New lint sliced_string_as_bytes

[wowinter13]

resurrection of #10984

fixes #10981

changelog: [sliced_string_as_bytes]: add new lint sliced_string_as_bytes

[rustbot]

r? @Manishearth

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[Manishearth]

nit: performance?

[wowinter13]

#10984 (comment)
I decided to follow @Jarcho 's category selection
But without a doubt I can revert it back to perf

[Manishearth]

Yeah, I think the behavior change should not matter. It is indeed a very minor performance win so that's a somewhat compelling argument for pedanticness. Curious what @Jarcho thinks now?

[samueltardieu]

LGTM, with two minor nits.

[wowinter13]

@Manishearth Would you have a second to check?

[Manishearth]

I still think it should be a perf lint, unless we're worried that it's going to be super noisy.

Thoughts @xFrednet @flip1995 ? (to get some random additional opinions)

[xFrednet]

I can't quite make up my mind. It doesn't feel like a warn-by-default lint to me, but I see how it could save performance, especially with long strings. So normally, I'd suggest pedantic as well, but I'd also be okay with your suggestion of perf.

Lintcheck shows 4 new lint triggers, so it shouldn't be too noisy.

[Manishearth]

I think "minor perf benefit but also not too noisy" makes it a perf lint in my book.

I tend to weight things by how likely they are to trigger.

[wowinter13]

@Manishearth changed to perf & resolved conflicts
(It looks like majority stands with perf lint)