useless conversion wrongly suggests removing .into_iter() when ExactSizeIterator is required #11300
Description
Summary
I have a function that takes an argument implementing IntoIterator + ExactSizeIterator. When I call it, I supply an array with .into_iter(). Clippy wrongly suggests removing the .into_iter() on the grounds that it's automatic. However, if I do that then the code fails to compile because ExactSizeIterator is not satisfied.
Lint Name
useless_conversion
Reproducer
I tried this code:
pub fn foo<I>(i: I)
where I: IntoIterator<Item=i32> + ExactSizeIterator
{
assert_eq!(i.len(), 3);
}
pub fn bar() {
foo([1, 2, 3].into_iter());
}I saw this happen:
warning: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
--> src/lib.rs:8:9
|
8 | foo([1, 2, 3].into_iter());
| ^^^^^^^^^^^^^^^^^^^^^ help: consider removing the `.into_iter()`: `[1, 2, 3]`
|
note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
--> src/lib.rs:2:10
|
2 | where I: IntoIterator<Item=i32> + ExactSizeIterator
| ^^^^^^^^^^^^^^^^^^^^^^
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_conversion
= note: `#[warn(clippy::useless_conversion)]` on by default
I expected to see this happen:
No errors.
If I apply Clippy's suggest and remove the .into_iter(), then this happens:
error[[E0277]](https://doc.rust-lang.org/stable/error_codes/E0277.html): the trait bound `[i32; 3]: ExactSizeIterator` is not satisfied
--> src/lib.rs:8:9
|
8 | foo([1, 2, 3]);
| --- ^^^^^^^^^ the trait `ExactSizeIterator` is not implemented for `[i32; 3]`
| |
| required by a bound introduced by this call
|
= help: the following other types implement trait `ExactSizeIterator`:
&mut I
Args
ArgsOs
ArrayChunksMut<'_, T, N>
ArrayWindows<'_, T, N>
Box<I, A>
Chunks<'_, T>
ChunksExact<'_, T>
and 109 others
note: required by a bound in `foo`
--> src/lib.rs:2:35
|
1 | pub fn foo<I>(i: I)
| --- required by a bound in this function
2 | where I: IntoIterator<Item=i32> + ExactSizeIterator
| ^^^^^^^^^^^^^^^^^ required by this bound in `foo`
Version
rustc 1.73.0-nightly (399b06823 2023-07-20)
binary: rustc
commit-hash: 399b068235ceea440540539b3bfd1aeb82214a28
commit-date: 2023-07-20
host: x86_64-unknown-freebsd
release: 1.73.0-nightly
LLVM version: 16.0.5
Additional Labels
@rustbot label +I-suggestion-causes-error