{"ast_node_type":"other","tokens":[{"end":121,"kind":"keyword","start":0,"text":"//"}]}
// link: https://github.com/rust-lang/rust/blob/9ebf47851a357faa4cd97f4b1dc7835f6376e639/src/libsyntax/ext/expand.rs#L141
// The following items are what `rustc` macro can be parsed into :
// * Expr(P<ast::Expr>)                     -> token_tree_to_expr