syntax_data: {"ast_node_type":"other","tokens":[{"end":42,"kind":"keyword","start":0,"text":"//"}]}
source_snippet: // `region_index` and `used_region_names`.
context_before: // HACK(eddyb) limited to `FmtPrinter` because of `binder_depth`,
context_after: impl<'tcx> FmtPrinter<'_, 'tcx> {