Add lint to check manual pattern char comparison

[AurelienFT]

This PR adds a new lint asked in #12490

This lint catches manual char comparison in pattern of string functions and propose to use char or array of char instead.

As it's my first contribution i'm not feeling very safe about not matching too much or missing some cases.

Thanks in advance for taking time to review and propose feedback !

changelog: new lint [manual_pattern_char_comparison]

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @Alexendoo (or someone else) some time within the next two weeks.

Please see the contribution instructions for more information. Namely, in order to ensure the minimum review times lag, PR authors and assigned reviewers should ensure that the review label (S-waiting-on-review and S-waiting-on-author) stays updated, invoking these commands when appropriate:

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[AurelienFT]

I have applied all the suggestions. Thank you for the very deep explanations as a first contributor it's very appreciable. I learnt a lot of things in Clippy and it motivate me to continue to contribute !

[AurelienFT]

@Alexendoo thank you for the heart, that's kind ! If there anything I need to do for this PR or I need to wait ? I don't want to be rude, it's because I'm not very familiar with the process so I prefer to ask

[Alexendoo]

I plan to do another read through of it soon, then after that I'll create a final comment period thread on Zulip for others to weigh in

[Alexendoo]

Opened the FCP here also: https://rust-lang.zulipchat.com/#narrow/stream/257328-clippy/topic/FCP.20.60manual_pattern_char_comparison.60

[bors]

☔ The latest upstream changes (presumably #12815) made this pull request unmergeable. Please resolve the merge conflicts.

[AurelienFT]

I addressed all the comments.

Furthermore I saw that last time I forget to push modification on function get_char_span that reduce the code to less than 10 lines thanks to your ideas @Alexendoo.

Everything should be fine now

[bors]

☔ The latest upstream changes (presumably #12915) made this pull request unmergeable. Please resolve the merge conflicts.

[Alexendoo]

If you could squash the commits I think this is ready to merge, the FCP has been running long enough without issue

[rustbot]

There are merge commits (commits with multiple parents) in your changes. We have a no merge policy so these commits will need to be removed for this pull request to be merged.

You can start a rebase with the following commands:

$ # rebase
$ git pull --rebase https://github.com/rust-lang/rust-clippy.git master
$ git push --force-with-lease

The following commits are merge commits:

• c658805

[AurelienFT]

@Alexendoo Seems ok to me. (I'm not very confident with my git skills 😆 )

[Alexendoo]

Yep, looks great thanks!

@bors r+

[bors]

📌 Commit c86b19f has been approved by Alexendoo

It is now in the queue for this repository.

[bors]

⌛ Testing commit c86b19f with merge 6f1b05b...

[bors]

💔 Test failed - checks-action_test

[Alexendoo]

@bors retry

[bors]

⌛ Testing commit c86b19f with merge 740b72e...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: Alexendoo
Pushing 740b72e to master...

[AurelienFT]

@Alexendoo I want to make you a special thanks for being so nice an pedagogy for this PR, loved it. You are really kind !

[Alexendoo]

Thank you! Congrats on the first contribution