Formatting `use` statements sometimes leaves behind spaces and newlines

[antonilol]

Formatting the following code with cargo fmt leaves behind a space and curly braces.

Before:

use core::{
    slice,
    
    fmt::{},
};

(there are 4 spaces on the seemingly empty line)

After:

use core::{ slice};

Expected:

use core::slice;

Here a newline is left behind and rustfmt reports an internal error.

Before:

use core::{
    
    fmt::{Debug, Display},
    slice::{},
};

(there are again 4 spaces on the seemingly empty line)

After:

use core::{
    
    fmt::{Debug, Display},
};

(there are again 4 spaces on the seemingly empty line, rustfmt didn't touch them)

Expected:

use core::fmt::{Debug, Display};

Command output:

$ cargo fmt -- --check file.rs 
Diff in /path/to/file.rs at line 1:
 use core::{
     
     fmt::{Debug, Display},
-    slice::{},
 };
 
error[internal]: left behind trailing whitespace
 --> /path/to/file.rs:2:2:1
  |
2 |     
  | ^^^^
  |

warning: rustfmt has failed to format. See previous 1 errors.

[ytmimi]

Thanks for the report. Confirming I can reproduce this with rustfmt 1.7.1-nightly (40f5075 2024-08-05)

[ytmimi]

Also marking this as a bug because it's not idempotent.