Prometheus: Fix calculating rate interval when there is no interval specified (#78193)

* Use data source scrape interval when no interval is specified

* scrape interval as 15s

pkg/tsdb/prometheus/models/query.go

@@ -96,6 +96,7 @@ func Parse(query backend.DataQuery, dsScrapeInterval string, intervalCalculator
 		query.Interval,
 		calculatedMinStep,
 		model.Interval,
+		dsScrapeInterval,
 		timeRange,
 	)
 	var rangeQuery, instantQuery bool
@@ -227,12 +228,14 @@ func calculateRateInterval(
 // queryInterval                Requested interval in milliseconds. This value may be overridden by MinStep in query options
 // calculatedMinStep            Calculated final step value. It was calculated in calculatePrometheusInterval
 // requestedMinStep             Requested minimum step value. QueryModel.interval
+// dsScrapeInterval             Data source scrape interval in the config
 // timeRange                    Requested time range for query
 func interpolateVariables(
 	expr string,
 	queryInterval time.Duration,
 	calculatedMinStep time.Duration,
 	requestedMinStep string,
+	dsScrapeInterval string,
 	timeRange time.Duration,
 ) string {
 	rangeMs := timeRange.Milliseconds()
@@ -245,6 +248,9 @@ func interpolateVariables(
 		if requestedMinStep == varInterval || requestedMinStep == varIntervalAlt {
 			requestedMinStep = calculatedMinStep.String()
 		}
+		if requestedMinStep == "" {
+			requestedMinStep = dsScrapeInterval
+		}
 		rateInterval = calculateRateInterval(queryInterval, requestedMinStep)
 	}
 

pkg/tsdb/prometheus/models/query_test.go

@@ -571,7 +571,7 @@ func TestRateInterval(t *testing.T) {
 				},
 			},
 			want: &models.Query{
-				Expr: "rate(rpc_durations_seconds_count[2m30s])",
+				Expr: "rate(rpc_durations_seconds_count[2m0s])",
 				Step: time.Second * 30,
 			},
 		},
@@ -637,6 +637,75 @@ func TestRateInterval(t *testing.T) {
 			require.Equal(t, tt.want.Step, res.Step)
 		})
 	}
+
+	t.Run("minStep is auto and ds scrape interval 30s and time range 1 hour", func(t *testing.T) {
+		query := backend.DataQuery{
+			RefID:         "G",
+			QueryType:     "",
+			MaxDataPoints: 1613,
+			Interval:      30 * time.Second,
+			TimeRange: backend.TimeRange{
+				From: now,
+				To:   now.Add(1 * time.Hour),
+			},
+			JSON: []byte(`{
+			"datasource":{"type":"prometheus","uid":"zxS5e5W4k"},
+			"datasourceId":38,
+			"editorMode":"code",
+			"exemplar":false,
+			"expr":"sum(rate(process_cpu_seconds_total[$__rate_interval]))",
+			"instant":false,
+			"interval":"",
+			"intervalMs":30000,
+			"key":"Q-f96b6729-c47a-4ea8-8f71-a79774cf9bd5-0",
+			"legendFormat":"__auto",
+			"maxDataPoints":1613,
+			"range":true,
+			"refId":"G",
+			"requestId":"1G",
+			"utcOffsetSec":3600
+		}`),
+		}
+		res, err := models.Parse(query, "30s", intervalCalculator, false)
+		require.NoError(t, err)
+		require.Equal(t, "sum(rate(process_cpu_seconds_total[2m0s]))", res.Expr)
+		require.Equal(t, 30*time.Second, res.Step)
+	})
+
+	t.Run("minStep is auto and ds scrape interval 15s and time range 5 minutes", func(t *testing.T) {
+		query := backend.DataQuery{
+			RefID:         "A",
+			QueryType:     "",
+			MaxDataPoints: 1055,
+			Interval:      15 * time.Second,
+			TimeRange: backend.TimeRange{
+				From: now,
+				To:   now.Add(5 * time.Minute),
+			},
+			JSON: []byte(`{
+			"datasource": {
+		        "type": "prometheus",
+		        "uid": "2z9d6ElGk"
+		    },
+		    "editorMode": "code",
+		    "expr": "sum(rate(cache_requests_total[$__rate_interval]))",
+		    "legendFormat": "__auto",
+		    "range": true,
+		    "refId": "A",
+		    "exemplar": false,
+		    "requestId": "1A",
+		    "utcOffsetSec": 0,
+		    "interval": "",
+		    "datasourceId": 508,
+		    "intervalMs": 15000,
+		    "maxDataPoints": 1055
+		}`),
+		}
+		res, err := models.Parse(query, "15s", intervalCalculator, false)
+		require.NoError(t, err)
+		require.Equal(t, "sum(rate(cache_requests_total[1m0s]))", res.Expr)
+		require.Equal(t, 15*time.Second, res.Step)
+	})
 }
 
 func mockQuery(expr string, interval string, intervalMs int64, timeRange *backend.TimeRange) backend.DataQuery {
@@ -647,7 +716,7 @@ func mockQuery(expr string, interval string, intervalMs int64, timeRange *backen
 		}
 	}
 	return backend.DataQuery{
-		Interval: 2 * time.Minute,
+		Interval: time.Duration(intervalMs) * time.Millisecond,
 		JSON: []byte(fmt.Sprintf(`{
 			"expr": "%s",
 			"format": "time_series",