syntax_data: {"ast_node_type":"variable","tokens":[{"end":29,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                     let lhs =
context_before:                     let kind = ExprKind::NamedConst { def_id: did, args, user_ty: None };
context_after:                         self.thir.exprs.push(Expr { temp_lifetime, ty: discr_ty, span, kind });