Update to tengo v2 (#976)

vendor/github.com/d5/tengo/v2/parser/ast.go

@@ -0,0 +1,69 @@
+package parser
+
+import (
+	"strings"
+)
+
+const (
+	nullRep = "<null>"
+)
+
+// Node represents a node in the AST.
+type Node interface {
+	// Pos returns the position of first character belonging to the node.
+	Pos() Pos
+	// End returns the position of first character immediately after the node.
+	End() Pos
+	// String returns a string representation of the node.
+	String() string
+}
+
+// IdentList represents a list of identifiers.
+type IdentList struct {
+	LParen  Pos
+	VarArgs bool
+	List    []*Ident
+	RParen  Pos
+}
+
+// Pos returns the position of first character belonging to the node.
+func (n *IdentList) Pos() Pos {
+	if n.LParen.IsValid() {
+		return n.LParen
+	}
+	if len(n.List) > 0 {
+		return n.List[0].Pos()
+	}
+	return NoPos
+}
+
+// End returns the position of first character immediately after the node.
+func (n *IdentList) End() Pos {
+	if n.RParen.IsValid() {
+		return n.RParen + 1
+	}
+	if l := len(n.List); l > 0 {
+		return n.List[l-1].End()
+	}
+	return NoPos
+}
+
+// NumFields returns the number of fields.
+func (n *IdentList) NumFields() int {
+	if n == nil {
+		return 0
+	}
+	return len(n.List)
+}
+
+func (n *IdentList) String() string {
+	var list []string
+	for i, e := range n.List {
+		if n.VarArgs && i == len(n.List)-1 {
+			list = append(list, "..."+e.String())
+		} else {
+			list = append(list, e.String())
+		}
+	}
+	return "(" + strings.Join(list, ", ") + ")"
+}