bump clippy crates to edition 2021

[matthiaskrgr]

Also helps with dogfooding edition 2021 a bit. :)
Tests passed locally.

---

changelog: bump edition from 2018 to 2021

[rust-highfive]

r? @xFrednet

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[xFrednet]

This looks good to me. However, I would like to also get some feedback from @flip1995 before merging this 🙃.

r? @flip1995

[xFrednet]

r? @flip1995

[flip1995]

Is there already a rust_2021_idioms lint group we can enable? This diff looks suspiciously small.

If not, r=me.

[matthiaskrgr]

There is rust_2021_compatibility I turned that on now and fix the only warning 🙃

warning: changes to closure capture in Rust 2021 will affect drop order
   --> clippy_utils/src/lib.rs:995:26
    |
995 |     v.allow_closure.then(|| v.captures)
    |                          ^^^----------
    |                             |
    |                             in Rust 2018, this closure captures all of `v`, but in Rust 2021, it will only capture `v.captures`
996 | }
    | - in Rust 2018, `v` is dropped here, but in Rust 2021, only `v.captures` will be dropped here as part of the closure
    |
note: the lint level is defined here
   --> clippy_utils/src/lib.rs:16:9
    |
16  | #![warn(rust_2021_compatibility)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^
    = note: `#[warn(rust_2021_incompatible_closure_captures)]` implied by `#[warn(rust_2021_compatibility)]`
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/disjoint-capture-in-closures.html>
help: add a dummy let to cause `v` to be fully captured
    |
995 |     v.allow_closure.then(|| { let _ = &v; v.captures })
    |                             +++++++++++++            +

[flip1995]

Nice, let's also keep the rust_2021_compatibility 👍

[flip1995]

We don't really care about fully capturing v, do we?

[camsteffen]

I think rust_2021_compatibility is only meant to be enabled before transitioning, not after?

[flip1995]

From the rustc book:

Lints used to transition code from the 2018 edition to 2021

A rust-2021-idioms lint group does not exist yet. So I guess we don't want to enable the compatibility group. But good to know, that only one of our closures "fails" this.

[matthiaskrgr]

removed the rust_2021_compatibility warnings again.

[flip1995]

@bors r+

Thanks!

[bors]

📌 Commit d888b4b has been approved by flip1995

[bors]

⌛ Testing commit d888b4b with merge 0c8799d...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: flip1995
Pushing 0c8799d to master...