabelEvent < Grape::Entity
+      expose :id
+      expose :user, using: Entities::UserBasic
+      expose :created_at
+      expose :resource_type do |event, options|
+        event.issuable.class.name
+      end
+      expose :resource_id do |event, options|
+        event.issuable.id
+      end
+      expose :label, using: Entities::LabelBasic
+      expose :action
+    end
   end
 end

lib/api/resource_label_events.rb

+# frozen_string_literal: true
+
+module API
+  class ResourceLabelEvents < Grape::API
+    include PaginationParams
+    helpers ::API::Helpers::NotesHelpers
+
+    before { authenticate! }
+
+    EVENTABLE_TYPES = [Issue, MergeRequest].freeze
+
+    EVENTABLE_TYPES.each do |eventable_type|
+      parent_type = eventable_type.parent_class.to_s.underscore
+      eventables_str = eventable_type.to_s.underscore.pluralize
+
+      params do
+        requires :id, type: String, desc: "The ID of a #{parent_type}"
+      end
+      resource parent_type.pluralize.to_sym, requirements: API::PROJECT_ENDPOINT_REQUIREMENTS do
+        desc "Get a list of #{eventable_type.to_s.downcase} resource label events" do
+          success Entities::ResourceLabelEvent
+          detail 'This feature was introduced in 11.3'
+        end
+        params do
+          requires :eventable_id, types: [Integer, String], desc: 'The ID of the eventable'
+          use :pagination
+        end
+        get ":id/#{eventables_str}/:eventable_id/resource_label_events" do
+          eventable = find_noteable(parent_type, eventables_str, params[:eventable_id])
+          events = eventable.resource_label_events.includes(:label, :user)
+
+          present paginate(events), with: Entities::ResourceLabelEvent
+        end
+
+        desc "Get a single #{eventable_type.to_s.downcase} resource label event" do
+          success Entities::ResourceLabelEvent
+          detail 'This feature was introduced in 11.3'
+        end
+        params do
+          requires :event_id, type: String, desc: 'The ID of a resource label event'
+          requires :eventable_id, types: [Integer, String], desc: 'The ID of the eventable'
+        end
+        get ":id/#{eventables_str}/:eventable_id/resource_label_events/:event_id" do
+          eventable = find_noteable(parent_type, eventables_str, params[:eventable_id])
+          event = eventable.resource_label_events.find(params[:event_id])
+
+          present event, with: Entities::ResourceLabelEvent
+        end
+      end
+    end
+  end
+end

lib/banzai/pipeline/label_pipeline.rb

+# frozen_string_literal: true
+
+module Banzai
+  module Pipeline
+    class LabelPipeline < BasePipeline
+      def self.filters
+        @filters ||= FilterArray[
+          Filter::SanitizationFilter,
+          Filter::LabelReferenceFilter
+        ]
+      end
+    end
+  end
+end

lib/gitlab/import_export/import_export.yml

@@ -19,6 +19,9 @@ project_tree:
     - milestone:
       - events:
         - :push_event_payload
+    - resource_label_events:
+      - label:
+          :priorities
     - :issue_assignees
   - snippets:
     - :award_emoji
@@ -45,6 +48,9 @@ project_tree:
     - milestone:
       - events:
         - :push_event_payload
+    - resource_label_events:
+      - label:
+          :priorities
   - pipelines:
     - notes:
       - :author
@@ -137,6 +143,10 @@ excluded_attributes:
     - :event_id
   project_badges:
     - :group_id
+  resource_label_events:
+    - :reference
+    - :reference_html
+    - :epic_id
 
 methods:
   labels:

locale/gitlab.pot

@@ -259,6 +259,9 @@ msgstr ""
 msgid "A default branch cannot be chosen for an empty project."
 msgstr ""
 
+msgid "A deleted user"
+msgstr ""
+
 msgid "A new branch will be created in your fork and a new merge request will be started."
 msgstr ""
 

spec/controllers/projects/notes_controller_spec.rb

@@ -154,7 +154,7 @@ describe Projects::NotesController do
         get :index, request_params
 
         expect(parsed_response[:notes].count).to eq(1)
-        expect(note_json[:id]).to eq(note.id)
+        expect(note_json[:id]).to eq(note.id.to_s)
       end
 
       it 'does not result in N+1 queries' do

spec/factories/resource_label_events.rb

@@ -2,9 +2,12 @@
 
 FactoryBot.define do
   factory :resource_label_event do
-    user { issue.project.creator }
     action :add
     label
-    issue
+    user { issuable&.author || create(:user) }
+
+    after(:build) do |event, evaluator|
+      event.issue = create(:issue) unless event.issuable
+    end
   end
 end

spec/features/issues/resource_label_events_spec.rb

+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe 'List issue resource label events', :js do
+  let(:user)     { create(:user) }
+  let(:project)  { create(:project, :public) }
+  let(:issue)    { create(:issue, project: project, author: user) }
+  let!(:label)    { create(:label, project: project, title: 'foo') }
+
+  context 'when user displays the issue' do
+    let!(:note)     { create(:note_on_issue, author: user, project: project, noteable: issue, note: 'some note') }
+    let!(:event)    { create(:resource_label_event, user: user, issue: issue, label: label) }
+
+    before do
+      visit project_issue_path(project, issue)
+      wait_for_requests
+    end
+
+    it 'shows both notes and resource label events' do
+      page.within('#notes') do
+        expect(find("#note_#{note.id}")).to have_content 'some note'
+        expect(find("#note_#{event.discussion_id}")).to have_content 'added foo label'
+      end
+    end
+  end
+
+  context 'when user adds label to the issue' do
+    def toggle_labels(labels)
+      page.within '.labels' do
+        click_link 'Edit'
+        wait_for_requests
+
+        labels.each { |label| click_link label }
+
+        click_link 'Edit'
+        wait_for_requests
+      end
+    end
+
+    before do
+      create(:label, project: project, title: 'bar')
+      project.add_developer(user)
+
+      sign_in(user)
+      visit project_issue_path(project, issue)
+      wait_for_requests
+    end
+
+    it 'shows add note for newly added labels' do
+      toggle_labels(%w(foo bar))
+      visit project_issue_path(project, issue)
+      wait_for_requests
+
+      page.within('#notes') do
+        expect(page).to have_content 'added bar foo labels'
+      end
+    end
+  end
+end

spec/javascripts/diffs/mock_data/diff_discussions.js

@@ -16,7 +16,7 @@ export default {
   expanded: true,
   notes: [
     {
-      id: 1749,
+      id: '1749',
       type: 'DiffNote',
       attachment: null,
       author: {
@@ -68,7 +68,7 @@ export default {
         '/gitlab-org/gitlab-test/issues/new?discussion_to_resolve=6b232e05bea388c6b043ccc243ba505faac04ea8&merge_request_to_resolve_discussions_of=20',
     },
     {
-      id: 1753,
+      id: '1753',
       type: 'DiffNote',
       attachment: null,
       author: {
@@ -120,7 +120,7 @@ export default {
         '/gitlab-org/gitlab-test/issues/new?discussion_to_resolve=6b232e05bea388c6b043ccc243ba505faac04ea8&merge_request_to_resolve_discussions_of=20',
     },
     {
-      id: 1754,
+      id: '1754',
       type: 'DiffNote',
       attachment: null,
       author: {
@@ -162,7 +162,7 @@ export default {
         '/gitlab-org/gitlab-test/issues/new?discussion_to_resolve=6b232e05bea388c6b043ccc243ba505faac04ea8&merge_request_to_resolve_discussions_of=20',
     },
     {
-      id: 1755,
+      id: '1755',
       type: 'DiffNote',
       attachment: null,
       author: {
@@ -204,7 +204,7 @@ export default {
         '/gitlab-org/gitlab-test/issues/new?discussion_to_resolve=6b232e05bea388c6b043ccc243ba505faac04ea8&merge_request_to_resolve_discussions_of=20',
     },
     {
-      id: 1756,
+      id: '1756',
       type: 'DiffNote',
       attachment: null,
       author: {

spec/javascripts/notes/components/note_actions_spec.js

@@ -28,7 +28,7 @@ describe('issue_note_actions component', () => {
         canEdit: true,
         canAwardEmoji: true,
         canReportAsAbuse: true,
-        noteId: 539,
+        noteId: '539',
         noteUrl: 'https://localhost:3000/group/project/merge_requests/1#note_1',
         reportAbusePath:
           '/abuse_reports/new?ref_url=http%3A%2F%2Flocalhost%3A3000%2Fgitlab-org%2Fgitlab-ce%2Fissues%2F7%23note_539&user_id=26',
@@ -59,6 +59,20 @@ describe('issue_note_actions component', () => {
         expect(vm.$el.querySelector(`a[href="${props.reportAbusePath}"]`)).toBeDefined();
       });
 
+      it('should be possible to copy link to a note', () => {
+        expect(vm.$el.querySelector('.js-btn-copy-note-link')).not.toBeNull();
+      });
+
+      it('should not show copy link action when `noteUrl` prop is empty', done => {
+        vm.noteUrl = '';
+        Vue.nextTick()
+          .then(() => {
+            expect(vm.$el.querySelector('.js-btn-copy-note-link')).toBeNull();
+          })
+          .then(done)
+          .catch(done.fail);
+      });
+
       it('should be possible to delete comment', () => {
         expect(vm.$el.querySelector('.js-note-delete')).toBeDefined();
       });
@@ -77,7 +91,7 @@ describe('issue_note_actions component', () => {
         canEdit: false,
         canAwardEmoji: false,
         canReportAsAbuse: false,
-        noteId: 539,
+        noteId: '539',
         noteUrl: 'https://localhost:3000/group/project/merge_requests/1#note_1',
         reportAbusePath:
           '/abuse_reports/new?ref_url=http%3A%2F%2Flocalhost%3A3000%2Fgitlab-org%2Fgitlab-ce%2Fissues%2F7%23note_539&user_id=26',

spec/javascripts/notes/components/note_awards_list_spec.js

@@ -30,7 +30,7 @@ describe('note_awards_list component', () => {
       propsData: {
         awards: awardsMock,
         noteAuthorId: 2,
-        noteId: 545,
+        noteId: '545',
         canAwardEmoji: true,
         toggleAwardPath: '/gitlab-org/gitlab-ce/notes/545/toggle_award_emoji',
       },
@@ -70,7 +70,7 @@ describe('note_awards_list component', () => {
         propsData: {
           awards: awardsMock,
           noteAuthorId: 2,
-          noteId: 545,
+          noteId: '545',
           canAwardEmoji: false,
           toggleAwardPath: '/gitlab-org/gitlab-ce/notes/545/toggle_award_emoji',
         },

spec/javascripts/notes/components/note_form_spec.js

@@ -19,7 +19,7 @@ describe('issue_note_form component', () => {
     props = {
       isEditing: false,
       noteBody: 'Magni suscipit eius consectetur enim et ex et commodi.',
-      noteId: 545,
+      noteId: '545',
     };
 
     vm = new Component({
@@ -32,6 +32,22 @@ describe('issue_note_form component', () => {
     vm.$destroy();
   });
 
+  describe('noteHash', () => {
+    it('returns note hash string based on `noteId`', () => {
+      expect(vm.noteHash).toBe(`#note_${props.noteId}`);
+    });
+
+    it('return note hash as `#` when `noteId` is empty', done => {
+      vm.noteId = '';
+      Vue.nextTick()
+        .then(() => {
+          expect(vm.noteHash).toBe('#');
+        })
+        .then(done)
+        .catch(done.fail);
+    });
+  });
+
   describe('conflicts editing', () => {
     it('should show conflict message if note changes outside the component', done => {
       vm.isEditing = true;

spec/javascripts/notes/components/note_header_spec.js

@@ -33,7 +33,7 @@ describe('note_header component', () => {
           },
           createdAt: '2017-08-02T10:51:58.559Z',
           includeToggle: false,
-          noteId: 1394,
+          noteId: '1394',
           expanded: true,
         },
       }).$mount();
@@ -47,6 +47,16 @@ describe('note_header component', () => {
     it('should render timestamp link', () => {
       expect(vm.$el.querySelector('a[href="#note_1394"]')).toBeDefined();
     });
+
+    it('should not render user information when prop `author` is empty object', done => {
+      vm.author = {};
+      Vue.nextTick()
+        .then(() => {
+          expect(vm.$el.querySelector('.note-header-author-name')).toBeNull();
+        })
+        .then(done)
+        .catch(done.fail);
+    });
   });
 
   describe('discussion', () => {
@@ -66,7 +76,7 @@ describe('note_header component', () => {
           },
           createdAt: '2017-08-02T10:51:58.559Z',
           includeToggle: true,
-          noteId: 1395,
+          noteId: '1395',
           expanded: true,
         },
       }).$mount();

spec/javascripts/notes/mock_data.js

@@ -66,7 +66,7 @@ export const individualNote = {
   individual_note: true,
   notes: [
     {
-      id: 1390,
+      id: '1390',
       attachment: {
         url: null,
         filename: null,
@@ -111,7 +111,7 @@ export const individualNote = {
 };
 
 export const note = {
-  id: 546,
+  id: '546',
   attachment: {
     url: null,
     filename: null,
@@ -174,7 +174,7 @@ export const discussionMock = {
   expanded: true,
   notes: [
     {
-      id: 1395,
+      id: '1395',
       attachment: {
         url: null,
         filename: null,
@@ -211,7 +211,7 @@ export const discussionMock = {
       path: '/gitlab-org/gitlab-ce/notes/1395',
     },
     {
-      id: 1396,
+      id: '1396',
       attachment: {
         url: null,
         filename: null,
@@ -257,7 +257,7 @@ export const discussionMock = {
       path: '/gitlab-org/gitlab-ce/notes/1396',
     },
     {
-      id: 1437,
+      id: '1437',
       attachment: {
         url: null,
         filename: null,
@@ -308,7 +308,7 @@ export const discussionMock = {
 };
 
 export const loggedOutnoteableData = {
-  id: 98,
+  id: '98',
   iid: 26,
   author_id: 1,
   description: '',
@@ -358,7 +358,7 @@ export const collapseNotesMock = [
     individual_note: true,
     notes: [
       {
-        id: 1390,
+        id: '1390',
         attachment: null,
         author: {
           id: 1,
@@ -393,7 +393,7 @@ export const collapseNotesMock = [
     individual_note: true,
     notes: [
       {
-        id: 1391,
+        id: '1391',
         attachment: null,
         author: {
           id: 1,
@@ -433,7 +433,7 @@ export const INDIVIDUAL_NOTE_RESPONSE_MAP = {
         expanded: true,
         notes: [
           {
-            id: 1390,
+            id: '1390',
             attachment: {
               url: null,
               filename: null,
@@ -495,7 +495,7 @@ export const INDIVIDUAL_NOTE_RESPONSE_MAP = {
         expanded: true,
         notes: [
           {
-            id: 1391,
+            id: '1391',
             attachment: {
               url: null,
               filename: null,
@@ -544,7 +544,7 @@ export const INDIVIDUAL_NOTE_RESPONSE_MAP = {
     '/gitlab-org/gitlab-ce/notes/1471': {
       commands_changes: null,
       valid: true,
-      id: 1471,
+      id: '1471',
       attachment: null,
       author: {
         id: 1,
@@ -600,7 +600,7 @@ export const DISCUSSION_NOTE_RESPONSE_MAP = {
         expanded: true,
         notes: [
           {
-            id: 1471,
+            id: '1471',
             attachment: {
               url: null,
               filename: null,
@@ -671,7 +671,7 @@ export const notesWithDescriptionChanges = [
     expanded: true,
     notes: [
       {
-        id: 901,
+        id: '901',
         type: null,
         attachment: null,
         author: {
@@ -718,7 +718,7 @@ export const notesWithDescriptionChanges = [
     expanded: true,
     notes: [
       {
-        id: 902,
+        id: '902',
         type: null,
         attachment: null,
         author: {
@@ -765,7 +765,7 @@ export const notesWithDescriptionChanges = [
     expanded: true,
     notes: [
       {
-        id: 903,
+        id: '903',
         type: null,
         attachment: null,
         author: {
@@ -809,7 +809,7 @@ export const notesWithDescriptionChanges = [
     expanded: true,
     notes: [
       {
-        id: 904,
+        id: '904',
         type: null,
         attachment: null,
         author: {
@@ -854,7 +854,7 @@ export const notesWithDescriptionChanges = [
     expanded: true,
     notes: [
       {
-        id: 905,
+        id: '905',
         type: null,
         attachment: null,
         author: {
@@ -898,7 +898,7 @@ export const notesWithDescriptionChanges = [
     expanded: true,
     notes: [
       {
-        id: 906,
+        id: '906',
         type: null,
         attachment: null,
         author: {
@@ -945,7 +945,7 @@ export const collapsedSystemNotes = [
     expanded: true,
     notes: [
       {
-        id: 901,
+        id: '901',
         type: null,
         attachment: null,
         author: {
@@ -992,7 +992,7 @@ export const collapsedSystemNotes = [
     expanded: true,
     notes: [
       {
-        id: 902,
+        id: '902',
         type: null,
         attachment: null,
         author: {
@@ -1039,7 +1039,7 @@ export const collapsedSystemNotes = [
     expanded: true,
     notes: [
       {
-        id: 904,
+        id: '904',
         type: null,
         attachment: null,
         author: {
@@ -1084,7 +1084,7 @@ export const collapsedSystemNotes = [
     expanded: true,
     notes: [
       {
-        id: 905,
+        id: '905',
         type: null,
         attachment: null,
         author: {
@@ -1129,7 +1129,7 @@ export const collapsedSystemNotes = [
     expanded: true,
     notes: [
       {
-        id: 906,
+        id: '906',
         type: null,
         attachment: null,
         author: {

spec/javascripts/vue_shared/components/notes/system_note_spec.js

@@ -9,7 +9,7 @@ describe('system note component', () => {
   beforeEach(() => {
     props = {
       note: {
-        id: 1424,
+        id: '1424',
         author: {
           id: 1,
           name: 'Root',

spec/lib/gitlab/import_export/all_models.yml

@@ -324,3 +324,9 @@ metrics:
 - latest_closed_by
 - merged_by
 - pipeline
+resource_label_events:
+- user
+- issue
+- merge_request
+- epic
+- label

spec/lib/gitlab/import_export/project.json

@@ -331,6 +331,28 @@
           },
           "events": []
         }
+      ],
+      "resource_label_events": [
+        {
+          "id":244,
+          "action":"remove",
+          "issue_id":40,
+          "merge_request_id":null,
+          "label_id":2,
+          "user_id":1,
+          "created_at":"2018-08-28T08:24:00.494Z",
+          "label": {
+            "id": 2,
+            "title": "test2",
+            "color": "#428bca",
+            "project_id": 8,
+            "created_at": "2016-07-22T08:55:44.161Z",
+            "updated_at": "2016-07-22T08:55:44.161Z",
+            "template": false,
+            "description": "",
+            "type": "ProjectLabel"
+          }
+        }
       ]
     },
     {
@@ -2515,6 +2537,17 @@
           "events": []
         }
       ],
+      "resource_label_events": [
+        {
+          "id":243,
+          "action":"add",
+          "issue_id":null,
+          "merge_request_id":27,
+          "label_id":null,
+          "user_id":1,
+          "created_at":"2018-08-28T08:24:00.494Z"
+        }
+      ],
       "merge_request_diff": {
         "id": 27,
         "state": "collected",

spec/lib/gitlab/import_export/project_tree_restorer_spec.rb

@@ -89,6 +89,14 @@ describe Gitlab::ImportExport::ProjectTreeRestorer do
         expect(ProtectedTag.first.create_access_levels).not_to be_empty
       end
 
+      it 'restores issue resource label events' do
+        expect(Issue.find_by(title: 'Voluptatem').resource_label_events).not_to be_empty
+      end
+
+      it 'restores merge requests resource label events' do
+        expect(MergeRequest.find_by(title: 'MR1').resource_label_events).not_to be_empty
+      end
+
       context 'event at forth level of the tree' do
         let(:event) { Event.where(action: 6).first }
 

spec/lib/gitlab/import_export/project_tree_saver_spec.rb

@@ -169,6 +169,14 @@ describe Gitlab::ImportExport::ProjectTreeSaver do
         expect(priorities.flatten).not_to be_empty
       end
 
+      it 'has issue resource label events' do
+        expect(saved_project_json['issues'].first['resource_label_events']).not_to be_empty
+      end
+
+      it 'has merge request resource label events' do
+        expect(saved_project_json['merge_requests'].first['resource_label_events']).not_to be_empty
+      end
+
       it 'saves the correct service type' do
         expect(saved_project_json['services'].first['type']).to eq('CustomIssueTrackerService')
       end
@@ -291,6 +299,9 @@ describe Gitlab::ImportExport::ProjectTreeSaver do
            project: project,
            commit_id: ci_build.pipeline.sha)
 
+    create(:resource_label_event, label: project_label, issue: issue)
+    create(:resource_label_event, label: group_label, merge_request: merge_request)
+
     create(:event, :created, target: milestone, project: project, author: user)
     create(:service, project: project, type: 'CustomIssueTrackerService', category: 'issue_tracker', properties: { one: 'value' })
 

spec/lib/gitlab/import_export/safe_model_attributes.yml

@@ -579,3 +579,11 @@ Badge:
 - type
 ProjectCiCdSetting:
 - group_runners_enabled
+ResourceLabelEvent:
+- id
+- action
+- issue_id
+- merge_request_id
+- label_id
+- user_id
+- created_at

spec/models/label_note_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe LabelNote do
+  set(:project)  { create(:project, :repository) }
+  set(:user)   { create(:user) }
+  set(:label) { create(:label, project: project) }
+  set(:label2) { create(:label, project: project) }
+  let(:resource_parent) { project }
+
+  context 'when resource is issue' do
+    set(:resource) { create(:issue, project: project) }
+
+    it_behaves_like 'label note created from events'
+  end
+
+  context 'when resource is merge request' do
+    set(:resource) { create(:merge_request, source_project: project, target_project: project) }
+
+    it_behaves_like 'label note created from events'
+  end
+end

spec/models/resource_label_event_spec.rb

@@ -3,7 +3,7 @@
 require 'rails_helper'
 
 RSpec.describe ResourceLabelEvent, type: :model do
-  subject { build(:resource_label_event) }
+  subject { build(:resource_label_event, issue: issue) }
   let(:issue) { create(:issue) }
   let(:merge_request) { create(:merge_request) }
 
@@ -16,8 +16,6 @@ RSpec.describe ResourceLabelEvent, type: :model do
 
   describe 'validations' do
     it { is_expected.to be_valid }
-    it { is_expected.to validate_presence_of(:label) }
-    it { is_expected.to validate_presence_of(:user) }
 
     describe 'Issuable validation' do
       it 'is invalid if issue_id and merge_request_id are missing' do
@@ -45,4 +43,52 @@ RSpec.describe ResourceLabelEvent, type: :model do
       end
     end
   end
+
+  describe '#expire_etag_cache' do
+    def expect_expiration(issue)
+      expect_any_instance_of(Gitlab::EtagCaching::Store)
+        .to receive(:touch)
+        .with("/#{issue.project.namespace.to_param}/#{issue.project.to_param}/noteable/issue/#{issue.id}/notes")
+    end
+
+    it 'expires resource note etag cache on event save' do
+      expect_expiration(subject.issuable)
+
+      subject.save!
+    end
+
+    it 'expires resource note etag cache on event destroy' do
+      subject.save!
+
+      expect_expiration(subject.issuable)
+
+      subject.destroy!
+    end
+  end
+
+  describe '#outdated_markdown?' do
+    it 'returns true if label is missing and reference is not empty' do
+      subject.attributes = { reference: 'ref', label_id: nil }
+
+      expect(subject.outdated_markdown?).to be true
+    end
+
+    it 'returns true if reference is not set yet' do
+      subject.attributes = { reference: nil }
+
+      expect(subject.outdated_markdown?).to be true
+    end
+
+    it 'returns true markdown is outdated' do
+      subject.attributes = { cached_markdown_version: 0 }
+
+      expect(subject.outdated_markdown?).to be true
+    end
+
+    it 'returns false if label and reference are set' do
+      subject.attributes = { reference: 'whatever', cached_markdown_version: CacheMarkdownField::CACHE_COMMONMARK_VERSION  }
+
+      expect(subject.outdated_markdown?).to be false
+    end
+  end
 end

spec/requests/api/resource_label_events_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe API::ResourceLabelEvents do
+  set(:user) { create(:user) }
+  set(:project) { create(:project, :public, :repository, namespace: user.namespace) }
+  set(:private_user)    { create(:user) }
+
+  before do
+    project.add_developer(user)
+  end
+
+  shared_examples 'resource_label_events API' do |parent_type, eventable_type, id_name|
+    describe "GET /#{parent_type}/:id/#{eventable_type}/:noteable_id/resource_label_events" do
+      it "returns an array of resource label events" do
+        get api("/#{parent_type}/#{parent.id}/#{eventable_type}/#{eventable[id_name]}/resource_label_events", user)
+
+        expect(response).to have_gitlab_http_status(200)
+        expect(response).to include_pagination_headers
+        expect(json_response).to be_an Array
+        expect(json_response.first['id']).to eq(event.id)
+      end
+
+      it "returns a 404 error when eventable id not found" do
+        get api("/#{parent_type}/#{parent.id}/#{eventable_type}/12345/resource_label_events", user)
+
+        expect(response).to have_gitlab_http_status(404)
+      end
+
+      it "returns 404 when not authorized" do
+        parent.update!(visibility_level: Gitlab::VisibilityLevel::PRIVATE)
+
+        get api("/#{parent_type}/#{parent.id}/#{eventable_type}/#{eventable[id_name]}/resource_label_events", private_user)
+
+        expect(response).to have_gitlab_http_status(404)
+      end
+    end
+
+    describe "GET /#{parent_type}/:id/#{eventable_type}/:noteable_id/resource_label_events/:event_id" do
+      it "returns a resource label event by id" do
+        get api("/#{parent_type}/#{parent.id}/#{eventable_type}/#{eventable[id_name]}/resource_label_events/#{event.id}", user)
+
+        expect(response).to have_gitlab_http_status(200)
+        expect(json_response['id']).to eq(event.id)
+      end
+
+      it "returns a 404 error if resource label event not found" do
+        get api("/#{parent_type}/#{parent.id}/#{eventable_type}/#{eventable[id_name]}/resource_label_events/12345", user)
+
+        expect(response).to have_gitlab_http_status(404)
+      end
+    end
+  end
+
+  context 'when eventable is an Issue' do
+    let(:issue) { create(:issue, project: project, author: user) }
+
+    it_behaves_like 'resource_label_events API', 'projects', 'issues', 'iid' do
+      let(:parent) { project }
+      let(:eventable) { issue }
+      let!(:event) { create(:resource_label_event, issue: issue) }
+    end
+  end
+
+  context 'when eventable is a Merge Request' do
+    let(:merge_request) { create(:merge_request, source_project: project, target_project: project, author: user) }
+
+    it_behaves_like 'resource_label_events API', 'projects', 'merge_requests', 'iid' do
+      let(:parent) { project }
+      let(:eventable) { merge_request }
+      let!(:event) { create(:resource_label_event, merge_request: merge_request) }
+    end
+  end
+end

spec/services/issuable/common_system_notes_service_spec.rb

@@ -12,12 +12,21 @@ describe Issuable::CommonSystemNotesService do
     it_behaves_like 'system note creation', { time_estimate: 5 }, 'changed time estimate'
 
     context 'when new label is added' do
+      let(:label) { create(:label, project: project) }
+
       before do
-        label = create(:label, project: project)
         issuable.labels << label
+        issuable.save
       end
 
-      it_behaves_like 'system note creation', {}, /added ~\w+ label/
+      it 'creates a resource label event' do
+        described_class.new(project, user).execute(issuable, [])
+        event = issuable.reload.resource_label_events.last
+
+        expect(event).not_to be_nil
+        expect(event.label_id).to eq label.id
+        expect(event.user_id).to eq user.id
+      end
     end
 
     context 'when new milestone is assigned' do

spec/services/issues/move_service_spec.rb

@@ -122,6 +122,17 @@ describe Issues::MoveService do
         end
       end
 
+      context 'issue with resource label events' do
+        it 'assigns resource label events to new issue' do
+          old_issue.resource_label_events = create_list(:resource_label_event, 2, issue: old_issue)
+
+          new_issue = move_service.execute(old_issue, new_project)
+
+          expected = old_issue.resource_label_events.map(&:label_id)
+          expect(new_issue.resource_label_events.map(&:label_id)).to match_array(expected)
+        end
+      end
+
       context 'generic issue' do
         include_context 'issue move executed'
 

spec/services/issues/update_service_spec.rb

@@ -189,11 +189,12 @@ describe Issues::UpdateService, :mailer do
           expect(note.note).to include "assigned to #{user2.to_reference}"
         end
 
-        it 'creates system note about issue label edit' do
-          note = find_note('added ~')
+        it 'creates a resource label event' do
+          event = issue.resource_label_events.last
 
-          expect(note).not_to be_nil
-          expect(note.note).to include "added #{label.to_reference} label"
+          expect(event).not_to be_nil
+          expect(event.label_id).to eq label.id
+          expect(event.user_id).to eq user.id
         end
 
         it 'creates system note about title change' do

spec/services/merge_requests/update_service_spec.rb

@@ -109,11 +109,12 @@ describe MergeRequests::UpdateService, :mailer do
         expect(note.note).to include "assigned to #{user2.to_reference}"
       end
 
-      it 'creates system note about merge_request label edit' do
-        note = find_note('added ~')
+      it 'creates a resource label event' do
+        event = merge_request.resource_label_events.last
 
-        expect(note).not_to be_nil
-        expect(note.note).to include "added #{label.to_reference} label"
+        expect(event).not_to be_nil
+        expect(event.label_id).to eq label.id
+        expect(event.user_id).to eq user.id
       end
 
       it 'creates system note about title change' do

spec/services/resource_events/change_labels_service_spec.rb

@@ -18,6 +18,14 @@ describe ResourceEvents::ChangeLabelsService do
       expect(event.action).to eq(action)
     end
 
+    it 'expires resource note etag cache' do
+      expect_any_instance_of(Gitlab::EtagCaching::Store)
+        .to receive(:touch)
+        .with("/#{resource.project.namespace.to_param}/#{resource.project.to_param}/noteable/issue/#{resource.id}/notes")
+
+      described_class.new(resource, author).execute(added_labels: [labels[0]])
+    end
+
     context 'when adding a label' do
       let(:added)   { [labels[0]] }
       let(:removed) { [] }

spec/services/resource_events/merge_into_notes_service_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe ResourceEvents::MergeIntoNotesService do
+  def create_event(params)
+    event_params = { action: :add, label: label, issue: resource,
+                     user: user }
+
+    create(:resource_label_event, event_params.merge(params))
+  end
+
+  def create_note(params)
+    opts = { noteable: resource, project: project }
+
+    create(:note_on_issue, opts.merge(params))
+  end
+
+  set(:project)  { create(:project) }
+  set(:user)   { create(:user) }
+  set(:resource) { create(:issue, project: project) }
+  set(:label) { create(:label, project: project) }
+  set(:label2) { create(:label, project: project) }
+  let(:time) { Time.now }
+
+  describe '#execute' do
+    it 'merges label events into notes in order of created_at' do
+      note1 = create_note(created_at: 4.days.ago)
+      note2 = create_note(created_at: 2.days.ago)
+      event1 = create_event(created_at: 3.days.ago)
+      event2 = create_event(created_at: 1.day.ago)
+
+      notes = described_class.new(resource, user).execute([note1, note2])
+
+      expected = [note1, event1, note2, event2].map(&:discussion_id)
+      expect(notes.map(&:discussion_id)).to eq expected
+    end
+
+    it 'squashes events with same time and author into single note' do
+      user2 = create(:user)
+
+      create_event(created_at: time)
+      create_event(created_at: time, label: label2, action: :remove)
+      create_event(created_at: time, user: user2)
+      create_event(created_at: 1.day.ago, label: label2)
+
+      notes = described_class.new(resource, user).execute()
+
+      expected = [
+        "added #{label.to_reference} label and removed #{label2.to_reference} label",
+        "added #{label.to_reference} label",
+        "added #{label2.to_reference} label"
+      ]
+
+      expect(notes.count).to eq 3
+      expect(notes.map(&:note)).to match_array expected
+    end
+
+    it 'fetches only notes created after last_fetched_at' do
+      create_event(created_at: 4.days.ago)
+      event = create_event(created_at: 1.day.ago)
+
+      notes = described_class.new(resource, user,
+                                  last_fetched_at: 2.days.ago.to_i).execute()
+
+      expect(notes.count).to eq 1
+      expect(notes.first.discussion_id).to eq event.discussion_id
+    end
+  end
+end

spec/services/system_note_service_spec.rb

@@ -197,45 +197,6 @@ describe SystemNoteService do
     end
   end
 
-  describe '.change_label' do
-    subject { described_class.change_label(noteable, project, author, added, removed) }
-
-    let(:labels)  { create_list(:label, 2, project: project) }
-    let(:added)   { [] }
-    let(:removed) { [] }
-
-    it_behaves_like 'a system note' do
-      let(:action) { 'label' }
-    end
-
-    context 'with added labels' do
-      let(:added)   { labels }
-      let(:removed) { [] }
-
-      it 'sets the note text' do
-        expect(subject.note).to eq "added ~#{labels[0].id} ~#{labels[1].id} labels"
-      end
-    end
-
-    context 'with removed labels' do
-      let(:added)   { [] }
-      let(:removed) { labels }
-
-      it 'sets the note text' do
-        expect(subject.note).to eq "removed ~#{labels[0].id} ~#{labels[1].id} labels"
-      end
-    end
-
-    context 'with added and removed labels' do
-      let(:added)   { [labels[0]] }
-      let(:removed) { [labels[1]] }
-
-      it 'sets the note text' do
-        expect(subject.note).to eq "added ~#{labels[0].id} and removed ~#{labels[1].id} labels"
-      end
-    end
-  end
-
   describe '.change_milestone' do
     context 'for a project milestone' do
       subject { described_class.change_milestone(noteable, project, author, milestone) }

spec/support/shared_examples/models/label_note_shared_examples.rb

+# frozen_string_literal: true
+
+shared_examples 'label note created from events' do
+  def create_event(params = {})
+    event_params = { action: :add, label: label, user: user }
+    resource_key = resource.class.name.underscore.to_s
+    event_params[resource_key] = resource
+
+    build(:resource_label_event, event_params.merge(params))
+  end
+
+  def label_refs(events)
+    sorted_labels = events.map(&:label).compact.sort_by(&:title)
+
+    sorted_labels.map { |l| l.to_reference}.join(' ')
+  end
+
+  let(:time) { Time.now }
+  let(:local_label_ids) { [label.id, label2.id] }
+
+  describe '.from_events' do
+    it 'returns system note with expected attributes' do
+      event = create_event
+
+      note = described_class.from_events([event, create_event])
+
+      expect(note.system).to be true
+      expect(note.author_id).to eq event.user_id
+      expect(note.discussion_id).to eq event.discussion_id
+      expect(note.noteable).to eq event.issuable
+      expect(note.note).to be_present
+      expect(note.note_html).to be_present
+    end
+
+    it 'updates markdown cache if reference is not set yet' do
+      event = create_event(reference: nil)
+
+      described_class.from_events([event])
+
+      expect(event.reference).not_to be_nil
+    end
+
+    it 'updates markdown cache if label was deleted' do
+      event = create_event(reference: 'some_ref', label: nil)
+
+      described_class.from_events([event])
+
+      expect(event.reference).to eq ''
+    end
+
+    it 'returns html note' do
+      events = [create_event(created_at: time)]
+
+      note = described_class.from_events(events)
+
+      expect(note.note_html).to include label.title
+    end
+
+    it 'returns text note for added labels' do
+      events = [create_event(created_at: time),
+                create_event(created_at: time, label: label2),
+                create_event(created_at: time, label: nil)]
+
+      note = described_class.from_events(events)
+
+      expect(note.note).to eq "added #{label_refs(events)} + 1 deleted label"
+    end
+
+    it 'returns text note for removed labels' do
+      events = [create_event(action: :remove, created_at: time),
+                create_event(action: :remove, created_at: time, label: label2),
+                create_event(action: :remove, created_at: time, label: nil)]
+
+      note = described_class.from_events(events)
+
+      expect(note.note).to eq "removed #{label_refs(events)} + 1 deleted label"
+    end
+
+    it 'returns text note for added and removed labels' do
+      add_events = [create_event(created_at: time),
+                    create_event(created_at: time, label: nil)]
+
+      remove_events = [create_event(action: :remove, created_at: time),
+                       create_event(action: :remove, created_at: time, label: nil)]
+
+      note = described_class.from_events(add_events + remove_events)
+
+      expect(note.note).to eq "added #{label_refs(add_events)} + 1 deleted label and removed #{label_refs(remove_events)} + 1 deleted label"
+    end
+
+    it 'returns text note for cross-project label' do
+      other_label = create(:label)
+      event = create_event(label: other_label)
+
+      note = described_class.from_events([event])
+
+      expect(note.note).to eq "added #{other_label.to_reference(resource_parent)} label"
+    end
+
+    it 'returns text note for cross-group label' do
+      other_label = create(:group_label)
+      event = create_event(label: other_label)
+
+      note = described_class.from_events([event])
+
+      expect(note.note).to eq "added #{other_label.to_reference(other_label.group, target_project: project, full: true)} label"
+    end
+  end
+end