Repository navigation
Iterator not found for referenced box array item #164751
Description
Code
I tried this code:
#[derive(Clone, Copy)]
pub struct Wrapper<T>(T);
impl<T> IntoIterator for Wrapper<T> {
type Item = T;
type IntoIter = std::option::IntoIter<T>;
fn into_iter(self) -> Self::IntoIter {
Some(self.0).into_iter()
}
}
#[unsafe(no_mangle)]
fn test(v: &Box<[Wrapper<usize>; 2]>) {
for v in v.into_iter().flatten() {
std::hint::black_box(v);
}
}I expected to see this happen: code compiles
Instead, this happened: compile error
error[E0277]: `&Wrapper<usize>` is not an iterator
--> <source>:14:28
|
14 | for v in v.into_iter().flatten() {
| ^^^^^^^ `&Wrapper<usize>` is not an iterator
|
= help: the trait `Iterator` is not implemented for `&Wrapper<usize>`
help: the trait `IntoIterator` is implemented for `Wrapper<T>`
Version it worked on
It most recently worked on: 1.98
Version with regression
Compile errors on all the following: 1.99.0, 1.99.1, beta, nightly
Notes
It seems to only occer when the type is &Box<[Wrapper<_>; _]>.
The following all errors on 1.98: &[Wrapper<_>], &[Wrapper<_>; _], &Box<[Wrapper<_>]>.
Bug does not occur (compile succeeds) if the Box isnt behind a reference.
@rustbot modify labels: +regression-from-stable-to-{channel} -regression-untriaged
Activity
rustbot commentedon Oct 22, 2026
Error: Unknown labels: regression-from-stable-to-{channel}
Please file an issue on GitHub at triagebot if there's a problem with this bot, or reach out on #triagebot on Zulip.
theemathas commentedon Oct 22, 2026
Presumably caused by #134021
The
v.into_iter()is now calling theIntoIterimplementation on the&Box<[_; _]>instead of on the[_; _]chokomancarr commentedon Oct 22, 2026
nevermind, looks like this is caused by the stabilized IntoIterator for boxed array
theemathas commentedon Oct 22, 2026
A crater run for that PR was done, and the small amount of breakage was accepted.
theemathas commentedon Oct 22, 2026
@chokomancarr I believe the relevant impl is on
&Box<[_; _]>, not onBox<[_; _]>