syntax_data: {"ast_node_type":"variable","tokens":[{"end":64,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:             let arg = recurse_build(tcx, body, arg, root_span)?;
context_before:             let arg_ty = body.exprs[arg].ty;
context_after:             ty::Const::new_expr(tcx, Expr::new_unop(tcx, op, arg_ty, arg))