if let ExprKind::Repeat(value, length) = expr.kind
    && let ExprKind::Lit(ref lit) = value.kind
    && let LitKind::Int(1, LitIntType::Unsigned(UintTy::U8)) = lit.node
    && let ConstArgKind::Anon(anon_const) = length.kind
    && expr1 = &cx.tcx.hir_body(anon_const.body).value
    && let ExprKind::Lit(ref lit1) = expr1.kind
    && let LitKind::Int(5, LitIntType::Unsuffixed) = lit1.node
{
    // report your lint here
}