`use` imports are wrapped unless double-nested imports are present

[cramertj]

rustfmt gives this:

use {
    fidl_fuchsia_hardware_ethernet_ext::EthernetQueueFlags, futures::TryStreamExt, std::fs::File,
    structopt::StructOpt,
};

which is, IMO, pretty gross as it mixes imports from many different crates all together onto the same line.

Adding a group after _ext:: and adding Bar to it gives this:

use {
    fidl_fuchsia_hardware_ethernet_ext::{Bar, EthernetQueueFlags},
    futures::TryStreamExt,
    std::fs::File,
    structopt::StructOpt,
};

which is more like what I would expect. What's going on here? Is there a setting that can be enabled to always get the bottom layout, even when no nested groups are present?

[topecongiro]

AFAIK using use statement like this has not been taken into account while implementing rustfmt. I think rustfmt should use vertical layout in the top-level import list.

Is there a setting that can be enabled to always get the bottom layout, even when no nested groups are present?

You could set imports_layout = "Vertical".

[cramertj]

I think rustfmt should use vertical layout in the top-level import list.

I agree.

[ytmimi]

@calebcartwright I think this can be closed. Although it's unstable, One could set the imports_layout option to something like imports_layout=HorizontalVertical to force a vertical layout when formatting horizontally is impossible. The reason why we get the Compressed formatting is because imports_layout=Mixed by default, and I don't think we can change the default value as that would be a breaking change. Or do we want to keep this open until imports_layout is stabilized?

input

use {
    fidl_fuchsia_hardware_ethernet_ext::EthernetQueueFlags, futures::TryStreamExt, std::fs::File,
    structopt::StructOpt,
}

output

use {
    fidl_fuchsia_hardware_ethernet_ext::EthernetQueueFlags,
    futures::TryStreamExt,
    std::fs::File,
    structopt::StructOpt,
};

[ytmimi]

Although they're unrelated issues, the use style being used here is being suggested as an option in #5360