syntax_data: {"ast_node_type":"other","tokens":[{"end":87,"kind":"keyword","start":0,"text":"self.highlight_regions.iter_mut().find(|s|"}]}
source_snippet:             self.highlight_regions.iter_mut().find(|s| s.is_none()).unwrap_or_else(|| {
context_before:         let first_avail_slot =
context_after:                 bug!("can only highlight {} placeholders at a time", num_slots,)