Using `!` for `c_void` would have the problem that pointers and
potentially references to an uninhabited type would be created, and at
least for references this is UB.

Also document in addition that newtype wrappers around `c_void` are not
recommended for representing opaque types (as a workaround for `extern
type` not being stable) but instead refer to the Nomicon.

…rent implementation

We need at least two variants of the enum as otherwise the compiler
complains about the #[repr(u8)] attribute and we also need at least one
variant as otherwise the enum would be uninhabitated and dereferencing
pointers to it would be UB.

As such, mark the variants not unstable because they should not actually
exist but because they are temporary implementation details until
`extern type` is stable and can be used instead.

- Cleanup the `impl PartialEq<BookFormat> for Book` implementation
- Implement `impl PartialEq<Book> for BookFormat` so it’s symmetric
  - Fixes rust-lang#53844.
- Removes the last example since it appears to be redundant with the
  previous two examples.

Fixes rust-lang#57306

This may be needed with some host compilers.

Fixes rust-lang#57323

A few items were referenced, but did not have links.

It's simpler and makes some benchmark run up to 1% faster. It also makes
`hir::ExprKind` more like `ast::ExprKind` (which underwent the
equivalent change in rust-lang#55777).

It's identical to `ast::Label`.

When given multiple lifetimes prior to type parameters in generic
parameters, do not ICE and print the correct suggestion.

Remove confusing comment about ideally using `!` for `c_void`

Using `!` for `c_void` would have the problem that pointers and
potentially references to an uninhabited type would be created, and at
least for references this is UB.

In addition document that newtype wrappers around `c_void` can be used
safely in place of `extern type` until the latter is stabilized.

----

I'm not 100% sure about the usage for opaque types as the [nomicon](https://doc.rust-lang.org/nomicon/ffi.html#representing-opaque-structs) still recommends using `#[repr(C)] pub struct Foo { _private: [u8; 0] }` but it seems like these two should be equivalent in the end? Also the `#[repr(C)]` (in both cases) should be unneeded because such types never being passed by value, never being dereferenced but only passed around as pointer or reference, so the representation of (*values* of) the type itself should not matter at all?

Also in context of `c_void` and `!` the second unresolved question in the [`extern type`](rust-lang#43467) stabilization ticket seems relevant

> In [std's](https://github.com/rust-lang/rust/blob/164619a8cfe6d376d25bd3a6a9a5f2856c8de64d/src/libstd/os/raw.rs#L59-L64) source, it is mentioned that LLVM expects i8* for C's void*.
> We'd need to continue to hack this for the two c_voids in std and libc.
> But perhaps this should be done across-the-board for all extern types?
> Somebody should check what Clang does.

Please correct me if my understanding is wrong and everything's actually fine as is.

…tsakis

Add a regression test for mutating a non-mut #[thread_local]

This should close rust-lang#54901 since the regression has since been fixed.

…acrum

Use correct tracking issue for c_variadic

Fixes rust-lang#57306

…etMisdreavus

Cleanup PartialEq docs.

- Cleanup the `impl PartialEq<BookFormat> for Book` implementation
- Implement `impl PartialEq<Book> for BookFormat` so it’s symmetric
  - Fixes rust-lang#53844.
- Removes the last example since it appears to be redundant with the
  previous two examples.

Support passing cflags/cxxflags/ldflags to LLVM build

This may be needed with some host compilers.

resolve: Add a test for issue rust-lang#57539

Add a test for the bugfix regression reported in rust-lang#57539

Closes rust-lang#57539

…erister

use structured macro and path resolve suggestions

… r=QuietMisdreavus

Fix sources sidebar not showing up

Fixes rust-lang#57601.

The order of imports made it so that the sidebar creation was called before the sidebar sources were created. Like this, when the sources are loaded, they create the sidebar as expected.

r? @QuietMisdreavus

…reavus

Fixes text becoming invisible when element targetted

Fixes rust-lang#57628.

r? @QuietMisdreavus

librustc_metadata: Pass a default value when unwrapping a span

Fixes rust-lang#57323.

When compiling with `static-nobundle` a-la

`rustc -l static-nobundle=nonexistent main.rs`

we now get a neat output in the form of:

```
error[E0658]: kind="static-nobundle" is feature gated (see issue rust-lang#37403)
  |
  = help: add #![feature(static_nobundle)] to the crate attributes to enable

error: aborting due to previous error

For more information about this error, try `rustc --explain E0658`.
```
The build and tests completed successfully on my machine. Should I be adding a new test?

Add some links in std::fs.

A few items were referenced, but did not have links.

…woerister

Two HIR tweaks

Two HIR tweaks that make things slightly simpler and faster.

Document Unpin in std::prelude documentation

…-applicability, r=withoutboats

Enhance `Pin` impl applicability for `PartialEq` and `PartialOrd`.

This allows for comparing for equality or ordering a `Pin<P>` and a `Pin<Q>` as long as `P` and `Q` are correspondingly comparable themselves *even when `P` and `Q` are different types*.
An example might be comparing a `Pin<&mut OsString>` to a `Pin<&mut PathBuf>`, which might arise from pin projections from a pair of larger contexts that aren't `Unpin`.

…etMisdreavus

Fix non-clickable urls

Fixes rust-lang#57695

I didn't find anywhere where this rule was useful. Why did you add it @JohnHeitmann?

r? @QuietMisdreavus

Fix suggestions given mulitple bad lifetimes

When given multiple lifetimes prior to type parameters in generic
parameters, do not ICE and print the correct suggestion.

r? @estebank

CC @pnkfelix

Fixes: rust-lang#57521

Use structured suggestion to surround struct literal with parenthesis