syntax_data: {"ast_node_type":"other","tokens":[{"end":85,"kind":"keyword","start":0,"text":"arms:"}]}
source_snippet:                             arms: arms.iter().map(|a| self.convert_arm(a)).collect(),
context_before:                             scrutinee: self.mirror_expr(scrutinee),
context_after:                             span: block_body_expr.span,