loki: handle ad hoc filters in backend mode (#50135)

* loki: handle ad hoc filters in backend mode

* devenv: better loki fake data

* added test

devenv/docker/blocks/loki/data/data.js

@@ -125,8 +125,8 @@ async function main() {
     await sleep(getNextSineWaveSleepDuration());
     const timestampMs = new Date().getTime();
     const item = getRandomLogItem(step + 1)
-    lokiSendLogLine(timestampMs, JSON.stringify(item), {place:'moon'});
-    lokiSendLogLine(timestampMs, logFmtLine(item), {place:'luna'});
+    lokiSendLogLine(timestampMs, JSON.stringify(item), {place:'moon', source: 'data'});
+    lokiSendLogLine(timestampMs, logFmtLine(item), {place:'luna', source: 'data'});
   }
 }
 

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

@@ -1058,6 +1058,15 @@ describe('isMetricsQuery', () => {
   });
 });
 
+describe('applyTemplateVariables', () => {
+  it('should add the adhoc filter to the query', () => {
+    const ds = createLokiDSForTests();
+    const spy = jest.spyOn(ds, 'addAdHocFilters');
+    ds.applyTemplateVariables({ expr: '{test}', refId: 'A' }, {});
+    expect(spy).toHaveBeenCalledWith('{test}');
+  });
+});
+
 function assertAdHocFilters(query: string, expectedResults: string, ds: LokiDatasource) {
   const lokiQuery: LokiQuery = { refId: 'A', expr: query };
   const result = ds.addAdHocFilters(lokiQuery.expr);

public/app/plugins/datasource/loki/datasource.ts

@@ -887,10 +887,12 @@ export class LokiDatasource
     // We want to interpolate these variables on backend
     const { __interval, __interval_ms, ...rest } = scopedVars;
 
+    const exprWithAdHoc = this.addAdHocFilters(target.expr);
+
     return {
       ...target,
       legendFormat: this.templateSrv.replace(target.legendFormat, rest),
-      expr: this.templateSrv.replace(target.expr, rest, this.interpolateQueryExpr),
+      expr: this.templateSrv.replace(exprWithAdHoc, rest, this.interpolateQueryExpr),
     };
   }