It relies on the Option::unwrap function which is not const-stable (yet).

Signed-off-by: cui fliter <imcusg@gmail.com>

…dr, r=joshtriplett

Move `unix_socket_abstract` feature API to `SocketAddrExt`.

The pre-stabilized API for abstract socket addresses exposes methods on `SocketAddr` that are only enabled for `cfg(any(target_os = "android", target_os = "linux"))`. Per discussion in <rust-lang#85410>, moving these methods to an OS-specific extension trait is required before stabilization can be considered.

This PR makes four changes:
1. The internal module `std::os::net` contains logic for the unstable feature `tcp_quickack` (rust-lang#96256). I moved that code into `linux_ext/tcp.rs` and tried to adjust the module tree so it could accommodate a second unstable feature there.
2. Moves the public API out of `impl SocketAddr`, into `impl SocketAddrExt for SocketAddr` (the headline change).
3. The existing function names and docs for `unix_socket_abstract` refer to addresses as being created from abstract namespaces, but a more accurate description is that they create sockets in *the* abstract namespace. I adjusted the function signatures correspondingly and tried to update the docs to be clearer.
4. I also tweaked `from_abstract_name` so it takes an `AsRef<[u8]>` instead of `&[u8]`, allowing `b""` literals to be passed directly.

Issues:
1. The public module `std::os::linux::net` is marked as part of `tcp_quickack`. I couldn't figure out how to mark a module as being part of two unstable features, so I just left the existing attributes in place. My hope is that this will be fixed as a side-effect of stabilizing either feature.

…, r=joshtriplett

Stabilize const char convert

Split out `const_char_from_u32_unchecked` from `const_char_convert` and stabilize the rest, i.e. stabilize the following functions:

```Rust
impl char {
    pub const fn from_u32(self, i: u32) -> Option<char>;
    pub const fn from_digit(self, num: u32, radix: u32) -> Option<char>;
    pub const fn to_digit(self, radix: u32) -> Option<u32>;
}

// Available through core::char and std::char
mod char {
    pub const fn from_u32(i: u32) -> Option<char>;
    pub const fn from_digit(num: u32, radix: u32) -> Option<char>;
}
```

And put the following under the `from_u32_unchecked` const stability gate as it needs `Option::unwrap` which isn't const-stable (yet):

```Rust
impl char {
    pub const unsafe fn from_u32_unchecked(i: u32) -> char;
}

// Available through core::char and std::char
mod char {
    pub const unsafe fn from_u32_unchecked(i: u32) -> char;
}
```

cc the tracking issue rust-lang#89259 (which I'd like to keep open for `const_char_from_u32_unchecked`).

…s, r=estebank

Recover from function pointer types with generic parameter list

Give a more helpful error when encountering function pointer types with a generic parameter list like `fn<'a>(&'a str) -> bool` or `fn<T>(T) -> T` and suggest moving lifetime parameters to a `for<>` parameter list.

I've added a bunch of extra code to properly handle (unlikely?) corner cases like `for<'a> fn<'b>()` (where there already exists a `for<>` parameter list) correctly suggesting `for<'a, 'b> fn()` (merging the lists). If you deem this useless, I can simplify the code by suggesting nothing at all in this case.

I am quite open to suggestions regarding the wording of the diagnostic messages.

Fixes rust-lang#103487.
``@rustbot`` label A-diagnostics
r? diagnostics

… r=davidtwco

Don't print full paths in overlap errors

We don't print the full path in other diagnostics -- I don't think it particularly helps with the error message. I also delayed the printing until actually needing to render the error message.

r? diagnostics

…ir-build, r=davidtwco

Don't ICE with inline const errors during MIR build

Fixes rust-lang#104277

…ou-se

Fixed some `_i32` notation in `maybe_uninit`’s doc

This PR just changed two lines in the documentation for `MaybeUninit`:

```rs
let val = 0x12345678i32;
```
was changed to:
```rs
let val = 0x12345678_i32;
```
in two doctests, making the values a tad easier to read.

It does not seem like there are other literals needing this change in the file.

fix some typos in comments

Fix x finding Python on Windows

`x` searches through the path for `{dir}/python{2|3}?`, but this fails on Windows because the appropriate path is `{dir}/python.exe`.

This PR adds the expected `.exe` extension on Windows while searching.

…=oli-obk

interpret: make check_mplace public

This helps avoid code duplication in rust-lang/miri#2661.

…omez

rustdoc: Resolve doc links in external traits having local impls

For external impls it was done in rust-lang#103192 right away, but the local impl case was forgotten.

Fixes rust-lang#104145.

Bump chalk to v0.87

1. Removes `ReEmpty` from chalk
2. Adds support for the `std::marker::Tuple` trait