New lint: redundant_test_prefix

[farazdagi]

This PR has started as an effort to proceed from the feedback in #12861.

• Checks test functions (functions marked with #[test] annotation) for redundant "test_" prefix.
• Auto-fix is supported (and handles collisions gracefully, see below).
  • If removing "test_" prefix from, say, test_foo() results in a name collision (either because function foo() is already defined within the current scope, or because the foo() call exists within function -- thus creating an unwanted recursion), lint suggests function rename, warning the user that a simple trimming of test_ prefix will result in a name collision.
  • If removing "test_" prefix results in invalid identifier (consider test_const, test_, test_42), then again no auto-fix is suggested, user is asked to rename function, with a note that a simple prefix trimming will result in an invalid function name. (Applicability::HasPlaceholders is used and user is suggested to: drop test_ prefix + add _works suffix, i.e. test_foo becomes foo_works -- but again, user has to apply those changes manually).
  • If trimmed version of the function name is a valid identifier, doesn't result in name collision or unwanted recursion, then user is able to run auto-fix.

fixes #8931

changelog: new lint: [redundant_test_prefix]

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @dswij (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:

• @rustbot author: the review is finished, PR author should check the comments and take action accordingly
• @rustbot review: the author is ready for a review, this PR will be queued again in the reviewer's queue

[farazdagi]

@dswij any ETA on when you'll be able to review (it has been more than 2 weeks -- so, I am not sure whether there needs to be some action on my part to get this rolling).

[farazdagi]

@J-ZhengLi @xFrednet sorry to bother you, but maybe you'll have time to review this PR (since you've provided good feedback on its previous incarnation -- and I've incorporated your suggestions).

Really eager to receive my first feedback on this one (still learning the clippy's tooling), before diving into any other open tasks/issues.

[xFrednet]

Hej, thank you for the ping. Sure, I'll add it to my reviewing list. You should get some feedback this weekend!

@J-ZhengLi You're welcome to also help with the review if you want. But also don't feel any pressure :)

r? @xFrednet

[xFrednet]

Very solid start. Thank you for picking up the other PR, it's nice to see it being worked on! :D

Please let me know if you have any questions.

[xFrednet]

I'm unassigning myself from this PR. @farazdagi if you want to continue this work, please request a new reviewer with r? clippy

[farazdagi]

Implemented suggestions from the review (thanks @xFrednet for great pointers)

r? clippy

[farazdagi]

@rustbot ready

[Manishearth]

r? @samueltardieu for now

[samueltardieu]

This is neater indeed without the configuration option.

I have some remarks left, about the style, it won't change anything in the uitest output.

[samueltardieu]

Almost there! Those latest comments are stylish issues, and some cleanups that could be done while you're editing this part of the code.

The only "performance" issue (and change proposal) is that it is more costly to intern things than to get their textual representation back, so it is best to intern only once.

Thanks for your patience.

[farazdagi]

Almost there! Those latest comments are stylish issues, and some cleanups that could be done while you're editing this part of the code.

The only "performance" issue (and change proposal) is that it is more costly to intern things than to get their textual representation back, so it is best to intern only once.

Thanks for your patience.

No problem at all -- learning from this review process almost more than from the lint's implementation itself. So, thank you for such an insightful review.

[samueltardieu]

Looks like you missed this one. The rest looks good to me!

[samueltardieu]

LGTM

@rustbot label -S-waiting-on-author

[samueltardieu]

Thanks @farazdagi. The new lint will likely appear in the nightly toolchain before the end of the week.