Repository navigation
FP redundant_clone: x.clone(); that clones & consumes #9898
Description
Summary
.
Lint Name
redundant_clone
Reproducer
I tried this code:
// run-pass
#![allow(unused_must_use)]
#![allow(unused_imports)]
// pretty-expanded FIXME #23616
#![allow(deprecated)]
use std::hash::{Hash, SipHasher};
// testing multiple separate deriving attributes
#[derive(PartialEq)]
#[derive(Clone)]
#[derive(Hash)]
struct Foo {
bar: usize,
baz: isize
}
fn hash<T: Hash>(_t: &T) {}
pub fn main() {
let a = Foo {bar: 4, baz: -3};
a == a; // check for PartialEq impl w/o testing its correctness
a.clone(); // check for Clone impl w/o testing its correctness
hash(&a); // check for Hash impl w/o testing its correctness
}I saw this happen:
cargo clippy --fix -- -Aclippy::all -Wclippy::redundant_clone
Checking clpy v0.1.0 (/tmp/clpy)
warning: failed to automatically apply fixes suggested by rustc to crate `clpy`
after fixes were automatically applied the compiler reported errors within these files:
* src/main.rs
This likely indicates a bug in either rustc or cargo itself,
and we would appreciate a bug report! You're likely to see
a number of compiler warnings after this message which cargo
attempted to fix but failed. If you could open an issue at
https://github.com/rust-lang/rust/issues
quoting the full output of this command we'd be very appreciative!
Note that you may be able to make some more progress in the near-term
fixing code with the `--broken-code` flag
The following errors were reported:
error[E0382]: borrow of moved value: `a`
--> src/main.rs:25:10
|
21 | let a = Foo {bar: 4, baz: -3};
| - move occurs because `a` has type `Foo`, which does not implement the `Copy` trait
...
24 | a; // check for Clone impl w/o testing its correctness
| - value moved here
25 | hash(&a); // check for Hash impl w/o testing its correctness
| ^^ value borrowed here after move
error: aborting due to previous error
For more information about this error, try `rustc --explain E0382`.
Original diagnostics will follow.
warning: redundant clone
--> src/main.rs:24:6
|
24 | a.clone(); // check for Clone impl w/o testing its correctness
| ^^^^^^^^ help: remove this
|
note: cloned value is neither consumed nor mutated
--> src/main.rs:24:5
|
24 | a.clone(); // check for Clone impl w/o testing its correctness
| ^^^^^^^^^
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_clone
= note: requested on the command line with `-W clippy::redundant-clone`
warning: `clpy` (bin "clpy") generated 1 warning (run `cargo fix --bin "clpy"` to apply 1 suggestion)
warning: `clpy` (bin "clpy" test) generated 1 warning (1 duplicate)
Finished dev [unoptimized + debuginfo] target(s) in 1.21s
I expected to see this happen:
Version
rustc 1.67.0-nightly (c5d82ed7a 2022-11-19)
binary: rustc
commit-hash: c5d82ed7a4ad94a538bb87e5016e7d5ce0bd434b
commit-date: 2022-11-19
host: x86_64-unknown-linux-gnu
release: 1.67.0-nightly
LLVM version: 15.0.4
Additional Labels
No response
Activity
KisaragiEffective commentedon Nov 23, 2022
You should consider use
static_assetions::assert_impl_allin above example, like this:[-]FP redundant_clone[/-][+]FP redundant_clone: x.clone(); that clones & consumes[/+]matthiaskrgr commentedon Nov 28, 2022
Much simple example:
in line 2 we would clone and directly consume the cloned value (because of the
;) but he lint does not recognize that if we removed JUST the clone here, we would instead consume the entire struct and prevent futher uses (line 3)CommanderStorm commentedon Aug 27, 2026
@rustbot label +L-nursery