Add milestone stats to GraphQL endpoint

This commit updates the milestone GraphQL type to allow statistics about
the milestone to be queried.

app/graphql/types/milestone_stats_type.rb

+# frozen_string_literal: true
+
+module Types
+  class MilestoneStatsType < BaseObject
+    graphql_name 'MilestoneStats'
+    description 'Contains statistics about a milestone'
+
+    authorize :read_milestone
+
+    field :total_issues_count, GraphQL::INT_TYPE, null: true,
+          description: 'Total number of issues associated with the milestone'
+
+    field :closed_issues_count, GraphQL::INT_TYPE, null: true,
+          description: 'Number of closed issues associated with the milestone'
+  end
+end

app/graphql/types/milestone_type.rb

@@ -9,6 +9,8 @@ module Types
 
     authorize :read_milestone
 
+    alias_method :milestone, :object
+
     field :id, GraphQL::ID_TYPE, null: false,
           description: 'ID of the milestone'
 
@@ -47,5 +49,14 @@ module Types
     field :subgroup_milestone, GraphQL::BOOLEAN_TYPE, null: false,
           description: 'Indicates if milestone is at subgroup level',
           method: :subgroup_milestone?
+
+    field :stats, Types::MilestoneStatsType, null: true,
+          description: 'Milestone statistics'
+
+    def stats
+      return unless Feature.enabled?(:graphql_milestone_stats, milestone.project || milestone.group, default_enabled: true)
+
+      milestone
+    end
   end
 end

changelogs/unreleased/nfriend-add-issue-stats-to-milestones-graphql.yml

+---
+title: Add milestone stats to GraphQL endpoint
+merge_request: 35066
+author:
+type: added

doc/api/graphql/reference/gitlab_schema.graphql

@@ -7676,6 +7676,11 @@ type Milestone {
   """
   state: MilestoneStateEnum!
 
+  """
+  Milestone statistics
+  """
+  stats: MilestoneStats
+
   """
   Indicates if milestone is at subgroup level
   """
@@ -7737,6 +7742,21 @@ enum MilestoneStateEnum {
   closed
 }
 
+"""
+Contains statistics about a milestone
+"""
+type MilestoneStats {
+  """
+  Number of closed issues associated with the milestone
+  """
+  closedIssuesCount: Int
+
+  """
+  Total number of issues associated with the milestone
+  """
+  totalIssuesCount: Int
+}
+
 """
 The position to which the adjacent object should be moved
 """

doc/api/graphql/reference/gitlab_schema.json

@@ -21487,6 +21487,20 @@
               "isDeprecated": false,
               "deprecationReason": null
             },
+            {
+              "name": "stats",
+              "description": "Milestone statistics",
+              "args": [
+
+              ],
+              "type": {
+                "kind": "OBJECT",
+                "name": "MilestoneStats",
+                "ofType": null
+              },
+              "isDeprecated": false,
+              "deprecationReason": null
+            },
             {
               "name": "subgroupMilestone",
               "description": "Indicates if milestone is at subgroup level",
@@ -21702,6 +21716,47 @@
           ],
           "possibleTypes": null
         },
+        {
+          "kind": "OBJECT",
+          "name": "MilestoneStats",
+          "description": "Contains statistics about a milestone",
+          "fields": [
+            {
+              "name": "closedIssuesCount",
+              "description": "Number of closed issues associated with the milestone",
+              "args": [
+
+              ],
+              "type": {
+                "kind": "SCALAR",
+                "name": "Int",
+                "ofType": null
+              },
+              "isDeprecated": false,
+              "deprecationReason": null
+            },
+            {
+              "name": "totalIssuesCount",
+              "description": "Total number of issues associated with the milestone",
+              "args": [
+
+              ],
+              "type": {
+                "kind": "SCALAR",
+                "name": "Int",
+                "ofType": null
+              },
+              "isDeprecated": false,
+              "deprecationReason": null
+            }
+          ],
+          "inputFields": null,
+          "interfaces": [
+
+          ],
+          "enumValues": null,
+          "possibleTypes": null
+        },
         {
           "kind": "ENUM",
           "name": "MoveType",

doc/api/graphql/reference/index.md

@@ -1180,11 +1180,21 @@ Represents a milestone.
 | `projectMilestone` | Boolean! | Indicates if milestone is at project level |
 | `startDate` | Time | Timestamp of the milestone start date |
 | `state` | MilestoneStateEnum! | State of the milestone |
+| `stats` | MilestoneStats | Milestone statistics |
 | `subgroupMilestone` | Boolean! | Indicates if milestone is at subgroup level |
 | `title` | String! | Title of the milestone |
 | `updatedAt` | Time! | Timestamp of last milestone update |
 | `webPath` | String! | Web path of the milestone |
 
+## MilestoneStats
+
+Contains statistics about a milestone
+
+| Name  | Type  | Description |
+| ---   |  ---- | ----------  |
+| `closedIssuesCount` | Int | Number of closed issues associated with the milestone |
+| `totalIssuesCount` | Int | Total number of issues associated with the milestone |
+
 ## Namespace
 
 | Name  | Type  | Description |

spec/graphql/types/milestone_stats_type_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe GitlabSchema.types['MilestoneStats'] do
+  it { expect(described_class).to require_graphql_authorizations(:read_milestone) }
+
+  it 'has the expected fields' do
+    expected_fields = %w[
+      total_issues_count closed_issues_count
+    ]
+
+    expect(described_class).to include_graphql_fields(*expected_fields)
+  end
+end

spec/graphql/types/milestone_type_spec.rb

@@ -6,4 +6,21 @@ RSpec.describe GitlabSchema.types['Milestone'] do
   specify { expect(described_class.graphql_name).to eq('Milestone') }
 
   specify { expect(described_class).to require_graphql_authorizations(:read_milestone) }
+
+  it 'has the expected fields' do
+    expected_fields = %w[
+      id title description state web_path
+      due_date start_date created_at updated_at
+      project_milestone group_milestone subgroup_milestone
+      stats
+    ]
+
+    expect(described_class).to have_graphql_fields(*expected_fields)
+  end
+
+  describe 'stats field' do
+    subject { described_class.fields['stats'] }
+
+    it { is_expected.to have_graphql_type(Types::MilestoneStatsType) }
+  end
 end

spec/requests/api/graphql/group/milestones_spec.rb

@@ -7,6 +7,8 @@ RSpec.describe 'Milestones through GroupQuery' do
 
   let_it_be(:user) { create(:user) }
   let_it_be(:now) { Time.now }
+
+  describe 'Get list of milestones from a group' do
     let_it_be(:group) { create(:group) }
     let_it_be(:milestone_1) { create(:milestone, group: group) }
     let_it_be(:milestone_2) { create(:milestone, group: group, state: :closed, start_date: now, due_date: now + 1.day) }
@@ -16,7 +18,6 @@ RSpec.describe 'Milestones through GroupQuery' do
 
     let(:milestone_data) { graphql_data['group']['milestones']['edges'] }
 
-  describe 'Get list of milestones from a group' do
     context 'when the request is correct' do
       before do
         fetch_milestones(user)
@@ -120,4 +121,89 @@ RSpec.describe 'Milestones through GroupQuery' do
       node_array(milestone_data, extract_attribute)
     end
   end
+
+  describe 'ensures each field returns the correct value' do
+    let_it_be(:group) { create(:group) }
+    let_it_be(:project) { create(:project, group: group) }
+    let_it_be(:milestone) { create(:milestone, group: group, start_date: now, due_date: now + 1.day) }
+    let_it_be(:open_issue) { create(:issue, project: project, milestone: milestone) }
+    let_it_be(:closed_issue) { create(:issue, :closed, project: project, milestone: milestone) }
+
+    let(:milestone_query) do
+      %{
+        id
+        title
+        description
+        state
+        webPath
+        dueDate
+        startDate
+        createdAt
+        updatedAt
+        projectMilestone
+        groupMilestone
+        subgroupMilestone
+      }
+    end
+
+    def post_query
+      full_query = graphql_query_for("group",
+        { full_path: group.full_path },
+        [query_graphql_field("milestones", nil, "nodes { #{milestone_query} }")]
+      )
+
+      post_graphql(full_query, current_user: user)
+
+      graphql_data.dig('group', 'milestones', 'nodes', 0)
+    end
+
+    it 'returns correct values for scalar fields' do
+      expect(post_query).to eq({
+        'id' => global_id_of(milestone),
+        'title' => milestone.title,
+        'description' => milestone.description,
+        'state' => 'active',
+        'webPath' => milestone_path(milestone),
+        'dueDate' => milestone.due_date.iso8601,
+        'startDate' => milestone.start_date.iso8601,
+        'createdAt' => milestone.created_at.iso8601,
+        'updatedAt' => milestone.updated_at.iso8601,
+        'projectMilestone' => false,
+        'groupMilestone' => true,
+        'subgroupMilestone' => false
+      })
+    end
+
+    context 'milestone statistics' do
+      let(:milestone_query) do
+        %{
+          stats {
+            totalIssuesCount
+            closedIssuesCount
+          }
+        }
+      end
+
+      it 'returns the correct milestone statistics' do
+        expect(post_query).to eq({
+          'stats' => {
+            'totalIssuesCount' => 2,
+            'closedIssuesCount' => 1
+          }
+        })
+      end
+
+      context 'when the graphql_milestone_stats feature flag is disabled' do
+        before do
+          stub_feature_flags(graphql_milestone_stats: false)
+        end
+
+        it 'returns nil for the stats field' do
+          expect(post_query).to eq({
+            'stats' => nil
+          })
+        end
+      end
+    end
+  end
 end