This is done by adding a global atomic variable (non-TLS) that counts how many threads are panicking. In order to check if the current thread is panicking, this variable is read and, if it is zero, no thread (including the one where `panicking` is being called) is panicking and `panicking` can return `false` immediately without needing to access TLS. If the global counter is not zero, the local counter is accessed from TLS to check if the current thread is panicking.

…results

…ents lint.

Context: this is needed to fix rust-lang/rustfmt#4263,
which currently records the span of a const generic param incorrectly
because the location of the `const` kw is not known.

I am not sure how to add tests for this; any guidance in how to do so
would be appreciated 🙂

Apply suggestions from code review

Co-authored-by: Josh Triplett <josh@joshtriplett.org>

…path into a separate cold function.

When encountering an used moved value where the previous move happened
in a `match` or `if let` pattern, suggest using `ref`. Fix rust-lang#63988.

When encountering a `&mut` value that is used in multiple iterations of
a loop, suggest reborrowing it with `&mut *`. Fix rust-lang#62112.

Add a fast path for `std::thread::panicking`.

This is done by adding a global atomic variable (non-TLS) that counts how many threads are panicking. In order to check if the current thread is panicking, this variable is read and, if it is zero, no thread (including the one where `panicking` is being called) is panicking and `panicking` can return `false` immediately without needing to access TLS. If the global counter is not zero, the local counter is accessed from TLS to check if the current thread is panicking.

…=Manishearth

Implement mixed script confusable lint.

This implements the mixed script confusable lint defined in RFC 2457.
This is blocked on rust-lang#72069 and unicode-rs/unicode-security#13, and will need a Cargo.toml version bump after those are resolved.

The lint message warning is sub-optimal for now. We'll need a mechanism to properly output  `AugmentScriptSet` to screen, this is to be added in `unicode-security` crate.

r? @Manishearth

…, r=kinnison

Don't move cursor in search box when using arrows to navigate results

## What happens

- Go to https://doc.rust-lang.org/stable/std/index.html
- Press 's' to focus the search box
- Type a query like 'test'
- Press the down arrow one or more times to change which search result is highlighted
- Press the up arrow once to go up one search result
- Notice the cursor in the search box is now at the beginning of your query, such that if you now typed 'a' the search box would contain 'atest', when it would be expected that the cursor would have remained where it was and if you typed 'a' at this point it would result in 'testa'
- Press the down arrow once to go down one search result
- Now notice the cursor is at the end of your query again

## What I expected

I expected that changing which search result was highlighted using the up and down arrows would have no effect on where the cursor was in the search box.

## The fix

This PR prevents the default action of the up and down arrows when the custom keydown events are happening during a search.

proc_macro: Stop flattening groups with dummy spans

Reduce the scope of the hack described in rust-lang#72545 (comment).

We still pass AST fragments to attribute and derive macros as single nonterminal tokens rather than as tokens streams, but now use a precise flag instead of the span-based heuristic that could do lead to incorrect behavior in unrelated cases.

rust-lang#73345 attempts to fully resolve this issue, but there are some compatibility issues to be addressed.

Implement `slice_strip` feature

Tracking issue: rust-lang#73413

Add unstable `core::mem::variant_count` intrinsic

Adds a new `const fn` intrinsic which can be used to determine the number of variants in an `enum`.

I've shown this to a couple of people and they invariably ask 'why on earth?', but there's actually a very neat use case:

At the moment, if you want to create an opaque array type that's indexed by an `enum` with one element for each variant, you either have to hard-code the number of variants, add a `LENGTH` variant or use a `Vec`, none of which are suitable in general (number of variants could change; pattern matching `LENGTH` becomes frustrating; might not have `alloc`). By including this intrinsic, it becomes possible to write the following:

```rust
#[derive(Copy, Clone)]
enum OpaqueIndex {
    A = 0,
    B,
    C,
}

struct OpaqueVec<T>(Box<[T; std::mem::num_variants::<OpaqueIndex>()]>);

impl<T> std::ops::Index<OpaqueIndex> for OpaqueVec<T> {
    type Output = T;

    fn index(&self, idx: OpaqueIndex) -> &Self::Output {
        &self.0[idx as usize]
    }
}
```

(We even have a use cases for this in `rustc` and I plan to use it to re-implement the lang-items table.)

… r=matthewjasper

Cleanup MinGW LLVM linkage workaround

LLVM correctly passes `uuid` for a long time, GCC unwinding library (either static or dynamic) comes from [windows_gnu_base](https://github.com/rust-lang/rust/blob/06e47688bf15d0215edbe05b21603062f6d2eb5d/src/librustc_target/spec/windows_gnu_base.rs).

…tthewjasper

Provide suggestions for some moved value errors

When encountering an used moved value where the previous move happened
in a `match` or `if let` pattern, suggest using `ref`. Fix rust-lang#63988.

When encountering a `&mut` value that is used in multiple iterations of
a loop, suggest reborrowing it with `&mut *`. Fix rust-lang#62112.

Create 0766 error code

…morse

Record span of `const` kw in GenericParamKind

Context: this is needed for a fix of rust-lang/rustfmt#4263,
which currently records the span of a const generic param incorrectly
because the location of the `const` kw is not known.

I am not sure how to add tests for this; any guidance in how to do so
would be appreciated 🙂

…abnik

Document the mod keyword

Partial fix for rust-lang#34601 .

Documentation for the `mod` keyword.

…abnik

Document the mut keyword

Partial fix for rust-lang#34601.

Documentation for the `mut` keyword. I think it's okay for it to be quite short, this is not the book not the reference, but if you find something is missing, do not hesitate to tell me.

…triplett

Document the return keyword

Partial fix of rust-lang#34601.

This documents the `return` keyword with two short example to explain it is not needed for the last expression in a function and a long example to show its use when interrupting a function execution early.

I did not put a link to the reference since the only link I found was https://doc.rust-lang.org/stable/reference/expressions/return-expr.html#return-expressions.

@rustbot modify labels: T-doc,C-enhancement

Fix ptr doc warnings.

rust-lang#73398 added some stray backtick lines which cause warnings when the docs are built.