[Tracking issue] Rearrange location of some of the existing lints

[magurotuna]

Currently, the lint rules grouped as "methods" reside in clippy_lints/src/methods as there are a number of rules belonging to the "methods" group.
However, although the other groups such as "loops", "types", "transmute" and "misc" also have many relavent rules, they reside not in clippy_lints/src/<group_name> but in clippy_lints/src.
It would be great to have these groups located under <group_name> directory just like "methods". So I open this issue to do this refactoring and to keep track of it.

• loops (done by @nahuakang & @Y-Nak Refactor: organize loops file into loops module (Delegated) #6824)
• types (done by @Y-Nak Tracking Issue for refactoring types.rs #6724)
• transmute (done by @magurotuna Refactor: arrange transmute lints #6716)
• functions (done by @Y-Nak Organize functions into functions module #6990)
• methods (also needs to be refactored because currently most of rule implementation are included in clippy_lints/src/methods/mod.rs. Would be good if the implementations went to clippy_lints/src/methods/<lint_name>.rs.) (done by @TaKO8Ki [Tracking Issue] Refactor lints in methods module #6886)
• misc (instead of creating a new directory named misc, split the lints one by one, and move them into where they fit most. )
• misc_early (same as misc) (in progress by @TaKO8Ki Refactor: arrange lints in misc_early module #7166, [Tracking Issue] Refactor lints in misc_early module #7208)
• matches (in progress by @Y-Nak)

How to rearrange is like the following, proposed by @flip1995 on zulip

I would keep the declare_clippy_lint! in the mod.rs Best case would be that mod.rs only contains the lint definitions and the LintPass impl. Utility functions of the module should probably go in methods/utils.rs and then reexported for the module in mod.rs.

proposed by @camsteffen:

For each lint, create a new module at clippy_lints/src/<group_name>/<lint_name>.rs. Within that module, add a function fn check(cx, ..) (with any needed arguments) and move the implementation there.

CC @nahuakang @camsteffen

[nahuakang]

@magurotuna @camsteffen Shall we kick this off sometime this month? I could focus on loops since I just came from it (and there are only 18 lints). But I think for methods we'd need to split carefully since it has 50+ lints 🤔

[flip1995]

Also feel free to split this not only in multiple commits, but also in multiple PRs.

[camsteffen]

@nahuakang Sure! But frankly I don't want to promise anything from me at this point. For organization, I would recommend we comment here on what group you're currently working on. But you don't have to do an entire group.

[phansch]

clippy_lints/src/<group_name>/<lint_name>.rs

If group_name refers to lint groups like restriction or pedantic, it's worth noting that these change quite often compared to lint names. So, if someone changes the lint group of a lint they will have to move it to the correct directory as well, adding some extra work. Not sure if that's fine?

If it just refers to unrelated group names, ignore what I said =)

[nahuakang]

@phansch The group_name would be methods or loops so that new contributors have an easier time finding lints or understanding the structure of the repo 😁 You are right that it shouldn't be the lint group categories.

[magurotuna]

I'll work on "transmute" group :)

[Y-Nak]

I'll work on types!

[flip1995]

@Y-Nak @nahuakang @magurotuna Do you want to cross-review your PRs to make sure that you all used the same "style" for the restructuring, so the Clippy code is consistent? That would be a big help for me reviewing those PRs because I don't have to compare them to eachother.