Co-authored-by: Bastian Kauschke <bastian_kauschke@hotmail.de>

Because there is at most one file.

Fix unused_parens false positive when using binary operations

Fixes rust-lang#71290

r? @cuviper who provided instructions

…matsakis

Fix hang in lexical_region_resolve

Regionck was stuck in a loop where a region value was changing between two equal regions.

Closes rust-lang#72051

…d_files, r=alexcrichton

Change `WorkProduct::saved_files` to an `Option`.

Because there is at most one file.

r? @bjorn3

…E0228, r=petrochenkov

add long error explanation for E0228

Add long explanation for the E0228 error code
Part of rust-lang#61137

Let me know if this is wrong at all (or can be written more clearly), I'm still learning Rust.

Warn against thread::sleep in async fn

I've seen `thread::sleep` wrecking havoc in async servers. There's already an [issue for clippy](rust-lang/rust-clippy#4377), but the std docs could warn against it too.

use `require_lang_item` over `unwrap`.

Does not yet replace all uses of `lang_items\(\)\.*\.unwrap\(\)`, as there are more
than I expected 😅

Fixes rust-lang#72099

r? @RalfJung

*edit: The goal of this this PR is to change ICE from missing lang items to a fatal error.*

…an-DPC

Clean up E0589 explanation

r? @Dylan-DPC

…tebank

Don't ICE on missing `Unsize` impl

Previously code of the form

```rust
#![feature(unsize, dispatch_from_dyn)]

use std::marker::Unsize;
use std::ops::DispatchFromDyn;

pub struct Foo<'a, T: ?Sized> {
    _inner: &'a &'a T,
}

impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Foo<'a, U>> for Foo<'a, T> {}
```

would generate an ICE due to the missing `Unsize` impl being run through the `suggest_change_mut` suggestion. This PR adds an early exit and a pointer to the appropriate docs regarding `Unsize` instead:

```
error[E0277]: the trait bound `&'a T: std::marker::Unsize<&'a U>` is not satisfied
  --> src/test/ui/issues/issue-71036.rs:11:1
   |
11 | impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Foo<'a, U>> for Foo<'a, T> {}
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::marker::Unsize<&'a U>` is not implemented for `&'a T`
   |
   = note: all implementations of `Unsize` are provided automatically by the compiler, see <https://doc.rust-lang.org/stable/std/marker/trait.Unsize.html> for more information
   = note: required because of the requirements on the impl of `std::ops::DispatchFromDyn<&'a &'a U>` for `&'a &'a T`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.
```

r? @estebank

Resolves rust-lang#71036