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FP unnecessary-operation, #![feature(capture_disjoint_fields)] #9896
Description
Summary
.
Lint Name
unnecessary-operation
Reproducer
I tried this code:
#![allow(incomplete_features)]
#![feature(capture_disjoint_fields)]
fn foo<MsU>(handler: impl FnOnce() -> MsU + Clone + 'static) {
Box::new(move |value| {
(|_| handler.clone()())(value);
None
}) as Box<dyn Fn(i32) -> Option<i32>>;
}
fn main() {}I saw this happen:
cargo clippy --fix -- -Aclippy::all -Wclippy::unnecessary_operation
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[E0282]: type annotations needed
--> src/main.rs:5:20
|
5 | Box::new(move |value| {
| ^^^^^
|
help: consider giving this closure parameter an explicit type
|
5 | Box::new(move |value: _| {
| +++
error: aborting due to previous error
For more information about this error, try `rustc --explain E0282`.
Original diagnostics will follow.
warning: function `foo` is never used
--> src/main.rs:4:4
|
4 | fn foo<MsU>(handler: impl FnOnce() -> MsU + Clone + 'static) {
| ^^^
|
= note: `#[warn(dead_code)]` on by default
warning: unnecessary operation
--> src/main.rs:5:5
|
5 | / Box::new(move |value| {
6 | | (|_| handler.clone()())(value);
7 | | None
8 | | }) as Box<dyn Fn(i32) -> Option<i32>>;
| |__________________________________________^
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_operation
= note: requested on the command line with `-W clippy::unnecessary-operation`
help: statement can be reduced to
|
5 ~ Box::new(move |value| {
6 + (|_| handler.clone()())(value);
7 + None
8 + });
|
warning: unused boxed `std::ops::Fn` trait object that must be used
--> src/main.rs:5:5
|
5 | / Box::new(move |value| {
6 | | (|_| handler.clone()())(value);
7 | | None
8 | | }) as Box<dyn Fn(i32) -> Option<i32>>;
| |_________________________________________^
|
= note: closures are lazy and do nothing unless called
= note: `#[warn(unused_must_use)]` on by default
warning: `clpy` (bin "clpy") generated 3 warnings (run `cargo fix --bin "clpy"` to apply 1 suggestion)
warning: `clpy` (bin "clpy" test) generated 3 warnings (3 duplicates)
Finished dev [unoptimized + debuginfo] target(s) in 0.47s
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
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