Encountered spurious `Does not need to be mutable` warning

[sadmac7000]

I had the following function in my code:

pub async fn forward_tcp(forward_port: bridge::ForwardPortProxy, cmd: TcpCommand) -> Result<()> {   
    let mut cmd = cmd;                                                                              
    forward_port                                                                                    
        .forward_port(None, &mut cmd.host_address, &mut cmd.target_address)                         
        .await?                                                                                     
        .map_err(|x| anyhow!("Failed to establish port forward: {:?}", x))                          
}

Getting rid of the mut on the second line and making the cmd argument mutable instead resulted in a "Warning: 'cmd' does not need to be mutable" message. Getting rid of the mut entirely caused the program to fail to compile due to the mutable references.

I've not gotten a simpler reproducer to behave this way in isolation.

[sadmac7000]

This looks to be caused due to some proc macro shenanigans that we're up to in this code base, hence the difficulty reproducing. Closing.