Merge remote-tracking branch 'upstream/master' into 5029-support-cluster-metrics

# Conflicts:
#	spec/controllers/projects/prometheus/metrics_controller_spec.rb
#	spec/models/concerns/prometheus_adapter_spec.rb

app/models/concerns/issuable.rb

@@ -233,6 +233,10 @@ module Issuable
     def to_ability_name
       model_name.singular
     end
+
+    def parent_class
+      ::Project
+    end
   end
 
   def today?

app/models/discussion_note.rb

@@ -3,7 +3,7 @@
 # A note of this type can be resolvable.
 class DiscussionNote < Note
   # Names of all implementers of `Noteable` that support discussions.
-  NOTEABLE_TYPES = %w(MergeRequest Issue Commit Snippet).freeze
+  NOTEABLE_TYPES = %w(MergeRequest Issue Commit Snippet Epic).freeze
 
   validates :noteable_type, inclusion: { in: NOTEABLE_TYPES }
 

app/models/note.rb

@@ -84,7 +84,7 @@ class Note < ActiveRecord::Base
   validates :author, presence: true
   validates :discussion_id, presence: true, format: { with: /\A\h{40}\z/ }
 
-  validate unless: [:for_commit?, :importing?, :for_personal_snippet?] do |note|
+  validate unless: [:for_commit?, :importing?, :skip_project_check?] do |note|
     unless note.noteable.try(:project) == note.project
       errors.add(:project, 'does not match noteable project')
     end
@@ -236,7 +236,7 @@ class Note < ActiveRecord::Base
   end
 
   def skip_project_check?
-    for_personal_snippet?
+    !for_project_noteable?
   end
 
   def commit
@@ -316,6 +316,11 @@ class Note < ActiveRecord::Base
     self.noteable.supports_discussions? && !part_of_discussion?
   end
 
+  def can_create_todo?
+    # Skip system notes, and notes on project snippet
+    !system? && !for_snippet?
+  end
+
   def discussion_class(noteable = nil)
     # When commit notes are rendered on an MR's Discussion page, they are
     # displayed in one discussion instead of individually.

app/models/snippet.rb

@@ -169,5 +169,9 @@ class Snippet < ActiveRecord::Base
     def search_code(query)
       fuzzy_search(query, [:content])
     end
+
+    def parent_class
+      ::Project
+    end
   end
 end

app/services/notes/build_service.rb

 module Notes
   class BuildService < ::BaseService
+    prepend ::EE::Notes::BuildService
+
     def execute
       in_reply_to_discussion_id = params.delete(:in_reply_to_discussion_id)
 
@@ -26,14 +28,19 @@ module Notes
       if project
         project.notes.find_discussion(discussion_id)
       else
-        # only PersonalSnippets can have discussions without project association
         discussion = Note.find_discussion(discussion_id)
         noteable = discussion.noteable
 
-        return nil unless noteable.is_a?(PersonalSnippet) && can?(current_user, :comment_personal_snippet, noteable)
+        return nil unless noteable_without_project?(noteable)
 
         discussion
       end
     end
+
+    def noteable_without_project?(noteable)
+      return true if noteable.is_a?(PersonalSnippet) && can?(current_user, :comment_personal_snippet, noteable)
+
+      false
+    end
   end
 end

app/services/notes/post_process_service.rb

@@ -11,7 +11,7 @@ module Notes
       unless @note.system?
         EventCreateService.new.leave_note(@note, @note.author)
 
-        return if @note.for_personal_snippet?
+        return unless @note.for_project_noteable?
 
         @note.create_cross_references!
         execute_note_hooks

app/services/notification_recipient_service.rb

@@ -280,7 +280,7 @@ module NotificationRecipientService
         add_participants(note.author)
         add_mentions(note.author, target: note)
 
-        unless note.for_personal_snippet?
+        if note.for_project_noteable?
           # Merge project watchers
           add_project_watchers
 

app/services/todo_service.rb

@@ -254,8 +254,7 @@ class TodoService
   end
 
   def handle_note(note, author, skip_users = [])
-    # Skip system notes, and notes on project snippet
-    return if note.system? || note.for_snippet?
+    return unless note.can_create_todo?
 
     project = note.project
     target  = note.noteable

doc/api/README.md

@@ -42,6 +42,7 @@ following locations:
 - [Group milestones](group_milestones.md)
 - [Namespaces](namespaces.md)
 - [Notes](notes.md) (comments)
+- [Threaded comments](discussions.md)
 - [Notification settings](notification_settings.md)
 - [Open source license templates](templates/licenses.md)
 - [Pages Domains](pages_domains.md)

ee/app/models/ee/epic.rb

@@ -69,6 +69,10 @@ module EE
           super
         end
       end
+
+      def parent_class
+        ::Group
+      end
     end
 
     def assignees

ee/app/models/ee/note.rb

 module EE
   module Note
     extend ActiveSupport::Concern
+    extend ::Gitlab::Utils::Override
 
     prepended do
       include ObjectStorage::BackgroundMove
     end
 
+    override :for_project_noteable?
     def for_epic?
       noteable.is_a?(Epic)
     end
 
+    override :for_project_noteable?
     def for_project_noteable?
       !for_epic? && super
     end
+
+    override :can_create_todo?
+    def can_create_todo?
+      !for_epic? && super
+    end
   end
 end

ee/app/policies/epic_policy.rb

 class EpicPolicy < BasePolicy
   delegate { @subject.group }
 
-  rule { can?(:read_epic) }.enable :read_epic_iid
+  rule { can?(:read_epic) }.policy do
+    enable :read_epic_iid
+    enable :read_note
+  end
+
+  rule { can?(:update_epic) }.policy do
+    enable :create_note
+  end
+
+  rule { can?(:admin_epic) }.policy do
+    enable :update_note
+    enable :admin_note
+  end
 end

ee/app/services/ee/notes/build_service.rb

+module EE
+  module Notes
+    module BuildService
+      extend ActiveSupport::Concern
+      extend ::Gitlab::Utils::Override
+
+      override :noteable_without_project?
+      def noteable_without_project?(noteable)
+        return true if noteable.is_a?(Epic) && can?(current_user, :create_note, noteable)
+
+        super
+      end
+    end
+  end
+end

ee/changelogs/unreleased/ee-discussions-api.yml

+---
+title: Add discussions API for Epics
+merge_request:
+author:
+type: added

ee/lib/ee/api/helpers/notes_helpers.rb

+module EE
+  module API
+    module Helpers
+      module NotesHelpers
+        def find_group_epic(id)
+          finder_params = { group_id: user_group.id }
+          EpicsFinder.new(current_user, finder_params).find(id)
+        end
+
+        def noteable_parent_str(noteable_class)
+          parent_class = ::Epic <= noteable_class ? ::Group : ::Project
+
+          parent_class.to_s.underscore
+        end
+      end
+    end
+  end
+end

lib/api/api.rb

@@ -148,6 +148,7 @@ module API
     mount ::API::MergeRequests
     mount ::API::Namespaces
     mount ::API::Notes
+    mount ::API::Discussions
     mount ::API::NotificationSettings
     mount ::API::PagesDomains
     mount ::API::Pipelines

lib/api/discussions.rb

+module API
+  class Discussions < Grape::API
+    include PaginationParams
+    helpers ::API::Helpers::NotesHelpers
+
+    before { authenticate! }
+
+    NOTEABLE_TYPES = [Issue, Snippet, Epic].freeze
+
+    NOTEABLE_TYPES.each do |noteable_type|
+      parent_type = noteable_type.parent_class.to_s.underscore
+      noteables_str = noteable_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 #{noteable_type.to_s.downcase} discussions" do
+          success Entities::Discussion
+        end
+        params do
+          requires :noteable_id, type: Integer, desc: 'The ID of the noteable'
+          use :pagination
+        end
+        get ":id/#{noteables_str}/:noteable_id/discussions" do
+          noteable = find_noteable(parent_type, noteables_str, params[:noteable_id])
+
+          return not_found!("Discussions") unless can?(current_user, noteable_read_ability_name(noteable), noteable)
+
+          notes = noteable.notes
+            .inc_relations_for_view
+            .includes(:noteable)
+            .fresh
+
+          notes = notes.reject { |n| n.cross_reference_not_visible_for?(current_user) }
+          discussions = Kaminari.paginate_array(Discussion.build_collection(notes, noteable))
+
+          present paginate(discussions), with: Entities::Discussion
+        end
+
+        desc "Get a single #{noteable_type.to_s.downcase} discussion" do
+          success Entities::Discussion
+        end
+        params do
+          requires :discussion_id, type: String, desc: 'The ID of a discussion'
+          requires :noteable_id, type: Integer, desc: 'The ID of the noteable'
+        end
+        get ":id/#{noteables_str}/:noteable_id/discussions/:discussion_id" do
+          noteable = find_noteable(parent_type, noteables_str, params[:noteable_id])
+          notes = readable_discussion_notes(noteable, params[:discussion_id])
+
+          if notes.empty? || !can?(current_user, noteable_read_ability_name(noteable), noteable)
+            return not_found!("Discussion")
+          end
+
+          discussion = Discussion.build(notes, noteable)
+
+          present discussion, with: Entities::Discussion
+        end
+
+        desc "Create a new #{noteable_type.to_s.downcase} discussion" do
+          success Entities::Discussion
+        end
+        params do
+          requires :noteable_id, type: Integer, desc: 'The ID of the noteable'
+          requires :body, type: String, desc: 'The content of a note'
+          optional :created_at, type: String, desc: 'The creation date of the note'
+        end
+        post ":id/#{noteables_str}/:noteable_id/discussions" do
+          noteable = find_noteable(parent_type, noteables_str, params[:noteable_id])
+
+          opts = {
+            note: params[:body],
+            created_at: params[:created_at],
+            type: 'DiscussionNote',
+            noteable_type: noteables_str.classify,
+            noteable_id: noteable.id
+          }
+
+          note = create_note(noteable, opts)
+
+          if note.valid?
+            present note.discussion, with: Entities::Discussion
+          else
+            bad_request!("Note #{note.errors.messages}")
+          end
+        end
+
+        desc "Get comments in a single #{noteable_type.to_s.downcase} discussion" do
+          success Entities::Discussion
+        end
+        params do
+          requires :discussion_id, type: String, desc: 'The ID of a discussion'
+          requires :noteable_id, type: Integer, desc: 'The ID of the noteable'
+        end
+        get ":id/#{noteables_str}/:noteable_id/discussions/:discussion_id/notes" do
+          noteable = find_noteable(parent_type, noteables_str, params[:noteable_id])
+          notes = readable_discussion_notes(noteable, params[:discussion_id])
+
+          if notes.empty? || !can?(current_user, noteable_read_ability_name(noteable), noteable)
+            return not_found!("Notes")
+          end
+
+          present notes, with: Entities::Note
+        end
+
+        desc "Add a comment to a #{noteable_type.to_s.downcase} discussion" do
+          success Entities::Note
+        end
+        params do
+          requires :noteable_id, type: Integer, desc: 'The ID of the noteable'
+          requires :discussion_id, type: String, desc: 'The ID of a discussion'
+          requires :body, type: String, desc: 'The content of a note'
+          optional :created_at, type: String, desc: 'The creation date of the note'
+        end
+        post ":id/#{noteables_str}/:noteable_id/discussions/:discussion_id/notes" do
+          noteable = find_noteable(parent_type, noteables_str, params[:noteable_id])
+          notes = readable_discussion_notes(noteable, params[:discussion_id])
+
+          return not_found!("Discussion") if notes.empty?
+          return bad_request!("Discussion is an individual note.") unless notes.first.part_of_discussion?
+
+          opts = {
+            note: params[:body],
+            type: 'DiscussionNote',
+            in_reply_to_discussion_id: params[:discussion_id],
+            created_at: params[:created_at]
+          }
+          note = create_note(noteable, opts)
+
+          if note.valid?
+            present note, with: Entities::Note
+          else
+            bad_request!("Note #{note.errors.messages}")
+          end
+        end
+
+        desc "Get a comment in a #{noteable_type.to_s.downcase} discussion" do
+          success Entities::Note
+        end
+        params do
+          requires :noteable_id, type: Integer, desc: 'The ID of the noteable'
+          requires :discussion_id, type: String, desc: 'The ID of a discussion'
+          requires :note_id, type: Integer, desc: 'The ID of a note'
+        end
+        get ":id/#{noteables_str}/:noteable_id/discussions/:discussion_id/notes/:note_id" do
+          noteable = find_noteable(parent_type, noteables_str, params[:noteable_id])
+
+          get_note(noteable, params[:note_id])
+        end
+
+        desc "Edit a comment in a #{noteable_type.to_s.downcase} discussion" do
+          success Entities::Note
+        end
+        params do
+          requires :noteable_id, type: Integer, desc: 'The ID of the noteable'
+          requires :discussion_id, type: String, desc: 'The ID of a discussion'
+          requires :note_id, type: Integer, desc: 'The ID of a note'
+          requires :body, type: String, desc: 'The content of a note'
+        end
+        put ":id/#{noteables_str}/:noteable_id/discussions/:discussion_id/notes/:note_id" do
+          noteable = find_noteable(parent_type, noteables_str, params[:noteable_id])
+
+          update_note(noteable, params[:note_id])
+        end
+
+        desc "Delete a comment in a #{noteable_type.to_s.downcase} discussion" do
+          success Entities::Note
+        end
+        params do
+          requires :noteable_id, type: Integer, desc: 'The ID of the noteable'
+          requires :discussion_id, type: String, desc: 'The ID of a discussion'
+          requires :note_id, type: Integer, desc: 'The ID of a note'
+        end
+        delete ":id/#{noteables_str}/:noteable_id/discussions/:discussion_id/notes/:note_id" do
+          noteable = find_noteable(parent_type, noteables_str, params[:noteable_id])
+
+          delete_note(noteable, params[:note_id])
+        end
+      end
+    end
+
+    helpers do
+      def readable_discussion_notes(noteable, discussion_id)
+        notes = noteable.notes
+          .where(discussion_id: discussion_id)
+          .inc_relations_for_view
+          .includes(:noteable)
+          .fresh
+
+        notes.reject { |n| n.cross_reference_not_visible_for?(current_user) }
+      end
+    end
+  end
+end

lib/api/entities.rb

@@ -672,6 +672,7 @@ module API
       NOTEABLE_TYPES_WITH_IID = %w(Issue MergeRequest).freeze
 
       expose :id
+      expose :type
       expose :note, as: :body
       expose :attachment_identifier, as: :attachment
       expose :author, using: Entities::UserBasic
@@ -683,6 +684,12 @@ module API
       expose(:noteable_iid) { |note| note.noteable.iid if NOTEABLE_TYPES_WITH_IID.include?(note.noteable_type) }
     end
 
+    class Discussion < Grape::Entity
+      expose :id
+      expose :individual_note?, as: :individual_note
+      expose :notes, using: Entities::Note
+    end
+
     class AwardEmoji < Grape::Entity
       expose :id
       expose :name

lib/api/helpers/notes_helpers.rb

+module API
+  module Helpers
+    module NotesHelpers
+      prepend EE::API::Helpers::NotesHelpers
+
+      def update_note(noteable, note_id)
+        note = noteable.notes.find(params[:note_id])
+
+        authorize! :admin_note, note
+
+        opts = {
+          note: params[:body]
+        }
+        parent = noteable_parent(noteable)
+        project = parent if parent.is_a?(Project)
+
+        note = ::Notes::UpdateService.new(project, current_user, opts).execute(note)
+
+        if note.valid?
+          present note, with: Entities::Note
+        else
+          bad_request!("Failed to save note #{note.errors.messages}")
+        end
+      end
+
+      def delete_note(noteable, note_id)
+        note = noteable.notes.find(note_id)
+
+        authorize! :admin_note, note
+
+        parent = noteable_parent(noteable)
+        project = parent if parent.is_a?(Project)
+        destroy_conditionally!(note) do |note|
+          ::Notes::DestroyService.new(project, current_user).execute(note)
+        end
+      end
+
+      def get_note(noteable, note_id)
+        note = noteable.notes.with_metadata.find(params[:note_id])
+        can_read_note = can?(current_user, noteable_read_ability_name(noteable), noteable) && !note.cross_reference_not_visible_for?(current_user)
+
+        if can_read_note
+          present note, with: Entities::Note
+        else
+          not_found!("Note")
+        end
+      end
+
+      def noteable_read_ability_name(noteable)
+        "read_#{noteable.class.to_s.underscore}".to_sym
+      end
+
+      def find_noteable(parent, noteables_str, noteable_id)
+        public_send("find_#{parent}_#{noteables_str.singularize}", noteable_id) # rubocop:disable GitlabSecurity/PublicSend
+      end
+
+      def noteable_parent(noteable)
+        public_send("user_#{noteable.class.parent_class.to_s.underscore}") # rubocop:disable GitlabSecurity/PublicSend
+      end
+
+      def create_note(noteable, opts)
+        noteables_str = noteable.model_name.to_s.underscore.pluralize
+
+        return not_found!(noteables_str) unless can?(current_user, noteable_read_ability_name(noteable), noteable)
+
+        authorize! :create_note, noteable
+
+        parent = noteable_parent(noteable)
+        if opts[:created_at]
+          opts.delete(:created_at) unless current_user.admin? || parent.owner == current_user
+        end
+
+        project = parent if parent.is_a?(Project)
+        ::Notes::CreateService.new(project, current_user, opts).execute
+      end
+    end
+  end
+end

lib/api/notes.rb

 module API
   class Notes < Grape::API
     include PaginationParams
+    helpers ::API::Helpers::NotesHelpers
 
     before { authenticate! }
 
-    NOTEABLE_TYPES = [Issue, MergeRequest, Snippet].freeze
+    NOTEABLE_TYPES = [Issue, MergeRequest, Snippet, Epic].freeze
 
-    params do
-      requires :id, type: String, desc: 'The ID of a project'
-    end
-    resource :projects, requirements: API::PROJECT_ENDPOINT_REQUIREMENTS do
-      NOTEABLE_TYPES.each do |noteable_type|
+    NOTEABLE_TYPES.each do |noteable_type|
+      parent_type = noteable_type.parent_class.to_s.underscore
+      noteables_str = noteable_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
         noteables_str = noteable_type.to_s.underscore.pluralize
 
-        desc 'Get a list of project +noteable+ notes' do
+        desc "Get a list of #{noteable_type.to_s.downcase} notes" do
           success Entities::Note
         end
         params do
@@ -25,7 +29,7 @@ module API
           use :pagination
         end
         get ":id/#{noteables_str}/:noteable_id/notes" do
-          noteable = find_project_noteable(noteables_str, params[:noteable_id])
+          noteable = find_noteable(parent_type, noteables_str, params[:noteable_id])
 
           if can?(current_user, noteable_read_ability_name(noteable), noteable)
             # We exclude notes that are cross-references and that cannot be viewed
@@ -46,7 +50,7 @@ module API
           end
         end
 
-        desc 'Get a single +noteable+ note' do
+        desc "Get a single #{noteable_type.to_s.downcase} note" do
           success Entities::Note
         end
         params do
@@ -54,18 +58,11 @@ module API
           requires :noteable_id, type: Integer, desc: 'The ID of the noteable'
         end
         get ":id/#{noteables_str}/:noteable_id/notes/:note_id" do
-          noteable = find_project_noteable(noteables_str, params[:noteable_id])
-          note = noteable.notes.with_metadata.find(params[:note_id])
-          can_read_note = can?(current_user, noteable_read_ability_name(noteable), noteable) && !note.cross_reference_not_visible_for?(current_user)
-
-          if can_read_note
-            present note, with: Entities::Note
-          else
-            not_found!("Note")
-          end
+          noteable = find_noteable(parent_type, noteables_str, params[:noteable_id])
+          get_note(noteable, params[:note_id])
         end
 
-        desc 'Create a new +noteable+ note' do
+        desc "Create a new #{noteable_type.to_s.downcase} note" do
           success Entities::Note
         end
         params do
@@ -74,34 +71,25 @@ module API
           optional :created_at, type: String, desc: 'The creation date of the note'
         end
         post ":id/#{noteables_str}/:noteable_id/notes" do
-          noteable = find_project_noteable(noteables_str, params[:noteable_id])
+          noteable = find_noteable(parent_type, noteables_str, params[:noteable_id])
 
           opts = {
             note: params[:body],
             noteable_type: noteables_str.classify,
-            noteable_id: noteable.id
+            noteable_id: noteable.id,
+            created_at: params[:created_at]
           }
 
-          if can?(current_user, noteable_read_ability_name(noteable), noteable)
-            authorize! :create_note, noteable
+          note = create_note(noteable, opts)
 
-            if params[:created_at] && (current_user.admin? || user_project.owner == current_user)
-              opts[:created_at] = params[:created_at]
-            end
-
-            note = ::Notes::CreateService.new(user_project, current_user, opts).execute
-
-            if note.valid?
-              present note, with: Entities.const_get(note.class.name)
-            else
-              not_found!("Note #{note.errors.messages}")
-            end
+          if note.valid?
+            present note, with: Entities.const_get(note.class.name)
           else
-            not_found!("Note")
+            bad_request!("Note #{note.errors.messages}")
           end
         end
 
-        desc 'Update an existing +noteable+ note' do
+        desc "Update an existing #{noteable_type.to_s.downcase} note" do
           success Entities::Note
         end
         params do
@@ -110,24 +98,12 @@ module API
           requires :body, type: String, desc: 'The content of a note'
         end
         put ":id/#{noteables_str}/:noteable_id/notes/:note_id" do
-          note = user_project.notes.find(params[:note_id])
+          noteable = find_noteable(parent_type, noteables_str, params[:noteable_id])
 
-          authorize! :admin_note, note
-
-          opts = {
-            note: params[:body]
-          }
-
-          note = ::Notes::UpdateService.new(user_project, current_user, opts).execute(note)
-
-          if note.valid?
-            present note, with: Entities::Note
-          else
-            render_api_error!("Failed to save note #{note.errors.messages}", 400)
-          end
+          update_note(noteable, params[:note_id])
         end
 
-        desc 'Delete a +noteable+ note' do
+        desc "Delete a #{noteable_type.to_s.downcase} note" do
           success Entities::Note
         end
         params do
@@ -135,25 +111,11 @@ module API
           requires :note_id, type: Integer, desc: 'The ID of a note'
         end
         delete ":id/#{noteables_str}/:noteable_id/notes/:note_id" do
-          note = user_project.notes.find(params[:note_id])
-
-          authorize! :admin_note, note
+          noteable = find_noteable(parent_type, noteables_str, params[:noteable_id])
 
-          destroy_conditionally!(note) do |note|
-            ::Notes::DestroyService.new(user_project, current_user).execute(note)
-          end
+          delete_note(noteable, params[:note_id])
         end
       end
     end
-
-    helpers do
-      def find_project_noteable(noteables_str, noteable_id)
-        public_send("find_project_#{noteables_str.singularize}", noteable_id) # rubocop:disable GitlabSecurity/PublicSend
-      end
-
-      def noteable_read_ability_name(noteable)
-        "read_#{noteable.class.to_s.underscore}".to_sym
-      end
-    end
   end
 end

spec/controllers/projects/prometheus/metrics_controller_spec.rb

@@ -8,13 +8,16 @@ describe Projects::Prometheus::MetricsController do
 
   before do
     allow(controller).to receive(:project).and_return(project)
-    allow(controller).to receive(:prometheus_adapter).and_return(prometheus_adapter)
 
     project.add_master(user)
     sign_in(user)
   end
 
   describe 'GET #active_common' do
+    before do
+      allow(controller).to receive(:prometheus_adapter).and_return(prometheus_adapter)
+    end
+
     context 'when prometheus metrics are enabled' do
       context 'when data is not present' do
         before do
@@ -53,6 +56,18 @@ describe Projects::Prometheus::MetricsController do
     end
   end
 
+  describe '#prometheus_adapter' do
+    before do
+      allow(controller).to receive(:project).and_return(project)
+    end
+
+    it 'calls prometheus adapter service' do
+      expect_any_instance_of(::Prometheus::AdapterService).to receive(:prometheus_adapter)
+
+      subject.__send__(:prometheus_adapter)
+    end
+  end
+
   def project_params(opts = {})
     opts.reverse_merge(namespace_id: project.namespace, project_id: project)
   end

spec/factories/notes.rb

@@ -16,6 +16,8 @@ FactoryBot.define do
     factory :note_on_personal_snippet,   traits: [:on_personal_snippet]
     factory :system_note,                traits: [:system]
 
+    factory :discussion_note, class: DiscussionNote
+
     factory :discussion_note_on_merge_request, traits: [:on_merge_request], class: DiscussionNote do
       association :project, :repository
 
@@ -31,6 +33,8 @@ FactoryBot.define do
 
     factory :discussion_note_on_personal_snippet, traits: [:on_personal_snippet], class: DiscussionNote
 
+    factory :discussion_note_on_snippet, traits: [:on_snippet], class: DiscussionNote
+
     factory :legacy_diff_note_on_commit, traits: [:on_commit, :legacy_diff_note], class: LegacyDiffNote
 
     factory :legacy_diff_note_on_merge_request, traits: [:on_merge_request, :legacy_diff_note], class: LegacyDiffNote do
@@ -96,6 +100,10 @@ FactoryBot.define do
       noteable { create(:issue, project: project) }
     end
 
+    trait :on_snippet do
+      noteable { create(:snippet, project: project) }
+    end
+
     trait :on_merge_request do
       noteable { create(:merge_request, source_project: project) }
     end

spec/fixtures/api/schemas/public_api/v4/notes.json

@@ -4,6 +4,7 @@
     "type": "object",
     "properties" : {
       "id": { "type": "integer" },
+      "type": { "type": ["string", "null"] },
       "body": { "type": "string" },
       "attachment": { "type": ["string", "null"] },
       "author": {

spec/requests/api/discussions_spec.rb

+require 'spec_helper'
+
+describe API::Discussions do
+  let(:user) { create(:user) }
+  let!(:project) { create(:project, :public, namespace: user.namespace) }
+  let(:private_user)    { create(:user) }
+
+  before do
+    project.add_reporter(user)
+  end
+
+  context "when noteable is an Issue" do
+    let!(:issue) { create(:issue, project: project, author: user) }
+    let!(:issue_note) { create(:discussion_note_on_issue, noteable: issue, project: project, author: user) }
+
+    it_behaves_like "discussions API", 'projects', 'issues', 'iid' do
+      let(:parent) { project }
+      let(:noteable) { issue }
+      let(:note) { issue_note }
+    end
+  end
+
+  context "when noteable is a Snippet" do
+    let!(:snippet) { create(:project_snippet, project: project, author: user) }
+    let!(:snippet_note) { create(:discussion_note_on_snippet, noteable: snippet, project: project, author: user) }
+
+    it_behaves_like "discussions API", 'projects', 'snippets', 'id' do
+      let(:parent) { project }
+      let(:noteable) { snippet }
+      let(:note) { snippet_note }
+    end
+  end
+
+  context "when noteable is an Epic" do
+    let(:group) { create(:group, :public, owner: user) }
+    let(:ext_group) { create(:group, :public) }
+    let(:epic) { create(:epic, group: group, author: user) }
+    let!(:epic_note) { create(:discussion_note, noteable: epic, project: project, author: user) }
+
+    before do
+      group.add_developer(user)
+      stub_licensed_features(epics: true)
+    end
+
+    it_behaves_like "discussions API", 'groups', 'epics', 'id' do
+      let(:parent) { group }
+      let(:noteable) { epic }
+      let(:note) { epic_note }
+    end
+  end
+end

spec/support/shared_examples/requests/api/discussions.rb

+shared_examples 'discussions API' do |parent_type, noteable_type, id_name|
+  describe "GET /#{parent_type}/:id/#{noteable_type}/:noteable_id/discussions" do
+    it "returns an array of discussions" do
+      get api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/discussions", 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(note.discussion_id)
+    end
+
+    it "returns a 404 error when noteable id not found" do
+      get api("/#{parent_type}/#{parent.id}/#{noteable_type}/12345/discussions", 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}/#{noteable_type}/#{noteable[id_name]}/discussions", private_user)
+
+      expect(response).to have_gitlab_http_status(404)
+    end
+  end
+
+  describe "GET /#{parent_type}/:id/#{noteable_type}/:noteable_id/discussions/:discussion_id" do
+    it "returns a discussion by id" do
+      get api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/discussions/#{note.discussion_id}", user)
+
+      expect(response).to have_gitlab_http_status(200)
+      expect(json_response['id']).to eq(note.discussion_id)
+      expect(json_response['notes'].first['body']).to eq(note.note)
+    end
+
+    it "returns a 404 error if discussion not found" do
+      get api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/discussions/12345", user)
+
+      expect(response).to have_gitlab_http_status(404)
+    end
+  end
+
+  describe "POST /#{parent_type}/:id/#{noteable_type}/:noteable_id/discussions" do
+    it "creates a new note" do
+      post api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/discussions", user), body: 'hi!'
+
+      expect(response).to have_gitlab_http_status(201)
+      expect(json_response['notes'].first['body']).to eq('hi!')
+      expect(json_response['notes'].first['author']['username']).to eq(user.username)
+    end
+
+    it "returns a 400 bad request error if body not given" do
+      post api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/discussions", user)
+
+      expect(response).to have_gitlab_http_status(400)
+    end
+
+    it "returns a 401 unauthorized error if user not authenticated" do
+      post api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/discussions"), body: 'hi!'
+
+      expect(response).to have_gitlab_http_status(401)
+    end
+
+    context 'when an admin or owner makes the request' do
+      it 'accepts the creation date to be set' do
+        creation_time = 2.weeks.ago
+        post api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/discussions", user),
+          body: 'hi!', created_at: creation_time
+
+        expect(response).to have_gitlab_http_status(201)
+        expect(json_response['notes'].first['body']).to eq('hi!')
+        expect(json_response['notes'].first['author']['username']).to eq(user.username)
+        expect(Time.parse(json_response['notes'].first['created_at'])).to be_like_time(creation_time)
+      end
+    end
+
+    context 'when user does not have access to read the discussion' do
+      before do
+        parent.update!(visibility_level: Gitlab::VisibilityLevel::PRIVATE)
+      end
+
+      it 'responds with 404' do
+        post api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/discussions", private_user),
+          body: 'Foo'
+
+        expect(response).to have_gitlab_http_status(404)
+      end
+    end
+  end
+
+  describe "POST /#{parent_type}/:id/#{noteable_type}/:noteable_id/discussions/:discussion_id/notes" do
+    it 'adds a new note to the discussion' do
+      post api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/"\
+               "discussions/#{note.discussion_id}/notes", user), body: 'Hello!'
+
+      expect(response).to have_gitlab_http_status(201)
+      expect(json_response['body']).to eq('Hello!')
+      expect(json_response['type']).to eq('DiscussionNote')
+    end
+
+    it 'returns a 400 bad request error if body not given' do
+      post api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/"\
+               "discussions/#{note.discussion_id}/notes", user)
+
+      expect(response).to have_gitlab_http_status(400)
+    end
+
+    it "returns a 400 bad request error if discussion is individual note" do
+      note.update_attribute(:type, nil)
+
+      post api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/"\
+               "discussions/#{note.discussion_id}/notes", user), body: 'hi!'
+
+      expect(response).to have_gitlab_http_status(400)
+    end
+  end
+
+  describe "PUT /#{parent_type}/:id/#{noteable_type}/:noteable_id/discussions/:discussion_id/notes/:note_id" do
+    it 'returns modified note' do
+      put api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/"\
+              "discussions/#{note.discussion_id}/notes/#{note.id}", user), body: 'Hello!'
+
+      expect(response).to have_gitlab_http_status(200)
+      expect(json_response['body']).to eq('Hello!')
+    end
+
+    it 'returns a 404 error when note id not found' do
+      put api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/"\
+              "discussions/#{note.discussion_id}/notes/12345", user),
+              body: 'Hello!'
+
+      expect(response).to have_gitlab_http_status(404)
+    end
+
+    it 'returns a 400 bad request error if body not given' do
+      put api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/"\
+              "discussions/#{note.discussion_id}/notes/#{note.id}", user)
+
+      expect(response).to have_gitlab_http_status(400)
+    end
+  end
+
+  describe "DELETE /#{parent_type}/:id/#{noteable_type}/:noteable_id/discussions/:discussion_id/notes/:note_id" do
+    it 'deletes a note' do
+      delete api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/"\
+                 "discussions/#{note.discussion_id}/notes/#{note.id}", user)
+
+      expect(response).to have_gitlab_http_status(204)
+      # Check if note is really deleted
+      delete api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/"\
+                 "discussions/#{note.discussion_id}/notes/#{note.id}", user)
+      expect(response).to have_gitlab_http_status(404)
+    end
+
+    it 'returns a 404 error when note id not found' do
+      delete api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/"\
+                 "discussions/#{note.discussion_id}/notes/12345", user)
+
+      expect(response).to have_gitlab_http_status(404)
+    end
+
+    it_behaves_like '412 response' do
+      let(:request) do
+        api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/"\
+            "discussions/#{note.discussion_id}/notes/#{note.id}", user)
+      end
+    end
+  end
+end

spec/support/shared_examples/requests/api/notes.rb

+shared_examples 'noteable API' do |parent_type, noteable_type, id_name|
+  describe "GET /#{parent_type}/:id/#{noteable_type}/:noteable_id/notes" do
+    context 'sorting' do
+      before do
+        params = { noteable: noteable, author: user }
+        params[:project] = parent if parent.is_a?(Project)
+
+        create_list(:note, 3, params)
+      end
+
+      it 'sorts by created_at in descending order by default' do
+        get api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/notes", user)
+
+        response_dates = json_response.map { |note| note['created_at'] }
+
+        expect(json_response.length).to eq(4)
+        expect(response_dates).to eq(response_dates.sort.reverse)
+      end
+
+      it 'sorts by ascending order when requested' do
+        get api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/notes?sort=asc", user)
+
+        response_dates = json_response.map { |note| note['created_at'] }
+
+        expect(json_response.length).to eq(4)
+        expect(response_dates).to eq(response_dates.sort)
+      end
+
+      it 'sorts by updated_at in descending order when requested' do
+        get api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/notes?order_by=updated_at", user)
+
+        response_dates = json_response.map { |note| note['updated_at'] }
+
+        expect(json_response.length).to eq(4)
+        expect(response_dates).to eq(response_dates.sort.reverse)
+      end
+
+      it 'sorts by updated_at in ascending order when requested' do
+        get api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/notes?order_by=updated_at&sort=asc", user)
+
+        response_dates = json_response.map { |note| note['updated_at'] }
+
+        expect(json_response.length).to eq(4)
+        expect(response_dates).to eq(response_dates.sort)
+      end
+    end
+
+    it "returns an array of notes" do
+      get api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/notes", 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['body']).to eq(note.note)
+    end
+
+    it "returns a 404 error when noteable id not found" do
+      get api("/#{parent_type}/#{parent.id}/#{noteable_type}/12345/notes", 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}/#{noteable_type}/#{noteable[id_name]}/notes", private_user)
+
+      expect(response).to have_gitlab_http_status(404)
+    end
+  end
+
+  describe "GET /#{parent_type}/:id/#{noteable_type}/:noteable_id/notes/:note_id" do
+    it "returns a note by id" do
+      get api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/notes/#{note.id}", user)
+
+      expect(response).to have_gitlab_http_status(200)
+      expect(json_response['body']).to eq(note.note)
+    end
+
+    it "returns a 404 error if note not found" do
+      get api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/notes/12345", user)
+
+      expect(response).to have_gitlab_http_status(404)
+    end
+  end
+
+  describe "POST /#{parent_type}/:id/#{noteable_type}/:noteable_id/notes" do
+    it "creates a new note" do
+      post api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/notes", user), body: 'hi!'
+
+      expect(response).to have_gitlab_http_status(201)
+      expect(json_response['body']).to eq('hi!')
+      expect(json_response['author']['username']).to eq(user.username)
+    end
+
+    it "returns a 400 bad request error if body not given" do
+      post api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/notes", user)
+
+      expect(response).to have_gitlab_http_status(400)
+    end
+
+    it "returns a 401 unauthorized error if user not authenticated" do
+      post api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/notes"), body: 'hi!'
+
+      expect(response).to have_gitlab_http_status(401)
+    end
+
+    it "creates an activity event when a note is created" do
+      expect(Event).to receive(:create!)
+
+      post api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/notes", user), body: 'hi!'
+    end
+
+    context 'when an admin or owner makes the request' do
+      it 'accepts the creation date to be set' do
+        creation_time = 2.weeks.ago
+        post api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/notes", user),
+          body: 'hi!', created_at: creation_time
+
+        expect(response).to have_gitlab_http_status(201)
+        expect(json_response['body']).to eq('hi!')
+        expect(json_response['author']['username']).to eq(user.username)
+        expect(Time.parse(json_response['created_at'])).to be_like_time(creation_time)
+      end
+    end
+
+    context 'when the user is posting an award emoji on a noteable created by someone else' do
+      it 'creates a new note' do
+        parent.add_developer(private_user)
+        post api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/notes", private_user), body: ':+1:'
+
+        expect(response).to have_gitlab_http_status(201)
+        expect(json_response['body']).to eq(':+1:')
+      end
+    end
+
+    context 'when the user is posting an award emoji on his/her own noteable' do
+      it 'creates a new note' do
+        post api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/notes", user), body: ':+1:'
+
+        expect(response).to have_gitlab_http_status(201)
+        expect(json_response['body']).to eq(':+1:')
+      end
+    end
+
+    context 'when user does not have access to read the noteable' do
+      before do
+        parent.update!(visibility_level: Gitlab::VisibilityLevel::PRIVATE)
+      end
+
+      it 'responds with 404' do
+        post api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/notes", private_user),
+          body: 'Foo'
+
+        expect(response).to have_gitlab_http_status(404)
+      end
+    end
+  end
+
+  describe "PUT /#{parent_type}/:id/#{noteable_type}/:noteable_id/notes/:note_id" do
+    it 'returns modified note' do
+      put api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/"\
+                "notes/#{note.id}", user), body: 'Hello!'
+
+      expect(response).to have_gitlab_http_status(200)
+      expect(json_response['body']).to eq('Hello!')
+    end
+
+    it 'returns a 404 error when note id not found' do
+      put api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/notes/12345", user),
+              body: 'Hello!'
+
+      expect(response).to have_gitlab_http_status(404)
+    end
+
+    it 'returns a 400 bad request error if body not given' do
+      put api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/"\
+                "notes/#{note.id}", user)
+
+      expect(response).to have_gitlab_http_status(400)
+    end
+  end
+
+  describe "DELETE /#{parent_type}/:id/#{noteable_type}/:noteable_id/notes/:note_id" do
+    it 'deletes a note' do
+      delete api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/"\
+                 "notes/#{note.id}", user)
+
+      expect(response).to have_gitlab_http_status(204)
+      # Check if note is really deleted
+      delete api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/"\
+                 "notes/#{note.id}", user)
+      expect(response).to have_gitlab_http_status(404)
+    end
+
+    it 'returns a 404 error when note id not found' do
+      delete api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/notes/12345", user)
+
+      expect(response).to have_gitlab_http_status(404)
+    end
+
+    it_behaves_like '412 response' do
+      let(:request) { api("/#{parent_type}/#{parent.id}/#{noteable_type}/#{noteable[id_name]}/notes/#{note.id}", user) }
+    end
+  end
+end