This PR is fixes typo "avaiable" to "available".

fix ci error

emit err for `impl_item`

It is not obvious (at least for me) that complexity of iteration over hash tables depends on capacity and not length. Especially comparing with other containers like Vec or String. I think, this behaviour is worth mentioning.

I run benchmark which tests iteration time for maps with length 50 and different capacities and get this results:
```
capacity - time
64       - 203.87 ns
256      - 351.78 ns
1024     - 607.87 ns
4096     - 965.82 ns
16384    - 3.1188 us
```

If you want to dig why it behaves such way, you can look current implementation in [hashbrown code](https://github.com/rust-lang/hashbrown/blob/f3a9f211d06f78c5beb81ac22ea08fdc269e068f/src/raw/mod.rs#L1933).

Benchmarks code would be presented in PR related to this commit.

…-type-for-type-parameter-error, r=oli-obk

Fix misleading `cannot infer type for type parameter` error

closes rust-lang#93198

Reverse condition in Vec::retain_mut doctest

I find that the doctest for `Vec::retain_mut` is easier to read and understand when the `if` block corresponds to the path that returns `true` and the `else` block returns `false`. Having the `if` block be the `false` path led me to stare at the example for somewhat longer than I probably had to.

Fix typo

This PR is fixes typo "avaiable" to "available".

…ylan-DPC

Minor tweaks to rustc book summary formatting.

This includes a few minor tweaks to the summary/titles of chapters for the rustc book:

* Use a consistent chapter capitalization and hyphenation.
* Move "Codegen Options" underneath "Command-line Arguments". I feel like they are two closely related chapters, where codegen is just a subset of the total arguments.
* Move "Target Tier Policy" underneath "Platform Support". That chapter includes that policy for platform support, and thus I feel it is more closely related to that grouping.

Do not emit the lint `unused_attributes` for *inherent* `#[doc(hidden)]` associated items

Fixes rust-lang#97205 (embarrassing oversight from rust-lang#96008).

`@rustbot` label A-lint

…teration_complexity_note, r=thomcc

Add complexity estimation of iterating over HashSet and HashMap

It is not obvious (at least for me) that complexity of iteration over hash tables depends on capacity and not length. Especially comparing with other containers like Vec or String. I think, this behaviour is worth mentioning.

I run benchmark which tests iteration time for maps with length 50 and different capacities and get this results:
```
capacity - time
64       - 203.87 ns
256      - 351.78 ns
1024     - 607.87 ns
4096     - 965.82 ns
16384    - 3.1188 us
```

If you want to dig why it behaves such way, you can look current implementation in [hashbrown code](https://github.com/rust-lang/hashbrown/blob/f3a9f211d06f78c5beb81ac22ea08fdc269e068f/src/raw/mod.rs#L1933).

Benchmarks code would be presented in PR related to this commit.

…rrors

Add regression test for#81827

Closes rust-lang#81827
r? `@compiler-errors`