Open
Description
Summary
Seen with Rust 1.85.1 when running clippy --fix on Packetry. at commit greatscottgadgets/packetry@e7c9dcc .
The problem involves a useless use of Vec, a reference to which is passed into a function that takes &[T].
When an array is used instead as suggested, the suggestion omits the necessary & operator.
Reproducer
Here's a minimised reproducer:
#[allow(clippy::result_unit_err)]
pub fn validate_packet(_packet: &[u8]) -> Result<(), ()> {
Ok(())
}
fn main() {
let packet = &vec![1, 2, 3, 4];
assert_eq!(validate_packet(packet), Ok(()));
}Running clippy-driver on this code results in:
warning: useless use of `vec!`
--> src/usb.rs:7:18
|
7 | let packet = &vec![1, 2, 3, 4];
| ^^^^^^^^^^^^^^^^^ help: you can use an array directly: `[1, 2, 3, 4]`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_vec
= note: `#[warn(clippy::useless_vec)]` on by default
warning: 1 warning emitted
If the suggestion is applied, then compilation fails:
error[E0308]: mismatched types
--> src/usb.rs:8:32
|
8 | assert_eq!(validate_packet(packet), Ok(()));
| --------------- ^^^^^^ expected `&[u8]`, found `[{integer}; 4]`
| |
| arguments to this function are incorrect
|
note: function defined here
--> src/usb.rs:2:8
|
2 | pub fn validate_packet(_packet: &[u8]) -> Result<(), ()> {
| ^^^^^^^^^^^^^^^ --------------
help: consider borrowing here
|
8 | assert_eq!(validate_packet(&packet), Ok(()));
| +
error: aborting due to 1 previous error
For more information about this error, try `rustc --explain E0308`.
The correct suggestion would be &[1, 2, 3, 4] which compiles successfully.
Version
rustc 1.85.1 (4eb161250 2025-03-15)
binary: rustc
commit-hash: 4eb161250e340c8f48f66e2b929ef4a5bed7c181
commit-date: 2025-03-15
host: x86_64-unknown-linux-gnu
release: 1.85.1
LLVM version: 19.1.7
Additional Labels
@rustbot label I-suggestion-causes-error