syntax_data: {"ast_node_type":"variable","tokens":[{"end":91,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:     let mut variant_fields: IndexVec<VariantIdx, IndexVec<FieldIdx, CoroutineSavedLocal>> =
context_before:     // Create a map from local indices to coroutine struct indices.
context_after:         iter::repeat(IndexVec::new()).take(CoroutineArgs::RESERVED_VARIANTS).collect();