Stabilize iterator_repeat_with

[tmccombs]

Fixes #48169

[rust-highfive]

r? @aidanhs

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[rust-highfive]

The job x86_64-gnu-llvm-3.9 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

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[01:03:37] travis_fold:start:test_stage1-core
travis_time:start:test_stage1-core
Testing core stage1 (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:03:37]    Compiling core v0.0.0 (file:///checkout/src/libcore)
[01:03:45] error[E0277]: the trait bound `std::iter::RepeatWith<[closure@libcore/../libcore/tests/iter.rs:1728:32: 1728:69 curr:_]>: std::iter::DoubleEndedIterator` is not satisfied
[01:03:45]     --> libcore/../libcore/tests/iter.rs:1729:22
[01:03:45]      |
[01:03:45] 1729 |                     .rev().take(4);
[01:03:45]      |                      ^^^ the trait `std::iter::DoubleEndedIterator` is not implemented for `std::iter::RepeatWith<[closure@libcore/../libcore/tests/iter.rs:1728:32: 1728:69 curr:_]>`
[01:03:45] 
[01:03:45] error[E0599]: no method named `take` found for type `std::iter::Rev<std::iter::RepeatWith<[closure@libcore/../libcore/tests/iter.rs:1728:32: 1728:69 curr:_]>>` in the current scope
[01:03:45]     --> libcore/../libcore/tests/iter.rs:1729:28
[01:03:45]      |
[01:03:45] 1729 |                     .rev().take(4);
[01:03:45]      |
[01:03:45]      |
[01:03:45]      = note: the method `take` exists but the following trait bounds were not satisfied:
[01:03:45]              `std::iter::Rev<std::iter::RepeatWith<[closure@libcore/../libcore/tests/iter.rs:1728:32: 1728:69 curr:_]>> : std::iter::Iterator`
[01:03:45]              `&mut std::iter::Rev<std::iter::RepeatWith<[closure@libcore/../libcore/tests/iter.rs:1728:32: 1728:69 curr:_]>> : std::iter::Iterator`
[01:03:51] error: aborting due to 2 previous errors
[01:03:51] 
[01:03:51] Some errors occurred: E0277, E0599.
[01:03:51] For more information about an error, try `rustc --explain E0277`.

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[Centril]

Thanks for filing this! There's a minor adjustment needed.

[Centril]

There is some documentation re. DEI left that needs to be removed:

An iterator produced by repeat_with() is a DoubleEndedIterator. It is important to note that reversing repeat_with(f) will produce the exact same sequence as the non-reversed iterator. In other words, repeat_with(f).rev().collect::<Vec<_>>() is equivalent to repeat_with(f).collect::<Vec<_>>().

I would replace this with a note saying that it isn't DEI and to ask users who need that to come forward and file an issue explaining their use case.

[tmccombs]

Fixed.

[kennytm]

@bors r=Centril,kennytm

[bors]

📌 Commit 87941b0 has been approved by Centril,kennytm

[bors]

⌛ Testing commit 87941b0 with merge c5a129e...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: Centril,kennytm
Pushing c5a129e to master...