syntax_data: {"ast_node_type":"other","tokens":[{"end":76,"kind":"keyword","start":0,"text":"ImplSource::Builtin(BuiltinImplSource::Misc,"}]}
source_snippet:                 ImplSource::Builtin(BuiltinImplSource::Misc, vtable_closure)
context_before:                 let vtable_closure = self.confirm_async_closure_candidate(obligation)?;
context_after:             }