parse

type Node struct {
	TokenType       token.Token
	NodeDocComments *ast.CommentGroup
	NodePosition    token.Position

	FieldName  string
	FieldValue ast.Expr

	FieldDocComments  *ast.CommentGroup
	FieldLineComments *ast.CommentGroup

	// var, const
	ValueSpec *ast.ValueSpec
	// value type; or nil
	ValueSpecType ast.Expr

	// type ...
	TypeSpec *ast.TypeSpec
	// *Ident, *ParenExpr, *SelectorExpr, *StarExpr, or any of the *XxxTypes
	TypeSpecType ast.Expr
}