[Lens] Make field stats work for index patterns without time fields (#56759) (#57503)

* Fix field stats not loaded without time field

* Add integration test for API

* Add unit test for API call

* Correct typo in comment

x-pack/legacy/plugins/lens/public/indexpattern_plugin/field_item.test.tsx

@@ -90,6 +90,24 @@ describe('IndexPattern Field Item', () => {
     } as unknown) as FieldFormatsStart;
   });
 
+  it('should request field stats without a time field, if the index pattern has none', async () => {
+    indexPattern.timeFieldName = undefined;
+    core.http.post.mockImplementationOnce(() => {
+      return Promise.resolve({});
+    });
+    const wrapper = mountWithIntl(<FieldItem {...defaultProps} />);
+    wrapper.find('[data-test-subj="lnsFieldListPanelField-bytes"]').simulate('click');
+
+    expect(core.http.post).toHaveBeenCalledWith(
+      '/api/lens/index_stats/my-fake-index-pattern/field',
+      expect.anything()
+    );
+    // Function argument types not detected correctly (https://github.com/microsoft/TypeScript/issues/26591)
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const { body } = (core.http.post.mock.calls[0] as any)[1];
+    expect(JSON.parse(body)).not.toHaveProperty('timeFieldName');
+  });
+
   it('should request field stats every time the button is clicked', async () => {
     let resolveFunction: (arg: unknown) => void;
 

x-pack/legacy/plugins/lens/server/routes/field_stats.ts

@@ -27,7 +27,7 @@ export async function initFieldsRoute(setup: CoreSetup) {
             dslQuery: schema.object({}, { allowUnknowns: true }),
             fromDate: schema.string(),
             toDate: schema.string(),
-            timeFieldName: schema.string(),
+            timeFieldName: schema.maybe(schema.string()),
             field: schema.object(
               {
                 name: schema.string(),
@@ -46,9 +46,8 @@ export async function initFieldsRoute(setup: CoreSetup) {
       const { fromDate, toDate, timeFieldName, field, dslQuery } = req.body;
 
       try {
-        const query = {
-          bool: {
-            filter: [
+        const filter = timeFieldName
+          ? [
               {
                 range: {
                   [timeFieldName]: {
@@ -58,7 +57,12 @@ export async function initFieldsRoute(setup: CoreSetup) {
                 },
               },
               dslQuery,
-            ],
+            ]
+          : [dslQuery];
+
+        const query = {
+          bool: {
+            filter,
           },
         };
 

x-pack/test/api_integration/apis/lens/field_stats.ts

@@ -47,6 +47,24 @@ export default ({ getService }: FtrProviderContext) => {
           .expect(404);
       });
 
+      it('should also work without specifying a time field', async () => {
+        const { body } = await supertest
+          .post('/api/lens/index_stats/logstash-2015.09.22/field')
+          .set(COMMON_HEADERS)
+          .send({
+            dslQuery: { match_all: {} },
+            fromDate: TEST_START_TIME,
+            toDate: TEST_END_TIME,
+            field: {
+              name: 'bytes',
+              type: 'number',
+            },
+          })
+          .expect(200);
+
+        expect(body).to.have.property('totalDocuments', 4633);
+      });
+
       it('should return an auto histogram for numbers and top values', async () => {
         const { body } = await supertest
           .post('/api/lens/index_stats/logstash-2015.09.22/field')