Expressions: Add support for variables (#41778)

public/app/features/expressions/ExpressionDatasource.ts

@@ -1,8 +1,16 @@
-import { DataSourceInstanceSettings, DataSourcePluginMeta, PluginType } from '@grafana/data';
+import {
+  DataQueryRequest,
+  DataQueryResponse,
+  DataSourceInstanceSettings,
+  DataSourcePluginMeta,
+  PluginType,
+  ScopedVars,
+} from '@grafana/data';
 import { ExpressionQuery, ExpressionQueryType } from './types';
 import { ExpressionQueryEditor } from './ExpressionQueryEditor';
-import { DataSourceWithBackend } from '@grafana/runtime';
+import { DataSourceWithBackend, getDataSourceSrv, getTemplateSrv } from '@grafana/runtime';
 import { ExpressionDatasourceRef } from '@grafana/runtime/src/utils/DataSourceWithBackend';
+import { Observable, from, mergeMap } from 'rxjs';
 
 /**
  * This is a singleton instance that just pretends to be a DataSource
@@ -12,10 +20,34 @@ export class ExpressionDatasourceApi extends DataSourceWithBackend<ExpressionQue
     super(instanceSettings);
   }
 
+  applyTemplateVariables(query: ExpressionQuery, scopedVars: ScopedVars): Record<string, any> {
+    const templateSrv = getTemplateSrv();
+    return {
+      ...query,
+      expression: templateSrv.replace(query.expression, scopedVars),
+      window: templateSrv.replace(query.window, scopedVars),
+    };
+  }
+
   getCollapsedText(query: ExpressionQuery) {
     return `Expression: ${query.type}`;
   }
 
+  query(request: DataQueryRequest<ExpressionQuery>): Observable<DataQueryResponse> {
+    let targets = request.targets.map(async (query: ExpressionQuery): Promise<ExpressionQuery> => {
+      const ds = await getDataSourceSrv().get(query.datasource);
+
+      if (!ds.interpolateVariablesInQueries) {
+        return query;
+      }
+
+      return ds?.interpolateVariablesInQueries([query], {})[0] as ExpressionQuery;
+    });
+
+    let sub = from(Promise.all(targets));
+    return sub.pipe(mergeMap((t) => super.query({ ...request, targets: t })));
+  }
+
   newQuery(query?: Partial<ExpressionQuery>): ExpressionQuery {
     return {
       refId: '--', // Replaced with query