ds-querier: account for -100 meaning __expr__ (#96565)

* ds-querier: account for -100 meaning __expr__

* temp debug log error parsing query

* var confusion

* log error

pkg/registry/apis/query/parser.go

@@ -208,7 +208,7 @@ func (p *queryParser) getValidDataSourceRef(ctx context.Context, ds *data.DataSo
 		if ds.UID == "" {
 			return nil, fmt.Errorf("missing name/uid in data source reference")
 		}
-		if ds.UID == expr.DatasourceType {
+		if expr.IsDataSource(ds.UID) {
 			return ds, nil
 		}
 		if p.legacy == nil {

pkg/registry/apis/query/query.go

@@ -147,6 +147,8 @@ func (r *queryREST) Connect(connectCtx context.Context, name string, _ runtime.O
 				},
 			}
 
+			b.log.Error("Error parsing query", "refId", refID, "message", message)
+
 			responder.Object(statusCode, qdr)
 			return
 		}