syntax_data: {"ast_node_type":"other","tokens":[{"end":81,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:                     // you either need to generate a shim body, or perhaps return
context_before:                     // For compiler developers who'd like to add new items to `Fn`/`FnMut`/`FnOnce`,
context_after:                     // `InstanceKind::Item` pointing to a trait default method body if