Expose 'blocked' attribute on epic issues endpoint

Expose blocked attribute on EpicIssuesController#Create
response.

EE: true
Changelog: other

app/services/issuable_links/list_service.rb

@@ -12,11 +12,16 @@ module IssuableLinks
     end
 
     def execute
-      serializer.new(current_user: current_user, issuable: issuable).represent(child_issuables)
+      serializer.new(current_user: current_user, issuable: issuable)
+        .represent(child_issuables, serializer_options)
     end
 
     private
 
+    def serializer_options
+      {}
+    end
+
     def serializer
       raise NotImplementedError
     end

ee/app/serializers/linked_epic_issue_entity.rb

@@ -15,6 +15,12 @@ class LinkedEpicIssueEntity < LinkedIssueEntity
 
   expose :epic_issue_id
 
+  with_options if: -> (_, options) { options[:blocked_issues_ids] } do
+    expose :blocked do |issue, options|
+      options[:blocked_issues_ids].include?(issue.id)
+    end
+  end
+
   private
 
   def can_admin_issue_link?(issue)

ee/app/services/epic_issues/list_service.rb

@@ -3,18 +3,30 @@
 module EpicIssues
   class ListService < IssuableLinks::ListService
     extend ::Gitlab::Utils::Override
+    include ::Gitlab::Utils::StrongMemoize
 
     private
 
     def child_issuables
-      return [] unless issuable&.group&.feature_available?(:epics)
+      strong_memoize(:child_issuables) do
+        next [] unless issuable&.group&.feature_available?(:epics)
 
-      issuable.issues_readable_by(current_user, preload: preload_for_collection)
+        issuable.issues_readable_by(current_user, preload: preload_for_collection)
+      end
     end
 
     override :serializer
     def serializer
       LinkedEpicIssueSerializer
     end
+
+    override :serializer_options
+    def serializer_options
+      child_issues_ids = child_issuables.map(&:id)
+
+      blocked_issues_ids = ::IssueLink.blocked_issue_ids(child_issues_ids)
+
+      super.merge(blocked_issues_ids: blocked_issues_ids)
+    end
   end
 end

ee/spec/services/epic_issues/list_service_spec.rb

@@ -36,6 +36,10 @@ RSpec.describe EpicIssues::ListService do
         stub_licensed_features(epics: true)
       end
 
+      before_all do
+        create(:issue_link, source: create(:issue), target: issue1, link_type: IssueLink::TYPE_BLOCKS)
+      end
+
       it 'does not have N+1 queries', :use_clean_rails_memory_store_caching, :request_store do
         # The control query is made with the worst case scenario:
         # * Two different issues from two different projects that belong to two different groups
@@ -61,6 +65,7 @@ RSpec.describe EpicIssues::ListService do
         milestone3 = create(:milestone, project: new_project)
         new_issue4 = create(:issue, project: new_project, milestone: milestone3)
         create(:epic_issue, issue: new_issue4, epic: epic, relative_position: 6)
+        create(:issue_link, source: create(:issue), target: issue2, link_type: IssueLink::TYPE_BLOCKS)
 
         expect { list_service.execute }.not_to exceed_query_limit(control_count)
       end
@@ -86,7 +91,8 @@ RSpec.describe EpicIssues::ListService do
               epic_issue_id: epic_issue2.id,
               due_date: nil,
               created_at: issue2.created_at,
-              closed_at: issue2.closed_at
+              closed_at: issue2.closed_at,
+              blocked: false
             },
             {
               id: issue1.id,
@@ -102,7 +108,8 @@ RSpec.describe EpicIssues::ListService do
               epic_issue_id: epic_issue1.id,
               due_date: nil,
               created_at: issue1.created_at,
-              closed_at: issue1.closed_at
+              closed_at: issue1.closed_at,
+              blocked: true
             },
             {
               id: issue3.id,
@@ -118,7 +125,8 @@ RSpec.describe EpicIssues::ListService do
               epic_issue_id: epic_issue3.id,
               due_date: nil,
               created_at: issue3.created_at,
-              closed_at: issue3.closed_at
+              closed_at: issue3.closed_at,
+              blocked: false
             }
           ]
 
@@ -147,7 +155,8 @@ RSpec.describe EpicIssues::ListService do
               epic_issue_id: epic_issue2.id,
               due_date: nil,
               created_at: issue2.created_at,
-              closed_at: issue2.closed_at
+              closed_at: issue2.closed_at,
+              blocked: false
             },
             {
               id: issue1.id,
@@ -163,7 +172,8 @@ RSpec.describe EpicIssues::ListService do
               epic_issue_id: epic_issue1.id,
               due_date: nil,
               created_at: issue1.created_at,
-              closed_at: issue1.closed_at
+              closed_at: issue1.closed_at,
+              blocked: true
             }
           ]