syntax_data: {"ast_node_type":"other","tokens":[{"end":58,"kind":"keyword","start":0,"text":"const"}]}
source_snippet:         const ONE: VariantIdx = VariantIdx::from_usize(1);
context_before:         const ZERO: VariantIdx = VariantIdx::ZERO;
context_after:         let rvalue = match self.coroutine_kind {