Currently, when a user uses a struct pattern to pattern match on
a tuple struct, the errors we emit generally suggest adding fields
using their field names, which are numbers. However, numbers are
not valid identifiers, so the suggestions, which use the shorthand
notation, are not valid syntax. This commit changes those errors
to suggest using the actual tuple struct pattern syntax instead,
which is a more actionable suggestion.

Apparently `"foo\""` has different behavior from `'foo\''` in Python
shlex. See the [discussion on Zulip][z] for more.

[z]: https://rust-lang.zulipchat.com/#narrow/stream/266220-rustdoc/topic/.40has.20checks.20.22no.20closing.20quotation.22

Following rust-lang#78026, `std::fs::hard_link` on most platforms does not follow
symlinks. Change the WASI implementation to also not follow symlinks.

Add diagnostic items to the following types:
  OsString (os_string_type)
  PathBuf (path_buf_type)
  Owned (to_owned_trait)

As well as the to_vec method on slice/[T]

Some newcomers are confused by the behavior of tail expressions,
interpreting that "leaving out the `;` makes it the return value".
To help them go in the right direction, suggest using `return` instead
when applicable.

When a tail expression isn't unit, we previously always suggested adding
a trailing `;` to turn it into a statement. This suggestion isn't
appropriate for any expression that doesn't have side-effects, as the
user will have likely wanted to call something else or do something with
the resulting value, instead of just discarding it.

Enable smart punctuation

Closes rust-lang#76690.

… r=KodrAus

Improve design of `assert_len`

It was discussed in the [tracking issue](rust-lang#76393 (comment)) that `assert_len`'s name and usage are confusing. This PR improves them based on a suggestion by ``@scottmcm`` in that issue.

I also improved the documentation to make it clearer when you might want to use this method.

Old example:

```rust
let range = range.assert_len(slice.len());
```

New example:

```rust
let range = range.ensure_subset_of(..slice.len());
```

Fixes rust-lang#81157

Improve suggestion for tuple struct pattern matching errors.

Closes rust-lang#80174

This change allows numbers to be parsed as field names when pattern matching on structs, which allows us to provide better error messages when tuple structs are matched using a struct pattern.

r? ``@estebank``

…urn, r=lcnr

Suggest `return`ing tail expressions that match return type

Some newcomers are confused by the behavior of tail expressions,
interpreting that "leaving out the `;` makes it the return value".
To help them go in the right direction, suggest using `return` instead
when applicable.

Slight perf improvement on char::to_ascii_lowercase

`char::to_ascii_lowercase()` was checking if it was ascii and then if it was in the right range. Instead propose to check once (I think removing a compare and a shift in the process: [godbolt](https://godbolt.org/z/e5Tora) ).

before:
```
        test char::methods::bench_to_ascii_lowercase                    ... bench:      11,196 ns/iter (+/- 632)
        test char::methods::bench_to_ascii_uppercase                    ... bench:      11,656 ns/iter (+/- 671)
```
after:
```
         test char::methods::bench_to_ascii_lowercase                    ... bench:       9,612 ns/iter (+/- 979)
         test char::methods::bench_to_ascii_uppercase                    ... bench:       8,241 ns/iter (+/- 701)
```

(calling u8::to_ascii_lowercase and letting that flip the 5th bit is also an option, but it's more instructions. I'm thinking for things around ascii and char we want to be as efficient as possible.)

…imulacrum

Avoid `cfg_if` in `std::os`

rust-analyzer cannot currently load the `cfg_if` crate, which means that rust-analyzer is unable to see `std::os::{unix, windows, linux}` here. This works around that by avoiding `cfg_if`; the `#[cfg]` expressions are simple enough to reasonably write by hand.

Fixes rust-lang/rust-analyzer#6038

Make WASI's `hard_link` behavior match other platforms.

Following rust-lang#78026, `std::fs::hard_link` on most platforms does not follow
symlinks. Change the WASI implementation to also not follow symlinks.

r? ```@alexcrichton```

… r=RalfJung

use PlaceRef abstractions more consistently

Addresses this [comment](https://github.com/rust-lang/rust/pull/80865/files#r558978715)
Associated issue: rust-lang#80647

r? ```@RalfJung```

… r=davidtwco

add diagnostic items for OsString/PathBuf/Owned as well as to_vec on slice

This is adding diagnostic items to be used by rust-lang/rust-clippy#6730, but my understanding is the clippy-side change does need to be done over there since I am adding a new clippy feature.

Add diagnostic items to the following types:
  OsString (os_string_type)
  PathBuf (path_buf_type)
  Owned (to_owned_trait)

As well as the to_vec method on slice/[T]

add s390x-unknown-linux-musl target

This is the first step in bringup for Rust on s390x.

The libc and std crates need modifications as well, but getting this upstream makes that work easier.

…n-esc, r=Nemo157

Remove query parameters when skipping search results

Fixes rust-lang#81330.

This PR changes the following: when pressing ESC and that no other "action" was performed (understand: no closing the search result, or hiding a menu or something along the line), then we discard the URL query parameters (the `?whatever=dsjfs`). What do you think about this change ```@rust-lang/rustdoc``` ?

EDIT: finally we're simply removing the query parameter when we're skipping the search results.

r? ```@Nemo157```

Make `treat_err_as_bug` Option<NonZeroUsize>

`rustc -Z treat-err-as-bug=N` already requires `N` to be nonzero when the argument is parsed, so changing the type from `Option<usize>` to `Option<NonZeroUsize>` is a low-hanging fruit in terms of layout optimization.