cargo clippy --fix leaves blank lines when removing entire use statements

[akonradi-signal]

Summary

cargo clippy --fix can remove entire use statements if all of the imported names are unused, but it leaves a blank line behind. With a large number of use lines, this can result in imports being fragmented into multiple blocks that won't ever be joined back together. If clippy removes an entire use statement, it should remove the trailing newline at the end, too.

Reproducer

I tried this code:

use std::any::Any;
use std::option::Option;
use std::result::Result;
use std::sync::Mutex;

pub fn use_some_imports() {
    let _ = Mutex::new(());
    let _ = Option::Some(32);
}

I expected to see this happen:
Running cargo clippy --fix should have removed the use lines for Any and Result and kept the block of imports together, like this:

use std::option::Option;
use std::sync::Mutex;

pub fn use_some_imports() {
    let _ = Mutex::new(());
    let _ = Option::Some(32);
}

Instead, this happened:
cargo clippy --fix left blank lines, splitting the block of imports:

use std::option::Option;

use std::sync::Mutex;

pub fn use_some_imports() {
    let _ = Mutex::new(());
    let _ = Option::Some(32);
}

Version

rustc 1.75.0 (82e1608df 2023-12-21)
binary: rustc
commit-hash: 82e1608dfa6e0b5569232559e3d385fea5a93112
commit-date: 2023-12-21
host: x86_64-unknown-linux-gnu
release: 1.75.0
LLVM version: 17.0.6

Additional Labels

No response

[y21]

This looks like an issue with the unused_imports lint specifically, which is implemented in rustc.
It can also be repro'd with cargo fix, so clippy is not needed for this.

Moving to rust-lang/rust since this is unactionable in the clippy repo

[ehuss]

Thanks for the report! I believe this is a duplicate of #120296, so closing in favor of that.