Datasource: Use intervalMs field of query model in GetIntervalFrom if interval field is not set (#34270)

The /api/ds/query and /api/tsdb/query endpoints extract the intervalMs field from
each query in the request, but it currently seems to be ignored, at
least for queries to a Prometheus datasource. This changes
GetIntervalFrom function to check for the presence of intervalMs in the
query model if interval is missing.

pkg/tsdb/interval/interval.go

@@ -69,6 +69,15 @@ func (ic *intervalCalculator) Calculate(timerange plugins.DataTimeRange, minInte
 func GetIntervalFrom(dsInfo *models.DataSource, queryModel *simplejson.Json, defaultInterval time.Duration) (time.Duration, error) {
 	interval := queryModel.Get("interval").MustString("")
 
+	// intervalMs field appears in the v2 plugins API and should be preferred
+	// if 'interval' isn't present.
+	if interval == "" {
+		intervalMS := queryModel.Get("intervalMs").MustInt(0)
+		if intervalMS != 0 {
+			return time.Duration(intervalMS) * time.Millisecond, nil
+		}
+	}
+
 	if interval == "" && dsInfo != nil && dsInfo.JsonData != nil {
 		dsInterval := dsInfo.JsonData.Get("timeInterval").MustString("")
 		if dsInterval != "" {

pkg/tsdb/interval/interval_test.go

@@ -8,6 +8,7 @@ import (
 	"github.com/grafana/grafana/pkg/models"
 	"github.com/grafana/grafana/pkg/plugins"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestIntervalCalculator_Calculate(t *testing.T) {
@@ -70,6 +71,8 @@ func TestFormatDuration(t *testing.T) {
 }
 
 func TestGetIntervalFrom(t *testing.T) {
+	dsJSON, err := simplejson.NewJson([]byte(`{"timeInterval": "60s"}`))
+	require.NoError(t, err)
 	testCases := []struct {
 		name            string
 		dsInfo          *models.DataSource
@@ -80,6 +83,13 @@ func TestGetIntervalFrom(t *testing.T) {
 		{"45s", nil, `{"interval": "45s"}`, time.Second * 15, time.Second * 45},
 		{"45", nil, `{"interval": "45"}`, time.Second * 15, time.Second * 45},
 		{"2m", nil, `{"interval": "2m"}`, time.Second * 15, time.Minute * 2},
+		{"intervalMs", nil, `{"intervalMs": 45000}`, time.Second * 15, time.Second * 45},
+		{"intervalMs sub-seconds", nil, `{"intervalMs": 45200}`, time.Second * 15, time.Millisecond * 45200},
+		{"dsInfo timeInterval", &models.DataSource{
+			JsonData: dsJSON,
+		}, `{}`, time.Second * 15, time.Second * 60},
+		{"defaultInterval when interval empty", nil, `{"interval": ""}`, time.Second * 15, time.Second * 15},
+		{"defaultInterval when intervalMs 0", nil, `{"intervalMs": 0}`, time.Second * 15, time.Second * 15},
 	}
 
 	for _, tc := range testCases {