Error when formatting `if let` with `&&`

[momvart]

If we chain multiple if let blocks into a single one with &&, rustfmt fails to format or gives

error[internal]: left behind trailing whitespace

Example:

fn main() {
    let x = Some(10);
    let y = None;

    if let Some(x) = x 
&& let Some(y) = y {
        println!("Hi");
    }
}

Version: 1.6.0-nightly (2023-07-27 500647f)

[xxchan]

This is because unstable feature let-chains is not formatted (WIP in #5203). Note a similar but different stable feature let-else can be formatted.

You need to manually format it, and remove the trailing spaces

[momvart]

I thought it should be a WIP but couldn't remember the feature name :).

[momvart]

Duplicate of #5177