Add support for relating epics

Add service to allow creating RelatedEpicLinks
Add create related epic links endpoint
Update pot files
Add specs
Expose relation_path in new entity

Changelog: other
EE: true

app/services/issuable_links/create_service.rb

@@ -36,6 +36,20 @@ module IssuableLinks
       success
     end
 
+    # rubocop: disable CodeReuse/ActiveRecord
+    def relate_issuables(referenced_issuable)
+      link = link_class.find_or_initialize_by(source: issuable, target: referenced_issuable)
+
+      set_link_type(link)
+
+      if link.changed? && link.save
+        create_notes(referenced_issuable)
+      end
+
+      link
+    end
+    # rubocop: enable CodeReuse/ActiveRecord
+
     private
 
     def render_conflict_error?
@@ -96,6 +110,23 @@ module IssuableLinks
       {}
     end
 
+    def issuables_assigned_message
+      _('%{issuable}(s) already assigned' % { issuable: target_issuable_type.capitalize })
+    end
+
+    def issuables_not_found_message
+      _('No matching %{issuable} found. Make sure that you are adding a valid %{issuable} URL.' % { issuable: target_issuable_type })
+    end
+
+    def target_issuable_type
+      :issue
+    end
+
+    def create_notes(referenced_issuable)
+      SystemNoteService.relate_issuable(issuable, referenced_issuable, current_user)
+      SystemNoteService.relate_issuable(referenced_issuable, issuable, current_user)
+    end
+
     def linkable_issuables(objects)
       raise NotImplementedError
     end
@@ -104,16 +135,12 @@ module IssuableLinks
       raise NotImplementedError
     end
 
-    def relate_issuables(referenced_object)
+    def link_class
       raise NotImplementedError
     end
 
-    def issuables_assigned_message
-      _("Issue(s) already assigned")
-    end
-
-    def issuables_not_found_message
-      _("No matching issue found. Make sure that you are adding a valid issue URL.")
+    def set_link_type(_link)
+      # no-op
     end
   end
 end

app/services/issue_links/create_service.rb

@@ -2,44 +2,25 @@
 
 module IssueLinks
   class CreateService < IssuableLinks::CreateService
-    # rubocop: disable CodeReuse/ActiveRecord
-    def relate_issuables(referenced_issue)
-      link = IssueLink.find_or_initialize_by(source: issuable, target: referenced_issue)
-
-      set_link_type(link)
-
-      if link.changed? && link.save
-        create_notes(referenced_issue)
-      end
-
-      link
-    end
-    # rubocop: enable CodeReuse/ActiveRecord
-
     def linkable_issuables(issues)
       @linkable_issuables ||= begin
         issues.select { |issue| can?(current_user, :admin_issue_link, issue) }
       end
     end
 
-    def create_notes(referenced_issue)
-      SystemNoteService.relate_issue(issuable, referenced_issue, current_user)
-      SystemNoteService.relate_issue(referenced_issue, issuable, current_user)
-    end
-
     def previous_related_issuables
       @related_issues ||= issuable.related_issues(current_user).to_a
     end
 
     private
 
-    def set_link_type(_link)
-      # EE only
-    end
-
     def track_event
       track_incident_action(current_user, issuable, :incident_relate)
     end
+
+    def link_class
+      IssueLink
+    end
   end
 end
 

app/services/system_note_service.rb

@@ -49,8 +49,8 @@ module SystemNoteService
     ::SystemNotes::IssuablesService.new(noteable: issuable, project: project, author: author).change_issuable_contacts(added_count, removed_count)
   end
 
-  def relate_issue(noteable, noteable_ref, user)
-    ::SystemNotes::IssuablesService.new(noteable: noteable, project: noteable.project, author: user).relate_issue(noteable_ref)
+  def relate_issuable(noteable, noteable_ref, user)
+    ::SystemNotes::IssuablesService.new(noteable: noteable, project: noteable.project, author: user).relate_issuable(noteable_ref)
   end
 
   def unrelate_issuable(noteable, noteable_ref, user)

app/services/system_notes/issuables_service.rb

@@ -10,8 +10,9 @@ module SystemNotes
     #   "marked this issue as related to gitlab-foss#9001"
     #
     # Returns the created Note object
-    def relate_issue(noteable_ref)
-      body = "marked this issue as related to #{noteable_ref.to_reference(noteable.project)}"
+    def relate_issuable(noteable_ref)
+      issuable_type = noteable.to_ability_name.humanize(capitalize: false)
+      body = "marked this #{issuable_type} as related to #{noteable_ref.to_reference(noteable.resource_parent)}"
 
       issue_activity_counter.track_issue_related_action(author: author) if noteable.is_a?(Issue)
 

ee/app/controllers/groups/epics/related_epic_links_controller.rb

@@ -10,7 +10,7 @@ class Groups::Epics::RelatedEpicLinksController < Groups::ApplicationController
   before_action :check_epics_available!
   before_action :check_related_epics_available!
   before_action :authorize_related_epic_link_association!, only: [:destroy]
-  before_action :authorize_admin!, only: [:destroy]
+  before_action :authorize_admin!, only: [:create, :destroy]
 
   feature_category :portfolio_management
   urgency :default
@@ -37,7 +37,15 @@ class Groups::Epics::RelatedEpicLinksController < Groups::ApplicationController
     Epics::RelatedEpicLinks::DestroyService.new(link, current_user)
   end
 
+  def create_service
+    Epics::RelatedEpicLinks::CreateService.new(epic, current_user, create_params)
+  end
+
   def ensure_related_epics_enabled!
     render_404 unless Feature.enabled?(:related_epics_widget, epic&.group, default_enabled: :yaml)
   end
+
+  def create_params
+    params.permit(:link_type, issuable_references: [])
+  end
 end

ee/app/serializers/epics/related_epic_entity.rb

@@ -2,10 +2,17 @@
 
 module Epics
   class RelatedEpicEntity < Grape::Entity
+    include Gitlab::Utils::StrongMemoize
     include RequestAwareEntity
 
     expose :id, :confidential, :title, :state, :created_at, :closed_at
 
+    expose :relation_path do |related_epic|
+      if can_admin_related_epic_links?(related_epic)
+        group_epic_related_epic_link_path(issuable.group, issuable.iid, related_epic.related_epic_link_id)
+      end
+    end
+
     expose :reference do |related_epic|
       related_epic.to_reference(request.issuable.group)
     end
@@ -17,5 +24,17 @@ module Epics
     expose :link_type do |related_epic|
       related_epic.epic_link_type
     end
+
+    private
+
+    def can_admin_related_epic_links?(epic)
+      user = request.current_user
+
+      Ability.allowed?(user, :admin_related_epic_link, issuable) && Ability.allowed?(user, :admin_epic, epic)
+    end
+
+    def issuable
+      request.issuable
+    end
   end
 end

ee/app/services/ee/issuable_links/create_service.rb

@@ -24,6 +24,19 @@ module EE
       def affected_epics(_issues)
         []
       end
+
+      override :set_link_type
+      def set_link_type(link)
+        return unless params[:link_type].present?
+
+        # `blocked_by` links are treated as `blocks` links where source and target is swapped.
+        if params[:link_type] == ::IssuableLink::TYPE_IS_BLOCKED_BY
+          link.source, link.target = link.target, link.source
+          link.link_type = ::IssuableLink::TYPE_BLOCKS
+        else
+          link.link_type = params[:link_type]
+        end
+      end
     end
   end
 end

ee/app/services/ee/issue_links/create_service.rb

@@ -13,18 +13,6 @@ module EE
 
       private
 
-      def set_link_type(link)
-        return unless params[:link_type].present?
-
-        # `blocked_by` links are treated as `blocks` links where source and target is swapped.
-        if params[:link_type] == ::IssueLink::TYPE_IS_BLOCKED_BY
-          link.source, link.target = link.target, link.source
-          link.link_type = ::IssueLink::TYPE_BLOCKS
-        else
-          link.link_type = params[:link_type]
-        end
-      end
-
       def link_type_available?
         # `blocked_by` is allowed as a param and handled in set_link_type
         return true unless [::IssueLink::TYPE_BLOCKS, ::IssueLink::TYPE_IS_BLOCKED_BY].include?(params[:link_type])

ee/app/services/epics/related_epic_links/create_service.rb

+# frozen_string_literal: true
+
+module Epics::RelatedEpicLinks
+  class CreateService < IssuableLinks::CreateService
+    def linkable_issuables(epics)
+      @linkable_issuables ||= begin
+        epics.select { |epic| can?(current_user, :admin_epic, epic) }
+      end
+    end
+
+    def previous_related_issuables
+      @related_epics ||= issuable.related_epics(current_user).to_a
+    end
+
+    private
+
+    def references(extractor)
+      extractor.epics
+    end
+
+    def extractor_context
+      { group: issuable.group }
+    end
+
+    def target_issuable_type
+      :epic
+    end
+
+    def link_class
+      Epic::RelatedEpicLink
+    end
+  end
+end

ee/app/services/epics/related_epic_links/destroy_service.rb

@@ -6,7 +6,7 @@ module Epics
       private
 
       def permission_to_remove_relation?
-        can?(current_user, :admin_related_epic_link, source) && can?(current_user, :admin_related_epic_link, target)
+        can?(current_user, :admin_related_epic_link, source) && can?(current_user, :admin_epic, target)
       end
 
       def track_event

ee/config/routes/group.rb

@@ -123,7 +123,7 @@ constraints(::Constraints::GroupUrlConstrainer.new) do
 
       scope module: :epics do
         resources :notes, only: [:index, :create, :destroy, :update], concerns: :awardable, constraints: { id: /\d+/ }
-        resources :related_epic_links, only: [:index, :destroy]
+        resources :related_epic_links, only: [:index, :create, :destroy]
       end
 
       collection do

ee/spec/controllers/projects/issues_controller_spec.rb

@@ -249,7 +249,7 @@ RSpec.describe Projects::IssuesController do
 
     context 'with a related system note' do
       let(:confidential_issue) { create(:issue, :confidential, project: project) }
-      let!(:system_note) { SystemNoteService.relate_issue(issue, confidential_issue, user) }
+      let!(:system_note) { SystemNoteService.relate_issuable(issue, confidential_issue, user) }
 
       shared_examples 'user can see confidential issue' do |access_level|
         context "when a user is a #{access_level}" do

ee/spec/fixtures/api/schemas/entities/related_epic.json

 {
   "type": "object",
-  "allOf": [
-    {
-      "required" : [
-        "id",
-        "confidential",
-        "title",
-        "state",
-        "created_at",
-        "closed_at",
-        "reference",
-        "path",
-        "link_type"
-      ],
   "properties" : {
     "id": { "type": "integer" },
     "confidential": { "type": "boolean" },
@@ -20,11 +7,22 @@
     "state": { "type": "string" },
     "created_at": { "type": "string", "format": "date-time" },
     "closed_at": { "type": ["string", "null"], "format": "date-time" },
+    "relation_path": { "type": ["string", "null"] },
     "reference": { "type": "string" },
     "path": { "type": "string" },
     "link_type": { "type": "string" }
   },
+  "required" : [
+    "id",
+    "confidential",
+    "title",
+    "state",
+    "created_at",
+    "closed_at",
+    "relation_path",
+    "reference",
+    "path",
+    "link_type"
+  ],
   "additionalProperties": false
-    }
-  ]
 }

ee/spec/requests/groups/epics/related_epic_links_controller_spec.rb

@@ -6,8 +6,10 @@ RSpec.describe Groups::Epics::RelatedEpicLinksController do
   let_it_be(:user) { create(:user) }
   let_it_be(:epic) { create(:epic) }
   let_it_be(:epic2) { create(:epic, group: epic.group) }
-  let_it_be(:epic_link1) { create(:related_epic_link, source: epic, target: epic2) }
+  let_it_be(:epic3) { create(:epic, group: epic.group) }
+  let_it_be(:epic_link1) { create(:related_epic_link, source: epic, target: epic3) }
   let_it_be(:epic_link2) { create(:related_epic_link, source: epic) }
+  let_it_be(:listing_service) { Epics::RelatedEpicLinks::ListService }
 
   before do
     stub_licensed_features(epics: true, related_epics: true)
@@ -113,4 +115,84 @@ RSpec.describe Groups::Epics::RelatedEpicLinksController do
       end
     end
   end
+
+  describe 'POST /groups/*group_id/-/epics/:epic_id/related_epic_links' do
+    let(:issuable_references) { [epic2.to_reference(full: true)] }
+
+    subject(:request) do
+      post group_epic_related_epic_links_path(related_epics_params(issuable_references: issuable_references))
+    end
+
+    before do
+      epic.group.add_developer(user)
+      epic2.group.add_developer(user)
+      login_as user
+    end
+
+    context 'with success' do
+      it 'returns JSON response' do
+        request
+
+        list_service_response = listing_service.new(epic, user).execute
+        expect(response).to have_gitlab_http_status(:ok)
+        expect(json_response).to eq('message' => nil,
+                                    'issuables' => list_service_response.as_json)
+      end
+
+      it 'delegates the creation of the related epic link to Epics::RelatedEpicLinks::CreateService' do
+        expect_next_instance_of(Epics::RelatedEpicLinks::CreateService) do |service|
+          expect(service).to receive(:execute).once.and_call_original
+        end
+
+        request
+
+        expect(response).to have_gitlab_http_status(:ok)
+      end
+
+      it 'creates a new Epic::RelatedEpicLink record' do
+        expect { request }.to change { Epic::RelatedEpicLink.count }.by(1)
+      end
+
+      it 'returns correct relation path in response' do
+        request
+        related_epic_link = Epic::RelatedEpicLink.find_by(source: epic, target: epic2)
+
+        expect(json_response['issuables'].last)
+          .to include('relation_path' => "/groups/#{epic.group.path}/-/epics/#{epic.iid}/related_epic_links/#{related_epic_link&.id}")
+      end
+    end
+
+    context 'with failure' do
+      context 'when unauthorized' do
+        it 'returns 403' do
+          epic.group.add_guest(user)
+
+          request
+
+          expect(response).to have_gitlab_http_status(:forbidden)
+        end
+      end
+
+      context 'when failing service result' do
+        let(:issuable_references) { ["##{non_existing_record_iid}"] }
+
+        it 'returns failure JSON' do
+          request
+
+          list_service_response = listing_service.new(epic, user).execute
+
+          expect(response).to have_gitlab_http_status(:not_found)
+          expect(json_response).to eq('message' => 'No matching epic found. Make sure that you are adding a valid epic URL.', 'issuables' => list_service_response.as_json)
+        end
+      end
+
+      it_behaves_like 'a not available action'
+    end
+  end
+
+  def related_epics_params(opts = {})
+    opts.reverse_merge(group_id: epic.group,
+                       epic_id: epic.iid,
+                       format: :json)
+  end
 end

ee/spec/serializers/epics/related_epic_entity_spec.rb

@@ -5,8 +5,9 @@ require 'spec_helper'
 RSpec.describe Epics::RelatedEpicEntity do
   let_it_be(:user) { create(:user) }
   let_it_be(:group) { create(:group) }
+  let_it_be(:group_2) { create(:group) }
   let_it_be(:source) { create(:epic, group: group) }
-  let_it_be(:target) { create(:epic, group: group) }
+  let_it_be(:target) { create(:epic, group: group_2) }
   let_it_be(:epic_link) { create(:related_epic_link, source: source, target: target) }
 
   let(:request) { EntityRequest.new(issuable: epic_link.source, current_user: user) }
@@ -18,9 +19,35 @@ RSpec.describe Epics::RelatedEpicEntity do
     group.add_developer(user)
   end
 
-  describe '#as_json' do
+  describe '#to_json' do
+    context 'when user can admin_epic on target epic group' do
+      before do
+        group_2.add_reporter(user)
+      end
+
       it 'matches json schema' do
         expect(entity.to_json).to match_schema('entities/related_epic', dir: 'ee')
       end
+
+      it 'returns relation_path' do
+        path = Gitlab::Routing.url_helpers.group_epic_related_epic_link_path(source.group, source.iid, epic_link.id)
+
+        expect(entity.as_json[:relation_path]).to eq(path)
+      end
+    end
+
+    context 'when user cannot admin_epic on target epic group' do
+      before do
+        group_2.add_guest(user)
+      end
+
+      it 'matches json schema' do
+        expect(entity.to_json).to match_schema('entities/related_epic', dir: 'ee')
+      end
+
+      it 'returns null relation_path' do
+        expect(entity.as_json[:relation_path]).to eq(nil)
+      end
+    end
   end
 end

ee/spec/services/ee/issue_links/create_service_spec.rb

@@ -50,27 +50,15 @@ RSpec.describe IssueLinks::CreateService do
         end
       end
 
-      it 'creates relationships' do
-        expect { subject }.to change(IssueLink, :count).from(0).to(2)
-
-        expect(IssueLink.find_by!(target: issue_a)).to have_attributes(source: issue, link_type: 'blocks')
-        expect(IssueLink.find_by!(target: another_project_issue)).to have_attributes(source: issue, link_type: 'blocks')
-      end
-
       it 'returns success status' do
         is_expected.to eq(status: :success)
       end
 
-      context 'when blocked_by relation is used' do
-        let(:params) do
-          { issuable_references: [issue_a_ref], link_type: 'is_blocked_by' }
-        end
-
-        it 'creates creates `blocks` relation with swapped source and target' do
-          expect { subject }.to change(IssueLink, :count).from(0).to(1)
-
-          expect(IssueLink.find_by!(source: issue_a)).to have_attributes(target: issue, link_type: 'blocks')
-        end
+      it_behaves_like 'issuable link creation with blocking link_type' do
+        let(:issuable_link_class) { IssueLink }
+        let(:issuable) { issue }
+        let(:issuable2) { issue_a }
+        let(:issuable3) { another_project_issue }
       end
     end
 

ee/spec/services/ee/system_notes/issuables_service_spec.rb

@@ -87,6 +87,17 @@ RSpec.describe ::SystemNotes::IssuablesService do
         subject
       end
     end
+
+    describe '#relate_issuable' do
+      let(:noteable) { epic }
+      let(:target) { create(:epic) }
+
+      it 'creates system notes when relating epics' do
+        result = service.relate_issuable(target)
+
+        expect(result.note).to eq("marked this epic as related to #{target.to_reference(target.group, full: true)}")
+      end
+    end
   end
 
   describe '#unrelate_issuable' do

ee/spec/services/epics/related_epic_links/create_service_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Epics::RelatedEpicLinks::CreateService do
+  describe '#execute' do
+    let_it_be(:user) { create :user }
+    let_it_be(:group) { create :group }
+    let_it_be(:issuable) { create :epic, group: group }
+    let_it_be(:issuable2) { create :epic, group: group }
+    let_it_be(:guest_issuable) { create :epic }
+    let_it_be(:another_group) { create :group }
+    let_it_be(:issuable3) { create :epic, group: another_group }
+    let_it_be(:issuable_a) { create :epic, group: group }
+    let_it_be(:issuable_b) { create :epic, group: group }
+    let_it_be(:issuable_link) { create :related_epic_link, source: issuable, target: issuable_b, link_type: IssuableLink::TYPE_RELATES_TO }
+
+    let(:issuable_parent) { issuable.group }
+    let(:issuable_type) { :epic }
+    let(:issuable_link_class) { Epic::RelatedEpicLink }
+    let(:params) { {} }
+
+    before do
+      stub_licensed_features(epics: true, related_epics: true)
+      group.add_developer(user)
+      guest_issuable.group.add_guest(user)
+      another_group.add_developer(user)
+    end
+
+    it_behaves_like 'issuable link creation'
+    it_behaves_like 'issuable link creation with blocking link_type' do
+      let(:params) do
+        { issuable_references: [issuable2.to_reference, issuable3.to_reference(issuable3.group, full: true)] }
+      end
+    end
+
+    context 'when related_epics is not available for target epic' do
+      let(:params) do
+        { issuable_references: [issuable3.to_reference(issuable3.group, full: true)] }
+      end
+
+      subject { described_class.new(issuable, user, params).execute }
+
+      before do
+        stub_licensed_features(epics: true, related_epics: false)
+        allow(issuable.group).to receive(:licensed_feature_available?).with(:related_epics).and_return(true)
+      end
+
+      it 'creates relationships' do
+        expect { subject }.to change(issuable_link_class, :count).by(1)
+
+        expect(issuable_link_class.find_by!(target: issuable3)).to have_attributes(source: issuable, link_type: 'relates_to')
+      end
+    end
+  end
+end

ee/spec/support/shared_examples/services/issuable_links/create_links_with_link_type.rb

+# frozen_string_literal: true
+
+shared_examples 'issuable link creation with blocking link_type' do
+  subject { described_class.new(issuable, user, params).execute }
+
+  context 'when is_blocked_by relation is used' do
+    before do
+      params[:link_type] = 'is_blocked_by'
+    end
+
+    it 'creates `blocks` relation with swapped source and target' do
+      expect { subject }.to change(issuable_link_class, :count).by(2)
+
+      expect(issuable_link_class.find_by!(source: issuable2)).to have_attributes(target: issuable, link_type: 'blocks')
+      expect(issuable_link_class.find_by!(source: issuable3)).to have_attributes(target: issuable, link_type: 'blocks')
+    end
+  end
+
+  context 'when blocks relation is used' do
+    before do
+      params[:link_type] = 'blocks'
+    end
+
+    it 'creates `blocks` relation' do
+      expect { subject }.to change(issuable_link_class, :count).by(2)
+
+      expect(issuable_link_class.find_by!(target: issuable2)).to have_attributes(source: issuable, link_type: 'blocks')
+      expect(issuable_link_class.find_by!(target: issuable3)).to have_attributes(source: issuable, link_type: 'blocks')
+    end
+  end
+end

locale/gitlab.pot

@@ -696,6 +696,9 @@ msgstr ""
 msgid "%{issuableType} will be removed! Are you sure?"
 msgstr ""
 
+msgid "%{issuable}(s) already assigned"
+msgstr ""
+
 msgid "%{issueType} actions"
 msgstr ""
 
@@ -20467,9 +20470,6 @@ msgstr ""
 msgid "Issue weight"
 msgstr ""
 
-msgid "Issue(s) already assigned"
-msgstr ""
-
 msgid "IssueAnalytics|Age"
 msgstr ""
 
@@ -24813,7 +24813,7 @@ msgstr ""
 msgid "No matches found"
 msgstr ""
 
-msgid "No matching issue found. Make sure that you are adding a valid issue URL."
+msgid "No matching %{issuable} found. Make sure that you are adding a valid %{issuable} URL."
 msgstr ""
 
 msgid "No matching labels"

spec/services/issue_links/create_service_spec.rb

@@ -4,181 +4,43 @@ require 'spec_helper'
 
 RSpec.describe IssueLinks::CreateService do
   describe '#execute' do
-    let(:namespace) { create :namespace }
-    let(:project) { create :project, namespace: namespace }
-    let(:issue) { create :issue, project: project }
-    let(:user) { create :user }
-    let(:params) do
-      {}
-    end
+    let_it_be(:user) { create :user }
+    let_it_be(:namespace) { create :namespace }
+    let_it_be(:project) { create :project, namespace: namespace }
+    let_it_be(:issuable) { create :issue, project: project }
+    let_it_be(:issuable2) { create :issue, project: project }
+    let_it_be(:guest_issuable) { create :issue }
+    let_it_be(:another_project) { create :project, namespace: project.namespace }
+    let_it_be(:issuable3) { create :issue, project: another_project }
+    let_it_be(:issuable_a) { create :issue, project: project }
+    let_it_be(:issuable_b) { create :issue, project: project }
+    let_it_be(:issuable_link) { create :issue_link, source: issuable, target: issuable_b, link_type: IssueLink::TYPE_RELATES_TO }
+
+    let(:issuable_parent) { issuable.project }
+    let(:issuable_type) { :issue }
+    let(:issuable_link_class) { IssueLink }
+    let(:params) { {} }
 
     before do
       project.add_developer(user)
-    end
-
-    subject { described_class.new(issue, user, params).execute }
-
-    context 'when the reference list is empty' do
-      let(:params) do
-        { issuable_references: [] }
-      end
-
-      it 'returns error' do
-        is_expected.to eq(message: 'No matching issue found. Make sure that you are adding a valid issue URL.', status: :error, http_status: 404)
-      end
-    end
-
-    context 'when Issue not found' do
-      let(:params) do
-        { issuable_references: ["##{non_existing_record_iid}"] }
-      end
-
-      it 'returns error' do
-        is_expected.to eq(message: 'No matching issue found. Make sure that you are adding a valid issue URL.', status: :error, http_status: 404)
-      end
-
-      it 'no relationship is created' do
-        expect { subject }.not_to change(IssueLink, :count)
-      end
-    end
-
-    context 'when user has no permission to target project Issue' do
-      let(:target_issuable) { create :issue }
-
-      let(:params) do
-        { issuable_references: [target_issuable.to_reference(project)] }
-      end
-
-      it 'returns error' do
-        target_issuable.project.add_guest(user)
-
-        is_expected.to eq(message: 'No matching issue found. Make sure that you are adding a valid issue URL.', status: :error, http_status: 404)
-      end
-
-      it 'no relationship is created' do
-        expect { subject }.not_to change(IssueLink, :count)
-      end
-    end
-
-    context 'source and target are the same issue' do
-      let(:params) do
-        { issuable_references: [issue.to_reference] }
-      end
-
-      it 'does not create notes' do
-        expect(SystemNoteService).not_to receive(:relate_issue)
-
-        subject
-      end
-
-      it 'no relationship is created' do
-        expect { subject }.not_to change(IssueLink, :count)
-      end
-    end
-
-    context 'when there is an issue to relate' do
-      let(:issue_a) { create :issue, project: project }
-      let(:another_project) { create :project, namespace: project.namespace }
-      let(:another_project_issue) { create :issue, project: another_project }
-
-      let(:issue_a_ref) { issue_a.to_reference }
-      let(:another_project_issue_ref) { another_project_issue.to_reference(project) }
-
-      let(:params) do
-        { issuable_references: [issue_a_ref, another_project_issue_ref] }
-      end
-
-      before do
+      guest_issuable.project.add_guest(user)
       another_project.add_developer(user)
     end
 
-      it 'creates relationships' do
-        expect { subject }.to change(IssueLink, :count).from(0).to(2)
-
-        expect(IssueLink.find_by!(target: issue_a)).to have_attributes(source: issue, link_type: 'relates_to')
-        expect(IssueLink.find_by!(target: another_project_issue)).to have_attributes(source: issue, link_type: 'relates_to')
-      end
-
-      it 'returns success status' do
-        is_expected.to eq(status: :success)
-      end
+    it_behaves_like 'issuable link creation'
 
-      it 'creates notes' do
-        # First two-way relation notes
-        expect(SystemNoteService).to receive(:relate_issue)
-          .with(issue, issue_a, user)
-        expect(SystemNoteService).to receive(:relate_issue)
-          .with(issue_a, issue, user)
+    context 'when target is an incident' do
+      let_it_be(:issue) { create(:incident, project: project) }
 
-        # Second two-way relation notes
-        expect(SystemNoteService).to receive(:relate_issue)
-          .with(issue, another_project_issue, user)
-        expect(SystemNoteService).to receive(:relate_issue)
-          .with(another_project_issue, issue, user)
-
-        subject
+      let(:params) do
+        { issuable_references: [issuable2.to_reference, issuable3.to_reference(another_project)] }
       end
 
-      context 'issue is an incident' do
-        let(:issue) { create(:incident, project: project) }
+      subject { described_class.new(issue, user, params).execute }
 
       it_behaves_like 'an incident management tracked event', :incident_management_incident_relate do
         let(:current_user) { user }
       end
     end
   end
-
-    context 'when reference of any already related issue is present' do
-      let(:issue_a) { create :issue, project: project }
-      let(:issue_b) { create :issue, project: project }
-      let(:issue_c) { create :issue, project: project }
-
-      before do
-        create :issue_link, source: issue, target: issue_b, link_type: IssueLink::TYPE_RELATES_TO
-        create :issue_link, source: issue, target: issue_c, link_type: IssueLink::TYPE_RELATES_TO
-      end
-
-      let(:params) do
-        {
-          issuable_references: [
-            issue_a.to_reference,
-            issue_b.to_reference,
-            issue_c.to_reference
-          ],
-          link_type: IssueLink::TYPE_RELATES_TO
-        }
-      end
-
-      it 'creates notes only for new relations' do
-        expect(SystemNoteService).to receive(:relate_issue).with(issue, issue_a, anything)
-        expect(SystemNoteService).to receive(:relate_issue).with(issue_a, issue, anything)
-        expect(SystemNoteService).not_to receive(:relate_issue).with(issue, issue_b, anything)
-        expect(SystemNoteService).not_to receive(:relate_issue).with(issue_b, issue, anything)
-        expect(SystemNoteService).not_to receive(:relate_issue).with(issue, issue_c, anything)
-        expect(SystemNoteService).not_to receive(:relate_issue).with(issue_c, issue, anything)
-
-        subject
-      end
-    end
-
-    context 'when there are invalid references' do
-      let(:issue_a) { create :issue, project: project }
-
-      let(:params) do
-        { issuable_references: [issue.to_reference, issue_a.to_reference] }
-      end
-
-      it 'creates links only for valid references' do
-        expect { subject }.to change { IssueLink.count }.by(1)
-      end
-
-      it 'returns error status' do
-        expect(subject).to eq(
-          status: :error,
-          http_status: 422,
-          message: "#{issue.to_reference} cannot be added: cannot be related to itself"
-        )
-      end
-    end
-  end
 end

spec/services/system_note_service_spec.rb

@@ -100,7 +100,7 @@ RSpec.describe SystemNoteService do
     end
   end
 
-  describe '.relate_issue' do
+  describe '.relate_issuable' do
     let(:noteable_ref) { double }
     let(:noteable) { double }
 
@@ -110,10 +110,10 @@ RSpec.describe SystemNoteService do
 
     it 'calls IssuableService' do
       expect_next_instance_of(::SystemNotes::IssuablesService) do |service|
-        expect(service).to receive(:relate_issue).with(noteable_ref)
+        expect(service).to receive(:relate_issuable).with(noteable_ref)
       end
 
-      described_class.relate_issue(noteable, noteable_ref, double)
+      described_class.relate_issuable(noteable, noteable_ref, double)
     end
   end
 

spec/services/system_notes/issuables_service_spec.rb

@@ -14,10 +14,10 @@ RSpec.describe ::SystemNotes::IssuablesService do
 
   let(:service) { described_class.new(noteable: noteable, project: project, author: author) }
 
-  describe '#relate_issue' do
+  describe '#relate_issuable' do
     let(:noteable_ref) { create(:issue) }
 
-    subject { service.relate_issue(noteable_ref) }
+    subject { service.relate_issuable(noteable_ref) }
 
     it_behaves_like 'a system note' do
       let(:action) { 'relate' }

spec/support/shared_examples/services/issuable_links/create_links_shared_examples.rb

+# frozen_string_literal: true
+
+shared_examples 'issuable link creation' do
+  describe '#execute' do
+    subject { described_class.new(issuable, user, params).execute }
+
+    context 'when the reference list is empty' do
+      let(:params) do
+        { issuable_references: [] }
+      end
+
+      it 'returns error' do
+        is_expected.to eq(message: "No matching #{issuable_type} found. Make sure that you are adding a valid #{issuable_type} URL.", status: :error, http_status: 404)
+      end
+    end
+
+    context 'when Issuable not found' do
+      let(:params) do
+        { issuable_references: ["##{non_existing_record_iid}"] }
+      end
+
+      it 'returns error' do
+        is_expected.to eq(message: "No matching #{issuable_type} found. Make sure that you are adding a valid #{issuable_type} URL.", status: :error, http_status: 404)
+      end
+
+      it 'no relationship is created' do
+        expect { subject }.not_to change(issuable_link_class, :count)
+      end
+    end
+
+    context 'when user has no permission to target issuable' do
+      let(:params) do
+        { issuable_references: [guest_issuable.to_reference(issuable_parent)] }
+      end
+
+      it 'returns error' do
+        is_expected.to eq(message: "No matching #{issuable_type} found. Make sure that you are adding a valid #{issuable_type} URL.", status: :error, http_status: 404)
+      end
+
+      it 'no relationship is created' do
+        expect { subject }.not_to change(issuable_link_class, :count)
+      end
+    end
+
+    context 'source and target are the same issuable' do
+      let(:params) do
+        { issuable_references: [issuable.to_reference] }
+      end
+
+      it 'does not create notes' do
+        expect(SystemNoteService).not_to receive(:relate_issuable)
+
+        subject
+      end
+
+      it 'no relationship is created' do
+        expect { subject }.not_to change(issuable_link_class, :count)
+      end
+    end
+
+    context 'when there is an issuable to relate' do
+      let(:params) do
+        { issuable_references: [issuable2.to_reference, issuable3.to_reference(issuable_parent)] }
+      end
+
+      it 'creates relationships' do
+        expect { subject }.to change(issuable_link_class, :count).by(2)
+
+        expect(issuable_link_class.find_by!(target: issuable2)).to have_attributes(source: issuable, link_type: 'relates_to')
+        expect(issuable_link_class.find_by!(target: issuable3)).to have_attributes(source: issuable, link_type: 'relates_to')
+      end
+
+      it 'returns success status' do
+        is_expected.to eq(status: :success)
+      end
+
+      it 'creates notes' do
+        # First two-way relation notes
+        expect(SystemNoteService).to receive(:relate_issuable)
+          .with(issuable, issuable2, user)
+        expect(SystemNoteService).to receive(:relate_issuable)
+          .with(issuable2, issuable, user)
+
+        # Second two-way relation notes
+        expect(SystemNoteService).to receive(:relate_issuable)
+          .with(issuable, issuable3, user)
+        expect(SystemNoteService).to receive(:relate_issuable)
+          .with(issuable3, issuable, user)
+
+        subject
+      end
+    end
+
+    context 'when reference of any already related issue is present' do
+      let(:params) do
+        {
+          issuable_references: [
+            issuable_a.to_reference,
+            issuable_b.to_reference
+          ],
+          link_type: IssueLink::TYPE_RELATES_TO
+        }
+      end
+
+      it 'creates notes only for new relations' do
+        expect(SystemNoteService).to receive(:relate_issuable).with(issuable, issuable_a, anything)
+        expect(SystemNoteService).to receive(:relate_issuable).with(issuable_a, issuable, anything)
+        expect(SystemNoteService).not_to receive(:relate_issuable).with(issuable, issuable_b, anything)
+        expect(SystemNoteService).not_to receive(:relate_issuable).with(issuable_b, issuable, anything)
+
+        subject
+      end
+    end
+
+    context 'when there are invalid references' do
+      let(:params) do
+        { issuable_references: [issuable.to_reference, issuable_a.to_reference] }
+      end
+
+      it 'creates links only for valid references' do
+        expect { subject }.to change { issuable_link_class.count }.by(1)
+      end
+
+      it 'returns error status' do
+        expect(subject).to eq(
+          status: :error,
+          http_status: 422,
+          message: "#{issuable.to_reference} cannot be added: cannot be related to itself"
+        )
+      end
+    end
+  end
+end