Chore: Expression engine to support relative time range (#57474)

* make TimeRange interface and add relative range
* make Execute methods support the current time
* update resample to support relative time range
* update DSNode to support relative time range
* update query service to create queries with absolute time
* make alerting evaluator create relative time ranges

pkg/services/ngalert/eval/eval.go

@@ -215,10 +215,7 @@ func getExprRequest(ctx EvaluationContext, data []models.AlertQuery, dsCacheServ
 		}
 
 		req.Queries = append(req.Queries, expr.Query{
-			TimeRange: expr.TimeRange{
-				From: q.RelativeTimeRange.ToTimeRange(ctx.At).From,
-				To:   q.RelativeTimeRange.ToTimeRange(ctx.At).To,
-			},
+			TimeRange:     q.RelativeTimeRange.ToTimeRange(),
 			DataSource:    ds,
 			JSON:          model,
 			Interval:      interval,
@@ -334,7 +331,7 @@ func executeQueriesAndExpressions(ctx EvaluationContext, data []models.AlertQuer
 		return nil, err
 	}
 
-	return exprService.TransformData(ctx.Ctx, queryDataReq)
+	return exprService.TransformData(ctx.Ctx, ctx.At, queryDataReq)
 }
 
 // datasourceUIDsToRefIDs returns a sorted slice of Ref IDs for each Datasource UID.

pkg/services/ngalert/models/alert_query.go

@@ -6,7 +6,6 @@ import (
 	"fmt"
 	"time"
 
-	"github.com/grafana/grafana-plugin-sdk-go/backend"
 	"github.com/grafana/grafana/pkg/expr"
 )
 
@@ -70,10 +69,10 @@ func (rtr *RelativeTimeRange) isValid() bool {
 	return rtr.From > rtr.To
 }
 
-func (rtr *RelativeTimeRange) ToTimeRange(now time.Time) backend.TimeRange {
-	return backend.TimeRange{
-		From: now.Add(-time.Duration(rtr.From)),
-		To:   now.Add(-time.Duration(rtr.To)),
+func (rtr *RelativeTimeRange) ToTimeRange() expr.TimeRange {
+	return expr.RelativeTimeRange{
+		From: -time.Duration(rtr.From),
+		To:   -time.Duration(rtr.To),
 	}
 }