syntax_data: {"ast_node_type":"other","tokens":[{"end":45,"kind":"keyword","start":0,"text":"variant_index:"}]}
source_snippet:                 variant_index: FIRST_VARIANT,
context_before:                 lhs: self.mirror_expr(source),
context_after:                 name: self.typeck_results.field_index(expr.hir_id),