Add a top-level GraphQL query for an iteration

This makes it easier to query a single iteration by ID regardless of
it being a project or group iteration

doc/api/graphql/reference/gitlab_schema.graphql

@@ -4313,6 +4313,11 @@ type DismissVulnerabilityPayload {
   vulnerability: Vulnerability
 }
 
+"""
+Identifier of EE::Iteration
+"""
+scalar EEIterationID
+
 interface Entry {
   """
   Flat path of the entry
@@ -12096,6 +12101,16 @@ type Query {
   """
   instanceSecurityDashboard: InstanceSecurityDashboard
 
+  """
+  Find an iteration
+  """
+  iteration(
+    """
+    Find an iteration by its ID
+    """
+    id: EEIterationID!
+  ): Iteration
+
   """
   Metadata about GitLab
   """

doc/api/graphql/reference/gitlab_schema.json

@@ -12009,6 +12009,16 @@
           "enumValues": null,
           "possibleTypes": null
         },
+        {
+          "kind": "SCALAR",
+          "name": "EEIterationID",
+          "description": "Identifier of EE::Iteration",
+          "fields": null,
+          "inputFields": null,
+          "interfaces": null,
+          "enumValues": null,
+          "possibleTypes": null
+        },
         {
           "kind": "INTERFACE",
           "name": "Entry",
@@ -35598,6 +35608,33 @@
               "isDeprecated": false,
               "deprecationReason": null
             },
+            {
+              "name": "iteration",
+              "description": "Find an iteration",
+              "args": [
+                {
+                  "name": "id",
+                  "description": "Find an iteration by its ID",
+                  "type": {
+                    "kind": "NON_NULL",
+                    "name": null,
+                    "ofType": {
+                      "kind": "SCALAR",
+                      "name": "EEIterationID",
+                      "ofType": null
+                    }
+                  },
+                  "defaultValue": null
+                }
+              ],
+              "type": {
+                "kind": "OBJECT",
+                "name": "Iteration",
+                "ofType": null
+              },
+              "isDeprecated": false,
+              "deprecationReason": null
+            },
             {
               "name": "metadata",
               "description": "Metadata about GitLab",

ee/app/graphql/ee/types/query_type.rb

@@ -6,6 +6,15 @@ module EE
       extend ActiveSupport::Concern
 
       prepended do
+        field :iteration, ::Types::IterationType,
+              null: true,
+              resolve: -> (_obj, args, _ctx) { ::GitlabSchema.find_by_gid(args[:id]) },
+              description: 'Find an iteration' do
+          argument :id, ::Types::GlobalIDType[Iteration],
+                   required: true,
+                   description: 'Find an iteration by its ID'
+        end
+
         field :vulnerabilities,
               ::Types::VulnerabilityType.connection_type,
               null: true,

ee/changelogs/unreleased/graphql-iterations-top-level.yml

+---
+title: Add GraphQL query for a single iteration
+merge_request: 38692
+author:
+type: added

ee/spec/graphql/types/query_type_spec.rb

@@ -5,6 +5,7 @@ require 'spec_helper'
 RSpec.describe GitlabSchema.types['Query'] do
   specify do
     expect(described_class).to have_graphql_fields(
+      :iteration,
       :geo_node,
       :vulnerabilities,
       :instance_security_dashboard,

ee/spec/requests/api/graphql/iteration_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe 'Querying an Iteration' do
+  include GraphqlHelpers
+
+  let_it_be(:current_user) { create(:user) }
+  let_it_be(:group) { create(:group, :private) }
+  let_it_be(:iteration) { create(:iteration, group: group) }
+
+  let(:query) do
+    graphql_query_for('iteration', { id: iteration.to_global_id.to_s }, 'title')
+  end
+
+  subject { graphql_data['iteration'] }
+
+  before do
+    post_graphql(query, current_user: current_user)
+  end
+
+  context 'when the user has access to the iteration' do
+    before_all do
+      group.add_guest(current_user)
+    end
+
+    it_behaves_like 'a working graphql query'
+
+    it { is_expected.to include('title' => iteration.name) }
+  end
+
+  context 'when the user does not have access to the iteration' do
+    it_behaves_like 'a working graphql query'
+
+    it { is_expected.to be_nil }
+  end
+
+  context 'when ID argument is missing' do
+    let(:query) do
+      graphql_query_for('iteration', {}, 'title')
+    end
+
+    it 'raises an exception' do
+      expect(graphql_errors).to include(a_hash_including('message' => "Field 'iteration' is missing required arguments: id"))
+    end
+  end
+end