Enable (and fix) extra lint groups required for in-tree build

[fasterthanlime]

This enables 3 lint groups that are required to build rust-analyzer as an "in-tree" (git subtree) tool in rust-lang/rust, and fixes all relevant diagnostics.

This change is tracked in:

• [Tracking issue] rust-analyzer in-tree build prerequisites #12818

Maintainer impact: more warnings, should be easy enough to fix them (it's mostly looking out for "rust-2015-isms", the lint group is poorly named). If you forget some, they'll show up during a ra=>rust sync.

[lnicola]

Seems reasonable, but it will probably make every open PR unmergeable (at least we don't have a lot of them right now).

[lnicola]

r? @Veykril

[fasterthanlime]

Seems reasonable, but it will probably make every open PR unmergeable (at least we don't have a lot of them right now).

Yeah :( That's the only "touches 260+ files" PR tracked by #12818 - the rest is nice small incremental changes, so I wanted to get it out of the way early.

[Veykril]

Seems reasonable, but it will probably make every open PR unmergeable (at least we don't have a lot of them right now).

Good thing I tried my best to get most merged over the past week

[Veykril]

Can't believe rust_2018_idiom is still not warned by default tbh, also thanks a lot for putting so much effort into this. Really excited for these changes!
@bors r+

[bors]

📌 Commit 7e285e1 has been approved by Veykril

It is now in the queue for this repository.

[bors]

⌛ Testing commit 7e285e1 with merge 28bab68...

[lnicola]

Good thing I tried my best to get most merged over the past week

Exactly :-).

Can't believe rust_2018_idiom is still not warned by default tbh

I think it should have been made into a warning in 2021.

[bors]

☀️ Test successful - checks-actions
Approved by: Veykril
Pushing 28bab68 to master...

[Veykril]

I don't think this added any new conflicts? 🎉