syntax_data: {"ast_node_type":"other","tokens":[{"end":67,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:                 // The yield ty is already `Poll<Option<yield_ty>>`
context_before:             CoroutineKind::Desugared(CoroutineDesugaring::AsyncGen, _) => {
context_after:                 old_yield_ty