Alerting: Fix DatasourceUID and RefID missing for DatasourceNoData alerts (#66733)

This commit fixes a bug where DatasourceUID and RefID annotations are
missing for DatasourceNoData alerts in Grafana 9.5. This bug affects
datasource plugins that have moved to using the data plane contract.

pkg/services/ngalert/eval/eval.go

@@ -321,16 +321,29 @@ func queryDataResponseToExecutionResults(c models.Condition, execResp *backend.Q
 
 	result := ExecutionResults{Results: make(map[string]data.Frames)}
 	for refID, res := range execResp.Responses {
-		if len(res.Frames) == 0 {
-			// to ensure that NoData is consistent with Results we do not initialize NoData
-			// unless there is at least one RefID that returned no data
+		// There are two possible frame formats for No Data:
+		//
+		// 1. A response with no frames
+		// 2. A response with 1 frame but no fields
+		//
+		// The first format is not documented in the data plane contract but needs to be
+		// supported for older datasource plugins. The second format is documented in
+		// https://github.com/grafana/grafana-plugin-sdk-go/blob/main/data/contract_docs/contract.md
+		// and is what datasource plugins should use going forward.
+		if len(res.Frames) <= 1 {
+			// To make sure NoData is nil when Results are also nil we wait to initialize
+			// NoData until there is at least one query or expression that returned no data
 			if result.NoData == nil {
 				result.NoData = make(map[string]string)
 			}
+			hasNoFrames := len(res.Frames) == 0
+			hasNoFields := len(res.Frames) == 1 && len(res.Frames[0].Fields) == 0
+			if hasNoFrames || hasNoFields {
 				if s, ok := datasourceUIDsForRefIDs[refID]; ok && s != datasourceExprUID {
 					result.NoData[refID] = s
 				}
 			}
+		}
 
 		// for each frame within each response, the response can contain several data types including time-series data.
 		// For now, we favour simplicity and only care about single scalar values.

pkg/services/ngalert/eval/eval_test.go

@@ -575,6 +575,26 @@ func TestEvaluate(t *testing.T) {
 				"ref_id":         "A",
 			},
 		}},
+	}, {
+		name: "is no data for one frame with no fields",
+		cond: models.Condition{
+			Data: []models.AlertQuery{{
+				RefID:         "A",
+				DatasourceUID: "test",
+			}},
+		},
+		resp: backend.QueryDataResponse{
+			Responses: backend.Responses{
+				"A": {Frames: []*data.Frame{{Fields: nil}}},
+			},
+		},
+		expected: Results{{
+			State: NoData,
+			Instance: data.Labels{
+				"datasource_uid": "test",
+				"ref_id":         "A",
+			},
+		}},
 	}}
 
 	for _, tc := range cases {