Add mutually exclusive labels

If a label title contains `::` then everything until last `::`
(greedy matching) is considered as a label 'key' and labels with
the same key are mutually exclusive:
* if multiple labels with the same key are added, only last selected
is added, also any existing labels with the same key are removed
* when removing an exclusive key, and multiple exclusive keys are
assigned (from before we introduced exclusive keys), all other
exclusive keys are kept

app/controllers/concerns/issuable_actions.rb

@@ -7,6 +7,9 @@ module IssuableActions
   included do
     before_action :authorize_destroy_issuable!, only: :destroy
     before_action :authorize_admin_issuable!, only: :bulk_update
+    before_action only: :show do
+      push_frontend_feature_flag(:scoped_labels, default_enabled: true)
+    end
   end
 
   def permitted_keys

app/helpers/labels_helper.rb

@@ -46,7 +46,7 @@ module LabelsHelper
     if block_given?
       link_to link, class: css_class, &block
     else
-      link_to render_colored_label(label, tooltip: tooltip), link, class: css_class
+      render_label(label, tooltip: tooltip, link: link, css: css_class)
     end
   end
 
@@ -78,19 +78,33 @@ module LabelsHelper
     end
   end
 
-  def render_colored_label(label, label_suffix = '', tooltip: true)
+  def render_label(label, tooltip: true, link: nil, css: nil)
+    # if scoped label is used then EE wraps label tag with scoped label
+    # doc link
+    html = render_colored_label(label, tooltip: tooltip)
+    html = link_to(html, link, class: css) if link
+
+    html
+  end
+
+  def render_colored_label(label, label_suffix: '', tooltip: true, title: nil)
     text_color = text_color_for_bg(label.color)
+    title ||= label_tooltip_title(label)
 
     # Intentionally not using content_tag here so that this method can be called
     # by LabelReferenceFilter
     span = %(<span class="badge color-label #{"has-tooltip" if tooltip}" ) +
-      %(style="background-color: #{label.color}; color: #{text_color}" ) +
-      %(title="#{escape_once(label.description)}" data-container="body">) +
+      %(data-html="true" style="background-color: #{label.color}; color: #{text_color}" ) +
+      %(title="#{escape_once(title)}" data-container="body">) +
       %(#{escape_once(label.name)}#{label_suffix}</span>)
 
     span.html_safe
   end
 
+  def label_tooltip_title(label)
+    label.description
+  end
+
   def suggested_colors
     [
       '#0033CC',
@@ -231,6 +245,33 @@ module LabelsHelper
     labels.sort_by(&:title)
   end
 
+  def label_dropdown_data(project, opts = {})
+    {
+      toggle: "dropdown",
+      field_name: opts[:field_name] || "label_name[]",
+      show_no: "true",
+      show_any: "true",
+      project_id: project&.try(:id),
+      namespace_path: project&.try(:namespace)&.try(:full_path),
+      project_path: project&.try(:path)
+    }.merge(opts)
+  end
+
+  def sidebar_label_dropdown_data(issuable_type, issuable_sidebar)
+    label_dropdown_data(nil, {
+     default_label: "Labels",
+     field_name: "#{issuable_type}[label_names][]",
+     ability_name: issuable_type,
+     namespace_path: issuable_sidebar[:namespace_path],
+     project_path: issuable_sidebar[:project_path],
+     issue_update: issuable_sidebar[:issuable_json_path],
+     labels: issuable_sidebar[:project_labels_path],
+     display: 'static'
+    })
+  end
+
   # Required for Banzai::Filter::LabelReferenceFilter
-  module_function :render_colored_label, :text_color_for_bg, :escape_once
+  module_function :render_colored_label, :text_color_for_bg, :escape_once, :label_tooltip_title
 end
+
+LabelsHelper.prepend(EE::LabelsHelper)

app/models/global_label.rb

@@ -4,7 +4,7 @@ class GlobalLabel
   attr_accessor :title, :labels
   alias_attribute :name, :title
 
-  delegate :color, :text_color, :description, to: :@first_label
+  delegate :color, :text_color, :description, :scoped_label?, to: :@first_label
 
   def for_display
     @first_label

app/models/label.rb

@@ -258,3 +258,5 @@ class Label < ApplicationRecord
     %w(color title).each { |attr| self[attr] = self[attr]&.strip }
   end
 end
+
+Label.prepend(EE::Label)

app/services/issuable_base_service.rb

@@ -107,12 +107,13 @@ class IssuableBaseService < BaseService
     @labels_service ||= ::Labels::AvailableLabelsService.new(current_user, parent, params)
   end
 
-  def process_label_ids(attributes, existing_label_ids: nil)
+  def process_label_ids(attributes, existing_label_ids: nil, extra_label_ids: [])
     label_ids = attributes.delete(:label_ids)
     add_label_ids = attributes.delete(:add_label_ids)
     remove_label_ids = attributes.delete(:remove_label_ids)
 
     new_label_ids = existing_label_ids || label_ids || []
+    new_label_ids |= extra_label_ids
 
     if add_label_ids.blank? && remove_label_ids.blank?
       new_label_ids = label_ids if label_ids
@@ -147,7 +148,7 @@ class IssuableBaseService < BaseService
 
     params.delete(:state_event)
     params[:author] ||= current_user
-    params[:label_ids] = issuable.label_ids.to_a + process_label_ids(params)
+    params[:label_ids] = process_label_ids(params, extra_label_ids: issuable.label_ids.to_a)
 
     issuable.assign_attributes(params)
 

app/views/shared/_delete_label_modal.html.haml

@@ -2,7 +2,7 @@
   .modal-dialog
     .modal-content
       .modal-header
-        %h3.page-title Delete #{render_colored_label(label, tooltip: false)} ?
+        %h3.page-title Delete #{render_label(label, tooltip: false)} ?
         %button.close{ type: "button", "data-dismiss": "modal", "aria-label" => _('Close') }
           %span{ "aria-hidden": true } ×
 

app/views/shared/_label_row.html.haml

@@ -8,7 +8,7 @@
   - if defined?(@project)
     = link_to_label(label, subject: @project, tooltip: false)
   - else
-    = render_colored_label(label, tooltip: false)
+    = render_label(label, tooltip: false)
 .label-description
   .append-right-default.prepend-left-default
     - if label.description.present?

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

@@ -21,13 +21,7 @@
         %button.dropdown-menu-toggle.js-label-select.js-multiselect.js-issue-board-sidebar{ type: "button",
           ":data-selected" => "selectedLabels",
           ":data-labels" => "issue.assignableLabelsEndpoint",
-          data: { toggle: "dropdown",
-            field_name: "issue[label_names][]",
-            show_no: "true",
-            show_any: "true",
-            project_id: @project&.try(:id),
-            namespace_path: @namespace_path,
-            project_path: @project.try(:path) } }
+          data: label_dropdown_data(@project, namespace_path: @namespace_path, field_name: "issue[label_names][]") }
           %span.dropdown-toggle-text
             {{ labelDropdownTitle }}
           = icon('chevron-down')

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

@@ -8,7 +8,7 @@
 - classes = local_assigns.fetch(:classes, [])
 - selected = local_assigns.fetch(:selected, nil)
 - dropdown_title = local_assigns.fetch(:dropdown_title, "Filter by label")
-- dropdown_data = {toggle: 'dropdown', field_name: "label_name[]", show_no: "true", show_any: "true", namespace_path: @project.try(:namespace).try(:full_path), project_path: @project.try(:path), labels: labels_filter_path_with_defaults, default_label: "Labels"}
+- dropdown_data = label_dropdown_data(@project, labels: labels_filter_path_with_defaults, default_label: "Labels")
 - dropdown_data.merge!(data_options)
 - label_name = local_assigns.fetch(:label_name, "Labels")
 - no_default_styles = local_assigns.fetch(:no_default_styles, false)

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

@@ -105,10 +105,9 @@
             = link_to _('Edit'), '#', class: 'js-sidebar-dropdown-toggle edit-link float-right'
         .value.issuable-show-labels.dont-hide.hide-collapsed.qa-labels-block{ class: ("has-labels" if selected_labels.any?) }
           - if selected_labels.any?
-            - selected_labels.each do |label|
-              = link_to sidebar_label_filter_path(issuable_sidebar[:project_issuables_path], label[:title]) do
-                %span.badge.color-label.has-tooltip{ style: "background-color: #{label[:color]}; color: #{label[:text_color]}", title: label[:description], data: { container: "body" } }
-                  = label[:title]
+            - selected_labels.each do |label_hash|
+              - label = Label.new(label_hash.slice(:color, :description, :title))
+              = render_label(label, link: sidebar_label_filter_path(issuable_sidebar[:project_issuables_path], label[:title]))
           - else
             %span.no-value
               = _('None')
@@ -116,7 +115,7 @@
           - selected_labels.each do |label|
             = hidden_field_tag "#{issuable_type}[label_names][]", label[:id], id: nil
           .dropdown
-            %button.dropdown-menu-toggle.js-label-select.js-multiselect.js-label-sidebar-dropdown{ type: "button", data: {toggle: "dropdown", default_label: "Labels", field_name: "#{issuable_type}[label_names][]", ability_name: issuable_type, show_no: "true", show_any: "true", namespace_path: issuable_sidebar[:namespace_path], project_path: issuable_sidebar[:project_path], issue_update: issuable_sidebar[:issuable_json_path], labels: issuable_sidebar[:project_labels_path], display: 'static' } }
+            %button.dropdown-menu-toggle.js-label-select.js-multiselect.js-label-sidebar-dropdown{ type: "button", data: sidebar_label_dropdown_data(issuable_type, issuable_sidebar) }
               %span.dropdown-toggle-text{ class: ("is-default" if selected_labels.empty?) }
                 = multi_label_name(selected_labels, "Labels")
               = icon('chevron-down', 'aria-hidden': 'true')

app/views/shared/labels/_form.html.haml

@@ -4,7 +4,9 @@
   .form-group.row
     = f.label :title, class: 'col-form-label col-sm-2'
     .col-sm-10
-      = f.text_field :title, class: "form-control qa-label-title", required: true, autofocus: true
+      = f.text_field :title, class: "form-control js-label-title qa-label-title", required: true, autofocus: true
+    = render_if_exists 'shared/labels/create_label_help_text'
+
   .form-group.row
     = f.label :description, class: 'col-form-label col-sm-2'
     .col-sm-10

app/views/shared/milestones/_issuable.html.haml

@@ -22,7 +22,7 @@
 
     - labels.each do |label|
       = link_to polymorphic_path(issuable_type_args, { milestone_title: @milestone.title, label_name: label.title, state: 'all' }) do
-        - render_colored_label(label)
+        - render_label(label)
 
     %span.assignee-icon
       - assignees.each do |assignee|

app/views/shared/milestones/_labels_tab.html.haml

@@ -5,8 +5,7 @@
     %li.is-not-draggable
       %span.label-row
         %span.label-name
-          = link_to milestones_label_path(options) do
-            - render_colored_label(label, tooltip: false)
+          = render_label(label, tooltip: false, link: milestones_label_path(options))
         %span.prepend-description-left
           = markdown_field(label, :description)
 

ee/app/helpers/ee/boards_helper.rb

@@ -31,7 +31,9 @@ module EE
         board_weight: board.weight,
         focus_mode_available: parent.feature_available?(:issue_board_focus_mode),
         weight_feature_available: parent.feature_available?(:issue_weights).to_s,
-        show_promotion: show_feature_promotion
+        show_promotion: show_feature_promotion,
+        scoped_labels: License.feature_available?(:scoped_labels),
+        scoped_labels_documentation_link: help_page_path('user/project/labels.md', anchor: 'scoped-labels')
       }
 
       super.merge(data)

ee/app/helpers/ee/labels_helper.rb

+# frozen_string_literal: true
+
+module EE
+  module LabelsHelper
+    def render_label(label, tooltip: true, link: nil, css: nil)
+      content = super
+      content = scoped_label_wrapper(content, label) if label.scoped_label?
+
+      content
+    end
+
+    def scoped_label_wrapper(link, label)
+      %(<span class="d-inline-block position-relative scoped-label-wrapper">#{link}#{scoped_labels_doc_link(label)}</span>).html_safe
+    end
+
+    def scoped_labels_doc_link(label)
+      text_color = ::LabelsHelper.text_color_for_bg(label.color)
+      content = %(<i class="fa fa-question-circle" style="background-color: #{label.color}; color: #{text_color}"></i>)
+      help_url = ::Gitlab::Routing.url_helpers.help_page_url('user/project/labels.md', anchor: 'scoped-labels')
+
+      %(<a href="#{help_url}" class="label scoped-label" target="_blank" rel="noopener">#{content}</a>)
+    end
+
+    def label_tooltip_title(label)
+      # can't use `super` because this is called also as a module method from
+      # banzai
+      tooltip = ::LabelsHelper.label_tooltip_title(label)
+      tooltip = %(<span class='font-weight-bold scoped-label-tooltip-title'>Scoped label</span><br />#{tooltip}) if label.scoped_label?
+
+      tooltip
+    end
+
+    def label_dropdown_data(project, opts = {})
+      super.merge({
+        scoped_labels: License.feature_available?(:scoped_labels)&.to_s,
+        scoped_labels_documentation_link: help_page_path('user/project/labels.md', anchor: 'scoped-labels')
+      })
+    end
+
+    module_function :scoped_label_wrapper, :scoped_labels_doc_link, :label_tooltip_title
+  end
+end

ee/app/helpers/epics_helper.rb

@@ -40,7 +40,9 @@ module EpicsHelper
       labels_path: group_labels_path(group, format: :json, only_group_labels: true, include_ancestor_groups: true),
       toggle_subscription_path: toggle_subscription_group_epic_path(group, epic),
       labels_web_url: group_labels_path(group),
-      epics_web_url: group_epics_path(group)
+      epics_web_url: group_epics_path(group),
+      scoped_labels: License.feature_available?(:scoped_labels),
+      scoped_labels_documentation_link: help_page_path('user/project/labels.md', anchor: 'scoped-labels')
     }
 
     epic_meta[:todo_delete_path] = dashboard_todo_path(todo) if todo.present?

ee/app/models/ee/label.rb

+# frozen_string_literal: true
+
+module EE
+  module Label
+    extend ActiveSupport::Concern
+
+    SCOPED_LABEL_PATTERN = /^.*::/.freeze
+
+    def scoped_label?
+      SCOPED_LABEL_PATTERN.match?(name) && ::License.feature_available?(:scoped_labels)
+    end
+
+    def scoped_label_key
+      title[Label::SCOPED_LABEL_PATTERN]
+    end
+  end
+end

ee/app/models/license.rb

@@ -52,6 +52,7 @@ class License < ApplicationRecord
     geo
     github_project_service_integration
     jira_dev_panel_integration
+    scoped_labels
     ldap_group_sync_filter
     multiple_clusters
     multiple_group_issue_boards

ee/app/models/scoped_label_set.rb

+# frozen_string_literal: true
+
+class ScopedLabelSet
+  attr_reader :labels, :key
+
+  def self.from_label_ids(ids)
+    by_key = Hash.new { |hash, key| hash[key] = new(key) }
+    labels = Label.select(:id, :title).where(id: ids)
+
+    labels.each do |label|
+      key = label.scoped_label_key
+      by_key[key].add(label)
+    end
+
+    by_key.values
+  end
+
+  def initialize(key, labels = [])
+    @key = key
+    @labels = labels
+  end
+
+  def add(label)
+    labels << label
+  end
+
+  def last_id_by_order(label_ids_order)
+    by_index = label_ids_order.map.with_index { |id, idx| [id.to_i, idx] }.to_h
+
+    label_ids.max do |id1, id2|
+      by_index[id1].to_i <=> by_index[id2].to_i
+    end
+  end
+
+  def valid?
+    key.nil? || labels.count < 2
+  end
+
+  def contains_any?(ids)
+    (label_ids & ids).present?
+  end
+
+  def label_ids
+    labels.map(&:id)
+  end
+end

ee/app/services/ee/issuable_base_service.rb

@@ -5,6 +5,8 @@ module EE
     extend ::Gitlab::Utils::Override
     include ::Gitlab::Utils::StrongMemoize
 
+    attr_reader :label_ids_ordered_by_selection
+
     private
 
     override :filter_params
@@ -20,10 +22,39 @@ module EE
       super
     end
 
+    override :filter_labels
+    def filter_labels
+      @label_ids_ordered_by_selection = params[:add_label_ids].to_a + params[:label_ids].to_a # rubocop:disable Gitlab/ModuleWithInstanceVariables
+
+      super
+    end
+
     def update_task_event?
       strong_memoize(:update_task_event) do
         params.key?(:update_task)
       end
     end
+
+    override :process_label_ids
+    def process_label_ids(attributes, existing_label_ids: nil, extra_label_ids: [])
+      ids = super
+      added_label_ids = ids - existing_label_ids.to_a
+
+      filter_mutually_exclusive_labels(ids, added_label_ids)
+    end
+
+    def filter_mutually_exclusive_labels(ids, added_label_ids)
+      return ids if added_label_ids.empty? || !::License.feature_available?(:scoped_labels)
+
+      label_sets = ScopedLabelSet.from_label_ids(ids)
+
+      label_sets.map do |set|
+        if set.valid? || !set.contains_any?(added_label_ids)
+          set.label_ids
+        else
+          set.last_id_by_order(label_ids_ordered_by_selection)
+        end
+      end.flatten
+    end
   end
 end

ee/app/views/groups/epics/_epic.html.haml

@@ -15,4 +15,4 @@
           - if epic.labels.any?
              
             - epic.labels.each do |label|
-              = link_to render_colored_label(label, tooltip: true), group_epics_path(@group, label_name:[label.name]), class: 'label-link'
+              = render_label(label, tooltip: true, link: group_epics_path(@group, label_name:[label.name]), css: 'label-link')

ee/app/views/shared/labels/_create_label_help_text.html.haml

+- docs_link = help_page_path('user/project/labels.md', anchor: 'scoped-labels')
+
+.col-sm-10.offset-sm-2.form-text.text-muted.js-has-scoped-labels.hidden
+  Using
+  %code ::
+  denotes a
+  %a{ href: docs_link, target: '_blank', rel: 'noopener noreferrer' } scoped label set
+.col-sm-10.offset-sm-2.form-text.text-muted.js-use-scoped-labels
+  Use
+  %code ::
+  to create a
+  %a{ href: docs_link, target: '_blank', rel: 'noopener noreferrer' } scoped label set
+  (eg.
+  %code priority::1
+  )

ee/changelogs/unreleased/keyval-labels-ee.yml

+---
+title: Added mutually exclusive key value labels
+merge_request:
+author:
+type: added

ee/lib/ee/banzai/filter/label_reference_filter.rb

+# frozen_string_literal: true
+
+module EE
+  module Banzai
+    module Filter
+      module LabelReferenceFilter
+        extend ::Gitlab::Utils::Override
+
+        override :wrap_link
+        def wrap_link(link, label)
+          content = super
+          content = ::EE::LabelsHelper.scoped_label_wrapper(content, label) if label.scoped_label?
+
+          content
+        end
+
+        def tooltip_title(label)
+          ::EE::LabelsHelper.label_tooltip_title(label)
+        end
+      end
+    end
+  end
+end

ee/spec/helpers/ee/labels_helper_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe LabelsHelper do
+  set(:project) { create(:project) }
+  set(:label) { create(:label, project: project) }
+  set(:scoped_label) { create(:label, name: 'key::value', project: project) }
+
+  describe '#render_label' do
+    context 'with scoped labels enabled' do
+      before do
+        stub_licensed_features(scoped_labels: true)
+      end
+
+      it 'includes link to scoped labels documentation' do
+        expect(render_label(scoped_label)).to match(%r(<span.+>#{scoped_label.name}</span><a.+>.*question-circle.*</a>))
+      end
+
+      it 'does not include link to scoped label documentation for common labels' do
+        expect(render_label(label)).to match(%r(<span.+>#{label.name}</span>$))
+      end
+    end
+
+    context 'with scoped labels disabled' do
+      before do
+        stub_licensed_features(scoped_labels: false)
+      end
+
+      it 'does not include link to scoped documentation' do
+        expect(render_label(scoped_label)).to match(%r(<span.+>#{scoped_label.name}</span>$))
+      end
+    end
+  end
+end

ee/spec/helpers/epics_helper_spec.rb

@@ -39,7 +39,7 @@ describe EpicsHelper do
         start_date_sourcing_milestone_title start_date_sourcing_milestone_dates
         due_date due_date_is_fixed due_date_fixed due_date_from_milestones due_date_sourcing_milestone_title
         due_date_sourcing_milestone_dates end_date state namespace labels_path toggle_subscription_path
-        labels_web_url epics_web_url lock_version
+        labels_web_url epics_web_url lock_version scoped_labels scoped_labels_documentation_link
       ])
       expect(meta_data['author']).to eq({
         'name' => user.name,
@@ -111,7 +111,7 @@ describe EpicsHelper do
           start_date_sourcing_milestone_title start_date_sourcing_milestone_dates
           due_date due_date_is_fixed due_date_fixed due_date_from_milestones due_date_sourcing_milestone_title
           due_date_sourcing_milestone_dates end_date state namespace labels_path toggle_subscription_path
-          labels_web_url epics_web_url lock_version
+          labels_web_url epics_web_url lock_version scoped_labels scoped_labels_documentation_link
         ])
         expect(meta_data['start_date']).to eq('2000-01-01')
         expect(meta_data['start_date_sourcing_milestone_title']).to eq(milestone1.title)

ee/spec/lib/banzai/filter/label_reference_filter_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Banzai::Filter::LabelReferenceFilter do
+  include FilterSpecHelper
+
+  let(:project)      { create(:project, :public, name: 'sample-project') }
+  let(:label)        { create(:label, name: 'label', project: project) }
+  let(:scoped_label) { create(:label, name: 'key::value', project: project) }
+
+  context 'with scoped labels enabled' do
+    before do
+      stub_licensed_features(scoped_labels: true)
+    end
+
+    it 'includes link to scoped documentation' do
+      doc = reference_filter("See #{scoped_label.to_reference}")
+
+      expect(doc.to_html).to match(%r(<a.+><span.+>#{scoped_label.name}</span></a><a.+>.*question-circle.*</a>))
+    end
+
+    it 'does not include link to scoped documentation for common labels' do
+      doc = reference_filter("See #{label.to_reference}")
+
+      expect(doc.to_html).to match(%r(<a.+><span.+>#{label.name}</span></a>$))
+    end
+  end
+
+  context 'with scoped labels disabled' do
+    before do
+      stub_licensed_features(scoped_labels: false)
+    end
+
+    it 'does not include link to scoped labels documentation' do
+      doc = reference_filter("See #{scoped_label.to_reference}")
+
+      expect(doc.to_html).to match(%r(<a.+><span.+>#{scoped_label.name}</span></a>$))
+    end
+  end
+end

ee/spec/models/scoped_label_set_spec.rb

+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe ScopedLabelSet do
+  set(:kv_label1) { create(:label, title: 'key::label1') }
+  set(:kv_label2) { create(:label, title: 'key::label2') }
+  set(:kv_label3) { create(:label, title: 'key::label3') }
+
+  describe '.from_label_ids' do
+    def get_labels(sets, key)
+      sets.find { |set| set.key == key }.label_ids
+    end
+
+    it 'groups labels by their key' do
+      labels = [
+        create(:label, title: 'label1'),
+        create(:label, title: 'label2'),
+        create(:label, title: 'key::label1'),
+        create(:label, title: 'key::label2'),
+        create(:label, title: 'key::another key::label1'),
+        create(:label, title: 'key::another key::label2')
+      ]
+
+      sets = described_class.from_label_ids(labels)
+
+      expect(sets.size).to eq 3
+      expect(get_labels(sets, nil)).to match_array([labels[0].id, labels[1].id])
+      expect(get_labels(sets, 'key::')).to match_array([labels[2].id, labels[3].id])
+      expect(get_labels(sets, 'key::another key::')).to match_array([labels[4].id, labels[5].id])
+    end
+  end
+
+  describe '#valid?' do
+    it 'returns true for not scoped labels' do
+      label1 = build(:label, title: 'label1')
+      label2 = build(:label, title: 'label2')
+
+      set = described_class.new(nil, [label1, label2])
+
+      expect(set.valid?).to eq(true)
+    end
+
+    it 'returns true for scoped labels with single label' do
+      set = described_class.new(nil, [kv_label1])
+
+      expect(set.valid?).to eq(true)
+    end
+
+    it 'returns false for scoped labels with multiple labels' do
+      set = described_class.new('key', [kv_label1, kv_label2])
+
+      expect(set.valid?).to eq(false)
+    end
+  end
+
+  describe '#add' do
+    it 'adds a label to the set' do
+      set = described_class.new('key')
+
+      set.add(kv_label1)
+
+      expect(set.labels).to eq([kv_label1])
+    end
+  end
+
+  describe '#contains_any?' do
+    it 'returns true if any of label ids is in set' do
+      set = described_class.new('key', [kv_label1, kv_label2])
+
+      expect(set.contains_any?([kv_label2.id])).to eq(true)
+    end
+
+    it 'returns true if any of label ids is in set' do
+      set = described_class.new('key', [kv_label1])
+
+      expect(set.contains_any?([kv_label2.id])).to eq(false)
+    end
+  end
+
+  describe '#last_id_by_order' do
+    it 'returns last label present in the set ordered by custom order of superset of label ids' do
+      set = described_class.new('key', [kv_label1, kv_label3])
+
+      expect(set.last_id_by_order([kv_label1.id, kv_label3.id, kv_label2.id])).to eq(kv_label3.id)
+    end
+  end
+end

ee/spec/services/ee/issues/create_service_spec.rb

@@ -31,4 +31,10 @@ describe Issues::CreateService do
       end
     end
   end
+
+  describe '#execute' do
+    it_behaves_like 'new issuable with scoped labels' do
+      let(:parent) { project }
+    end
+  end
 end

ee/spec/services/ee/issues/update_service_spec.rb

@@ -118,5 +118,10 @@ describe Issues::UpdateService do
         end
       end
     end
+
+    it_behaves_like 'existing issuable with scoped labels' do
+      let(:issuable) { issue }
+      let(:parent) { project }
+    end
   end
 end

ee/spec/services/ee/merge_requests/create_service_spec.rb

@@ -52,5 +52,9 @@ describe MergeRequests::CreateService do
         end
       end
     end
+
+    it_behaves_like 'new issuable with scoped labels' do
+      let(:parent) { project }
+    end
   end
 end

ee/spec/services/ee/merge_requests/update_service_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe MergeRequests::UpdateService do
+  include ProjectForksHelper
+
+  let(:project) { create(:project, :repository) }
+  let(:user) { create(:user) }
+  let(:service) { described_class.new(project, user, {}) }
+
+  let(:merge_request) do
+    create(:merge_request, :simple, title: 'Old title',
+                                    source_project: project,
+                                    author: user)
+  end
+
+  before do
+    allow(service).to receive(:execute_hooks)
+  end
+
+  describe '#execute' do
+    it_behaves_like 'existing issuable with scoped labels' do
+      let(:issuable) { merge_request }
+      let(:parent) { project }
+    end
+  end
+end

ee/spec/services/epics/create_service_spec.rb

@@ -19,5 +19,9 @@ describe Epics::CreateService do
       expect(epic.description).to eq('epic description')
       expect(NewEpicWorker).to have_received(:perform_async).with(epic.id, user.id)
     end
+
+    it_behaves_like 'new issuable with scoped labels' do
+      let(:parent) { group }
+    end
   end
 end

ee/spec/services/epics/update_service_spec.rb

@@ -211,5 +211,10 @@ describe Epics::UpdateService do
         end
       end
     end
+
+    it_behaves_like 'existing issuable with scoped labels' do
+      let(:issuable) { epic }
+      let(:parent) { group }
+    end
   end
 end

ee/spec/support/shared_examples/scoped_label_examples.rb

+# frozen_string_literal: true
+
+shared_context 'exclusive labels creation' do
+  def create_label(title)
+    if parent.is_a?(Group)
+      create(:group_label, group: parent, title: title)
+    else
+      create(:label, project: parent, title: title)
+    end
+  end
+
+  before do
+    parent.add_developer(user)
+  end
+end
+
+shared_examples_for 'new issuable with scoped labels' do
+  include_context 'exclusive labels creation' do
+    context 'scoped labels are avaialble' do
+      before do
+        stub_licensed_features(scoped_labels: true)
+      end
+
+      it 'adds only last selected exclusive scoped label' do
+        label1 = create_label('label1')
+        label2 = create_label('key::label1')
+        label3 = create_label('key::label2')
+        label4 = create_label('key::label3')
+
+        issuable = described_class.new(
+          parent, user, title: 'test', label_ids: [label1.id, label3.id, label4.id, label2.id]
+        ).execute
+
+        expect(issuable.labels).to match_array([label1, label2])
+      end
+    end
+
+    context 'scoped labels are not available' do
+      before do
+        stub_licensed_features(scoped_labels: false)
+      end
+
+      it 'adds only last selected exclusive scoped label' do
+        label1 = create_label('label1')
+        label2 = create_label('key::label1')
+        label3 = create_label('key::label2')
+        label4 = create_label('key::label3')
+
+        issuable = described_class.new(
+          parent, user, title: 'test', label_ids: [label1.id, label3.id, label4.id, label2.id]
+        ).execute
+
+        expect(issuable.labels).to match_array([label1, label2, label3, label4])
+      end
+    end
+  end
+end
+
+shared_examples_for 'existing issuable with scoped labels' do
+  include_context 'exclusive labels creation' do
+    let(:label1) { create_label('key::label1') }
+    let(:label2) { create_label('key::label2') }
+    let(:label3) { create_label('key::label3') }
+
+    context 'scoped labels are avaialble' do
+      before do
+        stub_licensed_features(scoped_labels: true, epics: true)
+      end
+
+      it 'adds only last selected exclusive scoped label' do
+        create(:label_link, label: label1, target: issuable)
+        create(:label_link, label: label2, target: issuable)
+
+        issuable.reload
+
+        described_class.new(
+          parent, user, label_ids: [label1.id, label3.id]
+        ).execute(issuable)
+
+        expect(issuable.reload.labels).to match_array([label3])
+      end
+
+      it 'it preserves multiple exclusive scoped labels when only removing labels' do
+        create(:label_link, label: label1, target: issuable)
+        create(:label_link, label: label2, target: issuable)
+        create(:label_link, label: label3, target: issuable)
+
+        issuable.reload
+
+        described_class.new(
+          parent, user, label_ids: [label2.id, label3.id]
+        ).execute(issuable)
+
+        expect(issuable.reload.labels).to match_array([label2, label3])
+      end
+    end
+
+    context 'scoped labels are not available' do
+      before do
+        stub_licensed_features(scoped_labels: false, epics: true)
+      end
+
+      it 'adds all scoped labels' do
+        create(:label_link, label: label1, target: issuable)
+        create(:label_link, label: label2, target: issuable)
+
+        issuable.reload
+
+        described_class.new(
+          parent, user, label_ids: [label1.id, label2.id, label3.id]
+        ).execute(issuable)
+
+        expect(issuable.reload.labels).to match_array([label1, label2, label3])
+      end
+    end
+  end
+end

lib/banzai/filter/abstract_reference_filter.rb

@@ -195,15 +195,21 @@ module Banzai
 
             content = link_content || object_link_text(object, matches)
 
-            %(<a href="#{url}" #{data}
-                 title="#{escape_once(title)}"
-                 class="#{klass}">#{content}</a>)
+            link = %(<a href="#{url}" #{data}
+                        title="#{escape_once(title)}"
+                        class="#{klass}">#{content}</a>)
+
+            wrap_link(link, object)
           else
             match
           end
         end
       end
 
+      def wrap_link(link, object)
+        link
+      end
+
       def data_attributes_for(text, parent, object, link_content: false, link_reference: false)
         object_parent_type = parent.is_a?(Group) ? :group : :project
 

lib/banzai/filter/label_reference_filter.rb

@@ -91,7 +91,11 @@ module Banzai
           label_suffix = " <i>in #{reference}</i>" if reference.present?
         end
 
-        LabelsHelper.render_colored_label(object, label_suffix)
+        LabelsHelper.render_colored_label(object, label_suffix: label_suffix, title: tooltip_title(object))
+      end
+
+      def tooltip_title(label)
+        nil
       end
 
       def full_path_ref?(matches)
@@ -113,3 +117,5 @@ module Banzai
     end
   end
 end
+
+Banzai::Filter::LabelReferenceFilter.prepend(EE::Banzai::Filter::LabelReferenceFilter)