Description
Summary
Dearest clippyists!
This is maybe one-and-a-half reports on clippy::let_and_return.
The first part involves missing parentheses (the clippy fix doesn't add them but they are given as a subsequent fix in the compiler error).
The second-ish is found in the same code whereby the as _ cast that clippy added as part of the fix can actually be removed for brevity, along with the parentheses that weren't there, so to speak...
Reproducer
I tried this code:
use std::mem::ManuallyDrop;
pub enum DropOrNot<T> {
DontDrop(ManuallyDrop<T>),
Drop(T),
}
impl<T> DropOrNot<T> {
pub fn inner(&self) -> &T {
let result = match self {
DropOrNot::DontDrop(x) => x,
DropOrNot::Drop(x) => x,
};
result
}
}in lib.rs with cargo clippy --fix
I saw this happen:
(the changed code)
pub fn inner(&self) -> &T {
match self {
DropOrNot::DontDrop(x) => x,
DropOrNot::Drop(x) => x,
} as _
}(the error message)
after fixes were automatically applied the compiler reported errors within these files:
* src\lib.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-clippy/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: expected expression, found `as`
--> src\lib.rs:15:11
|
15 | } as _
| ^^ expected expression
|
help: parentheses are required to parse this as an expression
|
12 ~ (match self {
13 | DropOrNot::DontDrop(x) => x,
14 | DropOrNot::Drop(x) => x,
15 ~ }) as _
|
error: aborting due to previous error
Original diagnostics will follow.
warning: returning the result of a `let` binding from a block
--> src\lib.rs:15:9
|
10 | / let result = match self {
11 | | DropOrNot::DontDrop(x) => x,
12 | | DropOrNot::Drop(x) => x,
13 | | };
| |__________- unnecessary `let` binding
14 |
15 | result
| ^^^^^^
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#let_and_return
= note: `#[warn(clippy::let_and_return)]` on by default
help: return the expression directly
|
10 ~
11 |
12 ~ match self {
13 + DropOrNot::DontDrop(x) => x,
14 + DropOrNot::Drop(x) => x,
15 + } as _
|
I expected to see this happen:
In a way, as above, but with parentheses around the match blocks (as suggested) so that the code compiles...
pub fn inner(&self) -> &T {
(match self {
DropOrNot::DontDrop(x) => x,
DropOrNot::Drop(x) => x,
}) as _
}You'll note that the as _ cast that was added along the way by clippy can also be removed.
pub fn inner(&self) -> &T {
match self {
DropOrNot::DontDrop(x) => x,
DropOrNot::Drop(x) => x,
}
}Version
rustc 1.73.0-nightly (1b198b3a1 2023-08-13)
binary: rustc
commit-hash: 1b198b3a196442e14fb06978166ab46a4618d131
commit-date: 2023-08-13
host: x86_64-pc-windows-msvc
release: 1.73.0-nightly
LLVM version: 17.0.0
Additional Labels
@rustbot label +I-suggestion-causes-error