SSE: Localize/Contain Errors within an Expression (#73163)

Changes SSE to not always fail all queries when one fails. Now only the query itself, and nodes that depend on it will error.
---------

Co-authored-by: Gilles De Mey <gilles.de.mey@gmail.com>

pkg/expr/graph.go

@@ -44,8 +44,13 @@ type Node interface {
 	ID() int64 // ID() allows the gonum graph node interface to be fulfilled
 	NodeType() NodeType
 	RefID() string
-	Execute(ctx context.Context, now time.Time, vars mathexp.Vars, s *Service) (mathexp.Results, error)
 	String() string
+	NeedsVars() []string
+}
+
+type ExecutableNode interface {
+	Node
+	Execute(ctx context.Context, now time.Time, vars mathexp.Vars, s *Service) (mathexp.Results, error)
 }
 
 // DataPipeline is an ordered set of nodes returned from DPGraph processing.
@@ -67,27 +72,48 @@ func (dp *DataPipeline) execute(c context.Context, now time.Time, s *Service) (m
 			dsNodes = append(dsNodes, node.(*DSNode))
 		}
 
-		if err := executeDSNodesGrouped(c, now, vars, s, dsNodes); err != nil {
-			return nil, err
-		}
+		executeDSNodesGrouped(c, now, vars, s, dsNodes)
 	}
 
 	for _, node := range *dp {
 		if groupByDSFlag && node.NodeType() == TypeDatasourceNode {
 			continue // already executed via executeDSNodesGrouped
 		}
+
+		// Don't execute nodes that have dependent nodes that have failed
+		var hasDepError bool
+		for _, neededVar := range node.NeedsVars() {
+			if res, ok := vars[neededVar]; ok {
+				if res.Error != nil {
+					errResult := mathexp.Results{
+						Error: makeDependencyError(node.RefID(), neededVar),
+					}
+					vars[node.RefID()] = errResult
+					hasDepError = true
+					break
+				}
+			}
+		}
+		if hasDepError {
+			continue
+		}
+
 		c, span := s.tracer.Start(c, "SSE.ExecuteNode")
 		span.SetAttributes("node.refId", node.RefID(), attribute.Key("node.refId").String(node.RefID()))
-		if node.NodeType() == TypeCMDNode {
-			cmdNode := node.(*CMDNode)
-			inputRefIDs := cmdNode.Command.NeedsVars()
+		if len(node.NeedsVars()) > 0 {
+			inputRefIDs := node.NeedsVars()
 			span.SetAttributes("node.inputRefIDs", inputRefIDs, attribute.Key("node.inputRefIDs").StringSlice(inputRefIDs))
 		}
 		defer span.End()
 
-		res, err := node.Execute(c, now, vars, s)
+		execNode, ok := node.(ExecutableNode)
+		if !ok {
+			return vars, makeUnexpectedNodeTypeError(node.RefID(), node.NodeType().String())
+		}
+
+		res, err := execNode.Execute(c, now, vars, s)
 		if err != nil {
-			return nil, err
+			res.Error = err
 		}
 
 		vars[node.RefID()] = res