[iter_without_into_iter]: fix papercuts in suggestion and restrict linting to exported types

[y21]

See #11692 for more context.

tldr: the lint iter_without_into_iter has suggestions that don't compile, which imo isn't that problematic because it does have the appropriate Applicability that tells external tools that it shouldn't be auto-applied.
However there were some obvious "errors" in the suggestion that really should've been included in my initial PR adding the lint, which is fixed by this PR:

• IntoIterator::into_iter needs a self argument.
• IntoIterator::Iter associated type doesn't exist. This should've just been Item.

This still doesn't make it machine applicable, and the remaining things are imho quite non-trivial to implement, as I've explained in #11692 (comment).
I personally think it's fine to leave it there and let the user change the remaining errors when copy-pasting the suggestion (e.g. errors caused by lifetimes that were permitted in fn return-position but are not in associated types).
This is how many of our other lint suggestions already work.

Also, we now restrict linting to only exported types. This required moving basically all of the tests around since they were previously in the main function. Same for into_iter_without_iter. The git diff is a bit useless here...

changelog: [iter_without_into_iter]: fix papercuts in suggestion and restrict linting to exported types

(cc @lopopolo, figured I should mention you since you created the issue)

[rustbot]

r? @xFrednet

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[xFrednet]

LGTM, I have one small suggestion, and then you can r=me. Also thank you for the fix :D

Clippy's documentation says that this lint will be stabilized in rust 1.74. Do you think this is worth a beta backport? It's a pedantic lint, which doesn't make it super necessary, but the restriction to only exported items, might make a big difference, to the amount of lint triggers 🤔

[xFrednet]

@bors delegate+

[bors]

✌️ @y21, you can now approve this pull request!

If @xFrednet told you to "r=me" after making some further change, please make that change, then do @bors r=@xFrednet

[y21]

Do you think this is worth a beta backport?

I think it's a good idea, even for a pedantic lint. It's not all that useful for private types imo and I think it could make a noticeable difference in how often the lint occurs. The errors in the suggestion were also pretty obvious so it would be nice if this fix gets into beta along with the PR that introduced this.
But if it's too much of a hassle or this is the only PR that is gonna be nominated for backporting, it might be unnecessary.

[lopopolo]

Please backport this. Paper cuts in clippy lints lead to them being disabled in my codebases. I almost never revisit an !#[allow(clippy::xxx)] once it gets added

[xFrednet]

I agree and this shouldn't be a problem, that's why I asked. @flip1995 Usually does the beta back ports, a week or so before the release. To indicate that a fix should be back ported, we just need to add the beta-nominated label.

@rustbot label +beta-nominated

[xFrednet]

The current version is fine. I would formulate it a bit differently, but this is mostly a question of taste. I leave the decision up to you, which one you like more, or if you want to combine the two versions :)

    /// ### Limitations
    /// This lint focusess on providing an idiomatic API. Therefore, it will only
    /// lint on types, which are accessible outside of the crate. For internal types
    /// these methods can be added on demand, if they are acually needed. Otherwise,
    /// it would trigger the [`dead_code`] lint for the unused method.
    ///
    /// [`dead_code`]: https://doc.rust-lang.org/rustc/lints/listing/warn-by-default.html#dead-code

[y21]

Adjusted the documentation a bit with your suggestions in mind.

[xFrednet]

LGTM, thank you for the update :)

@bors r+

[bors]

📌 Commit 9a10d32 has been approved by xFrednet

It is now in the queue for this repository.

[bors]

⌛ Testing commit 9a10d32 with merge f8409ef...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: xFrednet
Pushing f8409ef to master...

[flip1995]

This lint does not exist in beta yet and this PR was already synced to rustc. So this PR will be included when this lint gets to beta and ultimately stable. => Nothing to do for me. My favorite kind of backports 🙃