Create more than 2 lint groups

[mcarton]

Currently we have two lint groups, clippy and clippy_pendantic.

We’ve already discussed that we should have more.

I can think of:

• clippy_deprecated: group where we move lints we ultimately want to remove (ref as_slice will be stable in 1.7 #728);
• clippy_non_api_breaking: subgroup of clippy with only lints whose fix would not change the public API (eg. no ptr_arg, type_complexity, wrong_pub_self_convention, etc.). Useful for crate which did not use Clippy historically and don’t want to change their API. Or maybe clippy_api_breaking with only those lints? Or both and ensure any lint is in either one?

Can you think of other groups you’d want?

[llogiq]

Perhaps subgroups of clippy based on goals, like clippy_style, clippy_performance, clippy_badcode or something similar? On the other hand, there's probably not much value in having them besides documentation.

[mcarton]

Yep. While documentation is a good thing, I don’t know if that should be reflected in a lint group.

[Manishearth]

I don't think overlapping or nested groups work well.

Mostly; I was thinking of keeping pedantic, and adding three more. clippy_stable which suggests stable ways to do unstable things, clipy_restrictions for containing things which aren't style choices (see Graydon's issue), and clippy_deprecated for the deprecated ones.

I'd like to keep the Warn lints in clippy as much as possible.

[llogiq]

So cyclomatic_complexity would be our first restrictions lint, right?

[Manishearth]

idk. I think cyclomatic complexity with a sensible limit is a valid style lint.

[oli-obk]

restrictions are something like deny(allocations) or deny(unsafe) (actually when using restrictions one should use forbid). I'm not sure that a lint-group makes sense for restrictions, because it's unlikely you'll ever want to activate all of them.

[Manishearth]

Right, but I don't want any lints in clippy to be groupless.

[llogiq]

Perhaps we could also add a "newbie" lint group. IMHO inline_always and linked_list would happen to fall in that category. Those are lints that offer reasonable advice to newbies that experts will sometimes find good reason to act against.

[Manishearth]

I think almost all our lints have cases where experts will have good reason to act against. IMO newbie lints should be part of the regular stuff.

(note that inline_always's issues aren't common knowledge)

[clarfonthey]

FWIW I think that clippy_incorrect and clippy_idiomatic might be useful. The former lints things that are probably bugs, and the latter suggests rewording things to a more "rusty" way. Someone might not care about the latter, but still the former.