Support multi-assignees on merge requests

This mainly handles the search and replace approach
to using assignees instead assignee for merge requests.

It reuses existing logic from Issuable, where now
issues _and_ merge requests handles multiple assignees.

The feature is behind a feature flag, though, there's no
way to switch back and forth to using the old and new tables.
That's because we'd need a "sync" approach: Once the feature
is off, we'd have to sync old table with new table, once it's
on, new table with old table. Using the new
`merge_request_assignees` altogether will make things simpler to
handle, even though it's a bit "riskier".

app/assets/javascripts/issuable_bulk_update_actions.js

@@ -81,9 +81,6 @@ export default {
     const formData = {
       update: {
         state_event: this.form.find('input[name="update[state_event]"]').val(),
-        // For Merge Requests
-        assignee_id: this.form.find('input[name="update[assignee_id]"]').val(),
-        // For Issues
         assignee_ids: [this.form.find('input[name="update[assignee_ids][]"]').val()],
         milestone_id: this.form.find('input[name="update[milestone_id]"]').val(),
         issuable_ids: this.form.find('input[name="update[issuable_ids]"]').val(),

app/assets/javascripts/sidebar/components/assignees/assignees.vue

@@ -74,8 +74,7 @@ export default {
       }
 
       if (!this.users.length) {
-        const emptyTooltipLabel =
-          this.issuableType === 'issue' ? __('Assignee(s)') : __('Assignee');
+        const emptyTooltipLabel = __('Assignee(s)');
         names.push(emptyTooltipLabel);
       }
 
@@ -90,6 +89,27 @@ export default {
 
       return counter;
     },
+    mergeNotAllowedTooltipMessage() {
+      const assigneesCount = this.users.length;
+
+      if (this.issuableType !== 'merge_request' || assigneesCount === 0) {
+        return null;
+      }
+
+      const cannotMergeCount = this.users.filter(u => u.can_merge === false).length;
+      const canMergeCount = assigneesCount - cannotMergeCount;
+
+      if (canMergeCount === assigneesCount) {
+        // Everyone can merge
+        return null;
+      } else if (cannotMergeCount === assigneesCount && assigneesCount > 1) {
+        return 'No one can merge';
+      } else if (assigneesCount === 1) {
+        return 'Cannot merge';
+      }
+
+      return `${canMergeCount}/${assigneesCount} can merge`;
+    },
   },
   methods: {
     assignSelf() {
@@ -154,6 +174,15 @@ export default {
       </button>
     </div>
     <div class="value hide-collapsed">
+      <span
+        v-if="mergeNotAllowedTooltipMessage"
+        v-tooltip
+        :title="mergeNotAllowedTooltipMessage"
+        data-placement="left"
+        class="float-right cannot-be-merged"
+      >
+        <i aria-hidden="true" data-hidden="true" class="fa fa-exclamation-triangle"></i>
+      </span>
       <template v-if="hasNoUsers">
         <span class="assign-yourself no-value">
           No assignee

app/assets/stylesheets/pages/merge_requests.scss

@@ -498,6 +498,16 @@
       flex: 1;
     }
 
+    .issuable-meta {
+      .author-link {
+        display: inline-block;
+      }
+
+      .issuable-comments {
+        height: 18px;
+      }
+    }
+
     .merge-request-title {
       margin-bottom: 2px;
 

app/assets/stylesheets/pages/projects.scss

@@ -1158,6 +1158,8 @@ pre.light-well {
 .cannot-be-merged:hover {
   color: $red-500;
   margin-top: 2px;
+  position: relative;
+  z-index: 2;
 }
 
 .private-forks-notice .private-fork-icon {

app/controllers/concerns/issuable_actions.rb

@@ -192,12 +192,7 @@ module IssuableActions
 
   def bulk_update_params
     permitted_keys_array = permitted_keys.dup
-
-    if resource_name == 'issue'
-      permitted_keys_array << { assignee_ids: [] }
-    else
-      permitted_keys_array.unshift(:assignee_id)
-    end
+    permitted_keys_array << { assignee_ids: [] }
 
     params.require(:update).permit(permitted_keys_array)
   end

app/controllers/concerns/issuable_collections.rb

@@ -190,17 +190,17 @@ module IssuableCollections
                          end
   end
 
+  # rubocop:disable Gitlab/ModuleWithInstanceVariables
   def preload_for_collection
+    common_attributes = [:author, :assignees, :labels, :milestone]
     @preload_for_collection ||= case collection_type
                                 when 'Issue'
-                                  [:project, :author, :assignees, :labels, :milestone, project: :namespace]
+                                  common_attributes + [:project, project: :namespace]
                                 when 'MergeRequest'
-                                  [
-                                    :target_project, :author, :assignee, :labels, :milestone,
-                                    source_project: :route, head_pipeline: :project, target_project: :namespace, latest_merge_request_diff: :merge_request_diff_commits
-                                  ]
+                                  common_attributes + [:target_project, source_project: :route, head_pipeline: :project, target_project: :namespace, latest_merge_request_diff: :merge_request_diff_commits]
                                 end
   end
+  # rubocop:enable Gitlab/ModuleWithInstanceVariables
 end
 
 IssuableCollections.prepend(EE::IssuableCollections)

app/controllers/projects/merge_requests/application_controller.rb

@@ -20,7 +20,6 @@ class Projects::MergeRequests::ApplicationController < Projects::ApplicationCont
   def merge_request_params_attributes
     [
       :allow_collaboration,
-      :assignee_id,
       :description,
       :force_remove_source_branch,
       :lock_version,
@@ -35,6 +34,7 @@ class Projects::MergeRequests::ApplicationController < Projects::ApplicationCont
       :title,
       :discussion_locked,
       label_ids: [],
+      assignee_ids: [],
       update_task: [:index, :checked, :line_number, :line_source]
     ]
   end

app/finders/issuable_finder.rb

@@ -439,22 +439,6 @@ class IssuableFinder
   end
   # rubocop: enable CodeReuse/ActiveRecord
 
-  # rubocop: disable CodeReuse/ActiveRecord
-  def by_assignee(items)
-    if filter_by_no_assignee?
-      items.where(assignee_id: nil)
-    elsif filter_by_any_assignee?
-      items.where('assignee_id IS NOT NULL')
-    elsif assignee
-      items.where(assignee_id: assignee.id)
-    elsif assignee_id? || assignee_username? # assignee not found
-      items.none
-    else
-      items
-    end
-  end
-  # rubocop: enable CodeReuse/ActiveRecord
-
   def filter_by_no_assignee?
     # Assignee_id takes precedence over assignee_username
     [NONE, FILTER_NONE].include?(params[:assignee_id].to_s.downcase) || params[:assignee_username].to_s == NONE
@@ -478,6 +462,20 @@ class IssuableFinder
   end
   # rubocop: enable CodeReuse/ActiveRecord
 
+  def by_assignee(items)
+    if filter_by_no_assignee?
+      items.unassigned
+    elsif filter_by_any_assignee?
+      items.assigned
+    elsif assignee
+      items.assigned_to(assignee)
+    elsif assignee_id? || assignee_username? # assignee not found
+      items.none
+    else
+      items
+    end
+  end
+
   # rubocop: disable CodeReuse/ActiveRecord
   def by_milestone(items)
     if milestones?

app/finders/issues_finder.rb

@@ -144,20 +144,6 @@ class IssuesFinder < IssuableFinder
 
     current_user.blank?
   end
-
-  def by_assignee(items)
-    if filter_by_no_assignee?
-      items.unassigned
-    elsif filter_by_any_assignee?
-      items.assigned
-    elsif assignee
-      items.assigned_to(assignee)
-    elsif assignee_id? || assignee_username? # assignee not found
-      items.none
-    else
-      items
-    end
-  end
 end
 
 IssuesFinder.prepend(EE::IssuesFinder)

app/helpers/boards_helper.rb

@@ -69,7 +69,7 @@ module BoardsHelper
   end
 
   def board_sidebar_user_data
-    dropdown_options = issue_assignees_dropdown_options
+    dropdown_options = assignees_dropdown_options('issue')
 
     {
       toggle: 'dropdown',

app/helpers/form_helper.rb

@@ -19,8 +19,8 @@ module FormHelper
     end
   end
 
-  def issue_assignees_dropdown_options
-    {
+  def assignees_dropdown_options(issuable_type)
+    dropdown_data = {
       toggle_class: 'js-user-search js-assignee-search js-multiselect js-save-user-data',
       title: 'Select assignee',
       filter: true,
@@ -30,8 +30,8 @@ module FormHelper
         first_user: current_user&.username,
         null_user: true,
         current_user: true,
-        project_id: @project&.id,
-        field_name: 'issue[assignee_ids][]',
+        project_id: (@target_project || @project)&.id,
+        field_name: "#{issuable_type}[assignee_ids][]",
         default_label: 'Unassigned',
         'max-select': 1,
         'dropdown-header': 'Assignee',
@@ -41,5 +41,36 @@ module FormHelper
         current_user_info: UserSerializer.new.represent(current_user)
       }
     }
+
+    type = issuable_type.to_s
+
+    if type == 'issue' && issue_supports_multiple_assignees? ||
+        type == 'merge_request' && merge_request_supports_multiple_assignees?
+      dropdown_data = multiple_assignees_dropdown_options(dropdown_data)
+    end
+
+    dropdown_data
+  end
+
+  # Overwritten
+  def issue_supports_multiple_assignees?
+    false
+  end
+
+  # Overwritten
+  def merge_request_supports_multiple_assignees?
+    false
+  end
+
+  private
+
+  def multiple_assignees_dropdown_options(options)
+    new_options = options.dup
+
+    new_options[:title] = 'Select assignee(s)'
+    new_options[:data][:'dropdown-header'] = 'Assignee(s)'
+    new_options[:data].delete(:'max-select')
+
+    new_options
   end
 end

app/helpers/issuables_helper.rb

@@ -15,11 +15,14 @@ module IssuablesHelper
     sidebar_gutter_collapsed? ? _('Expand sidebar') : _('Collapse sidebar')
   end
 
-  def sidebar_assignee_tooltip_label(issuable)
-    if issuable.assignee
-      issuable.assignee.name
+  def assignees_label(issuable, include_value: true)
+    label = 'Assignee'.pluralize(issuable.assignees.count)
+
+    if include_value
+      sanitized_list = sanitize_name(issuable.assignee_list)
+      "#{label}: #{sanitized_list}"
     else
-      issuable.allows_multiple_assignees? ? _('Assignee(s)') : _('Assignee')
+      label
     end
   end
 

app/mailers/emails/merge_requests.rb

@@ -24,10 +24,12 @@ module Emails
     end
 
     # rubocop: disable CodeReuse/ActiveRecord
-    def reassigned_merge_request_email(recipient_id, merge_request_id, previous_assignee_id, updated_by_user_id, reason = nil)
+    def reassigned_merge_request_email(recipient_id, merge_request_id, previous_assignee_ids, updated_by_user_id, reason = nil)
       setup_merge_request_mail(merge_request_id, recipient_id)
 
-      @previous_assignee = User.find_by(id: previous_assignee_id) if previous_assignee_id
+      @previous_assignees = []
+      @previous_assignees = User.where(id: previous_assignee_ids) if previous_assignee_ids.any?
+
       mail_answer_thread(@merge_request, merge_request_thread_options(updated_by_user_id, recipient_id, reason))
     end
     # rubocop: enable CodeReuse/ActiveRecord

app/mailers/notify.rb

@@ -4,6 +4,7 @@ class Notify < BaseMailer
   include ActionDispatch::Routing::PolymorphicRoutes
   include GitlabRoutingHelper
   include EmailsHelper
+  include IssuablesHelper
 
   include Emails::Issues
   include Emails::MergeRequests
@@ -24,6 +25,7 @@ class Notify < BaseMailer
   helper MembersHelper
   helper AvatarsHelper
   helper GitlabRoutingHelper
+  helper IssuablesHelper
 
   def test_email(recipient_email, subject, body)
     mail(to: recipient_email,

app/models/concerns/issuable.rb

@@ -67,13 +67,6 @@ module Issuable
              allow_nil: true,
              prefix: true
 
-    delegate :name,
-             :email,
-             :public_email,
-             to: :assignee,
-             allow_nil: true,
-             prefix: true
-
     validates :author, presence: true
     validates :title, presence: true, length: { maximum: 255 }
     validate :milestone_is_valid
@@ -88,6 +81,19 @@ module Issuable
     scope :only_opened, -> { with_state(:opened) }
     scope :closed, -> { with_state(:closed) }
 
+    # rubocop:disable GitlabSecurity/SqlInjection
+    # The `to_ability_name` method is not an user input.
+    scope :assigned, -> do
+      where("EXISTS (SELECT TRUE FROM #{to_ability_name}_assignees WHERE #{to_ability_name}_id = #{to_ability_name}s.id)")
+    end
+    scope :unassigned, -> do
+      where("NOT EXISTS (SELECT TRUE FROM #{to_ability_name}_assignees WHERE #{to_ability_name}_id = #{to_ability_name}s.id)")
+    end
+    scope :assigned_to, ->(u) do
+      where("EXISTS (SELECT TRUE FROM #{to_ability_name}_assignees WHERE user_id = ? AND #{to_ability_name}_id = #{to_ability_name}s.id)", u.id)
+    end
+    # rubocop:enable GitlabSecurity/SqlInjection
+
     scope :left_joins_milestones,    -> { joins("LEFT OUTER JOIN milestones ON #{table_name}.milestone_id = milestones.id") }
     scope :order_milestone_due_desc, -> { left_joins_milestones.reorder('milestones.due_date IS NULL, milestones.id IS NULL, milestones.due_date DESC') }
     scope :order_milestone_due_asc,  -> { left_joins_milestones.reorder('milestones.due_date IS NULL, milestones.id IS NULL, milestones.due_date ASC') }
@@ -104,6 +110,7 @@ module Issuable
 
     participant :author
     participant :notes_with_associations
+    participant :assignees
 
     strip_attributes :title
 
@@ -272,6 +279,10 @@ module Issuable
     end
   end
 
+  def assignee_or_author?(user)
+    author_id == user.id || assignees.exists?(user.id)
+  end
+
   def today?
     Date.today == created_at.to_date
   end
@@ -316,11 +327,7 @@ module Issuable
       end
 
       if old_assignees != assignees
-        if self.is_a?(Issue)
-          changes[:assignees] = [old_assignees.map(&:hook_attrs), assignees.map(&:hook_attrs)]
-        else
-          changes[:assignee] = [old_assignees&.first&.hook_attrs, assignee&.hook_attrs]
-        end
+        changes[:assignees] = [old_assignees.map(&:hook_attrs), assignees.map(&:hook_attrs)]
       end
 
       if self.respond_to?(:total_time_spent)
@@ -357,10 +364,18 @@ module Issuable
   def card_attributes
     {
       'Author'   => author.try(:name),
-      'Assignee' => assignee.try(:name)
+      'Assignee' => assignee_list
     }
   end
 
+  def assignee_list
+    assignees.map(&:name).to_sentence
+  end
+
+  def assignee_username_list
+    assignees.map(&:username).to_sentence
+  end
+
   def notes_with_associations
     # If A has_many Bs, and B has_many Cs, and you do
     # `A.includes(b: :c).each { |a| a.b.includes(:c) }`, sadly ActiveRecord

app/models/issue.rb

@@ -49,10 +49,6 @@ class Issue < ApplicationRecord
 
   scope :in_projects, ->(project_ids) { where(project_id: project_ids) }
 
-  scope :assigned, -> { where('EXISTS (SELECT TRUE FROM issue_assignees WHERE issue_id = issues.id)') }
-  scope :unassigned, -> { where('NOT EXISTS (SELECT TRUE FROM issue_assignees WHERE issue_id = issues.id)') }
-  scope :assigned_to, ->(u) { where('EXISTS (SELECT TRUE FROM issue_assignees WHERE user_id = ? AND issue_id = issues.id)', u.id)}
-
   scope :with_due_date, -> { where.not(due_date: nil) }
   scope :without_due_date, -> { where(due_date: nil) }
   scope :due_before, ->(date) { where('issues.due_date < ?', date) }
@@ -75,8 +71,6 @@ class Issue < ApplicationRecord
   attr_spammable :title, spam_title: true
   attr_spammable :description, spam_description: true
 
-  participant :assignees
-
   state_machine :state, initial: :opened do
     event :close do
       transition [:opened] => :closed
@@ -155,22 +149,6 @@ class Issue < ApplicationRecord
     Gitlab::HookData::IssueBuilder.new(self).build
   end
 
-  # Returns a Hash of attributes to be used for Twitter card metadata
-  def card_attributes
-    {
-      'Author'   => author.try(:name),
-      'Assignee' => assignee_list
-    }
-  end
-
-  def assignee_or_author?(user)
-    author_id == user.id || assignees.exists?(user.id)
-  end
-
-  def assignee_list
-    assignees.map(&:name).to_sentence
-  end
-
   # `from` argument can be a Namespace or Project.
   def to_reference(from = nil, full: false)
     reference = "#{self.class.reference_prefix}#{iid}"

app/models/merge_request.rb

@@ -71,8 +71,7 @@ class MergeRequest < ApplicationRecord
   has_many :suggestions, through: :notes
 
   has_many :merge_request_assignees
-  # Will be deprecated at https://gitlab.com/gitlab-org/gitlab-ce/issues/59457
-  belongs_to :assignee, class_name: "User"
+  has_many :assignees, class_name: "User", through: :merge_request_assignees
 
   serialize :merge_params, Hash # rubocop:disable Cop/ActiveRecordSerialize
 
@@ -81,10 +80,6 @@ class MergeRequest < ApplicationRecord
   after_update :reload_diff_if_branch_changed
   after_save :ensure_metrics
 
-  # Required until the codebase starts using this relation for single or multiple assignees.
-  # TODO: Remove at gitlab-ee#2004 implementation.
-  after_save :refresh_merge_request_assignees, if: :assignee_id_changed?
-
   # When this attribute is true some MR validation is ignored
   # It allows us to close or modify broken merge requests
   attr_accessor :allow_broken
@@ -190,19 +185,14 @@ class MergeRequest < ApplicationRecord
   end
   scope :join_project, -> { joins(:target_project) }
   scope :references_project, -> { references(:target_project) }
-  scope :assigned, -> { where("assignee_id IS NOT NULL") }
-  scope :unassigned, -> { where("assignee_id IS NULL") }
-  scope :assigned_to, ->(u) { where(assignee_id: u.id)}
   scope :with_api_entity_associations, -> {
-    preload(:author, :assignee, :notes, :labels, :milestone, :timelogs,
+    preload(:assignees, :author, :notes, :labels, :milestone, :timelogs,
             latest_merge_request_diff: [:merge_request_diff_commits],
             metrics: [:latest_closed_by, :merged_by],
             target_project: [:route, { namespace: :route }],
             source_project: [:route, { namespace: :route }])
   }
 
-  participant :assignee
-
   after_save :keep_around_commit
 
   alias_attribute :project, :target_project
@@ -339,29 +329,28 @@ class MergeRequest < ApplicationRecord
     Gitlab::HookData::MergeRequestBuilder.new(self).build
   end
 
-  # Returns a Hash of attributes to be used for Twitter card metadata
-  def card_attributes
-    {
-      'Author'   => author.try(:name),
-      'Assignee' => assignee.try(:name)
-    }
+  # Used by APIs to keep backward compatibility
+  def assignee
+    assignees.first
   end
 
-  # These method are needed for compatibility with issues to not mess view and other code
   def assignees
-    Array(assignee)
-  end
-
-  def assignee_ids
-    Array(assignee_id)
-  end
-
-  def assignee_ids=(ids)
-    write_attribute(:assignee_id, ids.last)
-  end
+    # We're willing to write in the DB if we can't find the relation
+    # (i.e. migration at #26496 is not finished yet).
+    return super if Gitlab::Database.read_only?
+
+    # If there's an assignee_id and no relation, it means the background
+    # migration at #26496 didn't reach this merge request yet.
+    # This code should be removed in the clean-up phase of the
+    # background migration (#59457).
+    if persisted? && assignee_id && merge_request_assignees.empty?
+      transaction do
+        merge_request_assignees.create(user_id: assignee_id, merge_request_id: id)
+        update_column(:assignee_id, nil)
+      end
+    end
 
-  def assignee_or_author?(user)
-    author_id == user.id || assignee_id == user.id
+    super
   end
 
   # `from` argument can be a Namespace or Project.
@@ -684,15 +673,6 @@ class MergeRequest < ApplicationRecord
     merge_request_diff || create_merge_request_diff
   end
 
-  def refresh_merge_request_assignees
-    transaction do
-      # Using it instead relation.delete_all in order to avoid adding a
-      # dependent: :delete_all (we already have foreign key cascade deletion).
-      MergeRequestAssignee.where(merge_request_id: self).delete_all
-      merge_request_assignees.create(user_id: assignee_id) if assignee_id
-    end
-  end
-
   def create_merge_request_diff
     fetch_ref!
 
@@ -1210,7 +1190,7 @@ class MergeRequest < ApplicationRecord
       variables.append(key: 'CI_MERGE_REQUEST_PROJECT_URL', value: project.web_url)
       variables.append(key: 'CI_MERGE_REQUEST_TARGET_BRANCH_NAME', value: target_branch.to_s)
       variables.append(key: 'CI_MERGE_REQUEST_TITLE', value: title)
-      variables.append(key: 'CI_MERGE_REQUEST_ASSIGNEES', value: assignee.username) if assignee
+      variables.append(key: 'CI_MERGE_REQUEST_ASSIGNEES', value: assignee_username_list) if assignees.any?
       variables.append(key: 'CI_MERGE_REQUEST_MILESTONE', value: milestone.title) if milestone
       variables.append(key: 'CI_MERGE_REQUEST_LABELS', value: label_names.join(',')) if labels.present?
       variables.concat(source_project_variables)

app/models/project.rb

@@ -674,6 +674,10 @@ class Project < ApplicationRecord
     { scope: :project, status: auto_devops&.enabled || Feature.enabled?(:force_autodevops_on_by_default, self) }
   end
 
+  def multiple_mr_assignees_enabled?
+    Feature.enabled?(:multiple_merge_request_assignees, self)
+  end
+
   def daily_statistics_enabled?
     Feature.enabled?(:project_daily_statistics, self, default_enabled: true)
   end

app/serializers/issuable_sidebar_extras_entity.rb

@@ -11,4 +11,6 @@ class IssuableSidebarExtrasEntity < Grape::Entity
   expose :subscribed do |issuable|
     issuable.subscribed?(request.current_user, issuable.project)
   end
+
+  expose :assignees, using: API::Entities::UserBasic
 end

app/serializers/issue_sidebar_extras_entity.rb

 # frozen_string_literal: true
 
 class IssueSidebarExtrasEntity < IssuableSidebarExtrasEntity
-  expose :assignees, using: API::Entities::UserBasic
 end
 
 IssueSidebarExtrasEntity.prepend(EE::IssueSidebarExtrasEntity)

app/serializers/merge_request_assignee_entity.rb

+# frozen_string_literal: true
+
+class MergeRequestAssigneeEntity < ::API::Entities::UserBasic
+  expose :can_merge do |assignee, options|
+    options[:merge_request]&.can_be_merged_by?(assignee)
+  end
+end

app/serializers/merge_request_basic_entity.rb

 # frozen_string_literal: true
 
 class MergeRequestBasicEntity < Grape::Entity
-  expose :assignee_id
   expose :merge_status
   expose :merge_error
   expose :state
@@ -9,7 +8,7 @@ class MergeRequestBasicEntity < Grape::Entity
   expose :rebase_in_progress?, as: :rebase_in_progress
   expose :milestone, using: API::Entities::Milestone
   expose :labels, using: LabelEntity
-  expose :assignee, using: API::Entities::UserBasic
+  expose :assignees, using: API::Entities::UserBasic
   expose :task_status, :task_status_short
   expose :lock_version, :lock_version
 end

app/serializers/merge_request_serializer.rb

@@ -8,9 +8,9 @@ class MergeRequestSerializer < BaseSerializer
     entity =
       case opts[:serializer]
       when 'sidebar'
-        MergeRequestSidebarBasicEntity
+        IssuableSidebarBasicEntity
       when 'sidebar_extras'
-        IssuableSidebarExtrasEntity
+        MergeRequestSidebarExtrasEntity
       when 'basic'
         MergeRequestBasicEntity
       else

app/serializers/merge_request_sidebar_basic_entity.rb

-# frozen_string_literal: true
-
-class MergeRequestSidebarBasicEntity < IssuableSidebarBasicEntity
-  expose :assignee, if: lambda { |issuable| issuable.assignee } do
-    expose :assignee, merge: true, using: API::Entities::UserBasic
-
-    expose :can_merge do |issuable|
-      issuable.can_be_merged_by?(issuable.assignee)
-    end
-  end
-end

app/serializers/merge_request_sidebar_extras_entity.rb

+# frozen_string_literal: true
+
+class MergeRequestSidebarExtrasEntity < IssuableSidebarExtrasEntity
+  expose :assignees do |merge_request|
+    MergeRequestAssigneeEntity.represent(merge_request.assignees, merge_request: merge_request)
+  end
+end

app/services/issuable_base_service.rb

@@ -34,14 +34,20 @@ class IssuableBaseService < BaseService
   end
 
   def filter_assignee(issuable)
-    return unless params[:assignee_id].present?
+    return if params[:assignee_ids].blank?
 
-    assignee_id = params[:assignee_id]
+    unless issuable.allows_multiple_assignees?
+      params[:assignee_ids] = params[:assignee_ids].first(1)
+    end
+
+    assignee_ids = params[:assignee_ids].select { |assignee_id| assignee_can_read?(issuable, assignee_id) }
 
-    if assignee_id.to_s == IssuableFinder::NONE
-      params[:assignee_id] = ""
+    if params[:assignee_ids].map(&:to_s) == [IssuableFinder::NONE]
+      params[:assignee_ids] = []
+    elsif assignee_ids.any?
+      params[:assignee_ids] = assignee_ids
     else
-      params.delete(:assignee_id) unless assignee_can_read?(issuable, assignee_id)
+      params.delete(:assignee_ids)
     end
   end
 
@@ -352,7 +358,7 @@ class IssuableBaseService < BaseService
   end
 
   def has_changes?(issuable, old_labels: [], old_assignees: [])
-    valid_attrs = [:title, :description, :assignee_id, :milestone_id, :target_branch]
+    valid_attrs = [:title, :description, :assignee_ids, :milestone_id, :target_branch]
 
     attrs_changed = valid_attrs.any? do |attr|
       issuable.previous_changes.include?(attr.to_s)

app/services/issues/base_service.rb

@@ -20,7 +20,7 @@ module Issues
     private
 
     def create_assignee_note(issue, old_assignees)
-      SystemNoteService.change_issue_assignees(
+      SystemNoteService.change_issuable_assignees(
         issue, issue.project, current_user, old_assignees)
     end
 
@@ -31,26 +31,6 @@ module Issues
       issue.project.execute_services(issue_data, hooks_scope)
     end
 
-    # rubocop: disable CodeReuse/ActiveRecord
-    def filter_assignee(issuable)
-      return if params[:assignee_ids].blank?
-
-      unless issuable.allows_multiple_assignees?
-        params[:assignee_ids] = params[:assignee_ids].take(1)
-      end
-
-      assignee_ids = params[:assignee_ids].select { |assignee_id| assignee_can_read?(issuable, assignee_id) }
-
-      if params[:assignee_ids].map(&:to_s) == [IssuableFinder::NONE]
-        params[:assignee_ids] = []
-      elsif assignee_ids.any?
-        params[:assignee_ids] = assignee_ids
-      else
-        params.delete(:assignee_ids)
-      end
-    end
-    # rubocop: enable CodeReuse/ActiveRecord
-
     def update_project_counter_caches?(issue)
       super || issue.confidential_changed?
     end

app/services/issues/update_service.rb

@@ -39,7 +39,7 @@ module Issues
       if issue.assignees != old_assignees
         create_assignee_note(issue, old_assignees)
         notification_service.async.reassigned_issue(issue, current_user, old_assignees)
-        todo_service.reassigned_issue(issue, current_user, old_assignees)
+        todo_service.reassigned_issuable(issue, current_user, old_assignees)
       end
 
       if issue.previous_changes.include?('confidential')

app/services/merge_requests/base_service.rb

@@ -49,9 +49,9 @@ module MergeRequests
       MergeRequestMetricsService.new(merge_request.metrics)
     end
 
-    def create_assignee_note(merge_request)
-      SystemNoteService.change_assignee(
-        merge_request, merge_request.project, current_user, merge_request.assignee)
+    def create_assignee_note(merge_request, old_assignees)
+      SystemNoteService.change_issuable_assignees(
+        merge_request, merge_request.project, current_user, old_assignees)
     end
 
     def create_pipeline_for(merge_request, user)

app/services/merge_requests/update_service.rb

@@ -24,13 +24,13 @@ module MergeRequests
       update_task_event(merge_request) || update(merge_request)
     end
 
-    # rubocop:disable Metrics/AbcSize
     def handle_changes(merge_request, options)
       old_associations = options.fetch(:old_associations, {})
       old_labels = old_associations.fetch(:labels, [])
       old_mentioned_users = old_associations.fetch(:mentioned_users, [])
+      old_assignees = old_associations.fetch(:assignees, [])
 
-      if has_changes?(merge_request, old_labels: old_labels)
+      if has_changes?(merge_request, old_labels: old_labels, old_assignees: old_assignees)
         todo_service.mark_pending_todos_as_done(merge_request, current_user)
       end
 
@@ -45,15 +45,10 @@ module MergeRequests
                                   merge_request.target_branch)
       end
 
-      if merge_request.previous_changes.include?('assignee_id')
-        reassigned_merge_request_args = [merge_request, current_user]
-
-        old_assignee_id = merge_request.previous_changes['assignee_id'].first
-        reassigned_merge_request_args << User.find(old_assignee_id) if old_assignee_id
-
-        create_assignee_note(merge_request)
-        notification_service.async.reassigned_merge_request(*reassigned_merge_request_args)
-        todo_service.reassigned_merge_request(merge_request, current_user)
+      if merge_request.assignees != old_assignees
+        create_assignee_note(merge_request, old_assignees)
+        notification_service.async.reassigned_merge_request(merge_request, current_user, old_assignees)
+        todo_service.reassigned_issuable(merge_request, current_user, old_assignees)
       end
 
       if merge_request.previous_changes.include?('target_branch') ||
@@ -81,7 +76,6 @@ module MergeRequests
         )
       end
     end
-    # rubocop:enable Metrics/AbcSize
 
     def handle_task_changes(merge_request)
       todo_service.mark_pending_todos_as_done(merge_request, current_user)

app/services/notification_recipient_service.rb

@@ -247,15 +247,15 @@ module NotificationRecipientService
       attr_reader :target
       attr_reader :current_user
       attr_reader :action
-      attr_reader :previous_assignee
+      attr_reader :previous_assignees
       attr_reader :skip_current_user
 
-      def initialize(target, current_user, action:, custom_action: nil, previous_assignee: nil, skip_current_user: true)
+      def initialize(target, current_user, action:, custom_action: nil, previous_assignees: nil, skip_current_user: true)
         @target = target
         @current_user = current_user
         @action = action
         @custom_action = custom_action
-        @previous_assignee = previous_assignee
+        @previous_assignees = previous_assignees
         @skip_current_user = skip_current_user
       end
 
@@ -270,11 +270,7 @@ module NotificationRecipientService
 
         # Re-assign is considered as a mention of the new assignee
         case custom_action
-        when :reassign_merge_request
-          add_recipients(previous_assignee, :mention, nil)
-          add_recipients(target.assignee, :mention, NotificationReason::ASSIGNED)
-        when :reassign_issue
-          previous_assignees = Array(previous_assignee)
+        when :reassign_merge_request, :reassign_issue
           add_recipients(previous_assignees, :mention, nil)
           add_recipients(target.assignees, :mention, NotificationReason::ASSIGNED)
         end
@@ -287,17 +283,11 @@ module NotificationRecipientService
           # receive them, too.
           add_mentions(current_user, target: target)
 
-          # Add the assigned users, if any
-          assignees = case custom_action
-                      when :new_issue
-                        target.assignees
-                      else
-                        target.assignee
-                      end
-
           # We use the `:participating` notification level in order to match existing legacy behavior as captured
           # in existing specs (notification_service_spec.rb ~ line 507)
-          add_recipients(assignees, :participating, NotificationReason::ASSIGNED) if assignees
+          if target.is_a?(Issuable)
+            add_recipients(target.assignees, :participating, NotificationReason::ASSIGNED)
+          end
 
           add_labels_subscribers
         end

app/services/notification_service.rb

@@ -95,8 +95,8 @@ class NotificationService
 
   # When we reassign an issue we should send an email to:
   #
-  #  * issue old assignee if their notification level is not Disabled
-  #  * issue new assignee if their notification level is not Disabled
+  #  * issue old assignees if their notification level is not Disabled
+  #  * issue new assignees if their notification level is not Disabled
   #  * users with custom level checked with "reassign issue"
   #
   def reassigned_issue(issue, current_user, previous_assignees = [])
@@ -104,7 +104,7 @@ class NotificationService
       issue,
       current_user,
       action: "reassign",
-      previous_assignee: previous_assignees
+      previous_assignees: previous_assignees
     )
 
     previous_assignee_ids = previous_assignees.map(&:id)
@@ -140,7 +140,7 @@ class NotificationService
   # When create a merge request we should send an email to:
   #
   #  * mr author
-  #  * mr assignee if their notification level is not Disabled
+  #  * mr assignees if their notification level is not Disabled
   #  * project team members with notification level higher then Participating
   #  * watchers of the mr's labels
   #  * users with custom level checked with "new merge request"
@@ -184,23 +184,25 @@ class NotificationService
 
   # When we reassign a merge_request we should send an email to:
   #
-  #  * merge_request old assignee if their notification level is not Disabled
-  #  * merge_request assignee if their notification level is not Disabled
+  #  * merge_request old assignees if their notification level is not Disabled
+  #  * merge_request new assignees if their notification level is not Disabled
   #  * users with custom level checked with "reassign merge request"
   #
-  def reassigned_merge_request(merge_request, current_user, previous_assignee = nil)
+  def reassigned_merge_request(merge_request, current_user, previous_assignees = [])
     recipients = NotificationRecipientService.build_recipients(
       merge_request,
       current_user,
       action: "reassign",
-      previous_assignee: previous_assignee
+      previous_assignees: previous_assignees
     )
 
+    previous_assignee_ids = previous_assignees.map(&:id)
+
     recipients.each do |recipient|
       mailer.reassigned_merge_request_email(
         recipient.user.id,
         merge_request.id,
-        previous_assignee&.id,
+        previous_assignee_ids,
         current_user.id,
         recipient.reason
       ).deliver_later

app/services/system_note_service.rb

@@ -69,7 +69,7 @@ module SystemNoteService
 
   # Called when the assignees of an Issue is changed or removed
   #
-  # issue - Issue object
+  # issuable - Issuable object (responds to assignees)
   # project  - Project owning noteable
   # author   - User performing the change
   # assignees - Users being assigned, or nil
@@ -85,9 +85,9 @@ module SystemNoteService
   #   "assigned to @user1 and @user2"
   #
   # Returns the created Note object
-  def change_issue_assignees(issue, project, author, old_assignees)
-    unassigned_users = old_assignees - issue.assignees
-    added_users = issue.assignees.to_a - old_assignees
+  def change_issuable_assignees(issuable, project, author, old_assignees)
+    unassigned_users = old_assignees - issuable.assignees
+    added_users = issuable.assignees.to_a - old_assignees
 
     text_parts = []
     text_parts << "assigned to #{added_users.map(&:to_reference).to_sentence}" if added_users.any?
@@ -95,7 +95,7 @@ module SystemNoteService
 
     body = text_parts.join(' and ')
 
-    create_note(NoteSummary.new(issue, project, author, body, action: 'assignee'))
+    create_note(NoteSummary.new(issuable, project, author, body, action: 'assignee'))
   end
 
   # Called when the milestone of a Noteable is changed

app/services/todo_service.rb

@@ -49,12 +49,12 @@ class TodoService
     todo_users.each(&:update_todos_count_cache)
   end
 
-  # When we reassign an issue we should:
+  # When we reassign an issuable we should:
   #
-  #  * create a pending todo for new assignee if issue is assigned
+  #  * create a pending todo for new assignee if issuable is assigned
   #
-  def reassigned_issue(issue, current_user, old_assignees = [])
-    create_assignment_todo(issue, current_user, old_assignees)
+  def reassigned_issuable(issuable, current_user, old_assignees = [])
+    create_assignment_todo(issuable, current_user, old_assignees)
   end
 
   # When create a merge request we should:
@@ -82,14 +82,6 @@ class TodoService
     mark_pending_todos_as_done(merge_request, current_user)
   end
 
-  # When we reassign a merge request we should:
-  #
-  #  * creates a pending todo for new assignee if merge request is assigned
-  #
-  def reassigned_merge_request(merge_request, current_user)
-    create_assignment_todo(merge_request, current_user)
-  end
-
   # When merge a merge request we should:
   #
   #  * mark all pending todos related to the target for the current user as done

app/views/notify/_reassigned_issuable_email.html.haml

+%p
+  Assignee changed
+  - if previous_assignees.any?
+    from
+    %strong= sanitize_name(previous_assignees.map(&:name).to_sentence)
+  to
+  - if issuable.assignees.any?
+    %strong= sanitize_name(issuable.assignee_list)
+  - else
+    %strong Unassigned

app/views/notify/closed_merge_request_email.text.haml

@@ -5,4 +5,4 @@ Merge Request url: #{project_merge_request_url(@merge_request.target_project, @m
 = merge_path_description(@merge_request, 'to')
 
 Author: #{sanitize_name(@merge_request.author_name)}
-Assignee: #{sanitize_name(@merge_request.assignee_name)}
+= assignees_label(@merge_request)

app/views/notify/issue_due_email.html.haml

@@ -3,7 +3,7 @@
 
 - if @issue.assignees.any?
   %p
-    Assignee: #{@issue.assignee_list}
+    = assignees_label(@issue)
 %p
   This issue is due on: #{@issue.due_date.to_s(:medium)}
 

app/views/notify/issue_due_email.text.erb

@@ -2,6 +2,6 @@ The following issue is due on <%= @issue.due_date %>:
 
 Issue <%= @issue.iid %>: <%= url_for(project_issue_url(@issue.project, @issue)) %>
 Author:    <%= @issue.author_name %>
-Assignee:  <%= @issue.assignee_list %>
+<%= assignees_label(@issue) %>
 
 <%= @issue.description %>

app/views/notify/merge_request_status_email.text.haml

@@ -5,4 +5,4 @@ Merge Request url: #{project_merge_request_url(@merge_request.target_project, @m
 = merge_path_description(@merge_request, 'to')
 
 Author: #{sanitize_name(@merge_request.author_name)}
-Assignee: #{sanitize_name(@merge_request.assignee_name)}
+= assignees_label(@merge_request)

app/views/notify/merge_request_unmergeable_email.text.haml

@@ -5,4 +5,4 @@ Merge Request url: #{project_merge_request_url(@merge_request.target_project, @m
 = merge_path_description(@merge_request, 'to')
 
 Author: #{sanitize_name(@merge_request.author_name)}
-Assignee: #{sanitize_name(@merge_request.assignee_name)}
+= assignees_label(@merge_request)

app/views/notify/merged_merge_request_email.text.haml

@@ -5,4 +5,4 @@ Merge Request url: #{project_merge_request_url(@merge_request.target_project, @m
 = merge_path_description(@merge_request, 'to')
 
 Author: #{sanitize_name(@merge_request.author_name)}
-Assignee: #{sanitize_name(@merge_request.assignee_name)}
+= assignees_label(@merge_request)

app/views/notify/new_issue_email.html.haml

@@ -4,7 +4,7 @@
 
 - if @issue.assignees.any?
   %p
-    Assignee: #{@issue.assignee_list}
+    = assignees_label(@issue)
 
 - if @issue.description
   %div

app/views/notify/new_issue_email.text.erb

@@ -2,6 +2,6 @@ New Issue was created.
 
 Issue <%= @issue.iid %>: <%= url_for(project_issue_url(@issue.project, @issue)) %>
 Author:    <%= sanitize_name(@issue.author_name) %>
-Assignee:  <%= @issue.assignee_list %>
+<%= assignees_label(@issue) %>
 
 <%= @issue.description %>

app/views/notify/new_mention_in_issue_email.text.erb

@@ -2,6 +2,6 @@ You have been mentioned in an issue.
 
 Issue <%= @issue.iid %>: <%= url_for(project_issue_url(@issue.project, @issue)) %>
 Author:    <%= sanitize_name(@issue.author_name) %>
-Assignee:  <%= sanitize_name(@issue.assignee_list) %>
+<%= assignees_label(@issue) %>
 
 <%= @issue.description %>

app/views/notify/new_mention_in_merge_request_email.text.erb

@@ -4,6 +4,6 @@ You have been mentioned in Merge Request <%= @merge_request.to_reference %>
 
 <%= merge_path_description(@merge_request, 'to') %>
 Author:    <%= sanitize_name(@merge_request.author_name) %>
-Assignee:  <%= sanitize_name(@merge_request.assignee_name) %>
+= assignees_label(@merge_request)
 
 <%= @merge_request.description %>

app/views/notify/new_merge_request_email.html.haml

@@ -5,9 +5,9 @@
 %p.details
   != merge_path_description(@merge_request, '→')
 
-- if @merge_request.assignee_id.present?
+- if @merge_request.assignees.any?
   %p
-    Assignee: #{sanitize_name(@merge_request.assignee_name)}
+    = assignees_label(@merge_request)
 
 = render_if_exists 'notify/merge_request_approvers', presenter: @mr_presenter
 

app/views/notify/new_merge_request_email.text.erb

@@ -4,7 +4,7 @@ New Merge Request <%= @merge_request.to_reference %>
 
 <%= merge_path_description(@merge_request, 'to') %>
 Author:    <%= @merge_request.author_name %>
-Assignee:  <%= @merge_request.assignee_name %>
+<%= assignees_label(@merge_request) %>
 <%= render_if_exists 'notify/merge_request_approvers', presenter: @mr_presenter %>
 
 <%= @merge_request.description %>

app/views/notify/reassigned_issue_email.html.haml

-%p
-  Assignee changed
-  - if @previous_assignees.any?
-    from
-    %strong= sanitize_name(@previous_assignees.map(&:name).to_sentence)
-  to
-  - if @issue.assignees.any?
-    %strong= @issue.assignee_list
-  - else
-    %strong Unassigned
+= render 'reassigned_issuable_email', issuable: @issue, previous_assignees: @previous_assignees

app/views/notify/reassigned_merge_request_email.html.haml

-%p
-  Assignee changed
-  - if @previous_assignee
-    from
-    %strong= sanitize_name(@previous_assignee.name)
-  to
-  - if @merge_request.assignee_id
-    %strong= sanitize_name(@merge_request.assignee_name)
-  - else
-    %strong Unassigned
+= render 'reassigned_issuable_email', issuable: @merge_request, previous_assignees: @previous_assignees

app/views/notify/reassigned_merge_request_email.text.erb

@@ -2,5 +2,5 @@ Reassigned Merge Request <%= @merge_request.iid %>
 
 <%= url_for([@merge_request.project.namespace.becomes(Namespace), @merge_request.project, @merge_request, { only_path: false }]) %>
 
-Assignee changed <%= "from #{sanitize_name(@previous_assignee.name)}" if @previous_assignee -%>
- to <%= "#{@merge_request.assignee_id ? sanitize_name(@merge_request.assignee_name) : 'Unassigned'}" %>
+Assignee changed <%= "from #{sanitize_name(@previous_assignees.map(&:name).to_sentence)}" if @previous_assignees.any? -%>
+ to <%= "#{@merge_request.assignees.any? ? @merge_request.assignee_list : 'Unassigned'}" %>

app/views/projects/issues/_issue.html.haml

@@ -52,7 +52,7 @@
               CLOSED
           - if issue.assignees.any?
             %li
-              = render 'shared/issuable/assignees', project: @project, issue: issue
+              = render 'shared/issuable/assignees', project: @project, issuable: issue
 
           = render 'shared/issuable_meta_data', issuable: issue
 

app/views/projects/merge_requests/_merge_request.html.haml

@@ -53,9 +53,9 @@
           %li.issuable-pipeline-broken.d-none.d-sm-inline-block
             = link_to merge_request_path(merge_request), class: "has-tooltip", title: _('Cannot be merged automatically') do
               = icon('exclamation-triangle')
-        - if merge_request.assignee
+        - if merge_request.assignees.any?
           %li
-            = link_to_member(merge_request.source_project, merge_request.assignee, name: false, title: _('Assigned to :name'))
+            = render 'shared/issuable/assignees', project: merge_request.project, issuable: merge_request
         = render_if_exists 'projects/merge_requests/approvals_count', merge_request: merge_request
 
         = render 'shared/issuable_meta_data', issuable: merge_request

app/views/shared/boards/components/sidebar/_assignee.html.haml

@@ -19,7 +19,7 @@
         ":data-name" => "assignee.name",
         ":data-username" => "assignee.username" }
       .dropdown
-        - dropdown_options = issue_assignees_dropdown_options
+        - dropdown_options = assignees_dropdown_options('issue')
         %button.dropdown-menu-toggle.js-user-search.js-author-search.js-multiselect.js-save-user-data.js-issue-board-sidebar{ type: 'button', ref: 'assigneeDropdown', data: board_sidebar_user_data,
           ":data-issuable-id" => "issue.iid" }
           = dropdown_options[:title]

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

 - max_render = 4
-- assignees_rendering_overflow = issue.assignees.size > max_render
+- assignees_rendering_overflow = issuable.assignees.size > max_render
 - render_count = assignees_rendering_overflow ? max_render - 1 : max_render
-- more_assignees_count = issue.assignees.size - render_count
+- more_assignees_count = issuable.assignees.size - render_count
 
-- issue.assignees.take(render_count).each do |assignee| # rubocop: disable CodeReuse/ActiveRecord
+- issuable.assignees.take(render_count).each do |assignee| # rubocop: disable CodeReuse/ActiveRecord
   = link_to_member(@project, assignee, name: false, title: "Assigned to :name")
 
 - if more_assignees_count.positive?

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

@@ -21,10 +21,7 @@
         .title
           Assignee
         .filter-item
-          - if type == :issues
-            - field_name = "update[assignee_ids][]"
-          - else
-            - field_name = "update[assignee_id]"
+          - field_name = "update[assignee_ids][]"
           = dropdown_tag("Select assignee", options: { toggle_class: "js-user-search js-update-assignee js-filter-submit js-filter-bulk-update", title: "Assign to", filter: true, dropdown_class: "dropdown-menu-user dropdown-menu-selectable",
             placeholder: "Search authors", data: { first_user: (current_user.username if current_user), null_user: true, current_user: true, project_id: @project.id, field_name: field_name } })
       .block

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

 - issuable_type = issuable_sidebar[:type]
 - signed_in = !!issuable_sidebar.dig(:current_user, :id)
-- can_edit_issuable = issuable_sidebar.dig(:current_user, :can_edit)
 
-- if issuable_type == "issue"
-  #js-vue-sidebar-assignees{ data: { field: "#{issuable_type}[assignee_ids]", signed_in: signed_in } }
-    .title.hide-collapsed
-      = _('Assignee')
-      = icon('spinner spin')
-- else
-  - assignee = assignees.first
-  .sidebar-collapsed-icon.sidebar-collapsed-user{ data: { toggle: "tooltip", placement: "left", container: "body", boundary: 'viewport' }, title: (issuable_sidebar.dig(:assignee, :name) || _('Assignee')) }
-    - if issuable_sidebar[:assignee]
-      = link_to_member(@project, assignee, size: 24)
-    - else
-      = icon('user', 'aria-hidden': 'true')
+#js-vue-sidebar-assignees{ data: { field: "#{issuable_type}[assignee_ids]", signed_in: signed_in } }
   .title.hide-collapsed
     = _('Assignee')
-    = icon('spinner spin', class: 'hidden block-loading', 'aria-hidden': 'true')
-    - if can_edit_issuable
-      = link_to _('Edit'), '#', class: 'js-sidebar-dropdown-toggle edit-link float-right'
-    - if !signed_in
-      %a.gutter-toggle.float-right.js-sidebar-toggle{ role: "button", href: "#", "aria-label" => _('Toggle sidebar') }
-        = sidebar_gutter_toggle_icon
-  .value.hide-collapsed
-    - if issuable_sidebar[:assignee]
-      = link_to_member(@project, assignee, size: 32, extra_class: 'bold') do
-        - unless issuable_sidebar[:assignee][:can_merge]
-          %span.float-right.cannot-be-merged{ data: { toggle: 'tooltip', placement: 'left' }, title: _('Not allowed to merge') }
-            = icon('exclamation-triangle', 'aria-hidden': 'true')
-        %span.username
-          @#{issuable_sidebar[:assignee][:username]}
-    - else
-      %span.assign-yourself.no-value
-        = _('No assignee')
-        - if can_edit_issuable
-          \-
-          %a.js-assign-yourself{ href: '#' }
-            = _('assign yourself')
+    = icon('spinner spin')
 
 .selectbox.hide-collapsed
   - if assignees.none?
@@ -59,17 +27,15 @@
       ability_name: issuable_type,
       null_user: true,
       display: 'static' } }
-  - title = _('Select assignee')
 
-  - if issuable_type == "issue"
-    - dropdown_options = issue_assignees_dropdown_options
-    - title = dropdown_options[:title]
-    - options[:toggle_class] += ' js-multiselect js-save-user-data'
-    - data = { field_name: "#{issuable_type}[assignee_ids][]" }
-    - data[:multi_select] = true
-    - data['dropdown-title'] = title
-    - data['dropdown-header'] = dropdown_options[:data][:'dropdown-header']
-    - data['max-select'] = dropdown_options[:data][:'max-select'] if dropdown_options[:data][:'max-select']
-    - options[:data].merge!(data)
+  - dropdown_options = assignees_dropdown_options(issuable_type)
+  - title = dropdown_options[:title]
+  - options[:toggle_class] += ' js-multiselect js-save-user-data'
+  - data = { field_name: "#{issuable_type}[assignee_ids][]" }
+  - data[:multi_select] = true
+  - data['dropdown-title'] = title
+  - data['dropdown-header'] = dropdown_options[:data][:'dropdown-header']
+  - data['max-select'] = dropdown_options[:data][:'max-select'] if dropdown_options[:data][:'max-select']
+  - options[:data].merge!(data)
 
   = dropdown_tag(title, options: options)

app/views/shared/issuable/form/_merge_request_assignee.html.haml

-- merge_request = issuable
-.block.assignee
-  .sidebar-collapsed-icon.sidebar-collapsed-user{ data: { toggle: "tooltip", placement: "left", container: "body" }, title: sidebar_assignee_tooltip_label(issuable) }
-    - if merge_request.assignee
-      = link_to_member(@project, merge_request.assignee, size: 24)
-    - else
-      = icon('user', 'aria-hidden': 'true')
-  .title.hide-collapsed
-    Assignee
-    = icon('spinner spin', class: 'hidden block-loading', 'aria-hidden': 'true')
-    - if can_edit_issuable
-      = link_to 'Edit', '#', class: 'js-sidebar-dropdown-toggle edit-link float-right'
-  .value.hide-collapsed
-    - if merge_request.assignee
-      = link_to_member(@project, merge_request.assignee, size: 32, extra_class: 'bold') do
-        - unless merge_request.can_be_merged_by?(merge_request.assignee)
-          %span.float-right.cannot-be-merged{ data: { toggle: 'tooltip', placement: 'left' }, title: 'Not allowed to merge' }
-            = icon('exclamation-triangle', 'aria-hidden': 'true')
-        %span.username
-          = merge_request.assignee.to_reference
-    - else
-      %span.assign-yourself.no-value
-        No assignee
-        - if can_edit_issuable
-          \-
-          %a.js-assign-yourself{ href: '#' }
-            assign yourself
-
-  .selectbox.hide-collapsed
-    = f.hidden_field 'assignee_id', value: merge_request.assignee_id, id: 'issue_assignee_id'
-    = dropdown_tag('Select assignee', options: { toggle_class: 'js-user-search js-author-search', title: 'Assign to', filter: true, dropdown_class: 'dropdown-menu-user dropdown-menu-selectable dropdown-menu-author', placeholder: 'Search users', data: { first_user: (current_user.username if current_user), current_user: true, project_id: @project&.id, author_id: merge_request.author_id, field_name: 'merge_request[assignee_id]', issue_update: issuable_json_path(merge_request), ability_name: 'merge_request', null_user: true } })

app/views/shared/issuable/form/_metadata.html.haml

@@ -8,11 +8,8 @@
 %hr
 .row
   %div{ class: (has_due_date ? "col-lg-6" : "col-12") }
-    .form-group.row.issue-assignee
-      - if issuable.is_a?(Issue)
-        = render "shared/issuable/form/metadata_issue_assignee", issuable: issuable, form: form, has_due_date: has_due_date
-      - else
-        = render "shared/issuable/form/metadata_merge_request_assignee", issuable: issuable, form: form, has_due_date: has_due_date
+    .form-group.row.merge-request-assignee
+      = render "shared/issuable/form/metadata_issuable_assignee", issuable: issuable, form: form, has_due_date: has_due_date
     .form-group.row.issue-milestone
       = form.label :milestone_id, "Milestone", class: "col-form-label #{has_due_date ? "col-md-2 col-lg-4" : "col-sm-2"}"
       .col-sm-10{ class: ("col-md-8" if has_due_date) }

app/views/shared/issuable/form/_metadata_issue_assignee.html.haml → app/views/shared/issuable/form/_metadata_issuable_assignee.html.haml

-= form.label :assignee_ids, "Assignee", class: "col-form-label #{"col-md-2 col-lg-4" if has_due_date}"
+= form.label :assignee_id, "Assignee", class: "col-form-label #{has_due_date ? "col-lg-4" : "col-sm-2"}"
 .col-sm-10{ class: ("col-md-8" if has_due_date) }
   .issuable-form-select-holder.selectbox
     - issuable.assignees.each do |assignee|
@@ -7,5 +7,5 @@
     - if issuable.assignees.length === 0
       = hidden_field_tag "#{issuable.to_ability_name}[assignee_ids][]", 0, id: nil, data: { meta: '' }
 
-    = dropdown_tag(users_dropdown_label(issuable.assignees), options: issue_assignees_dropdown_options)
-  = link_to 'Assign to me', '#', class: "assign-to-me-link #{'hide' if issuable.assignees.include?(current_user)}"
+    = dropdown_tag(users_dropdown_label(issuable.assignees), options: assignees_dropdown_options(issuable.to_ability_name))
+  = link_to 'Assign to me', '#', class: "assign-to-me-link qa-assign-to-me-link #{'hide' if issuable.assignees.include?(current_user)}"

db/fixtures/development/10_merge_requests.rb

@@ -21,7 +21,7 @@ Gitlab::Seeder.quiet do
         title: FFaker::Lorem.sentence(6),
         description: FFaker::Lorem.sentences(3).join(" "),
         milestone: project.milestones.sample,
-        assignee: project.team.users.sample,
+        assignees: [project.team.users.sample],
         label_ids: label_ids
       }
 

ee/app/helpers/ee/form_helper.rb

@@ -2,16 +2,12 @@
 
 module EE
   module FormHelper
-    def issue_assignees_dropdown_options
-      options = super
-
-      if current_board_parent.feature_available?(:multiple_issue_assignees)
-        options[:title] = 'Select assignee(s)'
-        options[:data][:'dropdown-header'] = 'Assignee(s)'
-        options[:data].delete(:'max-select')
-      end
+    def issue_supports_multiple_assignees?
+      current_board_parent.feature_available?(:multiple_issue_assignees)
+    end
 
-      options
+    def merge_request_supports_multiple_assignees?
+      @merge_request&.allows_multiple_assignees?
     end
   end
 end

ee/app/models/ee/merge_request.rb

@@ -54,6 +54,11 @@ module EE
       super
     end
 
+    def allows_multiple_assignees?
+      project.multiple_mr_assignees_enabled? &&
+        project.feature_available?(:multiple_merge_request_assignees)
+    end
+
     def supports_weight?
       false
     end

ee/app/models/license.rb

@@ -26,6 +26,7 @@ class License < ApplicationRecord
     merge_request_approvers
     multiple_ldap_servers
     multiple_issue_assignees
+    multiple_merge_request_assignees
     multiple_project_issue_boards
     push_rules
     protected_refs_for_users

ee/app/views/notify/add_merge_request_approver_email.html.haml

@@ -4,9 +4,13 @@
 %p.details
   != merge_path_description(@merge_request, '→')
 
-- if @merge_request.assignee_id.present?
+- if @merge_request.assignees.any?
   %p
-    Assignee: #{@merge_request.author_name} → #{@merge_request.assignee_name}
+    - label = assignees_label(@merge_request, include_value: false)
+    - author_name = sanitize_name(@merge_request.author_name)
+    - assignee_list = sanitize_name(@merge_request.assignee_list)
+
+    "#{label}: #{author_name} → #{assignee_list}"
 
 = render_if_exists 'notify/merge_request_approvers', presenter: @mr_presenter
 

ee/app/views/notify/add_merge_request_approver_email.text.erb

@@ -4,5 +4,5 @@
 
 <%= merge_path_description(@merge_request, 'to') %>
 Author:    <%= sanitize_name(@merge_request.author_name) %>
-Assignee:  <%= sanitize_name(@merge_request.assignee_name) %>
+<%= assignees_label(@merge_request) %>
 <%= render_if_exists 'notify/merge_request_approvers', presenter: @mr_presenter %>

ee/app/views/notify/approved_merge_request_email.html.haml

@@ -41,6 +41,19 @@
               padding-right: 10px !important;
           }
       }
+
+      ul.assignees-list {
+          list-style: none;
+          padding: 0px;
+          display: block;
+          margin-top: 0px;
+      }
+      ul.assignees-list li {
+          display: inline-block;
+          padding-right: 12px;
+          padding-top: 8px;
+      }
+
   %body{ style: "background-color:#fafafa;margin:0;padding:0;text-align:center;min-width:640px;width:100%;height:100%;font-family:'Helvetica Neue',Helvetica,Arial,sans-serif;" }
     %table#body{ border: "0", cellpadding: "0", cellspacing: "0", style: "background-color:#fafafa;margin:0;padding:0;text-align:center;min-width:640px;width:100%;" }
       %tbody
@@ -122,18 +135,17 @@
                                             %a.muted{ href: user_url(@merge_request.author), style: "color:#333333;text-decoration:none;" }
                                               = @merge_request.author.name
 
-                                - if @merge_request.assignee
+                                - if @merge_request.assignees.any?
                                   %tr
-                                    %td{ style: "font-family:'Helvetica Neue',Helvetica,Arial,sans-serif;font-size:15px;line-height:1.4;color:#8c8c8c;font-weight:300;padding:14px 0;margin:0;border-top:1px solid #ededed;" } Assignee
-                                    %td{ style: "font-family:'Helvetica Neue',Helvetica,Arial,sans-serif;font-size:15px;line-height:1.4;color:#8c8c8c;font-weight:300;padding:14px 0;margin:0;color:#333333;font-weight:400;width:75%;padding-left:5px;border-top:1px solid #ededed;" }
-                                      %table.img{ border: "0", cellpadding: "0", cellspacing: "0", style: "border-collapse:collapse;" }
-                                        %tbody
-                                          %tr
-                                            %td{ style: "font-family:'Helvetica Neue',Helvetica,Arial,sans-serif;font-size:15px;line-height:1.4;vertical-align:middle;padding-right:5px;" }
-                                              %img.avatar{ height: "24", src: avatar_icon_for_user(@merge_request.assignee, 24, only_path: false), style: "display:block;border-radius:12px;margin:-2px 0;", width: "24", alt: "Avatar" }/
-                                            %td{ style: "font-family:'Helvetica Neue',Helvetica,Arial,sans-serif;font-size:15px;line-height:1.4;vertical-align:middle;" }
-                                              %a.muted{ href: user_url(@merge_request.assignee), style: "color:#333333;text-decoration:none;" }
-                                                = @merge_request.assignee.name
+                                    %td{ style: "font-family:'Helvetica Neue',Helvetica,Arial,sans-serif;font-size:15px;line-height:1.4;color:#8c8c8c;font-weight:300;padding:14px 0;margin:0;border-top:1px solid #ededed;" }
+                                      = assignees_label(@merge_request, include_value: false)
+                                    %td{ style: "font-family: 'Helvetica Neue',Helvetica,Arial,sans-serif; margin: 0; padding: 14px 0 0px 5px; font-size: 15px; line-height: 1.4; color: #333333; font-weight: 400; width: 75%; border-top-style: solid; border-top-color: #ededed; border-top-width: 1px; -webkit-text-size-adjust: 100%; -ms-text-size-adjust: 100%; mso-table-lspace: 0pt; mso-table-rspace: 0pt;" }
+                                      %ul.assignees-list{ style: "font-family: 'Helvetica Neue',Helvetica,Arial,sans-serif; font-size: 15px; line-height: 1.4; padding-right: 5px; -webkit-text-size-adjust: 100%; -ms-text-size-adjust: 100%; mso-table-lspace: 0pt; mso-table-rspace: 0pt;" }
+                                        - @merge_request.assignees.each do |assignee|
+                                          %li
+                                            %img.avatar{ alt: "Avatar", height: "24", src: avatar_icon_for_user(assignee, 24, only_path: false), style: "border-radius: 12px; max-width: 100%; height: auto; -ms-interpolation-mode: bicubic; margin: -2px 0;", width: "24" }/
+                                            %a.muted{ href: user_url(assignee), style: "color: #333333; text-decoration: none; -webkit-text-size-adjust: 100%; -ms-text-size-adjust: 100%; vertical-align: top;" }
+                                              = assignee.name
 
         -# EE-specific start
         = render 'layouts/mailer/additional_text'

ee/app/views/notify/approved_merge_request_email.text.haml

@@ -5,4 +5,4 @@ Merge Request url: #{project_merge_request_url(@merge_request.target_project, @m
 = merge_path_description(@merge_request, 'to')
 
 Author: #{sanitize_name(@merge_request.author_name)}
-Assignee: #{sanitize_name(@merge_request.assignee_name)}
+= assignees_label(@merge_request)

ee/app/views/notify/unapproved_merge_request_email.html.haml

@@ -41,6 +41,19 @@
               padding-right: 10px !important;
           }
       }
+
+      ul.assignees-list {
+          list-style: none;
+          padding: 0px;
+          display: block;
+          margin-top: 0px;
+      }
+      ul.assignees-list li {
+          display: inline-block;
+          padding-right: 12px;
+          padding-top: 8px;
+      }
+
   %body{ style: "background-color:#fafafa;margin:0;padding:0;text-align:center;min-width:640px;width:100%;height:100%;font-family:'Helvetica Neue',Helvetica,Arial,sans-serif;" }
     %table#body{ border: "0", cellpadding: "0", cellspacing: "0", style: "background-color:#fafafa;margin:0;padding:0;text-align:center;min-width:640px;width:100%;" }
       %tbody
@@ -121,18 +134,17 @@
                                           %td{ style: "font-family:'Helvetica Neue',Helvetica,Arial,sans-serif;font-size:15px;line-height:1.4;vertical-align:middle;" }
                                             %a.muted{ href: user_url(@merge_request.author), style: "color:#333333;text-decoration:none;" }
                                               = @merge_request.author.name
-                                - if @merge_request.assignee
+                                - if @merge_request.assignees.any?
                                   %tr
-                                    %td{ style: "font-family:'Helvetica Neue',Helvetica,Arial,sans-serif;font-size:15px;line-height:1.4;color:#8c8c8c;font-weight:300;padding:14px 0;margin:0;border-top:1px solid #ededed;" } Assignee
-                                    %td{ style: "font-family:'Helvetica Neue',Helvetica,Arial,sans-serif;font-size:15px;line-height:1.4;color:#8c8c8c;font-weight:300;padding:14px 0;margin:0;color:#333333;font-weight:400;width:75%;padding-left:5px;border-top:1px solid #ededed;" }
-                                      %table.img{ border: "0", cellpadding: "0", cellspacing: "0", style: "border-collapse:collapse;" }
-                                        %tbody
-                                          %tr
-                                            %td{ style: "font-family:'Helvetica Neue',Helvetica,Arial,sans-serif;font-size:15px;line-height:1.4;vertical-align:middle;padding-right:5px;" }
-                                              %img.avatar{ height: "24", src: avatar_icon_for_user(@merge_request.assignee, 24), style: "display:block;border-radius:12px;margin:-2px 0;", width: "24", alt: "Avatar" }/
-                                            %td{ style: "font-family:'Helvetica Neue',Helvetica,Arial,sans-serif;font-size:15px;line-height:1.4;vertical-align:middle;" }
-                                              %a.muted{ href: user_url(@merge_request.assignee), style: "color:#333333;text-decoration:none;" }
-                                                = @merge_request.assignee.name
+                                    %td{ style: "font-family:'Helvetica Neue',Helvetica,Arial,sans-serif;font-size:15px;line-height:1.4;color:#8c8c8c;font-weight:300;padding:14px 0;margin:0;border-top:1px solid #ededed;" }
+                                      = assignees_label(@merge_request, include_value: false)
+                                    %td{ style: "font-family: 'Helvetica Neue',Helvetica,Arial,sans-serif; margin: 0; padding: 14px 0 0px 5px; font-size: 15px; line-height: 1.4; color: #333333; font-weight: 400; width: 75%; border-top-style: solid; border-top-color: #ededed; border-top-width: 1px; -webkit-text-size-adjust: 100%; -ms-text-size-adjust: 100%; mso-table-lspace: 0pt; mso-table-rspace: 0pt;" }
+                                      %ul.assignees-list{ style: "font-family: 'Helvetica Neue',Helvetica,Arial,sans-serif; font-size: 15px; line-height: 1.4; padding-right: 5px; -webkit-text-size-adjust: 100%; -ms-text-size-adjust: 100%; mso-table-lspace: 0pt; mso-table-rspace: 0pt;" }
+                                        - @merge_request.assignees.each do |assignee|
+                                          %li
+                                            %img.avatar{ alt: "Avatar", height: "24", src: avatar_icon_for_user(assignee, 24, only_path: false), style: "border-radius: 12px; max-width: 100%; height: auto; -ms-interpolation-mode: bicubic; margin: -2px 0;", width: "24" }/
+                                            %a.muted{ href: user_url(assignee), style: "color: #333333; text-decoration: none; -webkit-text-size-adjust: 100%; -ms-text-size-adjust: 100%; vertical-align: top;" }
+                                              = assignee.name
 
         -# EE-specific start
         = render 'layouts/mailer/additional_text'

ee/app/views/notify/unapproved_merge_request_email.text.haml

@@ -5,4 +5,4 @@ Merge Request url: #{project_merge_request_url(@merge_request.target_project, @m
 = merge_path_description(@merge_request, 'to')
 
 Author: #{sanitize_name(@merge_request.author_name)}
-Assignee: #{sanitize_name(@merge_request.assignee_name)}
+= assignees_label(@merge_request)

ee/changelogs/unreleased/osw-multi-assignees-merge-requests-ee.yml

+---
+title: Support multiple assignees for merge requests
+merge_request: 10161
+author:
+type: added

ee/lib/api/github/entities.rb

@@ -135,7 +135,9 @@ module API
 
       class PullRequest < Grape::Entity
         expose :title
-        expose :assignee, using: User
+        expose :assignee, using: User do |merge_request|
+          merge_request.assignee
+        end
         expose :author, as: :user, using: User
         expose :created_at
         expose :description, as: :body

ee/spec/controllers/projects/merge_requests/drafts_controller_spec.rb

@@ -17,7 +17,7 @@ describe Projects::MergeRequests::DraftsController do
 
   before do
     sign_in(user)
-    stub_licensed_features(batch_comments: true)
+    stub_licensed_features(batch_comments: true, multiple_merge_request_assignees: true)
     stub_commonmark_sourcepos_disabled
   end
 
@@ -237,15 +237,17 @@ describe Projects::MergeRequests::DraftsController do
     end
 
     it 'publishes a draft note with quick actions and applies them' do
-      create(:draft_note, merge_request: merge_request, author: user, note: "/assign #{user.to_reference}")
+      project.add_developer(user2)
+      create(:draft_note, merge_request: merge_request, author: user,
+                          note: "/assign #{user.to_reference} #{user2.to_reference}")
 
-      expect(merge_request.assignee_id).to be_nil
+      expect(merge_request.assignees).to be_empty
 
       expect { post :publish, params: params }.to change { Note.count }.by(1)
         .and change { DraftNote.count }.by(-1)
 
       expect(response).to have_gitlab_http_status(200)
-      expect(merge_request.reload.assignee_id).to eq(user.id)
+      expect(merge_request.reload.assignee_ids).to match_array([user.id, user2.id])
       expect(Note.last.system?).to be true
     end
 

ee/spec/features/issues/form_spec.rb

@@ -35,8 +35,8 @@ describe 'New/edit issue', :js do
         # the original method, resulting in infinite recurison when called.
         # This is likely a bug with helper modules included into dynamically generated view classes.
         # To work around this, we have to hold on to and call to the original implementation manually.
-        original_issue_dropdown_options = EE::FormHelper.instance_method(:issue_assignees_dropdown_options)
-        allow_any_instance_of(EE::FormHelper).to receive(:issue_assignees_dropdown_options).and_wrap_original do |original, *args|
+        original_issue_dropdown_options = FormHelper.instance_method(:assignees_dropdown_options)
+        allow_any_instance_of(FormHelper).to receive(:assignees_dropdown_options).and_wrap_original do |original, *args|
           options = original_issue_dropdown_options.bind(original.receiver).call(*args)
           options[:data][:per_page] = 2
 

ee/spec/features/merge_request/user_creates_multiple_assignees_mr_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe 'Merge request > User creates MR with multiple assignees' do
+  include_context 'merge request create context'
+
+  before do
+    stub_licensed_features(multiple_merge_request_assignees: true)
+  end
+
+  it_behaves_like 'multiple assignees merge request', 'creates', 'Submit merge request'
+end

ee/spec/features/merge_request/user_edits_multiple_assignees_mr_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe 'Merge request > User edits MR with multiple assignees' do
+  include_context 'merge request edit context'
+
+  before do
+    stub_licensed_features(multiple_merge_request_assignees: true)
+  end
+
+  it_behaves_like 'multiple assignees merge request', 'updates', 'Save changes'
+end

ee/spec/mailers/notify_spec.rb

@@ -12,12 +12,13 @@ describe Notify do
   set(:user) { create(:user) }
   set(:current_user) { create(:user, email: "current@email.com") }
   set(:assignee) { create(:user, email: 'assignee@example.com', name: 'John Doe') }
+  set(:assignee2) { create(:user, email: 'assignee2@example.com', name: 'Jane Doe') }
 
   set(:merge_request) do
     create(:merge_request, source_project: project,
                            target_project: project,
                            author: current_user,
-                           assignee: assignee,
+                           assignees: [assignee, assignee2],
                            description: 'Awesome description')
   end
 
@@ -85,9 +86,7 @@ describe Notify do
         end
 
         subject do
-          described_class.new_merge_request_email(
-            merge_request.assignee_id, merge_request.id
-          )
+          described_class.new_merge_request_email(assignee.id, merge_request.id)
         end
 
         it "contains the approvers list" do
@@ -100,7 +99,7 @@ describe Notify do
         subject { described_class.approved_merge_request_email(recipient.id, merge_request.id, last_approver.id) }
 
         before do
-          merge_request.approvals.create(user: merge_request.assignee)
+          merge_request.approvals.create(user: assignee)
           merge_request.approvals.create(user: last_approver)
         end
 
@@ -130,13 +129,20 @@ describe Notify do
         end
 
         it 'contains the names of all of the approvers' do
-          is_expected.to have_body_text /#{merge_request.assignee.name}/
-          is_expected.to have_body_text /#{last_approver.name}/
+          merge_request.approvals.each do |approval|
+            is_expected.to have_body_text /#{approval.user.name}/
+          end
+        end
+
+        it 'contains the names of all assignees' do
+          merge_request.assignees.each do |assignee|
+            is_expected.to have_body_text /#{assignee.name}/
+          end
         end
 
         context 'when merge request has no assignee' do
           before do
-            merge_request.update(assignee: nil)
+            merge_request.update(assignees: [])
           end
 
           it 'does not show the assignee' do
@@ -150,7 +156,7 @@ describe Notify do
         subject { described_class.unapproved_merge_request_email(recipient.id, merge_request.id, last_unapprover.id) }
 
         before do
-          merge_request.approvals.create(user: merge_request.assignee)
+          merge_request.approvals.create(user: assignee)
         end
 
         it_behaves_like 'a multiple recipients email'
@@ -179,7 +185,15 @@ describe Notify do
         end
 
         it 'contains the names of all of the approvers' do
-          is_expected.to have_body_text /#{merge_request.assignee.name}/
+          merge_request.approvals.each do |approval|
+            is_expected.to have_body_text /#{approval.user.name}/
+          end
+        end
+
+        it 'contains the names of all assignees' do
+          merge_request.assignees.each do |assignee|
+            is_expected.to have_body_text /#{assignee.name}/
+          end
         end
       end
     end
@@ -190,7 +204,7 @@ describe Notify do
         subject { described_class.unapproved_merge_request_email(recipient.id, merge_request_without_assignee.id, last_unapprover.id) }
 
         before do
-          merge_request_without_assignee.approvals.create(user: merge_request_without_assignee.assignee)
+          merge_request_without_assignee.approvals.create(user: merge_request_without_assignee.assignees.first)
         end
 
         it 'contains the new status' do

ee/spec/models/merge_request_spec.rb

@@ -24,6 +24,33 @@ describe MergeRequest do
     let(:set_mentionable_text) { ->(txt) { subject.description = txt } }
   end
 
+  describe '#allows_multiple_assignees?' do
+    it 'does not allow multiple assignees without license' do
+      stub_licensed_features(multiple_merge_request_assignees: false)
+
+      merge_request = build_stubbed(:merge_request)
+
+      expect(merge_request.allows_multiple_assignees?).to be(false)
+    end
+
+    it 'allows multiple assignees when licensed' do
+      stub_licensed_features(multiple_merge_request_assignees: true)
+
+      merge_request = build(:merge_request)
+
+      expect(merge_request.allows_multiple_assignees?).to be(true)
+    end
+
+    it 'does not allows multiple assignees when licensed and feature flag is disabled' do
+      stub_licensed_features(multiple_merge_request_assignees: true)
+      stub_feature_flags(multiple_merge_request_assignees: false)
+
+      merge_request = build(:merge_request)
+
+      expect(merge_request.allows_multiple_assignees?).to be(false)
+    end
+  end
+
   describe 'approval_rules' do
     context 'when project contains approval_rules' do
       let!(:project_rule1) {  project.approval_rules.create(name: 'p1') }

ee/spec/requests/api/merge_request_approvals_spec.rb

@@ -3,9 +3,10 @@ require 'spec_helper'
 describe API::MergeRequestApprovals do
   set(:user)          { create(:user) }
   set(:user2)         { create(:user) }
+  set(:user3)         { create(:user) }
   set(:admin)         { create(:user, :admin) }
   set(:project)       { create(:project, :public, :repository, creator: user, namespace: user.namespace, only_allow_merge_if_pipeline_succeeds: false) }
-  set(:merge_request) { create(:merge_request, :simple, author: user, assignee: user, source_project: project, target_project: project, title: "Test", created_at: Time.now) }
+  set(:merge_request) { create(:merge_request, :simple, author: user, assignees: [user, user3], source_project: project, target_project: project, title: "Test", created_at: Time.now) }
 
   before do
     project.update_attribute(:approvals_before_merge, 2)
@@ -394,7 +395,7 @@ describe "API::MergeRequestApprovals with approval_rule enabled" do
   set(:user2)         { create(:user) }
   set(:admin)         { create(:user, :admin) }
   set(:project)       { create(:project, :public, :repository, creator: user, namespace: user.namespace, only_allow_merge_if_pipeline_succeeds: false) }
-  set(:merge_request) { create(:merge_request, :simple, author: user, assignee: user, source_project: project, target_project: project, title: "Test", created_at: Time.now) }
+  set(:merge_request) { create(:merge_request, :simple, author: user, assignees: [user], source_project: project, target_project: project, title: "Test", created_at: Time.now) }
 
   set(:approver) { create :user }
   set(:group) { create :group }

ee/spec/requests/api/merge_requests_spec.rb

@@ -5,10 +5,11 @@ describe API::MergeRequests do
 
   let(:base_time)   { Time.now }
   let(:user)        { create(:user) }
+  let(:user2)       { create(:user) }
   let!(:project)    { create(:project, :public, :repository, creator: user, namespace: user.namespace, only_allow_merge_if_pipeline_succeeds: false) }
   let(:milestone)   { create(:milestone, title: '1.0.0', project: project) }
   let(:milestone1) { create(:milestone, title: '0.9', project: project) }
-  let!(:merge_request) { create(:merge_request, :simple, milestone: milestone1, author: user, assignee: user, source_project: project, target_project: project, title: "Test", created_at: base_time) }
+  let!(:merge_request) { create(:merge_request, :simple, milestone: milestone1, author: user, assignees: [user, user2], source_project: project, target_project: project, title: "Test", created_at: base_time) }
   let!(:label) do
     create(:label, title: 'label', color: '#FFAABB', project: project)
   end

ee/spec/requests/api/v3/github_spec.rb

@@ -215,11 +215,12 @@ describe API::V3::Github do
 
   describe 'repo pulls' do
     let(:assignee) { create(:user) }
+    let(:assignee2) { create(:user) }
     let!(:merge_request) do
-      create(:merge_request, source_project: project, target_project: project, author: user, assignee: assignee)
+      create(:merge_request, source_project: project, target_project: project, author: user, assignees: [assignee])
     end
     let!(:merge_request_2) do
-      create(:merge_request, source_project: project2, target_project: project2, author: user, assignee: assignee)
+      create(:merge_request, source_project: project2, target_project: project2, author: user, assignees: [assignee, assignee2])
     end
 
     describe 'GET /-/jira/pulls' do

ee/spec/services/draft_notes/publish_service_spec.rb

@@ -168,10 +168,15 @@ describe DraftNotes::PublishService do
 
   context 'with quick actions' do
     it 'performs quick actions' do
-      create(:draft_note, merge_request: merge_request, author: user, note: "thanks\n/assign #{user.to_reference}")
+      other_user = create(:user)
+      project.add_developer(other_user)
+
+      create(:draft_note, merge_request: merge_request,
+                          author: user,
+                          note: "thanks\n/assign #{user.to_reference} #{other_user.to_reference}")
 
       expect { publish }.to change { DraftNote.count }.by(-1).and change { Note.count }.by(2)
-      expect(merge_request.reload.assignee).to eq(user)
+      expect(merge_request.reload.assignees).to match_array([user, other_user])
       expect(merge_request.notes.last).to be_system
     end
 
@@ -179,7 +184,7 @@ describe DraftNotes::PublishService do
       create(:draft_note, merge_request: merge_request, author: user, note: "/assign #{user.to_reference}")
 
       expect { publish }.to change { DraftNote.count }.by(-1).and change { Note.count }.by(1)
-      expect(merge_request.reload.assignee).to eq(user)
+      expect(merge_request.reload.assignees).to eq([user])
       expect(merge_request.notes.last).to be_system
     end
   end

ee/spec/services/ee/notification_service_spec.rb

@@ -124,8 +124,9 @@ describe EE::NotificationService, :mailer do
   context 'new review' do
     let(:project) { create(:project, :repository) }
     let(:user) { create(:user) }
+    let(:user2) { create(:user) }
     let(:reviewer) { create(:user) }
-    let(:merge_request) { create(:merge_request, source_project: project, assignee: user, author: create(:user)) }
+    let(:merge_request) { create(:merge_request, source_project: project, assignees: [user, user2], author: create(:user)) }
     let(:review) { create(:review, merge_request: merge_request, project: project, author: reviewer) }
     let(:note) { create(:diff_note_on_merge_request, project: project, noteable: merge_request, author: reviewer, review: review) }
 
@@ -133,7 +134,7 @@ describe EE::NotificationService, :mailer do
       build_team(review.project, merge_request)
       project.add_maintainer(merge_request.author)
       project.add_maintainer(reviewer)
-      project.add_maintainer(merge_request.assignee)
+      merge_request.assignees.each { |assignee| project.add_maintainer(assignee) }
 
       create(:diff_note_on_merge_request,
              project: project,
@@ -146,7 +147,9 @@ describe EE::NotificationService, :mailer do
     it 'sends emails' do
       expect(Notify).not_to receive(:new_review_email).with(review.author.id, review.id)
       expect(Notify).not_to receive(:new_review_email).with(@unsubscriber.id, review.id)
-      expect(Notify).to receive(:new_review_email).with(merge_request.assignee.id, review.id).and_call_original
+      merge_request.assignee_ids.each do |assignee_id|
+        expect(Notify).to receive(:new_review_email).with(assignee_id, review.id).and_call_original
+      end
       expect(Notify).to receive(:new_review_email).with(merge_request.author.id, review.id).and_call_original
       expect(Notify).to receive(:new_review_email).with(@u_watcher.id, review.id).and_call_original
       expect(Notify).to receive(:new_review_email).with(@u_mentioned.id, review.id).and_call_original
@@ -513,10 +516,11 @@ describe EE::NotificationService, :mailer do
   context 'Merge Requests' do
     let(:notification) { NotificationService.new }
     let(:assignee) { create(:user) }
+    let(:assignee2) { create(:user) }
     let(:group) { create(:group) }
     let(:project) { create(:project, :public, :repository, namespace: group) }
     let(:another_project) { create(:project, :public, namespace: group) }
-    let(:merge_request) { create :merge_request, source_project: project, assignee: create(:user), description: 'cc @participant' }
+    let(:merge_request) { create :merge_request, source_project: project, assignees: [assignee, assignee2], description: 'cc @participant' }
 
     around do |example|
       perform_enqueued_jobs do
@@ -528,7 +532,7 @@ describe EE::NotificationService, :mailer do
       stub_feature_flags(approval_rules: false)
 
       project.add_maintainer(merge_request.author)
-      project.add_maintainer(merge_request.assignee)
+      merge_request.assignees.each { |assignee| project.add_maintainer(assignee) }
       build_team(merge_request.target_project)
       add_users_with_subscription(merge_request.target_project, merge_request)
       update_custom_notification(:new_merge_request, @u_guest_custom, resource: project)
@@ -537,6 +541,12 @@ describe EE::NotificationService, :mailer do
     end
 
     describe '#new_merge_request' do
+      it 'emails all assignees' do
+        notification.new_merge_request(merge_request, assignee)
+
+        merge_request.assignees.each { |assignee| should_email(assignee) }
+      end
+
       context 'when the target project has approvers set' do
         let(:project_approvers) { create_list(:user, 3) }
 

ee/spec/services/quick_actions/interpret_service_spec.rb

@@ -11,7 +11,8 @@ describe QuickActions::InterpretService do
   let(:service) { described_class.new(project, current_user) }
 
   before do
-    stub_licensed_features(multiple_issue_assignees: true)
+    stub_licensed_features(multiple_issue_assignees: true,
+                           multiple_merge_request_assignees: true)
 
     project.add_developer(current_user)
   end
@@ -39,6 +40,42 @@ describe QuickActions::InterpretService do
           end
         end
       end
+
+      context 'Merge Request' do
+        let(:merge_request) { create(:merge_request, source_project: project) }
+
+        it 'fetches assignees and populates them if content contains /assign' do
+          merge_request.update(assignee_ids: [user.id])
+
+          _, updates = service.execute("/assign @#{user2.username}", merge_request)
+
+          expect(updates[:assignee_ids]).to match_array([user.id, user2.id])
+        end
+
+        context 'assign command with multiple assignees' do
+          it 'fetches assignee and populates assignee_ids if content contains /assign' do
+            merge_request.update(assignee_ids: [user.id])
+
+            _, updates = service.execute("/assign @#{user.username}\n/assign @#{user2.username} @#{user3.username}", issue)
+
+            expect(updates[:assignee_ids]).to match_array([user.id, user2.id, user3.id])
+          end
+
+          context 'unlicensed' do
+            before do
+              stub_licensed_features(multiple_merge_request_assignees: false)
+            end
+
+            it 'does not recognize /assign with multiple user references' do
+              merge_request.update(assignee_ids: [user.id])
+
+              _, updates = service.execute("/assign @#{user2.username} @#{user3.username}", merge_request)
+
+              expect(updates[:assignee_ids]).to match_array([user2.id])
+            end
+          end
+        end
+      end
     end
 
     context 'unassign command' do
@@ -69,6 +106,42 @@ describe QuickActions::InterpretService do
           expect(updates[:assignee_ids]).to be_empty
         end
       end
+
+      context 'Merge Request' do
+        let(:merge_request) { create(:merge_request, source_project: project) }
+
+        it 'unassigns user if content contains /unassign @user' do
+          merge_request.update(assignee_ids: [user.id, user2.id])
+
+          _, updates = service.execute("/unassign @#{user2.username}", merge_request)
+
+          expect(updates[:assignee_ids]).to match_array([user.id])
+        end
+
+        context 'unassign command with multiple assignees' do
+          it 'unassigns both users if content contains /unassign @user @user1' do
+            merge_request.update(assignee_ids: [user.id, user2.id, user3.id])
+
+            _, updates = service.execute("/unassign @#{user.username} @#{user2.username}", merge_request)
+
+            expect(updates[:assignee_ids]).to match_array([user3.id])
+          end
+
+          context 'unlicensed' do
+            before do
+              stub_licensed_features(multiple_merge_request_assignees: false)
+            end
+
+            it 'does not recognize /unassign @user' do
+              merge_request.update(assignee_ids: [user.id, user2.id, user3.id])
+
+              _, updates = service.execute("/unassign @#{user.username}", merge_request)
+
+              expect(updates[:assignee_ids]).to be_empty
+            end
+          end
+        end
+      end
     end
 
     context 'reassign command' do
@@ -77,10 +150,22 @@ describe QuickActions::InterpretService do
       context 'Merge Request' do
         let(:merge_request) { create(:merge_request, source_project: project) }
 
-        it 'does not recognize /reassign @user' do
-          _, updates = service.execute(content, merge_request)
+        context 'unlicensed' do
+          before do
+            stub_licensed_features(multiple_merge_request_assignees: false)
+          end
+
+          it 'does not recognize /reassign @user' do
+            _, updates = service.execute(content, merge_request)
 
-          expect(updates).to be_empty
+            expect(updates).to be_empty
+          end
+        end
+
+        it 'reassigns user if content contains /reassign @user' do
+          _, updates = service.execute("/reassign @#{current_user.username}", merge_request)
+
+          expect(updates[:assignee_ids]).to match_array([current_user.id])
         end
       end
 

lib/api/entities.rb

@@ -663,7 +663,11 @@ module API
       expose(:user_notes_count) { |merge_request, options| issuable_metadata(merge_request, options, :user_notes_count) }
       expose(:upvotes)          { |merge_request, options| issuable_metadata(merge_request, options, :upvotes) }
       expose(:downvotes)        { |merge_request, options| issuable_metadata(merge_request, options, :downvotes) }
-      expose :author, :assignee, using: Entities::UserBasic
+      expose :assignee, using: ::API::Entities::UserBasic do |merge_request|
+        merge_request.assignee
+      end
+      expose :author, :assignees, using: Entities::UserBasic
+
       expose :source_project_id, :target_project_id
       expose :labels do |merge_request|
         # Avoids an N+1 query since labels are preloaded

lib/banzai/reference_parser/merge_request_parser.rb

@@ -10,7 +10,7 @@ module Banzai
           nodes,
           MergeRequest.includes(
             :author,
-            :assignee,
+            :assignees,
             {
               # These associations are primarily used for checking permissions.
               # Eager loading these ensures we don't end up running dozens of

lib/gitlab/hook_data/issuable_builder.rb

@@ -20,11 +20,7 @@ module Gitlab
           repository: issuable.project.hook_attrs.slice(:name, :url, :description, :homepage)
         }
 
-        if issuable.is_a?(Issue)
-          hook_data[:assignees] = issuable.assignees.map(&:hook_attrs) if issuable.assignees.any?
-        else
-          hook_data[:assignee] = issuable.assignee.hook_attrs if issuable.assignee
-        end
+        hook_data[:assignees] = issuable.assignees.map(&:hook_attrs) if issuable.assignees.any?
 
         hook_data
       end

lib/gitlab/hook_data/merge_request_builder.rb

@@ -34,7 +34,6 @@ module Gitlab
       end
 
       SAFE_HOOK_RELATIONS = %i[
-        assignee
         labels
         total_time_spent
       ].freeze
@@ -51,7 +50,9 @@ module Gitlab
           work_in_progress: merge_request.work_in_progress?,
           total_time_spent: merge_request.total_time_spent,
           human_total_time_spent: merge_request.human_total_time_spent,
-          human_time_estimate: merge_request.human_time_estimate
+          human_time_estimate: merge_request.human_time_estimate,
+          assignee_ids: merge_request.assignee_ids,
+          assignee_id: merge_request.assignee_ids.first # This key is deprecated
         }
 
         merge_request.attributes.with_indifferent_access.slice(*self.class.safe_hook_attributes)

lib/gitlab/import_export/import_export.yml

@@ -47,6 +47,7 @@ project_tree:
     - label_links:
       - label:
           :priorities
+    - :merge_request_assignees
     - milestone:
       - events:
         - :push_event_payload

locale/gitlab.pot

@@ -1338,9 +1338,6 @@ msgstr ""
 msgid "Assigned Merge Requests"
 msgstr ""
 
-msgid "Assigned to :name"
-msgstr ""
-
 msgid "Assigned to me"
 msgstr ""
 
@@ -7354,9 +7351,6 @@ msgstr ""
 msgid "No activities found"
 msgstr ""
 
-msgid "No assignee"
-msgstr ""
-
 msgid "No branches found"
 msgstr ""
 
@@ -7468,9 +7462,6 @@ msgstr ""
 msgid "None"
 msgstr ""
 
-msgid "Not allowed to merge"
-msgstr ""
-
 msgid "Not available"
 msgstr ""
 
@@ -9692,9 +9683,6 @@ msgstr ""
 msgid "Select an existing Kubernetes cluster or create a new one"
 msgstr ""
 
-msgid "Select assignee"
-msgstr ""
-
 msgid "Select branch/tag"
 msgstr ""
 
@@ -12846,9 +12834,6 @@ msgstr ""
 msgid "among other things"
 msgstr ""
 
-msgid "assign yourself"
-msgstr ""
-
 msgid "at"
 msgstr ""
 

qa/qa/page/merge_request/new.rb

@@ -26,7 +26,7 @@ module QA
           element :issuable_label
         end
 
-        view 'app/views/shared/issuable/form/_metadata_merge_request_assignee.html.haml' do
+        view 'app/views/shared/issuable/form/_metadata_issuable_assignee.html.haml' do
           element :assign_to_me_link
         end
 

spec/controllers/projects/merge_requests_controller_spec.rb

@@ -238,11 +238,11 @@ describe Projects::MergeRequestsController do
         assignee = create(:user)
         project.add_developer(assignee)
 
-        update_merge_request({ assignee_id: assignee.id }, format: :json)
+        update_merge_request({ assignee_ids: [assignee.id] }, format: :json)
+
         body = JSON.parse(response.body)
 
-        expect(body['assignee'].keys)
-          .to match_array(%w(name username avatar_url id state web_url))
+        expect(body['assignees']).to all(include(*%w(name username avatar_url id state web_url)))
       end
     end
 

spec/features/dashboard/issuables_counter_spec.rb

@@ -8,7 +8,7 @@ describe 'Navigation bar counter', :use_clean_rails_memory_store_caching do
 
   before do
     issue.assignees = [user]
-    merge_request.update(assignee: user)
+    merge_request.update(assignees: [user])
     sign_in(user)
   end
 
@@ -33,7 +33,7 @@ describe 'Navigation bar counter', :use_clean_rails_memory_store_caching do
 
     expect_counters('merge_requests', '1')
 
-    merge_request.update(assignee: nil)
+    merge_request.update(assignees: [])
 
     user.invalidate_cache_counts
 

spec/features/dashboard/merge_requests_spec.rb

@@ -50,14 +50,14 @@ describe 'Dashboard Merge Requests' do
 
     let!(:assigned_merge_request) do
       create(:merge_request,
-        assignee: current_user,
+        assignees: [current_user],
         source_project: project,
         author: create(:user))
     end
 
     let!(:assigned_merge_request_from_fork) do
       create(:merge_request,
-              source_branch: 'markdown', assignee: current_user,
+              source_branch: 'markdown', assignees: [current_user],
               target_project: public_project, source_project: forked_project,
               author: create(:user))
     end

spec/features/groups/merge_requests_spec.rb

@@ -38,7 +38,7 @@ describe 'Group merge requests page' do
 
   context 'when merge request assignee to user' do
     before do
-      issuable.update!(assignee: user)
+      issuable.update!(assignees: [user])
 
       visit path
     end

spec/features/issues/form_spec.rb

@@ -32,8 +32,8 @@ describe 'New/edit issue', :js do
         # the original method, resulting in infinite recursion when called.
         # This is likely a bug with helper modules included into dynamically generated view classes.
         # To work around this, we have to hold on to and call to the original implementation manually.
-        original_issue_dropdown_options = EE::FormHelper.instance_method(:issue_assignees_dropdown_options)
-        allow_any_instance_of(EE::FormHelper).to receive(:issue_assignees_dropdown_options).and_wrap_original do |original, *args|
+        original_issue_dropdown_options = FormHelper.instance_method(:assignees_dropdown_options)
+        allow_any_instance_of(FormHelper).to receive(:assignees_dropdown_options).and_wrap_original do |original, *args|
           options = original_issue_dropdown_options.bind(original.receiver).call(*args)
           options[:data][:per_page] = 2
 

spec/features/merge_request/user_creates_merge_request_spec.rb

@@ -108,15 +108,15 @@ describe "User creates a merge request", :js do
         fill_in("Title", with: title)
       end
 
-      click_button("Assignee")
-
       expect(find(".js-assignee-search")["data-project-id"]).to eq(project.id.to_s)
+      find('.js-assignee-search').click
 
       page.within(".dropdown-menu-user") do
         expect(page).to have_content("Unassigned")
                    .and have_content(user.name)
                    .and have_content(project.users.first.name)
       end
+      find('.js-assignee-search').click
 
       click_button("Submit merge request")
 

spec/features/merge_request/user_creates_mr_spec.rb

 require 'rails_helper'
 
 describe 'Merge request > User creates MR' do
-  it_behaves_like 'a creatable merge request'
+  include ProjectForksHelper
 
-  context 'from a forked project' do
-    include ProjectForksHelper
+  before do
+    stub_licensed_features(multiple_merge_request_assignees: false)
+  end
 
+  context 'non-fork merge request' do
+    include_context 'merge request create context'
+    it_behaves_like 'a creatable merge request'
+  end
+
+  context 'from a forked project' do
     let(:canonical_project) { create(:project, :public, :repository) }
 
     let(:source_project) do
@@ -15,6 +22,7 @@ describe 'Merge request > User creates MR' do
     end
 
     context 'to canonical project' do
+      include_context 'merge request create context'
       it_behaves_like 'a creatable merge request'
     end
 
@@ -25,6 +33,7 @@ describe 'Merge request > User creates MR' do
           namespace: user.namespace)
       end
 
+      include_context 'merge request create context'
       it_behaves_like 'a creatable merge request'
     end
   end

spec/features/merge_request/user_edits_mr_spec.rb

-require 'rails_helper'
+require 'spec_helper'
 
 describe 'Merge request > User edits MR' do
   include ProjectForksHelper
 
-  it_behaves_like 'an editable merge request'
+  before do
+    stub_licensed_features(multiple_merge_request_assignees: false)
+  end
+
+  context 'non-fork merge request' do
+    include_context 'merge request edit context'
+    it_behaves_like 'an editable merge request'
+  end
 
   context 'for a forked project' do
-    it_behaves_like 'an editable merge request' do
-      let(:source_project) { fork_project(target_project, nil, repository: true) }
-    end
+    let(:source_project) { fork_project(target_project, nil, repository: true) }
+
+    include_context 'merge request edit context'
+    it_behaves_like 'an editable merge request'
   end
 end

spec/features/merge_requests/user_filters_by_assignees_spec.rb

@@ -7,7 +7,7 @@ describe 'Merge Requests > User filters by assignees', :js do
   let(:user)    { project.creator }
 
   before do
-    create(:merge_request, assignee: user, title: 'Bugfix1', source_project: project, target_project: project, source_branch: 'bugfix1')
+    create(:merge_request, assignees: [user], title: 'Bugfix1', source_project: project, target_project: project, source_branch: 'bugfix1')
     create(:merge_request, title: 'Bugfix2', source_project: project, target_project: project, source_branch: 'bugfix2')
 
     sign_in(user)

spec/features/merge_requests/user_filters_by_multiple_criteria_spec.rb

@@ -10,7 +10,7 @@ describe 'Merge requests > User filters by multiple criteria', :js do
 
   before do
     sign_in(user)
-    mr = create(:merge_request, title: 'Bugfix2', author: user, assignee: user, source_project: project, target_project: project, milestone: milestone)
+    mr = create(:merge_request, title: 'Bugfix2', author: user, assignees: [user], source_project: project, target_project: project, milestone: milestone)
     mr.labels << wontfix
 
     visit project_merge_requests_path(project)