Make *const (), *mut () okay for FFI

Pointer-to-() is used occasionally in the standard library to mean "pointer to none-of-your-business". Examples:

- `RawWakerVTable::new` https://doc.rust-lang.org/1.51.0/std/task/struct.RawWakerVTable.html#method.new
- `<*const T>::to_raw_parts` https://doc.rust-lang.org/nightly/std/primitive.pointer.html#method.to_raw_parts

I believe it's useful for the same purpose in FFI signatures, even while `()` itself is not FFI safe. The following should be allowed:

```rust
extern "C" {
    fn demo(pc: *const (), pm: *mut ());
}
```

Prior to this PR, those pointers were not considered okay for an extern signature.

```console
warning: `extern` block uses type `()`, which is not FFI-safe
 --> src/main.rs:2:17
  |
2 |     fn demo(pc: *const (), pm: *mut ());
  |                 ^^^^^^^^^ not FFI-safe
  |
  = note: `#[warn(improper_ctypes)]` on by default
  = help: consider using a struct instead
  = note: tuples have unspecified layout

warning: `extern` block uses type `()`, which is not FFI-safe
 --> src/main.rs:2:32
  |
2 |     fn demo(pc: *const (), pm: *mut ());
  |                                ^^^^^^^ not FFI-safe
  |
  = help: consider using a struct instead
  = note: tuples have unspecified layout
```

Make diangostic item naming consistent

Right now there is about a 50/50 split of naming diagnostic items as `vec_type` vs `Vec`. So it is hard to guess a diagnostic item name with confidence. I know it's not great to change these retroactively, but I think it will be much easier to maintain consistency after consistency is established.

…olnay

Optimize unnecessary check in Vec::retain

The function `vec::Vec::retain` only have two stages:

1. Nothing was deleted.
2. Some elements were deleted.

Here is an unnecessary check `if g.deleted_cnt > 0` in the loop, and it's difficult for compiler to optimize it. I split the loop into two stages manully and keep the code clean using const generics.

I write a special but common bench case for this optimization. I call retain on vec but keep all elements.

Before and after this optimization:

```
test vec::bench_retain_whole_100000                      ... bench:      84,803 ns/iter (+/- 17,314)
```

```
test vec::bench_retain_whole_100000                      ... bench:      42,638 ns/iter (+/- 16,910)
```

The result is expected, there are two `if`s before the optimization and one `if` after.

Among other changes, documents whether allocations are necessary
to complete the type conversion.

Part of rust-lang#51430

Co-authored-by: Giacomo Stevanato <giaco.stevanato@gmail.com>

Co-authored-by: Joshua Nelson <github@jyn.dev>

…51430-document-from

Implement `non_send_field_in_send_ty` lint

changelog: Implement [`non_send_fields_in_send_ty`] lint

Fixes rust-lang#7703

…docker images

exclude enum from derivable impls

fix rust-lang#7753

changelog: Exclude enum from ``[`derivable_impls`]``

Use bitand when checking for signed integer division overflow

For `self == Self::MIN && rhs == -1`, LLVM does not realize that this is the same check made by `self / rhs`, so the code generated may have some unnecessary duplication. For `(self == Self::MIN) & (rhs == -1)`, LLVM realizes it is the same check.

Fixed numerus of error message

Removed superfluous argument

Using pluralize!() instead of code duplication

Adjusted a test

Detects rust-lang#88545

… that overlay row entries after a UA specific amount of rows

…r=dtolnay

Make `<[T]>::split_at_unchecked` and `<[T]>::split_at_mut_unchecked` public

The methods were originally added in rust-lang#75936 (sdroege@30dc32b), but for some reason as private. Nevertheless, the methods have documentation and even a [tracking issue](rust-lang#76014).

It's very weird to have a tracking issue for private methods and these methods may be useful outside of the standard library. As such, this PR makes the methods public.

This is cleaner and removes an unstable feature usage

BTree: toughen panicky test of clone()

Test did not cover the second half of `clone_subtree` and why this clones key & value first.

These two functions are essentially no-ops (and compile to just a load and
return), but show up in process_obligations profiles with a high call count --
so worthwhile to try and inline them away.

…ate, r=Mark-Simulacrum

Update Let's Encrypt ROOT CA certificate in dist-(i686|x86_64)-linux docker images

The DST Root CA X3 used by Let's Encrypt has expired ([Let's Encrypt announcement](https://letsencrypt.org/docs/dst-root-ca-x3-expiration-september-2021/)). This patch installs the new root certificate (ISRG Root X1) and disables the old one. Disabling the old one is necessary because otherwise curl still fails to download from servers with Let's Encrypt certs even though they are cross-signed.

Fixes rust-lang#89484.

…_loops

Co-authored-by: kennytm <kennytm@gmail.com>

…earth

Add expansion to while desugar spans

In the same vein as rust-lang#88163, this reverts a change in Clippy behavior as a result of rust-lang#80357 (and reverts some `#[allow]`s): This changes `clippy::blocks_in_if_conditions` to not fire on `while` loops. Though we might actually want Clippy to lint those cases, we should introduce the change purposefully, with tests, and possibly under a different lint name.

The actual change here is to add a desugaring expansion to the spans when lowering a `while` loop.

r? `@Manishearth`

…earth

Add expansion to while desugar spans

In the same vein as rust-lang#88163, this reverts a change in Clippy behavior as a result of rust-lang#80357 (and reverts some `#[allow]`s): This changes `clippy::blocks_in_if_conditions` to not fire on `while` loops. Though we might actually want Clippy to lint those cases, we should introduce the change purposefully, with tests, and possibly under a different lint name.

The actual change here is to add a desugaring expansion to the spans when lowering a `while` loop.

r? `@Manishearth`

Fixes rust-lang#55825

Fixes rust-lang#73159

This is similar to rust-lang#69350 - if the user didn't initially
write out a 'static lifetime, adding 'static in response to
a lifetime error is usually the wrong thing to do.

…ding

… r=joshtriplett

Fix read_to_end to not grow an exact size buffer

If you know how much data to expect and use `Vec::with_capacity` to pre-allocate a buffer of that capacity, `Read::read_to_end` will still double its capacity. It needs some space to perform a read, even though that read ends up returning `0`.

It's a bummer to carefully pre-allocate 1GB to read a 1GB file into memory and end up using 2GB.

This fixes that behavior by special casing a full buffer and reading into a small "probe" buffer instead. If that read returns `0` then it's confirmed that the buffer was the perfect size. If it doesn't, the probe buffer is appended to the normal buffer and the read loop continues.

Fixing this allows several workarounds in the standard library to be removed:

- `Take` no longer needs to override `Read::read_to_end`.
- The `reservation_size` callback that allowed `Take` to inhibit the previous over-allocation behavior isn't needed.
- `fs::read` doesn't need to reserve an extra byte in `initial_buffer_size`.

Curiously, there was a unit test that specifically checked that `Read::read_to_end` *does* over-allocate. I removed that test, too.

…plett

Add `Ipv6Addr::is_benchmarking`

This PR adds the unstable method `Ipv6Addr::is_benchmarking`. This method is added for parity with `Ipv4Addr::is_benchmarking`, and I intend to use it in a future rework of `Ipv6Addr::is_global` (edit: rust-lang#86634) to more accurately follow the [IANA Special Address Registry](https://www.iana.org/assignments/iana-ipv6-special-registry/iana-ipv6-special-registry.xhtml) (like is done in `Ipv4Addr::is_global`).

With `Ipv6Addr::is_benchmarking` and `Ipv4Addr::is_benchmarking` now both existing, `IpAddr::is_benchmarking` is also added.

…-replace, r=joshtriplett

const fn for option copied, take & replace

Tracking issue: [rust-lang#67441](rust-lang#67441)

Adding const fn for the copied, take and replace method of Option. Also adding necessary unit test.

It's my first contribution so I am pretty sure I don't know what I'm doing but there's a first for everything!

BTree: refine some comments

…metics_as_const, r=joshtriplett

Mark unsafe methods NonZero*::unchecked_(add|mul) as const.

Now that rust-lang/rfcs#3016 has landed, these two unstable `std` function can be marked `const`, according to this detail of rust-lang#84186.

…block-std, r=dtolnay

Remove unnecessary unsafe block in `process_unix`

Because it's nested under this unsafe fn!

This block isn't detected as unnecessary because of a bug in the compiler: rust-lang#88260.

Manual Debug for Unix ExitCode ExitStatus ExitStatusError

These structs have misleading names.  An ExitStatus[Error] is actually a Unix wait status; an ExitCode is actually an exit status.  These misleading names appear in the `Debug` output.

The `Display` impls on Unix have been improved, but the `Debug` impls are still misleading, as reported in rust-lang#74832.

Fix this by pretending that these internal structs are called `unix_exit_status` and `unix_wait_status` as applicable.  (We can't actually rename the structs because of the way that the cross-platform machinery works: the names are cross-platform.)

After this change, this program
```
#![feature(exit_status_error)]
fn main(){
    let x = std::process::Command::new("false").status().unwrap();
    dbg!(x.exit_ok());
    eprintln!("x={:?}",x);
}
```
produces this output
```
[src/main.rs:4] x.exit_ok() = Err(
    ExitStatusError(
        unix_wait_status(
            256,
        ),
    ),
)
x=ExitStatus(unix_wait_status(256))
```

Closes rust-lang#74832

…oshtriplett

Partially stabilize `array_methods`

This stabilizes `<[T; N]>::as_slice` and `<[T; N]>::as_mut_slice`, which is forms part of the `array_methods` feature: rust-lang#76118.

This also makes `<[T; N]>::as_slice` const due to its trivial nature.

Add missing `# Panics` section to `Vec` method

namely `Vec::extend_from_within`

…llot

Remove some feature gates

The first commit removes various feature gates that are unused. The second commit replaces some `Fn` implementations with `Iterator` implementations, which is much cleaner IMO. The third commit replaces an unboxed_closures feature gate with min_specialization. For some reason the unboxed_closures feature gate suppresses the min_specialization feature gate from triggering on an `TrustedStep` impl. The last comment just turns a regular comment into a doc comment as drive by cleanup. I can move it to a separate PR if preferred.

Fix link in Ipv6Addr::to_ipv4 docs

Add truncate note to Vec::resize

A very minor addition to the `Vec::resize` documentation to point out the `truncate` method.
When I was searching for something matching `truncate` I managed to miss it, along with some colleagues. We later found it by chance. We did find `resize` however, so I was hoping to point it out in the documentation.

Fix typos in rustdoc/lints

This PR merely fixes a few typos in a recently introduced change :)

Refs: rust-lang#85223

Only register `WSACleanup` if `WSAStartup` is actually ever called

See rust-lang#85595

Fixes rust-lang#85441

…mulacrum

Add regression test for spurious const error with NLL

Fixes rust-lang#55825

This decomposes an error message in generic constants into more specific branches, for better
readability.

…arth

Rollup of 14 pull requests

Successful merges:

 - rust-lang#86434 (Add `Ipv6Addr::is_benchmarking`)
 - rust-lang#86828 (const fn for option copied, take & replace)
 - rust-lang#87679 (BTree: refine some comments)
 - rust-lang#87910 (Mark unsafe methods NonZero*::unchecked_(add|mul) as const.)
 - rust-lang#88286 (Remove unnecessary unsafe block in `process_unix`)
 - rust-lang#88305 (Manual Debug for Unix ExitCode ExitStatus ExitStatusError)
 - rust-lang#88353 (Partially stabilize `array_methods`)
 - rust-lang#88370 (Add missing `# Panics` section to `Vec` method)
 - rust-lang#88481 (Remove some feature gates)
 - rust-lang#89138 (Fix link in Ipv6Addr::to_ipv4 docs)
 - rust-lang#89401 (Add truncate note to Vec::resize)
 - rust-lang#89467 (Fix typos in rustdoc/lints)
 - rust-lang#89472 (Only register `WSACleanup` if `WSAStartup` is actually ever called)
 - rust-lang#89505 (Add regression test for spurious const error with NLL)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

- Avoid multiple <h1>s on a page.
- The <h#> tags should follow a semantic hierarchy.
- Cap at h6 (no h7)

Fix unsound optimization with explicit variant discriminants

Fixes rust-lang#89485.

optimize str::from_utf8() validation when slice contains multibyte chars and str.chars().count() in all cases

The change shows small but consistent improvements across several x86 target feature levels. I also tried to optimize counting with `slice.as_chunks` but that yielded more inconsistent results, bigger improvements for some optimization levels, lesser ones in others.

```
old, -O2, x86-64
test str::str_char_count_emoji                                  ... bench:       1,924 ns/iter (+/- 26)
test str::str_char_count_lorem                                  ... bench:         879 ns/iter (+/- 12)
test str::str_char_count_lorem_short                            ... bench:           5 ns/iter (+/- 0)

new, -O2, x86-64
test str::str_char_count_emoji                                  ... bench:       1,878 ns/iter (+/- 21)
test str::str_char_count_lorem                                  ... bench:         851 ns/iter (+/- 11)
test str::str_char_count_lorem_short                            ... bench:           4 ns/iter (+/- 0)

old, -O2, x86-64-v2
test str::str_char_count_emoji                                  ... bench:       1,477 ns/iter (+/- 46)
test str::str_char_count_lorem                                  ... bench:         675 ns/iter (+/- 15)
test str::str_char_count_lorem_short                            ... bench:           5 ns/iter (+/- 0)

new, -O2, x86-64-v2
test str::str_char_count_emoji                                  ... bench:       1,323 ns/iter (+/- 39)
test str::str_char_count_lorem                                  ... bench:         593 ns/iter (+/- 18)
test str::str_char_count_lorem_short                            ... bench:           4 ns/iter (+/- 0)

old, -O2, x86-64-v3
test str::str_char_count_emoji                                  ... bench:         748 ns/iter (+/- 7)
test str::str_char_count_lorem                                  ... bench:         348 ns/iter (+/- 2)
test str::str_char_count_lorem_short                            ... bench:           5 ns/iter (+/- 0)

new, -O2, x86-64-v3
test str::str_char_count_emoji                                  ... bench:         650 ns/iter (+/- 4)
test str::str_char_count_lorem                                  ... bench:         301 ns/iter (+/- 1)
test str::str_char_count_lorem_short                            ... bench:           5 ns/iter (+/- 0)
```

and for the multibyte-char string validation:

```
old, -O2, x86-64
test str::str_validate_emoji                                    ... bench:       4,606 ns/iter (+/- 64)

new, -O2, x86-64
test str::str_validate_emoji                                    ... bench:       3,837 ns/iter (+/- 60)
```

When `cargo report future-incompatibilities` is stabilized
(see rust-lang#71249), this will cause dependencies that trigger
this lint to be included in the report.

…r=Manishearth

Fix ICE in `implicit_hasher`

close rust-lang#7712

changelog: Fix ICE in [`implicit_hasher`]

Add lint `equatable_if_let`

This is my attempt for rust-lang#1716. There is a major false positive, which is people may implement `PartialEq` in a different way. It is unactionable at the moment so I put it into `nursery`.

There is a trait `StructuralPartialEq` for solving this problem which is promising but it has several problems currently:
* Integers and tuples doesn't implement it.
* Some types wrongly implement it, like `Option<T>` when `T` doesn't implement it.

I consider them bugs and against the propose of `StructuralPartialEq`. When they become fixed, this lint can become a useful lint with a single line change.

changelog: New lint: [`equatable_if_let`]

…kingjubilee

[aarch64] add target feature outline-atomics

Enable outline-atomics by default as enabled in clang by the following commit
https://reviews.llvm.org/rGc5e7e649d537067dec7111f3de1430d0fc8a4d11

Performance improves by several orders of magnitude when using the LSE instructions
instead of the ARMv8.0 compatible load/store exclusive instructions.

Tested on Graviton2 aarch64-linux with
x.py build && x.py install && x.py test

…shtriplett

implement advance_(back_)_by on more iterators

Add more efficient, non-default implementations for `feature(iter_advance_by)` (rust-lang#77404) on more iterators and adapters.

This PR only contains implementations where skipping over items doesn't elide any observable side-effects such as user-provided closures or `clone()` functions. I'll put those in a separate PR.

Fix an ICE caused by type mismatch errors being ignored

This PR fixes rust-lang#87771. It turns out that the check on `compiler/rustc_typeck/src/check/demand.rs:148` leads to the ICE. I removed it because the early return in [`check_expr_assign`](https://github.com/theo-lw/rust/blob/dec7fc3ced5bc3c18d0e5d29921d087f93189cb8/compiler/rustc_typeck/src/check/expr.rs#L928) already prevents unnecessary error messages from the call to `check_expr_coercable_to_type`.

…u-se

VecDeque: improve performance for From<[T; N]>

Create `VecDeque` directly from the array instead of inserting items one-by-one.

Benchmark
```
./x.py bench library/alloc --test-args vec_deque::bench_from_array_1000
```

* Before
```
test vec_deque::bench_from_array_1000                    ... bench:       3,991 ns/iter (+/- 717)
```

* After
```
test vec_deque::bench_from_array_1000                    ... bench:         268 ns/iter (+/- 37)
```

…x, r=dtolnay

Improve wording of `map_or_else` docs

Changes doc text to refer to the "default" parameter as the "default"
function.

Previously, the doc text referred to the "f" parameter as the "default" function; and the "default" parameter as the "fallback" function.

…avidtwco

Recommend running `cargo clean` in E0514 output

This suggestion has worked for me before. Seems to me it could help others.

Include the length in BTree hashes

This change makes it consistent with `Hash` for all other collections.

…=jyn514

rustdoc: use slice::contains instead of open-coding it

Improve error message for missing angle brackets in `[_]::method`

Fixes rust-lang#89388.