Prometheus: Avoid parsing unused legacy datasource property (#87224)

* query cleanup

* parse query

* more comments

pkg/promlib/models/query.go

@@ -137,6 +137,8 @@ const (
 var safeResolution = 11000
 
 // QueryModel includes both the common and specific values
+// NOTE: this struct may have issues when decoding JSON that requires the special handling
+// registered in https://github.com/grafana/grafana-plugin-sdk-go/blob/v0.228.0/experimental/apis/data/v0alpha1/query.go#L298
 type QueryModel struct {
 	PrometheusQueryProperties    `json:",inline"`
 	sdkapi.CommonQueryProperties `json:",inline"`
@@ -172,8 +174,22 @@ type Scope struct {
 	Matchers []*labels.Matcher
 }
 
+// This internal query struct is just like QueryModel, except it does not include:
+// sdkapi.CommonQueryProperties -- this avoids errors where the unused "datasource" property
+// may be either a string or DataSourceRef
+type internalQueryModel struct {
+	PrometheusQueryProperties `json:",inline"`
+	//sdkapi.CommonQueryProperties `json:",inline"`
+	IntervalMS float64 `json:"intervalMs,omitempty"`
+
+	// The following properties may be part of the request payload, however they are not saved in panel JSON
+	// Timezone offset to align start & end time on backend
+	UtcOffsetSec int64  `json:"utcOffsetSec,omitempty"`
+	Interval     string `json:"interval,omitempty"`
+}
+
 func Parse(span trace.Span, query backend.DataQuery, dsScrapeInterval string, intervalCalculator intervalv2.Calculator, fromAlert bool, enableScope bool) (*Query, error) {
-	model := &QueryModel{}
+	model := &internalQueryModel{}
 	if err := json.Unmarshal(query.JSON, model); err != nil {
 		return nil, err
 	}

pkg/promlib/models/query_test.go

@@ -436,6 +436,25 @@ func TestParse(t *testing.T) {
 		require.Equal(t, "rate(ALERTS{job=\"test\" [135000]}) + rate(ALERTS{job=\"test\" [2m15s]})", res.Expr)
 	})
 
+	t.Run("parsing query model with legacy datasource reference", func(t *testing.T) {
+		timeRange := backend.TimeRange{
+			From: now,
+			To:   now.Add(48 * time.Hour),
+		}
+
+		// query with legacy datasource reference
+		q := queryContext(`{
+			"datasource": "hello",
+			"format": "time_series",
+			"intervalFactor": 1,
+			"refId": "A"
+		}`, timeRange, 2*time.Minute)
+
+		res, err := models.Parse(span, q, "15s", intervalCalculator, false, false)
+		require.NoError(t, err)
+		require.Equal(t, "A", res.RefId)
+	})
+
 	t.Run("parsing query model with ${__rate_interval_ms} and ${__rate_interval} variable", func(t *testing.T) {
 		timeRange := backend.TimeRange{
 			From: now,