syntax_data: {"ast_node_type":"variable","tokens":[{"end":30,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:         let first_avail_slot =
context_before:         let num_slots = self.highlight_regions.len();
context_after:             self.highlight_regions.iter_mut().find(|s| s.is_none()).unwrap_or_else(|| {