syntax_data: {"ast_node_type":"variable","tokens":[{"end":56,"kind":"keyword","start":0,"text":"if"}]}
source_snippet:         if let Some(i) = maybe_unsizing_param_idx(arg) {
context_before:     for arg in tcx.type_of(tail_field.did).instantiate_identity().walk() {
context_after:             unsizing_params.insert(i);