Add `include_subgroups` to GraphQL Issues

`include_subgroups` is necessary if we want issues belonging to
subgroups returned in the result.

app/graphql/resolvers/group_issues_resolver.rb

+# frozen_string_literal: true
+
+module Resolvers
+  class GroupIssuesResolver < IssuesResolver
+    argument :include_subgroups, GraphQL::BOOLEAN_TYPE,
+             required: false,
+             default_value: false,
+             description: 'Include issues belonging to subgroups.'
+  end
+end

app/graphql/types/group_type.rb

@@ -47,7 +47,7 @@ module Types
           Types::IssueType.connection_type,
           null: true,
           description: 'Issues of the group',
-          resolver: Resolvers::IssuesResolver
+          resolver: Resolvers::GroupIssuesResolver
 
     field :milestones, Types::MilestoneType.connection_type, null: true,
           description: 'Milestones of the group',

changelogs/unreleased/229433-graphql-issue-subgroup.yml

+---
+title: 'GraphQL: Issues - Added ''include_subgroup'' parameter'
+merge_request: 39279
+author:
+type: added

doc/api/graphql/reference/gitlab_schema.graphql

@@ -5928,6 +5928,11 @@ type Group {
     """
     iids: [String!]
 
+    """
+    Include issues belonging to subgroups.
+    """
+    includeSubgroups: Boolean = false
+
     """
     Iterations applied to the issue
     """

doc/api/graphql/reference/gitlab_schema.json

@@ -16521,6 +16521,16 @@
                   },
                   "defaultValue": null
                 },
+                {
+                  "name": "includeSubgroups",
+                  "description": "Include issues belonging to subgroups.",
+                  "type": {
+                    "kind": "SCALAR",
+                    "name": "Boolean",
+                    "ofType": null
+                  },
+                  "defaultValue": "false"
+                },
                 {
                   "name": "after",
                   "description": "Returns the elements in the list that come after the specified cursor.",

spec/graphql/resolvers/group_issues_resolver_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Resolvers::GroupIssuesResolver do
+  include GraphqlHelpers
+
+  let_it_be(:current_user) { create(:user) }
+
+  let_it_be(:group)         { create(:group) }
+  let_it_be(:project)       { create(:project, group: group) }
+  let_it_be(:other_project) { create(:project, group: group) }
+  let_it_be(:subgroup)      { create(:group, parent: group) }
+  let_it_be(:subproject)    { create(:project, group: subgroup) }
+
+  let_it_be(:issue1)    { create(:incident, project: project, state: :opened, created_at: 3.hours.ago, updated_at: 3.hours.ago) }
+  let_it_be(:issue2)    { create(:issue, project: project, state: :closed, title: 'foo', created_at: 1.hour.ago, updated_at: 1.hour.ago, closed_at: 1.hour.ago) }
+  let_it_be(:issue3)    { create(:issue, project: other_project, state: :closed, title: 'foo', created_at: 1.hour.ago, updated_at: 1.hour.ago, closed_at: 1.hour.ago) }
+  let_it_be(:issue4)    { create(:issue) }
+
+  let_it_be(:subissue1) { create(:issue, project: subproject) }
+  let_it_be(:subissue2) { create(:issue, project: subproject) }
+  let_it_be(:subissue3) { create(:issue, project: subproject) }
+
+  before_all do
+    group.add_developer(current_user)
+    subgroup.add_developer(current_user)
+  end
+
+  describe '#resolve' do
+    it 'finds all group issues' do
+      result = resolve(described_class, obj: group, ctx: { current_user: current_user })
+
+      expect(result).to contain_exactly(issue1, issue2, issue3)
+    end
+
+    it 'finds all group and subgroup issues' do
+      result = resolve(described_class, obj: group, args: { include_subgroups: true }, ctx: { current_user: current_user })
+
+      expect(result).to contain_exactly(issue1, issue2, issue3, subissue1, subissue2, subissue3)
+    end
+  end
+end