syntax_data: {"ast_node_type":"other","tokens":[{"end":66,"kind":"keyword","start":0,"text":"for"}]}
source_snippet:                 for (idx, variant) in variants.iter_enumerated() {
context_before:                 assert!(*niche_start <= niche_size.unsigned_int_max());
context_after:                     // Ensure all inhabited variants are accounted for.