syntax_data: {"ast_node_type":"variable","tokens":[{"end":41,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:     let span = match fn_sig.decl.output {
context_before:     let hir::ImplItemKind::Fn(fn_sig, _) = impl_fn.kind else { bug!("expected decl") };
context_after:         hir::FnRetTy::DefaultReturn(_) => tcx.def_span(impl_fn.owner_id),