syntax_data: {"ast_node_type":"other","tokens":[{"end":54,"kind":"keyword","start":0,"text":"hir::CoroutineSource::Closure,"}]}
source_snippet:                         hir::CoroutineSource::Closure,
context_before:                         hir::CoroutineDesugaring::AsyncGen,
context_after:                     ) => "async gen closure",