ds-querier: return error if failed to get ds client (#97698)

* ds-querier: return error if failed to get ds client

* add log line

* no empty ref

* fix test

pkg/registry/apis/query/query.go

@@ -125,7 +125,7 @@ func (r *queryREST) Connect(connectCtx context.Context, name string, _ runtime.O
 			var refError ErrorWithRefID
 			statusCode := http.StatusBadRequest
 			message := err
-			refID := ""
+			refID := "A"
 
 			if errors.Is(err, datasources.ErrDataSourceNotFound) {
 				statusCode = http.StatusNotFound
@@ -187,6 +187,11 @@ func (b *QueryAPIBuilder) execute(ctx context.Context, req parsedRequestInfo) (q
 		qdr, err = b.executeConcurrentQueries(ctx, req.Requests)
 	}
 
+	if err != nil {
+		b.log.Debug("error in query phase, skipping expressions", "error", err)
+		return qdr, err //return early here to prevent expressions from being executed if we got an error during the query phase
+	}
+
 	if len(req.Expressions) > 0 {
 		b.log.Debug("executing expressions")
 		qdr, err = b.handleExpressions(ctx, req, qdr)
@@ -232,7 +237,9 @@ func (b *QueryAPIBuilder) handleQuerySingleDatasource(ctx context.Context, req d
 		req.Headers,
 	)
 	if err != nil {
-		return nil, err
+		b.log.Debug("error getting single datasource client", "error", err, "reqUid", req.UID)
+		qdr := buildErrorResponse(err, req)
+		return qdr, err
 	}
 
 	code, rsp, err := client.QueryData(ctx, *req.Request)

pkg/tests/apis/query/query_test.go

@@ -140,7 +140,7 @@ func TestIntegrationSimpleQuery(t *testing.T) {
 		require.Error(t, err, "expecting a 400")
 		require.JSONEq(t, `{
 			"results": {
-				"": {
+				"A": {
 					"error": "[sse.dependencyError] did not execute expression [Y] due to a failure to of the dependent expression or query [X]",
 					"status": 400,
 					"errorSource": ""