stdPackages []string                     // names, omitting "unsafe", internal, and vendored packages
	importMap   map[string]map[string]string // importer dir -> import path -> canonical path
	importDir   map[string]string            // canonical import path -> dir

}

func NewWalker(context *build.Context, root string) *Walker {
	w := &Walker{
		context:  context,
		root:     root,
		features: map[string]bool{},