DirEntryExt2 is a new trait with the same purpose as DirEntryExt,
but sealed

In the docs for intrinsics::abort():

 * Strengthen the recommendation by to use process::abort instead.
 * Document the fact that it (ab)uses an LLVM debug trap and what the
   likely consequences are.
 * State that the precise behaviour is unstable.

In the docs for process::abort():

 * Promise that we have the same behaviour as C `abort()`.
 * Document the likely consequences, including, specifically, the
   consequences on Unix.

In the internal comment for unix::abort_internal:

 * Refer to the public docs for the public API functions.
 * Correct and expand the description of libc::abort.  Specifically:
 * Do not claim that abort() unregisters signal handlers.  It doesn't;
   it honours the SIGABRT handler.
 * Discuss, extensively, the issue with abort() flushing stdio buffers.
 * Describe the glibc behaviour in some detail.

Co-authored-by: Mark Wooding <mdw@distorted.org.uk>
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

As per discussion here
 rust-lang#85377 (review)

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

There is discussion of this in rust-lang#40230 which requests clarification.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

And withdraw the allegation of "abuse".

Adapted from a suggestion by @m-ou-se.

Co-authored-by: Mara Bos <m-ou.se@m-ou.se>
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

Adapted from a suggestion by @m-ou-se.

Co-authored-by: Mara Bos <m-ou.se@m-ou.se>
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

Co-authored-by: Yuki Okushi <jtitor@2k36.org>

Co-authored-by: Yuki Okushi <jtitor@2k36.org>

These were only used once, in a place where it was trivial to replace.
Also, it's unclear what 'clean' would mean for these, so it seems better
to be explicit.

…ame, r=m-ou-se

Add std::os::unix::fs::DirEntryExt2::file_name_ref(&self) -> &OsStr

Greetings!

This is my first PR here, so please forgive me if I've missed an important step or otherwise done something wrong. I'm very open to suggestions/fixes/corrections.

This PR adds a function that allows `std::fs::DirEntry` to vend a borrow of its filename on Unix platforms, which is especially useful for sorting. (Windows has (as I understand it) encoding differences that require an allocation.) This new function sits alongside the cross-platform [`file_name(&self) -> OsString`](https://doc.rust-lang.org/std/fs/struct.DirEntry.html#method.file_name) function.

I pitched this idea in an [internals thread](https://internals.rust-lang.org/t/allow-std-direntry-to-vend-borrows-of-its-filename/14328/4), and no one objected vehemently, so here we are.

I understand features in general, I believe, but I'm not at all confident that my whole-cloth invention of a new feature string (as required by the compiler) was correct (or that the name is appropriate). Further, there doesn't appear to be a test for the sibling `ino` function, so I didn't add one for this similarly trivial function either. If it's desirable that I should do so, I'd be happy to [figure out how to] do that.

The following is a trivial sample of a use-case for this function, in which directory entries are sorted without any additional allocations:

```rust
use std::os::unix::fs::DirEntryExt;
use std::{fs, io};

fn main() -> io::Result<()> {
    let mut entries = fs::read_dir(".")?.collect::<Result<Vec<_>, io::Error>>()?;
    entries.sort_unstable_by(|a, b| a.file_name_ref().cmp(b.file_name_ref()));

    for p in entries {
        println!("{:?}", p);
    }

    Ok(())
}
```

aborts: Clarify documentation and comments

In the docs for intrinsics::abort():

 * Strengthen the recommendation by to use process::abort instead.
 * Document the fact that it sometimes (ab)uses an LLVM debug trap and what the likely consequences are.
 * State that the precise behaviour is unstable.

In the docs for process::abort():

 * Promise that we have the same behaviour as C `abort()`.
 * Document the likely consequences, including, specifically, the consequences on Unix.

In the internal comment for unix::abort_internal:

 * Refer to the public docs for the public API functions.
 * Correct and expand the description of libc::abort.  Specifically:
 * Do not claim that abort() unregisters signal handlers.  It doesn't; it honours the SIGABRT handler.
 * Discuss, extensively, the issue with abort() flushing stdio buffers.
 * Describe the glibc behaviour in some detail.

Co-authored-by: Mark Wooding <mdw@distorted.org.uk>
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

Fixes rust-lang#40230

double-check mutability inside Allocation

r? `@oli-obk`

…-ou-se

Stabilize `Seek::rewind()`

This stabilizes `Seek::rewind`. It seemed to fit into one of the existing tests, so I extended that test rather than adding a new one.

Closes rust-lang#85149.

…riplett

Remove some doc aliases

As per the new doc alias policy in rust-lang/std-dev-guide#25, this removes some controversial doc aliases:
- `malloc`, `alloc`, `realloc`, etc.
- `length` (alias for `len`)
- `delete` (alias for `remove` in collections and also file/directory deletion)

r? `@joshtriplett`

…=lnicola

⬆️ rust-analyzer

…Gomez

Remove `impl Clean for {Ident, Symbol}`

These were only used once, in a place where it was trivial to replace.
Also, it's unclear what 'clean' would mean for these, so it seems better
to be explicit.

Found while reviewing rust-lang#86841, which makes the same change to `build_macro`, so the two will conflict.

r? `@GuillaumeGomez`