Add GraphQL structure for DescendantWeightSum

- Add fields to GraphQL behind feature flag :unfiltered_epic_aggregates
- Return placeholders of -1 if the feature flag gets turned on

doc/api/graphql/reference/gitlab_schema.graphql

@@ -1862,6 +1862,12 @@ type Epic implements Noteable {
   """
   descendantCounts: EpicDescendantCount
 
+  """
+  Total weight of open and closed descendant epic's issues. Available only when
+  feature flag unfiltered_epic_aggregates is enabled.
+  """
+  descendantWeightSum: EpicDescendantWeights
+
   """
   Description of the epic
   """
@@ -2178,6 +2184,21 @@ type EpicDescendantCount {
   openedIssues: Int
 }
 
+"""
+Total weight of open and closed descendant issues
+"""
+type EpicDescendantWeights {
+  """
+  Total weight of completed (closed) issues in this epic, including epic descendants
+  """
+  closedIssues: Int
+
+  """
+  Total weight of opened issues in this epic, including epic descendants
+  """
+  openedIssues: Int
+}
+
 """
 An edge in a connection.
 """

doc/api/graphql/reference/index.md

@@ -294,6 +294,7 @@ Represents an epic.
 | `closedAt` | Time | Timestamp of the epic's closure |
 | `createdAt` | Time | Timestamp of the epic's creation |
 | `descendantCounts` | EpicDescendantCount | Number of open and closed descendant epics and issues |
+| `descendantWeightSum` | EpicDescendantWeights | Total weight of open and closed descendant epic's issues. Available only when feature flag unfiltered_epic_aggregates is enabled. |
 | `description` | String | Description of the epic |
 | `downvotes` | Int! | Number of downvotes the epic has received |
 | `dueDate` | Time | Due date of the epic |
@@ -334,6 +335,15 @@ Counts of descendent epics.
 | `openedEpics` | Int | Number of opened sub-epics |
 | `openedIssues` | Int | Number of opened epic issues |
 
+## EpicDescendantWeights
+
+Total weight of open and closed descendant issues
+
+| Name  | Type  | Description |
+| ---   |  ---- | ----------  |
+| `closedIssues` | Int | Total weight of completed (closed) issues in this epic, including epic descendants |
+| `openedIssues` | Int | Total weight of opened issues in this epic, including epic descendants |
+
 ## EpicIssue
 
 Relationship between an epic and an issue

ee/app/graphql/types/epic_descendant_weight_sum_type.rb

+# frozen_string_literal: true
+
+module Types
+  # rubocop: disable Graphql/AuthorizeTypes
+  class EpicDescendantWeightSumType < BaseObject
+    graphql_name 'EpicDescendantWeights'
+    description 'Total weight of open and closed descendant issues'
+
+    field :opened_issues, GraphQL::INT_TYPE, null: true,
+          description: 'Total weight of opened issues in this epic, including epic descendants'
+    field :closed_issues, GraphQL::INT_TYPE, null: true,
+          description: 'Total weight of completed (closed) issues in this epic, including epic descendants'
+  end
+  # rubocop: enable Graphql/AuthorizeTypes
+end

ee/app/graphql/types/epic_type.rb

@@ -121,10 +121,22 @@ module Types
           resolver: Resolvers::EpicIssuesResolver
 
     field :descendant_counts, Types::EpicDescendantCountType, null: true, complexity: 10,
-      description: 'Number of open and closed descendant epics and issues',
-      resolve: -> (epic, args, ctx) do
-        Epics::DescendantCountService.new(epic, ctx[:current_user])
-      end
+          description: 'Number of open and closed descendant epics and issues',
+          resolve: -> (epic, args, ctx) do
+            Epics::DescendantCountService.new(epic, ctx[:current_user])
+          end
+
+    field :descendant_weight_sum, Types::EpicDescendantWeightSumType, null: true, complexity: 10,
+          description: "Total weight of open and closed descendant epic's issues",
+          feature_flag: :unfiltered_epic_aggregates
+
+    def descendant_weight_sum
+      OpenStruct.new(
+        # We shouldn't stop the whole query, so returning -1 for a semi-noisy error
+        opened_issues: -1,
+        closed_issues: -1
+      )
+    end
 
     field :health_status,
       ::Types::HealthStatusEnum,

ee/spec/graphql/types/epic_descendant_weight_sum_type_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe GitlabSchema.types['EpicDescendantWeights'] do
+  it { expect(described_class.graphql_name).to eq('EpicDescendantWeights') }
+
+  it 'has specific fields' do
+    %i[opened_issues closed_issues].each do |field_name|
+      expect(described_class).to have_graphql_field(field_name)
+    end
+  end
+end

ee/spec/graphql/types/epic_type_spec.rb

@@ -11,7 +11,7 @@ describe GitlabSchema.types['Epic'] do
       closed_at created_at updated_at children has_children has_issues
       web_path web_url relation_path reference issues user_permissions
       notes discussions relative_position subscribed participants
-      descendant_counts upvotes downvotes health_status
+      descendant_counts descendant_weight_sum upvotes downvotes health_status
     ]
   end
 

ee/spec/requests/api/graphql/group/epic/epic_aggregate_query_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe 'Epic aggregates (count and weight)' do
+  include GraphqlHelpers
+
+  let_it_be(:current_user) { create(:user) }
+  let_it_be(:group) { create(:group, :public) }
+  let_it_be(:parent_epic) { create(:epic, id: 1, group: group, title: 'parent epic') }
+
+  let(:query) do
+    graphql_query_for('group', { fullPath: group.full_path }, query_graphql_field('epics', { iid: parent_epic.iid }, epic_aggregates_query))
+  end
+
+  let(:epic_aggregates_query) do
+    <<~QUERY
+        nodes {
+          descendantWeightSum {
+            openedIssues
+            closedIssues
+          }
+          descendantCounts {
+            openedEpics
+            closedEpics
+            openedIssues
+            closedIssues
+          }
+        }
+    QUERY
+  end
+
+  before do
+    stub_licensed_features(epics: true)
+  end
+
+  context 'with feature flag enabled' do
+    before do
+      stub_feature_flags(unfiltered_epic_aggregates: true)
+    end
+
+    it 'returns a placeholder with -1 weights and does not error' do
+      post_graphql(query, current_user: current_user)
+
+      actual_result = graphql_data.dig('group', 'epics', 'nodes').first
+      expected_result = {
+        "descendantWeightSum" => {
+          "openedIssues" => -1,
+          "closedIssues" => -1
+        }
+      }
+
+      expect(actual_result).to include expected_result
+    end
+  end
+
+  context 'with feature flag disabled' do
+    before do
+      stub_feature_flags(unfiltered_epic_aggregates: false)
+    end
+
+    context 'when requesting counts' do
+      let(:epic_aggregates_query) do
+        <<~QUERY
+        nodes {
+          descendantCounts {
+            openedEpics
+            closedEpics
+            openedIssues
+            closedIssues
+          }
+        }
+        QUERY
+      end
+
+      it 'uses the DescendantCountService' do
+        expect(Epics::DescendantCountService).to receive(:new)
+
+        post_graphql(query, current_user: current_user)
+      end
+    end
+
+    context 'when requesting weights' do
+      let(:epic_aggregates_query) do
+        <<~QUERY
+        nodes {
+          descendantWeightSum {
+            openedIssues
+            closedIssues
+          }
+        }
+        QUERY
+      end
+
+      it 'returns an error' do
+        post_graphql(query, current_user: current_user)
+
+        expect_graphql_errors_to_include /Field 'descendantWeightSum' doesn't exist on type 'Epic/
+      end
+    end
+  end
+end