Auto-import destroys previous formatting of nested-imports (merges all into one line)

rust-analyzer version: 0.3.1995-standalone

rustc version: rustc 1.78.0 (9b00956e5 2024-04-29)

editor or extension: VSCode (extension version v0.3.1995)

code snippet to reproduce:

use std::{
    collections::HashMap,
    net::IpAddr,
    fs::{File, copy},
};

fn main() {
    let x = HashSet::new();
}

When triggering an auto-import for HashSet in above snippet, the import is changed to:

use std::{
    collections::{HashMap, HashSet}, fs::{copy, File}, net::IpAddr
};

This makes the import a lot less readable and leads to more diff-noise in git. Instead, I would have expected this:

use std::{
    collections::{HashMap, HashSet},
    net::IpAddr,
    fs::{File, copy},
};

This bug is already present for quite a while (years, if my memory serves me right).

Start by reproducing the reported Rust snippet in rust-analyzer with the VSCode extension and trace the auto-import path that formats nested imports. The fix is done when adding HashSet preserves separate import lines and existing formatting, and the behavior is covered by the relevant rust-analyzer test if one is found.