Add lint: from_iter_instead_of_collect

[pitiK3U]

Fixes #5679

This implements lint for ::from_iter() from #5679 not the general issue (std::ops::Add::add, etc.).
This lint checks if expression is function call with from_iter name and if it's implementation of the std::iter::FromIterator trait.

changelog: Introduce from_iter_instead_of_collect lint

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @flip1995 (or someone else) soon.

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[pitiK3U]

I am not sure how to resolve the get_unwrap failing test.
If I am supposed to update .stderr of the test, change the test code, ignore this lint in the test or change category of this lint.

[flip1995]

LGTM overall. Some comments for cleanup and to get it aligned with the rest of the codebase.

[flip1995]

About the get_unwrap test: Just allow the new lint in the get_unwrap test file. You may have to update the get_unwrap.stderr file, because line numbers may change.

---

Please also remove the empty stdout file.

[flip1995]

Last NIT, after that it's ready to get merged 🚀

[flip1995]

The lint you implemented detected this problem in Clippy itself:

error: usage of `FromIterator::from_iter`
   --> clippy_lints/src/lifetimes.rs:217:24
    |
217 |           .intersection(&FxHashSet::from_iter(
    |  ________________________^
218 | |             input_visitor
219 | |                 .nested_elision_site_lts
220 | |                 .iter()
...   |
223 | |                 .filter(|v| matches!(v, RefLt::Named(_))),
224 | |         ))
    | |_________^
    |
    = note: `-D clippy::from-iter-instead-of-collect` implied by `-D clippy::all`
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#from_iter_instead_of_collect
help: use `.collect()` instead of `::from_iter()`
    |
217 |         .intersection(&input_visitor
218 |                 .nested_elision_site_lts
219 |                 .iter()
220 |                 .chain(output_visitor.nested_elision_site_lts.iter())
221 |                 .cloned()
222 |                 .filter(|v| matches!(v, RefLt::Named(_))).collect())
    |

[flip1995]

ping from triage @pitiK3U. There's only a small fix left to be done. Do you have any questions on how to proceed here?

[pitiK3U]

ping from triage @pitiK3U. There's only a small fix left to be done. Do you have any questions on how to proceed here?

Sorry for taking me too long to finish this. My college had started and I hadn't had time to finish it. Will try to do so asap.

[flip1995]

Thanks! Only the dogfood error (#6101 (comment)) is now left to fix

[bors]

☔ The latest upstream changes (presumably #6227) made this pull request unmergeable. Please resolve the merge conflicts.

Note that reviewers usually do not review pull requests until merge conflicts are resolved! Once you resolve the conflicts, you should change the labels applied by bors to indicate that your PR is ready for review. Post this as a comment to change the labels:

@rustbot modify labels: +S-waiting-on-review -S-waiting-on-author

[flip1995]

@bors r+

Thanks! I rebased it for you, so I can directly r+ it, so that there won't be another rebase required.

[bors]

📌 Commit ddf23d6 has been approved by flip1995

[bors]

⌛ Testing commit ddf23d6 with merge a2bf404...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: flip1995
Pushing a2bf404 to master...

[pitiK3U]

@flip1995 Thank you!