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FP redundant_clone: Box #10517
Description
Summary
.
Lint Name
redundant_clone
Reproducer
I tried this code:
pub fn main() {
let i: Box<_> = Box::new(1);
let j = i.clone();
assert_eq!(*i, 2);
}I saw this happen:
warning: redundant clone
--> unique-decl-init-copy.rs:3:14
|
3 | let j = i.clone();
| ^^^^^^^^ help: remove this
|
note: cloned value is neither consumed nor mutated
--> unique-decl-init-copy.rs:3:13
|
3 | let j = i.clone();
| ^^^^^^^^^
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_clone
= note: `#[warn(clippy::redundant_clone)]` on by defaul
But
pub fn main() {
let i: Box<_> = Box::new(1);
let j = i;
assert_eq!(*i, 2);
}does not compile
warning: unused variable: `j`
--> unique-decl-init-copy.rs:3:9
|
3 | let j = i;
| ^ help: if this is intentional, prefix it with an underscore: `_j`
|
= note: `#[warn(unused_variables)]` on by default
error[E0382]: borrow of moved value: `i`
--> unique-decl-init-copy.rs:4:5
|
2 | let i: Box<_> = Box::new(1);
| - move occurs because `i` has type `std::boxed::Box<i32>`, which does not implement the `Copy` trait
3 | let j = i;
| - value moved here
4 | assert_eq!(*i, 2);
| ^^^^^^^^^^^^^^^^^ value borrowed here after move
|
= note: this error originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider cloning the value if the performance cost is acceptable
|
3 | let j = i.clone();
| ++++++++
error: aborting due to previous error; 1 warning emitted
Version
rustc 1.70.0-nightly (511364e78 2023-03-16)
binary: rustc
commit-hash: 511364e7874dba9649a264100407e4bffe7b5425
commit-date: 2023-03-16
host: x86_64-unknown-linux-gnu
release: 1.70.0-nightly
LLVM version: 15.0.7
Additional Labels
No response
Activity
matthiaskrgr commentedon Mar 17, 2023
This seems to be a regression, at least on beta, there is no such warning, hm.
matthiaskrgr commentedon Mar 17, 2023
Hmm,
nightly-2023-03-15-x86_64-unknown-linux-gnudoesn't have this FP whilerustc 1.70.0-nightly (511364e78 2023-03-16)doesmatthiaskrgr commentedon Mar 17, 2023
Ooh, I bet this broke in rust-lang/rust#108958 cc @clubby789
clubby789 commentedon Mar 17, 2023
@rustbot claim
clubby789 commentedon Mar 17, 2023
Hmm. I'm not sure how this specifically could have broken it - that PR pretty much just removes it from match arms, the expression itself hasn't emitted since I removed it in rust-lang/rust#108516. I'll try a bisect
searched nightlies: from nightly-2023-03-15 to nightly-2023-03-17
regressed nightly: nightly-2023-03-17
searched commit range: rust-lang/rust@ab65486...511364e
regressed commit: rust-lang/rust@511364e
bisected with cargo-bisect-rustc v0.6.5
Host triple: x86_64-unknown-linux-gnu
Reproduce with:
clubby789 commentedon Mar 17, 2023
cc @cjgillot
@rustbot release
matthiaskrgr commentedon Mar 17, 2023
Oh my bad then, sorry 😅 this looked like the obvious contender to me since it removed box stuff and I thought maybe it removed a "saveguard" when linting against boxes...
Jarcho commentedon Mar 18, 2023
I remember seeing this come up before, but can't find the issue now. This isn't a false positive as the new value isn't used, but the suggestion should be to remove the whole binding.
ryoqun commentedon May 18, 2023
I think this issue's root cause is same as this (see my cross post: #10577 (comment))
this is fine with
+nightly-2023-03-16-x86_64-unknown-linux-gnubut starts to emit false positives with+nightly-2023-03-17-x86_64-unknown-linux-gnuthen again, i think this pr is suspicious: rust-lang/rust#108944
Auto merge of #10873 - Alexendoo:redundant-clone-nursery, r=flip1995
CommanderStorm commentedon Aug 27, 2026
Issue sounds like aliasing, not sure.
@rustbot label +L-nursary
rustbot commentedon Aug 27, 2026
Error: Unknown labels: L-nursary
Please file an issue on GitHub at triagebot if there's a problem with this bot, or reach out on #triagebot on Zulip.
CommanderStorm commentedon Aug 27, 2026
@rustbot label +L-nursery