Suggest changing iter/into_iter when the other was meant

[estebank]

When encountering a call to iter that should have been into_iter and vice-versa, provide a structured suggestion:

error[E0271]: type mismatch resolving `<IntoIter<{integer}, 3> as IntoIterator>::Item == &{integer}`
  --> $DIR/into_iter-when-iter-was-intended.rs:5:37
   |
LL |     let _a = [0, 1, 2].iter().chain([3, 4, 5].into_iter());
   |                               ----- ^^^^^^^^^^^^^^^^^^^^^ expected `&{integer}`, found integer
   |                               |
   |                               required by a bound introduced by this call
   |
note: the method call chain might not have had the expected associated types
  --> $DIR/into_iter-when-iter-was-intended.rs:5:47
   |
LL |     let _a = [0, 1, 2].iter().chain([3, 4, 5].into_iter());
   |                                     --------- ^^^^^^^^^^^ `IntoIterator::Item` is `{integer}` here
   |                                     |
   |                                     this expression has type `[{integer}; 3]`
note: required by a bound in `std::iter::Iterator::chain`
  --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL
help: consider not consuming the `[{integer}, 3]` to construct the `Iterator`
   |
LL -     let _a = [0, 1, 2].iter().chain([3, 4, 5].into_iter());
LL +     let _a = [0, 1, 2].iter().chain([3, 4, 5].iter());
   |

Finish addressing the original case in #68095. Only the case of chaining a Vec or [] is left unhandled.

[rustbot]

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[mati865]

@bors r+

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[rust-bors]

📌 Commit 2b32446 has been approved by mati865

It is now in the queue for this repository.

[mati865]

@bors rollup