Allow fetching milestones of subgroups/subprojects

When includes_descendant parameter is passed, also milestones
from all subgroups and subprojects are returned but only
if visible to user.

app/graphql/resolvers/milestone_resolver.rb

@@ -9,6 +9,10 @@ module Resolvers
               required: false,
               description: 'Filter milestones by state'
 
+    argument :include_descendants, GraphQL::BOOLEAN_TYPE,
+              required: false,
+              description: 'Return also milestones in all subgroups and subprojects'
+
     type Types::MilestoneType, null: true
 
     def resolve(**args)
@@ -26,16 +30,16 @@ module Resolvers
         state: args[:state] || 'all',
         start_date: args[:start_date],
         end_date: args[:end_date]
-      }.merge(parent_id_parameter)
+      }.merge(parent_id_parameter(args))
     end
 
     def parent
       @parent ||= object.respond_to?(:sync) ? object.sync : object
     end
 
-    def parent_id_parameter
+    def parent_id_parameter(args)
       if parent.is_a?(Group)
-        { group_ids: parent.id }
+        group_parameters(args)
       elsif parent.is_a?(Project)
         { project_ids: parent.id }
       end
@@ -46,5 +50,26 @@ module Resolvers
     def authorize!
       Ability.allowed?(context[:current_user], :read_milestone, parent) || raise_resource_not_available_error!
     end
+
+    def group_parameters(args)
+      return { group_ids: parent.id } unless include_descendants?(args)
+
+      {
+        group_ids: parent.self_and_descendants.public_or_visible_to_user(current_user).select(:id),
+        project_ids: group_projects.with_issues_or_mrs_available_for_user(current_user)
+      }
+    end
+
+    def include_descendants?(args)
+      args[:include_descendants].present? && Feature.enabled?(:group_milestone_descendants, parent)
+    end
+
+    def group_projects
+      GroupProjectsFinder.new(
+        group: parent,
+        current_user: current_user,
+        options: { include_subgroups: true }
+      ).execute
+    end
   end
 end

doc/api/graphql/reference/gitlab_schema.graphql

@@ -4105,6 +4105,11 @@ type Group {
     """
     first: Int
 
+    """
+    Return also milestones in all subgroups and subprojects
+    """
+    includeDescendants: Boolean
+
     """
     Returns the last _n_ elements from the list.
     """

doc/api/graphql/reference/gitlab_schema.json

@@ -11425,6 +11425,16 @@
                   },
                   "defaultValue": null
                 },
+                {
+                  "name": "includeDescendants",
+                  "description": "Return also milestones in all subgroups and subprojects",
+                  "type": {
+                    "kind": "SCALAR",
+                    "name": "Boolean",
+                    "ofType": null
+                  },
+                  "defaultValue": null
+                },
                 {
                   "name": "after",
                   "description": "Returns the elements in the list that come after the specified cursor.",

spec/graphql/resolvers/milestone_resolver_spec.rb

@@ -8,14 +8,14 @@ describe Resolvers::MilestoneResolver do
   describe '#resolve' do
     let_it_be(:current_user) { create(:user) }
 
+    def resolve_group_milestones(args = {}, context = { current_user: current_user })
+      resolve(described_class, obj: group, args: args, ctx: context)
+    end
+
     context 'for group milestones' do
       let_it_be(:now) { Time.now }
       let_it_be(:group) { create(:group, :private) }
 
-      def resolve_group_milestones(args = {}, context = { current_user: current_user })
-        resolve(described_class, obj: group, args: args, ctx: context)
-      end
-
       before do
         group.add_developer(current_user)
       end
@@ -89,5 +89,25 @@ describe Resolvers::MilestoneResolver do
         end
       end
     end
+
+    context 'when including descendant milestones in a public group' do
+      let_it_be(:group) { create(:group, :public) }
+      let(:args) { { include_descendants: true } }
+
+      it 'finds milestones only in accessible projects and groups' do
+        accessible_group = create(:group, :private, parent: group)
+        accessible_project = create(:project, group: accessible_group)
+        accessible_group.add_developer(current_user)
+        inaccessible_group = create(:group, :private, parent: group)
+        inaccessible_project = create(:project, :private, group: group)
+        milestone1 = create(:milestone, group: group)
+        milestone2 = create(:milestone, group: accessible_group)
+        milestone3 = create(:milestone, project: accessible_project)
+        create(:milestone, group: inaccessible_group)
+        create(:milestone, project: inaccessible_project)
+
+        expect(resolve_group_milestones(args)).to match_array([milestone1, milestone2, milestone3])
+      end
+    end
   end
 end

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

@@ -7,7 +7,7 @@ describe 'Milestones through GroupQuery' do
 
   let_it_be(:user) { create(:user) }
   let_it_be(:now) { Time.now }
-  let_it_be(:group) { create(:group, :private) }
+  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) }
   let_it_be(:milestone_3) { create(:milestone, group: group, start_date: now, due_date: now + 2.days) }
@@ -17,10 +17,6 @@ describe 'Milestones through GroupQuery' do
   let(:milestone_data) { graphql_data['group']['milestones']['edges'] }
 
   describe 'Get list of milestones from a group' do
-    before do
-      group.add_developer(user)
-    end
-
     context 'when the request is correct' do
       before do
         fetch_milestones(user)
@@ -51,6 +47,48 @@ describe 'Milestones through GroupQuery' do
       end
     end
 
+    context 'when including milestones from decendants' do
+      let_it_be(:accessible_group) { create(:group, :private, parent: group) }
+      let_it_be(:accessible_project) { create(:project, group: accessible_group) }
+      let_it_be(:inaccessible_group) { create(:group, :private, parent: group) }
+      let_it_be(:inaccessible_project) { create(:project, :private, group: group) }
+      let_it_be(:submilestone_1) { create(:milestone, group: accessible_group) }
+      let_it_be(:submilestone_2) { create(:milestone, project: accessible_project) }
+      let_it_be(:submilestone_3) { create(:milestone, group: inaccessible_group) }
+      let_it_be(:submilestone_4) { create(:milestone, project: inaccessible_project) }
+
+      let(:args) { { include_descendants: true } }
+
+      before do
+        accessible_group.add_developer(user)
+      end
+
+      it 'returns milestones also from subgroups and subprojects visible to user' do
+        fetch_milestones(user, args)
+
+        expect_array_response(
+          milestone_1.to_global_id.to_s, milestone_2.to_global_id.to_s,
+          milestone_3.to_global_id.to_s, milestone_4.to_global_id.to_s,
+          submilestone_1.to_global_id.to_s, submilestone_2.to_global_id.to_s
+        )
+      end
+
+      context 'when group_milestone_descendants is disabled' do
+        before do
+          stub_feature_flags(group_milestone_descendants: false)
+        end
+
+        it 'ignores descendant milestones' do
+          fetch_milestones(user, args)
+
+          expect_array_response(
+            milestone_1.to_global_id.to_s, milestone_2.to_global_id.to_s,
+            milestone_3.to_global_id.to_s, milestone_4.to_global_id.to_s
+          )
+        end
+      end
+    end
+
     def fetch_milestones(user = nil, args = {})
       post_graphql(milestones_query(args), current_user: user)
     end