Use a Serializer for related issues/epics

Use serializers for:
- EpicLinks
- EpicIssueLinks
- IssueLinks

ee/app/serializers/linked_epic_entity.rb

+# frozen_string_literal: true
+
+class LinkedEpicEntity < Grape::Entity
+  include RequestAwareEntity
+
+  expose :id, :title, :state
+
+  expose :reference do |epic|
+    epic.to_reference(request.issuable.group)
+  end
+
+  expose :path do |epic|
+    group_epic_path(epic.group, epic)
+  end
+
+  expose :relation_path do |epic|
+    group_epic_link_path(epic.group, request.issuable.iid, epic.id)
+  end
+end

ee/app/serializers/linked_epic_issue_entity.rb

+# frozen_string_literal: true
+
+class LinkedEpicIssueEntity < LinkedIssueEntity
+  include RequestAwareEntity
+
+  expose :relation_path, override: true do |issue|
+    if can_admin_issue_link?(issue)
+      group_epic_issue_path(issuable.group, issuable.iid, issue.epic_issue_id)
+    end
+  end
+
+  expose :reference, override: true do |issue|
+    issue.to_reference(full: true)
+  end
+
+  expose :epic_issue_id
+
+  private
+
+  def can_admin_issue_link?(issue)
+    Ability.allowed?(current_user, :admin_epic_issue, issue) && Ability.allowed?(current_user, :admin_epic, issuable)
+  end
+end

ee/app/serializers/linked_epic_issue_serializer.rb

+# frozen_string_literal: true
+
+class LinkedEpicIssueSerializer < BaseSerializer
+  entity LinkedEpicIssueEntity
+end

ee/app/serializers/linked_epic_serializer.rb

+# frozen_string_literal: true
+
+class LinkedEpicSerializer < BaseSerializer
+  entity LinkedEpicEntity
+end

ee/app/serializers/linked_issue_entity.rb

+# frozen_string_literal: true
+
+class LinkedIssueEntity < Grape::Entity
+  include RequestAwareEntity
+
+  expose :id, :confidential, :title
+
+  expose :assignees, using: UserEntity
+
+  expose :state
+
+  expose :milestone, using: API::Entities::Milestone
+
+  expose :weight
+
+  expose :reference do |link|
+    link.to_reference(issuable.project)
+  end
+
+  expose :path do |link|
+    project_issue_path(link.project, link.iid)
+  end
+
+  expose :relation_path
+
+  expose :due_date, :created_at, :closed_at
+
+  private
+
+  def current_user
+    request.current_user
+  end
+
+  def issuable
+    request.issuable
+  end
+end

ee/app/serializers/linked_project_issue_entity.rb

+# frozen_string_literal: true
+
+class LinkedProjectIssueEntity < LinkedIssueEntity
+  include Gitlab::Utils::StrongMemoize
+
+  expose :relation_path, override: true do |issue|
+    # Make sure the user can admin both the current issue AND the
+    # referenced issue projects in order to return the removal link.
+    if can_admin_issue_link_on_current_project? && can_admin_issue_link?(issue.project)
+      project_issue_link_path(issuable.project, issuable.iid, issue.issue_link_id)
+    end
+  end
+
+  private
+
+  def can_admin_issue_link_on_current_project?
+    strong_memoize(:can_admin_on_current_project) do
+      can_admin_issue_link?(issuable.project)
+    end
+  end
+
+  def can_admin_issue_link?(project)
+    Ability.allowed?(current_user, :admin_issue_link, project)
+  end
+end

ee/app/serializers/linked_project_issue_serializer.rb

+# frozen_string_literal: true
+
+class LinkedProjectIssueSerializer < BaseSerializer
+  entity LinkedProjectIssueEntity
+end

ee/app/services/epic_issues/list_service.rb

@@ -2,6 +2,8 @@
 
 module EpicIssues
   class ListService < IssuableLinks::ListService
+    extend ::Gitlab::Utils::Override
+
     private
 
     def child_issuables
@@ -10,22 +12,9 @@ module EpicIssues
       issuable.issues_readable_by(current_user, preload: preload_for_collection)
     end
 
-    def relation_path(issue)
-      if can_admin_issue_link?(issue)
-        group_epic_issue_path(issuable.group, issuable.iid, issue.epic_issue_id)
-      end
-    end
-
-    def can_admin_issue_link?(issue)
-      Ability.allowed?(current_user, :admin_epic_issue, issue) && Ability.allowed?(current_user, :admin_epic, issuable)
-    end
-
-    def reference(issue)
-      issue.to_reference(full: true)
-    end
-
-    def to_hash(issue)
-      super.merge(epic_issue_id: issue.epic_issue_id)
+    override :serializer
+    def serializer
+      LinkedEpicIssueSerializer
     end
   end
 end

ee/app/services/epic_links/list_service.rb

@@ -2,6 +2,8 @@
 
 module EpicLinks
   class ListService < IssuableLinks::ListService
+    extend ::Gitlab::Utils::Override
+
     private
 
     def child_issuables
@@ -10,27 +12,9 @@ module EpicLinks
       EpicsFinder.new(current_user, parent_id: issuable.id, group_id: issuable.group.id).execute
     end
 
-    def reference(epic)
-      epic.to_reference(issuable.group)
-    end
-
-    def issuable_path(epic)
-      group_epic_path(epic.group, epic)
-    end
-
-    def relation_path(epic)
-      group_epic_link_path(epic.group, issuable.iid, epic.id)
-    end
-
-    def to_hash(object)
-      {
-        id: object.id,
-        title: object.title,
-        state: object.state,
-        reference: reference(object),
-        path: issuable_path(object),
-        relation_path: relation_path(object)
-      }
+    override :serializer
+    def serializer
+      LinkedEpicSerializer
     end
   end
 end

ee/app/services/issuable_links/list_service.rb

@@ -11,47 +11,17 @@ module IssuableLinks
     end
 
     def execute
-      child_issuables.map do |referenced_object|
-        to_hash(referenced_object)
-      end
+      serializer.new(current_user: current_user, issuable: issuable).represent(child_issuables)
     end
 
     private
 
-    def preload_for_collection
-      [{ project: :namespace }, :assignees]
-    end
-
-    def relation_path(object)
+    def serializer
       raise NotImplementedError
     end
 
-    def reference(object)
-      object.to_reference(issuable.project)
-    end
-
-    def issuable_path(object)
-      project_issue_path(object.project, object.iid)
-    end
-
-    # rubocop: disable CodeReuse/Serializer
-    def to_hash(object)
-      {
-        id: object.id,
-        confidential: object.confidential,
-        title: object.title,
-        assignees: UserSerializer.new.represent(object.assignees),
-        state: object.state,
-        milestone: MilestoneSerializer.new.represent(object.milestone),
-        weight: object.weight,
-        reference: reference(object),
-        path: issuable_path(object),
-        relation_path: relation_path(object),
-        due_date: object.due_date,
-        created_at: object.created_at,
-        closed_at: object.closed_at
-      }
+    def preload_for_collection
+      [{ project: :namespace }, :assignees]
     end
-    # rubocop: enable CodeReuse/Serializer
   end
 end

ee/app/services/issue_links/list_service.rb

@@ -2,7 +2,7 @@
 
 module IssueLinks
   class ListService < IssuableLinks::ListService
-    include Gitlab::Utils::StrongMemoize
+    extend ::Gitlab::Utils::Override
 
     private
 
@@ -10,26 +10,9 @@ module IssueLinks
       issuable.related_issues(current_user, preload: preload_for_collection)
     end
 
-    def relation_path(issue)
-      # Make sure the user can admin both the current issue AND the
-      # referenced issue projects in order to return the removal link.
-      if can_admin_issue_link_on_current_project? && can_admin_issue_link?(issue.project)
-        project_issue_link_path(current_project, issuable.iid, issue.issue_link_id)
-      end
-    end
-
-    def can_admin_issue_link_on_current_project?
-      strong_memoize(:can_admin_on_current_project) do
-        can_admin_issue_link?(current_project)
-      end
-    end
-
-    def can_admin_issue_link?(project)
-      Ability.allowed?(current_user, :admin_issue_link, project)
-    end
-
-    def current_project
-      issuable.project
+    override :serializer
+    def serializer
+      LinkedProjectIssueSerializer
     end
   end
 end