{"ast_node_type":"impl","tokens":[{"end":54,"kind":"keyword","start":0,"text":"impl"}]}
impl ToInternal<SmallVec<[tokenstream::TokenTree; 2]>>
// We use a `SmallVec` because the output size is always one or two `TokenTree`s.
    for (TokenTree<TokenStream, Span, Symbol>, &mut Rustc<'_, '_>)