Instead of skipping functions with internal ABIs, check that the
signature doesn't contain any fn-ptr types with external ABIs that
aren't FFI-safe.

Signed-off-by: David Wood <david.wood@huawei.com>

Remove an `unwrap` that assumed FFI-safe types in foreign fn-ptr types.

Signed-off-by: David Wood <david.wood@huawei.com>

Extend previous commit's support for checking for external fn-ptrs in
internal fn types to report errors for multiple found fn-ptrs.

Signed-off-by: David Wood <david.wood@huawei.com>

Extend previous checks for external ABI fn-ptrs to use in internal
statics, constants, type aliases and algebraic data types.

Signed-off-by: David Wood <david.wood@huawei.com>

`rustc_arena`.

…omez,jyn514,notriddle

rustdoc: Add a new lint for broken inline code

This patch adds `rustdoc::unescaped_backticks`, a new rustdoc lint that will detect broken inline code nodes.

The lint woks by finding stray backticks and with some heuristics tries to guess where the second backtick might be missing.

Here is how it looks:
```rust
#![warn(rustdoc::unescaped_backticks)]

/// `add(a, b) is the same as `add(b, a)`.
pub fn add(a: i32, b: i32) -> i32 { a + b }
```
```text
warning: unescaped backtick
 --> src/lib.rs:3:41
  |
3 | /// `add(a, b) is the same as `add(b, a)`.
  |                                         ^
  |
help: a previous inline code might be longer than expected
  |
3 | /// `add(a, b)` is the same as `add(b, a)`.
  |               +
help: if you meant to use a literal backtick, escape it
  |
3 | /// `add(a, b) is the same as `add(b, a)\`.
  |                                         +
```

If we can't get proper spans, for example if the doc comment comes from a macro expansion, we print the suggestion in help messages instead. Here's a [real-world example](https://docs.rs/tracing-subscriber/0.3.17/tracing_subscriber/layer/trait.Filter.html#method.max_level_hint):

```text
warning: unescaped backtick
    --> /tracing-subscriber-0.3.17/src/layer/mod.rs:1400:9
     |
1400 | /         /// Returns an optional hint of the highest [verbosity level][level] that
1401 | |         /// this `Filter` will enable.
1402 | |         ///
1403 | |         /// If this method returns a [`LevelFilter`], it will be used as a hint to
...    |
1427 | |         /// [`Interest`]: tracing_core::subscriber::Interest
1428 | |         /// [rebuild]: tracing_core::callsite::rebuild_interest_cache
     | |_____________________________________________________________________^
     |
     = help: a previous inline code might be longer than expected
              change: Therefore, if the `Filter will change the value returned by this
             to this: Therefore, if the `Filter` will change the value returned by this
     = help: if you meant to use a literal backtick, escape it
              change: [`rebuild_interest_cache`][rebuild] is called after the value of the max
             to this: [`rebuild_interest_cache\`][rebuild] is called after the value of the max
```

You can find more examples [here](https://gist.github.com/lukas-code/7678ddf5c608aee97b3a669de80d3465).

A limitation of the current implementation is, that it cannot suggest removing misplaced backticks, for example [here](https://docs.rs/tikv-jemalloc-sys/0.5.3+5.3.0-patched/tikv_jemalloc_sys/fn.mallctl.html).

The lint is allowed by default ~~and nightly-only~~ for now, ~~but without a feature gate. This is similar to how `rustdoc::invalid_html_tags` and `rustdoc::bare_urls` were handled.~~

…-fn-ptr-in-internal-abi-fn, r=jackh726

lint/ctypes: ext. abi fn-ptr in internal abi fn

Fixes rust-lang#94223.

- In the improper ctypes lint, instead of skipping functions with internal ABIs, check that the signature doesn't contain any fn-ptr types with external ABIs that aren't FFI-safe.
- When computing the ABI for fn-ptr types, remove an `unwrap` that assumed FFI-safe types in foreign fn-ptr types.
  - I'm not certain that this is the correct approach.

…w-response, r=lcnr

Clear response values for overflow in new solver

When we have an overflow, return a trivial query response. This fixes an ICE with the code described in rust-lang#110544:

```rust
trait Trait {}

struct W<T>(T);

impl<T, U> Trait for W<(W<T>, W<U>)>
where
    W<T>: Trait,
    W<U>: Trait,
{}

fn impls<T: Trait>() {}

fn main() {
    impls::<W<_>>()
}
```

Where, while proving `W<?0>: Trait`, we overflow but still apply the query response of `?0 = (W<?1>, W<?2>)`. Then while re-processing the query to validate that our evaluation result was stable, we get a different query response that looks like `?1 = (W<?3>, W<?4>), ?2 = (W<?5>, W<?6>)`, and so we trigger the ICE.

Also, by returning a trivial query response we also avoid the infinite-loop/OOM behavior of the old solver.

r? ``@lcnr``

…c, r=notriddle

rustdoc: Fix missing `repr` attribute in doc(inline) on foreign items

Fixes rust-lang#110698.

r? `@notriddle`

…=Nilstrieb

Use `NonNull::new_unchecked` and `NonNull::len` in `rustc_arena`.

This avoids a few extra dereferences as well as an `unwrap`.

According to the docs for [`NonNull::len`](https://doc.rust-lang.org/std/ptr/struct.NonNull.html#method.len) this also ensures that:

> This function is safe, even when the non-null raw slice cannot be dereferenced to a slice because the pointer does not have a valid address.

I am also fairly sure that the `unwrap` is unneeded in this case, as the docs for [`Box::into_raw`](https://doc.rust-lang.org/std/boxed/struct.Box.html#method.into_raw) also state:

> Consumes the Box, returning a wrapped raw pointer.
**The pointer will be properly aligned and non-null.**