Jaeger: Show a better error msg if no service is selected when using search (#54172)

public/app/plugins/datasource/jaeger/datasource.test.ts

@@ -135,6 +135,17 @@ describe('JaegerDatasource', () => {
     expect(response.data[0].fields[0].name).toBe('traceID');
   });
 
+  it('should show the correct error message if no service name is selected', async () => {
+    const ds = new JaegerDatasource(defaultSettings, timeSrvStub);
+    const response = await lastValueFrom(
+      ds.query({
+        ...defaultQuery,
+        targets: [{ queryType: 'search', refId: 'a', service: undefined, operation: '/api/services' }],
+      })
+    );
+    expect(response.error?.message).toBe('You must select a service.');
+  });
+
   it('should remove operation from the query when all is selected', async () => {
     const mock = setupFetchMock({ data: [testResponse] });
     const ds = new JaegerDatasource(defaultSettings, timeSrvStub);

public/app/plugins/datasource/jaeger/datasource.ts

@@ -48,14 +48,23 @@ export class JaegerDatasource extends DataSourceApi<JaegerQuery, JaegerJsonData>
     return res.data.data;
   }
 
+  isSearchFormValid(query: JaegerQuery): boolean {
+    return !!query.service;
+  }
+
   query(options: DataQueryRequest<JaegerQuery>): Observable<DataQueryResponse> {
     // At this moment we expect only one target. In case we somehow change the UI to be able to show multiple
     // traces at one we need to change this.
     const target: JaegerQuery = options.targets[0];
+
     if (!target) {
       return of({ data: [emptyTraceDataFrame] });
     }
 
+    if (target.queryType === 'search' && !this.isSearchFormValid(target)) {
+      return of({ error: { message: 'You must select a service.' }, data: [] });
+    }
+
     if (target.queryType !== 'search' && target.query) {
       return this._request(
         `/api/traces/${encodeURIComponent(this.templateSrv.replace(target.query, options.scopedVars))}`