[WIP] BARE_TRAIT_OBJECTS -> Deny

[Centril]

Based on https://github.com/rust-lang/rfcs/blob/master/text/2113-dyn-trait-syntax.md#migration.

Let's first crater this for both editions to see what the fallout is. (I expect it will be large)
I suspect the likely outcome will be Warn on at least Rust 2015 for a start.

r? @oli-obk

[Centril]

Before I try this; let's let travis have a go at it.

[oli-obk]

I'm probably not the most reasonable choice for a reviewer here as I'm strongly of the opinion that lints are but sound and smoke. Irrelevant of the "fallout" (in quotes, because it doesn't break dependencies, is trivial to fix, even rustfixable), I think we should just merge this. Going through a warning phase is pretty useless, as (subjectively, I have no data) Rust developers don't really commit (or at least publish) code that has warnings.

[Centril]

@oli-obk Oh hmm... the lint is Allow right now tho so it generates no warnings. Let's discuss on Thursday's T-Lang meeting and see how we feel about jumping straight to Deny on both editions.

[jethrogb]

Regarding all of these rust_2018_idioms changes, I couldn't find much previous discussion on the proposed deprecation paths, but I feel like these changes should've happened as part of the edition release and it's too late to start failing on them now.

[Centril]

@jethrogb This is specified in https://github.com/rust-lang/rfcs/blob/master/text/2113-dyn-trait-syntax.md#migration. This is just executing the already agreed-to plan. (And we decided that we would wait with ramping up the idioms lints until later into the edition)

[jethrogb]

RFC 2113 just covers this PR, what about the other 3?

Also it seems bad to change a lint from allow to deny without a warning period.

[Centril]

@jethrogb Left comments on those.

Also it seems bad to change a lint from allow to deny without a warning period.

Please see the first comment in the PR. The idea is to measure the impact and deciding how to proceed from there.

[Centril]

We discussed this on this weeks lang meeting; the general consensus was to crater and see how things fall out and move on from there.

[Dylan-DPC-zz]

ping from triage, closing this due to inactivity