syntax_data: {"ast_node_type":"struct","tokens":[{"end":67,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:     // Create a map from local indices to coroutine struct indices.
context_before:     // Build the coroutine variant field list.
context_after:     let mut variant_fields: IndexVec<VariantIdx, IndexVec<FieldIdx, CoroutineSavedLocal>> =