syntax_data: {"ast_node_type":"variable","tokens":[{"end":58,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:         let span = tcx.def_span(specializing_impl_def_id);
context_before:     if !tcx.specialization_enabled_in(specializing_impl_def_id.krate) {
context_after:         if !span.allows_unstable(sym::specialization)