Stabilize `Path::try_exists()` and improve doc

This stabilizes the `Path::try_exists()` method which returns
`Result<bool, io::Error>` instead of `bool` allowing handling of errors
unrelated to the file not existing. (e.g permission errors)

Along with the stabilization it also:

* Warns that the `exists()` method is error-prone and suggests to use
  the newly stabilized one.
* Suggests it instead of `metadata()` to handle errors.
* Mentions TOCTOU bugs to avoid false assumption that `try_exists()` is
  completely safe fixed version of `exists()`.
* Renames the feature of still-unstable `std::fs::try_exists()` to
  `fs_try_exists` to avoid name conflict.

The tracking issue #83186 remains open to track `fs_try_exists`.

Add `core::mem::copy` to complement `core::mem::drop`.

This is useful for combinators. I didn't add `clone` since you can already
use `Clone::clone` in its place; copy has no such corresponding function.

This is useful for combinators. I didn't add `clone` since you can already
use `Clone::clone` in its place; copy has no such corresponding function.

Move RegionKind to rustc_type_ir

(Also UniverseIndex)

r? rust-lang/types

proc_macro/bridge: remove `#[repr(C)]` from non-ABI-relevant types.

Not sure how this happened, maybe some of these were passed through the bridge a long time ago?

r? `@bjorn3`

Rollup of 5 pull requests

Successful merges:

 - #98105 (rustdoc: remove tuple link on round braces)
 - #98136 (Rename `impl_constness` to `constness`)
 - #98146 (Remove --memory-init-file flag when linking with Emscripten)
 - #98219 (Skip late bound regions in GATSubstCollector)
 - #98233 (Remove accidental uses of `&A: Allocator`)

Failed merges:

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

Remove accidental uses of `&A: Allocator`

Cc https://github.com/rust-lang/rust/issues/98232

Fixes https://github.com/rust-lang/rust/issues/98176 (for real this time)

Skip late bound regions in GATSubstCollector

#93227 liberated late bound regions when collecting GAT substs in wfcheck.  It should simply skip late bound regions instead.

r? ``@compiler-errors``

Remove --memory-init-file flag when linking with Emscripten

This flag does nothing. It only applies when generating asmjs JavaScript.
``@sbc100``

Rename `impl_constness` to `constness`

The current code is a basis for `is_const_fn_raw`, and `impl_constness`
is no longer a valid name, which is previously used for determining the
constness of impls, and not items in general.

r? `@oli-obk`

rustdoc: remove tuple link on round braces

This is #98069 but for tuples. The reasoning is the same:

* This PR also changes it so that tuples with all-generic elements still link to the primitive.tuple.html page, just like slices. So there still plenty of on-ramps for anybody who doesn't know about it.
* It's too hard to see when round braces are a separate link from the type inside of them.
* It's too hard to click even if you do notice them.

Before:

* impl [ToSocketAddrs](https://doc.rust-lang.org/nightly/std/net/trait.ToSocketAddrs.html) for [(](https://doc.rust-lang.org/nightly/std/primitive.tuple.html)[IpAddr](https://doc.rust-lang.org/nightly/std/net/enum.IpAddr.html), [u16](https://doc.rust-lang.org/nightly/std/primitive.u16.html)[)](https://doc.rust-lang.org/nightly/std/primitive.tuple.html)
* impl<K, V> [FromIterator](https://notriddle.com/notriddle-rustdoc-test/std/iter/trait.FromIterator.html)<[(](https://notriddle.com/notriddle-rustdoc-test/std/primitive.tuple.html)K, V[)](https://notriddle.com/notriddle-rustdoc-test/std/primitive.tuple.html)> for [BTreeMap](https://notriddle.com/notriddle-rustdoc-test/std/collections/struct.BTreeMap.html)<K, V>

After:

* impl [ToSocketAddrs](https://doc.rust-lang.org/nightly/std/net/trait.ToSocketAddrs.html) for ([IpAddr](https://doc.rust-lang.org/nightly/std/net/enum.IpAddr.html), [u16](https://doc.rust-lang.org/nightly/std/primitive.u16.html))
* impl<K, V> [FromIterator](https://notriddle.com/notriddle-rustdoc-test/std/iter/trait.FromIterator.html)<[(K, V)](https://notriddle.com/notriddle-rustdoc-test/std/primitive.tuple.html)> for [BTreeMap](https://notriddle.com/notriddle-rustdoc-test/std/collections/struct.BTreeMap.html)<K, V>

Make some lints incremental.

Those lints do not track a state, so don't need to be performed for the full crate at once.

Make {Mutex, Condvar, RwLock}::new() const.

This makes it possible to have `static M: Mutex<_> = Mutex::new(..);` 🎉

Our implementations [on Linux](https://github.com/rust-lang/rust/pull/95035), [on Windows](https://github.com/rust-lang/rust/pull/77380), and various BSDs and some tier 3 platforms have already been using a non-allocating const-constructible implementation. As of https://github.com/rust-lang/rust/pull/97647, the remaining platforms (most notably macOS) now have a const-constructible implementation as well. This means we can finally make these functions publicly const.

Tracking issue: https://github.com/rust-lang/rust/issues/93740

Stabilize checked slice->str conversion functions

This PR stabilizes the following APIs as `const` functions in Rust 1.63:
```rust
// core::str

pub const fn from_utf8(v: &[u8]) -> Result<&str, Utf8Error>;

impl Utf8Error {
    pub const fn valid_up_to(&self) -> usize;
    pub const fn error_len(&self) -> Option<usize>;
}
```

Note that the `from_utf8_mut` function is not stabilized as unique references (`&mut _`) are [unstable in const context].

FCP: https://github.com/rust-lang/rust/issues/91006#issuecomment-1134593095

[unstable in const context]: https://github.com/rust-lang/rust/issues/57349

Update FreeBSD toolchain to 12.3

Update the FreeBSD toolchain to 12.3. FreeBSD 11 is EOL since September 30, 2021.

I've locally verified that the `dist-x86_64-freebsd` docker image builds successfully.

r? `@Mark-Simulacrum`

Rollup of 5 pull requests

Successful merges:

 - #97511 (Don't build the compiler before building rust-demangler)
 - #98165 (once cell renamings)
 - #98207 (Update cargo)
 - #98229 (Add new eslint checks)
 - #98230 (Fix weird js condition)

Failed merges:

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

Fix weird js condition

While going around the code, I found this weird condition. Fixing also affects the generated results in some cases apparently (could only find this one).

Any idea maybe `@notriddle?`

r? `@notriddle`

Add new eslint checks

r? ```@Dylan-DPC```

Update cargo

4 commits in 4d92f07f34ba7fb7d7f207564942508f46c225d3..8d42b0e8794ce3787c9f7d6d88b02ae80ebe8d19
2022-06-10 01:11:04 +0000 to 2022-06-17 16:46:26 +0000
- Use specific terminology for sparse HTTP-based registry (rust-lang/cargo#10764)
- chore: Upgrade to clap 3.2 (rust-lang/cargo#10753)
- Improve testing framework for http registries (rust-lang/cargo#10738)
- doc: Improve example of using the links field (rust-lang/cargo#10728)

once cell renamings

This PR does the renamings proposed in https://github.com/rust-lang/rust/issues/74465#issuecomment-1153703128

- Move/rename `lazy::{OnceCell, Lazy}` to `cell::{OnceCell, LazyCell}`
- Move/rename `lazy::{SyncOnceCell, SyncLazy}` to `sync::{OnceLock, LazyLock}`

(I used `Lazy...` instead of `...Lazy` as it seems to be more consistent, easier to pronounce, etc)

```@rustbot``` label +T-libs-api -T-libs

Don't build the compiler before building rust-demangler

This saves a lot of time compiling, since rust-demangler doesn't actually use any unstable features.

This is not quite ideal because it uses ToolStd, not ToolBootstrap, so rust-demangler would be able to add unstable library features in the future. But it's a lot better than before, and `builder.cargo` doesn't currently know how to handle stages other than 0.

update Miri

Fixes https://github.com/rust-lang/rust/issues/98107
r? `@ghost` Cc `@rust-lang/miri`

Pass all paths to `Step::run` at once when using `ShouldRun::krate`

Helps with https://github.com/rust-lang/rust/pull/95503. The goal is to run `cargo test -p rustc_data_structures -p rustc_lint_defs` instead of `cargo test -p rustc_data_structures; cargo test -p rustc_lint_defs`, which should both recompile less and avoid replaying cached warnings.

This was surprisingly complicated. The main changes are:
1. Invert the order of iteration in `StepDescription::run`.

    Previously, it did something like:
    ```python
    for path in paths:
    for (step, should_run) in should_runs:
        if let Some(set) = should_run.pathset_for_path(path):
        step.run(builder, set)
    ```

    That worked ok for individual paths, but didn't allow passing more than one path at a time to `Step::run`
    (since `pathset_for_paths` only had one path available to it).
    Change it to instead look at the intersection of `paths` and `should_run.paths`:

    ```python
    for (step, should_run) in should_runs:
    if let Some(set) = should_run.pathset_for_paths(paths):
        step.run(builder, set)
    ```

2. Change `pathset_for_path` to take multiple pathsets.

    The goal is to avoid `x test library/alloc` testing *all* library crates, instead of just alloc.
    The changes here are similarly subtle, to use the intersection between the paths rather than all
    paths in `should_run.paths`. I added a test for the behavior to try and make it more clear.

    Note that we use pathsets instead of just paths to allow for sets with multiple aliases (*cough* `all_krates` *cough*).
    See the documentation added in the next commit for more detail.

3. Change `StepDescription::run` to explicitly handle 0 paths.

    Before this was implicitly handled by the `for` loop, which just didn't excute when there were no paths.
    Now it needs a check, to avoid trying to run all steps (this is a problem for steps that use `default_condition`).

4. Change `RunDescription` to have a list of pathsets, rather than a single path.

5. Remove paths as they're matched

    This allows checking at the end that no invalid paths are left over.
    Note that if two steps matched the same path, this will no longer run both;
    but that's a bug anyway.

6. Handle suite paths separately from regular sets.

    Running multiple suite paths at once instead of in separate `make_run` invocations is both tricky and not particularly useful.
    The respective test Steps already handle this by introspecting the original paths.

    Avoid having to deal with it by moving suite handling into a seperate loop than `PathSet::Set` checks.

`@rustbot` label +A-rustbuild

Avoid `thread::panicking()` in non-poisoning methods of `Mutex` and `RwLock`

`Mutex::lock()` and `RwLock::write()` are poison-guarded against panics,
in that they set the poison flag if a panic occurs while they're locked.
But if we're already in a panic (`thread::panicking()`), they leave the
poison flag alone.

That check is a bit of a waste for methods that never set the poison
flag though, namely `get_mut()`, `into_inner()`, and `RwLock::read()`.
These use-cases are now split to avoid that unnecessary call.

This was surprisingly complicated. The main changes are:
1. Invert the order of iteration in `StepDescription::run`.

    Previously, it did something like:
    ```python
    for path in paths:
    for (step, should_run) in should_runs:
        if let Some(set) = should_run.pathset_for_path(path):
        step.run(builder, set)
    ```

    That worked ok for individual paths, but didn't allow passing more than one path at a time to `Step::run`
    (since `pathset_for_paths` only had one path available to it).
    Change it to instead look at the intersection of `paths` and `should_run.paths`:

    ```python
    for (step, should_run) in should_runs:
    if let Some(set) = should_run.pathset_for_paths(paths):
        step.run(builder, set)
    ```

2. Change `pathset_for_path` to take multiple pathsets.

    The goal is to avoid `x test library/alloc` testing *all* library crates, instead of just alloc.
    The changes here are similarly subtle, to use the intersection between the paths rather than all
    paths in `should_run.paths`. I added a test for the behavior to try and make it more clear.

    Note that we use pathsets instead of just paths to allow for sets with multiple aliases (*cough* `all_krates` *cough*).
    See the documentation added in the next commit for more detail.

3. Change `StepDescription::run` to explicitly handle 0 paths.

   Before this was implicitly handled by the `for` loop, which just didn't excute when there were no paths.
   Now it needs a check, to avoid trying to run all steps (this is a problem for steps that use `default_condition`).

4. Change `RunDescription` to have a list of pathsets, rather than a single path.

5. Remove paths as they're matched

   This allows checking at the end that no invalid paths are left over.
   Note that if two steps matched the same path, this will no longer run both;
   but that's a bug anyway.

6. Handle suite paths separately from regular sets.

   Running multiple suite paths at once instead of in separate `make_run` invocations is both tricky and not particularly useful.
   The respective test Steps already handle this by introspecting the original paths.

   Avoid having to deal with it by moving suite handling into a seperate loop than `PathSet::Set` checks.

 * no-sequences
 * no-throw-literal

Add VecDeque::extend from TrustedLen specialization

Continuation of #95904

Inspired by how [`VecDeque::copy_slice` works](https://github.com/rust-lang/rust/blob/c08b235a5ce10167632bb0fddcd0c5d67f2d42e3/library/alloc/src/collections/vec_deque/mod.rs#L437-L454).

## Benchmarks

Before

```
test vec_deque::bench_extend_chained_bytes      ... bench:       1,026 ns/iter (+/- 17)
test vec_deque::bench_extend_chained_trustedlen ... bench:       1,024 ns/iter (+/- 40)
test vec_deque::bench_extend_trustedlen         ... bench:         637 ns/iter (+/- 693)
```

After

```
test vec_deque::bench_extend_chained_bytes      ... bench:         828 ns/iter (+/- 24)
test vec_deque::bench_extend_chained_trustedlen ... bench:          25 ns/iter (+/- 1)
test vec_deque::bench_extend_trustedlen         ... bench:          21 ns/iter (+/- 0)
```

## Why do it this way

https://rust.godbolt.org/z/15qY1fMYh

The Compiler Explorer example shows how "just" removing the capacity check, like the [`Vec` `TrustedLen` specialization](https://github.com/rust-lang/rust/blob/c08b235a5ce10167632bb0fddcd0c5d67f2d42e3/library/alloc/src/vec/spec_extend.rs#L22-L58) does, wouldn't have been enough for `VecDeque`. `wrap_add` would still have greatly limited what LLVM could do while optimizing.

---

r? `@the8472`

Fix `MissingDoc` quadratic behaviour

Best reviewed one commit at a time.

r? `@cjgillot`