The lifetime bound `B::Owned: 'a` is redundant and doesn't make a difference,
because `Cow<'a, B>` comes with an implicit `B: 'a`, and associated types
will outlive lifetimes outlived by the `Self` type (and all the trait's
generic parameters, of which there are none in this case), so the implicit `B: 'a`
implies `B::Owned: 'a` anyway.

The explicit lifetime bound here does however end up in documentation,
and that's confusing in my opinion, so let's remove it ^^

This is the first (known) step towards starting to use `unix_sigpipe` in
the wild. Eventually, `rustc_driver::set_sigpipe_handler` can be removed
and all clients can use `unix_sigpipe` instead.

For now we just start using `unix_sigpipe` in once place: `rustc`
itself.

It is easy to manually verify this change. If you remove
`#[unix_sigpipe = "sig_dfl"]` and run `./x.py build` you will get an ICE
when you do `./build/x86_64-unknown-linux-gnu/stage1/bin/rustc --help |
false`. Add back `#[unix_sigpipe = "sig_dfl"]` and the ICE disappears
again.

These targets have system limits on the thread names, 16 and 64 bytes
respectively, and `pthread_setname_np` returns an error if the name is
longer. However, we're not in a context that can propagate errors when
we call this, and we used to implicitly truncate on Linux with `prctl`,
so now we manually truncate these names ahead of time.

…ry_enum_discriminant, r=joshtriplett

Stabilize arbitrary_enum_discriminant, take 2

Documentation has been updated in rust-lang/reference#1055. cc rust-lang#86860 for previous stabilization report.

Not yet marks rust-lang#60553 as done: need documentation in the rust reference.

…thomcc

Remove redundant lifetime bound from `impl Borrow for Cow`

The lifetime bound `B::Owned: 'a` is redundant and doesn't make a difference,
because `Cow<'a, B>` comes with an implicit `B: 'a`, and associated types
will outlive lifetimes outlived by the `Self` type (and all the trait's
generic parameters, of which there are none in this case), so the implicit `B: 'a`
implies `B::Owned: 'a` anyway.

The explicit lifetime bound here does however [end up in documentation](https://doc.rust-lang.org/std/borrow/enum.Cow.html#impl-Borrow%3CB%3E),
and that's confusing in my opinion, so let's remove it ^^

_(Documentation right now, compare to `AsRef`, too:)_
![Screenshot_20220722_014055](https://user-images.githubusercontent.com/3986214/180332665-424d0c05-afb3-40d8-a330-a57a2c9a494b.png)

Fake capture closures if typeck results are empty

This ICE happens because `closure_min_captures` is empty, the reason it's empty is with the 2021 edition `enable_precise_capture` is set to true, which makes it so that we can't fake capture any information because that result of the `unwrap` is none hence the ICE.

Other solution is editing [maybe_read_scrutinee](https://doc.rust-lang.org/nightly/nightly-rustc/src/rustc_typeck/expr_use_visitor.rs.html#453-463) to this since empty slice contains no sub patterns.

Fixes rust-lang#93242

```rust
PatKind::Slice(_, ref slice, _) => {
    if slice.is_none(){
    need_to_be_read = true;
    }
}
// instead of
PatKind::Or(_)
| PatKind::Box(_)
| PatKind::Slice(..)
| PatKind::Ref(..)
| PatKind::Wild => {}
```

…h726

rustc: Use `unix_sigpipe` instead of `rustc_driver::set_sigpipe_handler`

This is the first (known) step towards starting to use `unix_sigpipe` in the wild. Eventually, `rustc_driver::set_sigpipe_handler` can be removed and all clients can use `unix_sigpipe` instead.

For now we just start using `unix_sigpipe` in one place: `rustc` itself.

It is easy to manually verify this change. If you remove `#[unix_sigpipe = "sig_dfl"]` and run `./x.py build` you will get an ICE when you do `./build/x86_64-unknown-linux-gnu/stage1/bin/rustc --help | false`. Add back `#[unix_sigpipe = "sig_dfl"]` and the ICE disappears again.

PR that added `set_sigpipe_handler`: rust-lang#49606

Tracking issue for `unix_sigpipe`: rust-lang#97889

Not sure exactly how to label this PR. Going with T-libs for now since this is a T-libs feature.

`@rustdoc` labels +T-libs

…acrum

Don't link to `libresolv` in libstd on Darwin

Currently we link `libresolv` into every Rust program on apple targets despite never using it (as of rust-lang#44965). I had thought we needed this for `getaddrinfo` or something, but we do not / cannot safely use it.

I'd like to fix this for `libiconv` too (the other library we pull in. that's harder since it's coming in through `libc`, which is rust-lang/libc#2944)).

---

This may warrant release notes. I'm not sure but I've added the flag regardless -- It's a change to the list of dylibs every Rust program pulls in, so it's worth mentioning.

It's pretty unlikely anybody was relying on this being pulled in, and `std` does not guarantee that it will link (and thus transitively provide access to) any particular system library -- anybody relying on that behavior would already be broken when dynamically linking std. That is, there's an outside chance something will fail to link on macOS and iOS because it was accidentally relying on our unnecessary dependency.

(If that *does* happen, that project could be easily fixed by linking libresolv explicitly on those platforms, probably via `#[link(name = "resolv")] extern {}`,` -Crustc-link-lib=resolv`, `println!("cargo:rustc-link-lib=resolv")`, or one of several places in `.config/cargo.toml`)

---

I'm also going to preemptively add the nomination for discussing this in the libs meeting. Basically: Do we care about programs that assume we will bring libraries in that we do not use. `libresolv` and `libiconv` on macOS/iOS are in this camp (`libresolv` because we used to use it, and `libiconv` because the `libc` crate was unintentionally(?) pulling it in to every Rust program).

I'd like to remove them both, but this may cause link issues programs that are relying on `std` to depend on them transitively. (Relying on std for this does not work in all build configurations, so this seems very fragile, and like a use case we should not support).

More generally, IMO we should not guarantee the specific set of system-provided libraries we use (beyond what is implied by an OS version requirement), which means we'd be free to remove this cruft.

Remove misc_cast and validate types when casting

Continuing our work in rust-lang#102675

r? `@oli-obk`

…omcc

Truncate thread names on Linux and Apple targets

These targets have system limits on the thread names, 16 and 64 bytes
respectively, and `pthread_setname_np` returns an error if the name is
longer. However, we're not in a context that can propagate errors when
we call this, and we used to implicitly truncate on Linux with `prctl`,
so now we manually truncate these names ahead of time.

r? `@thomcc`