Help is suggesting to use __iterator_get_unchecked

[MultisampledNight]

Code

fn i_can_has_iterator() -> impl Iterator<Item = u32> {
    Box::new(1..=10) as Box<dyn Iterator>
}

Current output

Compiling iterconfusion v0.1.0 (/irrelevant/iterconfusion)
error[E0191]: the value of the associated type `Item` (from trait `Iterator`) must be specified
 --> src/lib.rs:2:33
  |
2 |     Box::new(1..=10) as Box<dyn Iterator>
  |                                 ^^^^^^^^ help: specify the associated type: `Iterator<Item = Type>`

error[E0271]: expected `Box<dyn Iterator>` to be an iterator that yields `u32`, but it yields `<dyn Iterator as Iterator>::Item`
    --> src/lib.rs:1:28
     |
1    | fn i_can_has_iterator() -> impl Iterator<Item = u32> {
     |                            ^^^^^^^^^^^^^^^^^^^^^^^^^ expected associated type, found `u32`
2    |     Box::new(1..=10) as Box<dyn Iterator>
     |     ------------------------------------- return type was inferred to be `Box<dyn Iterator>` here
     |
     = note: expected associated type `<dyn Iterator as Iterator>::Item`
                           found type `u32`
help: a method is available that returns `<dyn Iterator as Iterator>::Item`
    --> /home/multisn8/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/iter/traits/iterator.rs:3852:5
     |
3852 | /     unsafe fn __iterator_get_unchecked(&mut self, _idx: usize) -> Self::Item
3853 | |     where
3854 | |         Self: TrustedRandomAccessNoCoerce,
     | |__________________________________________^ consider calling `__iterator_get_unchecked`

Some errors have detailed explanations: E0191, E0271.
For more information about an error, try `rustc --explain E0191`.
error: could not compile `iterconfusion` due to 2 previous errors

Desired output

error[E0191]: the value of the associated type `Item` (from trait `Iterator`) must be specified
 --> src/lib.rs:2:33
  |
2 |     Box::new(1..=10) as Box<dyn Iterator>
  |                                 ^^^^^^^^ help: specify the associated type: `Iterator<Item = Type>`
help: likely you want this to match the output type, `Iterator<Item = u32>`
 --> src/lib.rs:2:40
  |
2 |     Box::new(1..=10) as Box<dyn Iterator<Item = u32>>
  |                                         ++++++++++++

Rationale and extra context

I don't think I as an outside user of stdlib should be confronted with using internal unsafe APIs such as __iterator_get_unchecked.

Other cases

No response

Anything else?

rustc -V: rustc 1.69.0-nightly (5b8f28453 2023-02-12)

[mejrs]

This seems like a prime use case for #51992