Compiler warns "variable does not need to be mutable" incorrectly?

[avkonst]

I have got actix web api handler function, which receives body argument. The compiler warns that body does not have to be mutable for the api_handler. However, the handler calls a function which requires body to be mutable. Is it incorrect compiler's warning or I am doing something incorrectly?

async fn api_handler(_req: HttpRequest, mut body: web::Payload) -> Result<HttpResponse, Error> {
    let body = utils::receive_body_as_string(body).await?;
    ...
}

pub async fn receive_body_as_string(mut body: actix_web::web::Payload) -> Result<String, actix_web::Error> {
    ...
}

[jhpratt]

Because the value is owned, you only need to declare it mutable if you're mutating it in that function.

[avkonst]

Thanks. This makes sense now