func (t *Tree) add() {
	tree := t.treeSet[t.Name]
	if tree == nil || IsEmptyTree(tree.Root) {
		t.treeSet[t.Name] = t
		return
	}
	if !IsEmptyTree(t.Root) {
		t.errorf("template: multiple definition of template %q", t.Name)
	}
}

// IsEmptyTree reports whether this tree (node) is empty of everything but space or comments.
func IsEmptyTree(n Node) bool {
	switch n := n.(type) {
	case nil:
		return true

func (t *Template) associate(new *Template, tree *parse.Tree) bool {
	if new.common != t.common {
		panic("internal error: associate not common")
	}
	if old := t.tmpl[new.name]; old != nil && parse.IsEmptyTree(tree.Root) && old.Tree != nil {
		// If a template by that name exists,
		// don't replace it with an empty template.
		return false
	}
	t.tmpl[new.name] = new
	return true

}

func TestIsEmpty(t *testing.T) {
	if !IsEmptyTree(nil) {
		t.Errorf("nil tree is not empty")
	}
	for _, test := range isEmptyTests {
		tree, err := New("root").Parse(test.input, "", "", make(map[string]*Tree), nil)
		if err != nil {
			t.Errorf("%q: unexpected error: %v", test.name, err)
			continue
		}
		if empty := IsEmptyTree(tree.Root); empty != test.empty {

		{"IdentifierNode.Ident", Field, 0},
		{"IdentifierNode.NodeType", Field, 0},
		{"IdentifierNode.Pos", Field, 1},
		{"IfNode", Type, 0},
		{"IfNode.BranchNode", Field, 0},
		{"IsEmptyTree", Func, 0},
		{"ListNode", Type, 0},
		{"ListNode.NodeType", Field, 0},
		{"ListNode.Nodes", Field, 0},
		{"ListNode.Pos", Field, 1},
		{"Mode", Type, 16},
		{"New", Func, 0},

pkg text/template/parse, const NodeText NodeType
pkg text/template/parse, const NodeVariable NodeType
pkg text/template/parse, const NodeWith NodeType
pkg text/template/parse, func IsEmptyTree(Node) bool
pkg text/template/parse, func New(string, ...map[string]interface{}) *Tree
pkg text/template/parse, func NewIdentifier(string) *IdentifierNode