rustdoc: add header map to the table of contents

## Summary

Add header sections to the sidebar TOC.

### Preview

![image](https://github.com/user-attachments/assets/eae4df02-86aa-4df4-8c61-a95685cd8829)

* http://notriddle.com/rustdoc-html-demo-9/toc/rust/std/index.html
* http://notriddle.com/rustdoc-html-demo-9/toc/rust-derive-builder/derive_builder/index.html

## Motivation

Some pages are very wordy, like these.

| crate | word count |
|--|--|
| [std::option](https://doc.rust-lang.org/stable/std/option/index.html) | 2,138
| [derive_builder](https://docs.rs/derive_builder/0.13.0/derive_builder/index.html) | 2,403
| [tracing](https://docs.rs/tracing/0.1.40/tracing/index.html) | 3,912
| [regex](https://docs.rs/regex/1.10.3/regex/index.html) | 8,412

This kind of very long document is more navigable with a table of contents, like Wikipedia's or the one [GitHub recently added](https://github.blog/changelog/2021-04-13-table-of-contents-support-in-markdown-files/) for READMEs.

In fact, the use case is so compelling, that it's been requested multiple times and implemented in an extension:

* rust-lang#80858
* rust-lang#28056
* rust-lang#14475
* https://rust.extension.sh/#show-table-of-content

(Some of these issues ask for more than this, so don’t close them.)

It's also been implemented by hand in some crates, because the author really thought it was needed. Protip: for a more exhaustive list, run [`site:docs.rs table of contents`](https://duckduckgo.com/?t=ffab&q=site%3Adocs.rs+table+of+contents&ia=web), though some of them are false positives.

* https://docs.rs/figment/0.10.14/figment/index.html#table-of-contents
* https://docs.rs/csv/1.3.0/csv/tutorial/index.html#table-of-contents
* https://docs.rs/axum/0.7.4/axum/response/index.html#table-of-contents
* https://docs.rs/regex-automata/0.4.5/regex_automata/index.html#table-of-contents

Unfortunately for these hand-built ToCs, because they're just part of the docs, there's no consistent way to turn them off if the reader doesn't want them. It's also more complicated to ensure they stay in sync with the docs they're supposed to describe, and they don't stay with you when you scroll like Wikipedia's [does now](https://uxdesign.cc/design-notes-on-the-2023-wikipedia-redesign-d6573b9af28d).

## Guide-level explanation

When writing docs for a top-level item, the first and second level of headers will be shown in an outline in the sidebar. In this context, "top level" means "not associated".

This means, if you're writing very long guides or explanations, and you want it to have a table of contents in the sidebar for its headings, the ideal place to attach it is usually the *module* or *crate*, because this page has fewer other things on it (and is the ideal place to describe "cross-cutting concerns" for its child items).

If you're reading documentation, and want to get rid of the table of contents, open the ![image](https://github.com/rust-lang/rust/assets/1593513/2ad82466-5fe3-4684-b1c2-6be4c99a8666) Settings panel and checkmark "Hide table of contents."

## Reference-level explanation

Top-level items have an outline generated. This works for potentially-malformed header trees by pairing a header with the nearest header with a higher level. For example:

```markdown
## A
# B
# C
## D
## E
```

A, B, and C are all siblings, and D and E are children of C.

Rustdoc only presents two layers of tree, but it tracks up to the full depth of 6 while preparing it.

That means that these two doc comment both generate the same outline:

```rust
/// # First
/// ## Second
struct One;
/// ## First
/// ### Second
struct Two;
```

## Drawbacks

The biggest drawback is adding more stuff to the sidebar.

My crawl through docs.rs shows this to, surprisingly, be less of a problem than I thought. The manually-built tables of contents, and the pages with dozens of headers, usually seem to be modules or crates, not types (where extreme scrolling would become a problem, since they already have methods to deal with).

The best example of a type with many headers is [vec::Vec](https://doc.rust-lang.org/1.75.0/std/vec/struct.Vec.html), which still only has five headers, not dozens like [axum::extract](https://docs.rs/axum/0.7.4/axum/extract/index.html).

## Rationale and alternatives

### Why in the existing sidebar?

The method links and the top-doc header links have more in common with each other than either of them do with the "In [parent module]" links, and should go together.

### Why limited to two levels?

The sidebar is pretty narrow, and I don't want too much space used by indentation. Making the sidebar wider, while it has some upsides, also takes up more space on middling-sized screens or tiled WMs.

### Why not line wrap?

That behaves strangely when resizing.

## Prior art

### Doc generators that have TOC for headers

https://hexdocs.pm/phoenix/Phoenix.Controller.html is very close, in the sense that it also has header sections directly alongside functions and types.

Another example, referenced as part of the [early sidebar discussion](rust-lang#37856) that added methods, Ruby will show a table of contents in the sidebar (for example, on the [ARGF](https://docs.ruby-lang.org/en/master/ARGF.html) class). According to their changelog, [they added it in 2013](https://github.com/ruby/rdoc/blob/06137bde8ccc48cd502bc28178bcd8f2dfe37624/History.rdoc#400--2013-02-24-).

Haskell seems to mix text and functions even more freely than Elixir. For example, this [Naming conventions](https://hackage.haskell.org/package/base-4.19.0.0/docs/Control-Monad.html#g:3) is plain text, and is immediately followed by functions. And the [Pandoc top level](https://hackage.haskell.org/package/pandoc-3.1.11.1/docs/Text-Pandoc.html) has items split up by function, rather than by kind. Their TOC matches exactly with the contents of the page.

### Doc generators that don't have header TOC, but still have headers

Elm, interestingly enough, seems to have the same setup that Rust used to have: sibling navigation between modules, and no index within a single page. [They keep Haskell's habit of named sections with machine-generated type signatures](https://package.elm-lang.org/packages/elm/browser/latest/Browser-Dom), though.

[PHP](https://www.php.net/manual/en/book.datetime.php), like elm, also has a right-hand sidebar with sibling navigation. However, PHP has a single page for a single method, unlike Rust's page for an entire "class." So even though these pages have headers, it's never more than ten at most. And when they have guides, those guides are also multi-page.

## Unresolved questions

* Writing recommendations for anyone who wants to take advantage of this.
* Right now, it does not line wrap. That might be a bad idea: a lot of these are getting truncated.
* Split sidebars, which I [tried implementing](https://rust-lang.zulipchat.com/#narrow/stream/266220-t-rustdoc/topic/Table.20of.20contents), are not required. The TOC can be turned off, if it's really a problem. Implemented in rust-lang#120818, but needs more, separate, discussion.

## Future possibilities

I would like to do a better job of distinguishing global navigation from local navigation. Rustdoc has a pretty reasonable information architecture, if only we did a better job of communicating it.

This PR aims, mostly, to help doc authors help their users by writing docs that can be more effectively skimmed. But it doesn't do anything to make it easier to tell the TOC and the Module Nav apart.

…iaskrgr

Rollup of 10 pull requests

Successful merges:

 - rust-lang#101339 (enable -Zrandomize-layout in debug CI builds )
 - rust-lang#120736 (rustdoc: add header map to the table of contents)
 - rust-lang#127021 (Add target support for RTEMS Arm)
 - rust-lang#128928 (CI: rfl: add more tools and steps)
 - rust-lang#129584 (warn the user if the upstream master branch is old)
 - rust-lang#129664 (Arbitrary self types v2: pointers feature gate.)
 - rust-lang#129752 (Make supertrait and implied predicates queries defaulted)
 - rust-lang#129918 (Update docs of `missing_abi` lint)
 - rust-lang#129919 (Stabilize `waker_getters`)
 - rust-lang#129925 (remove deprecated option `rust.split-debuginfo`)

Failed merges:

 - rust-lang#129789 (rustdoc: use strategic boxing to shrink `clean::Item`)

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

…iaskrgr

Rollup of 10 pull requests

Successful merges:

 - rust-lang#101339 (enable -Zrandomize-layout in debug CI builds )
 - rust-lang#120736 (rustdoc: add header map to the table of contents)
 - rust-lang#127021 (Add target support for RTEMS Arm)
 - rust-lang#128928 (CI: rfl: add more tools and steps)
 - rust-lang#129584 (warn the user if the upstream master branch is old)
 - rust-lang#129664 (Arbitrary self types v2: pointers feature gate.)
 - rust-lang#129752 (Make supertrait and implied predicates queries defaulted)
 - rust-lang#129918 (Update docs of `missing_abi` lint)
 - rust-lang#129919 (Stabilize `waker_getters`)
 - rust-lang#129925 (remove deprecated option `rust.split-debuginfo`)

Failed merges:

 - rust-lang#129789 (rustdoc: use strategic boxing to shrink `clean::Item`)

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

Rollup merge of rust-lang#120736 - notriddle:notriddle/toc, r=t-rustdoc

rustdoc: add header map to the table of contents

## Summary

Add header sections to the sidebar TOC.

### Preview

![image](https://github.com/user-attachments/assets/eae4df02-86aa-4df4-8c61-a95685cd8829)

* http://notriddle.com/rustdoc-html-demo-9/toc/rust/std/index.html
* http://notriddle.com/rustdoc-html-demo-9/toc/rust-derive-builder/derive_builder/index.html

## Motivation

Some pages are very wordy, like these.

| crate | word count |
|--|--|
| [std::option](https://doc.rust-lang.org/stable/std/option/index.html) | 2,138
| [derive_builder](https://docs.rs/derive_builder/0.13.0/derive_builder/index.html) | 2,403
| [tracing](https://docs.rs/tracing/0.1.40/tracing/index.html) | 3,912
| [regex](https://docs.rs/regex/1.10.3/regex/index.html) | 8,412

This kind of very long document is more navigable with a table of contents, like Wikipedia's or the one [GitHub recently added](https://github.blog/changelog/2021-04-13-table-of-contents-support-in-markdown-files/) for READMEs.

In fact, the use case is so compelling, that it's been requested multiple times and implemented in an extension:

* rust-lang#80858
* rust-lang#28056
* rust-lang#14475
* https://rust.extension.sh/#show-table-of-content

(Some of these issues ask for more than this, so don’t close them.)

It's also been implemented by hand in some crates, because the author really thought it was needed. Protip: for a more exhaustive list, run [`site:docs.rs table of contents`](https://duckduckgo.com/?t=ffab&q=site%3Adocs.rs+table+of+contents&ia=web), though some of them are false positives.

* https://docs.rs/figment/0.10.14/figment/index.html#table-of-contents
* https://docs.rs/csv/1.3.0/csv/tutorial/index.html#table-of-contents
* https://docs.rs/axum/0.7.4/axum/response/index.html#table-of-contents
* https://docs.rs/regex-automata/0.4.5/regex_automata/index.html#table-of-contents

Unfortunately for these hand-built ToCs, because they're just part of the docs, there's no consistent way to turn them off if the reader doesn't want them. It's also more complicated to ensure they stay in sync with the docs they're supposed to describe, and they don't stay with you when you scroll like Wikipedia's [does now](https://uxdesign.cc/design-notes-on-the-2023-wikipedia-redesign-d6573b9af28d).

## Guide-level explanation

When writing docs for a top-level item, the first and second level of headers will be shown in an outline in the sidebar. In this context, "top level" means "not associated".

This means, if you're writing very long guides or explanations, and you want it to have a table of contents in the sidebar for its headings, the ideal place to attach it is usually the *module* or *crate*, because this page has fewer other things on it (and is the ideal place to describe "cross-cutting concerns" for its child items).

If you're reading documentation, and want to get rid of the table of contents, open the ![image](https://github.com/rust-lang/rust/assets/1593513/2ad82466-5fe3-4684-b1c2-6be4c99a8666) Settings panel and checkmark "Hide table of contents."

## Reference-level explanation

Top-level items have an outline generated. This works for potentially-malformed header trees by pairing a header with the nearest header with a higher level. For example:

```markdown
## A
# B
# C
## D
## E
```

A, B, and C are all siblings, and D and E are children of C.

Rustdoc only presents two layers of tree, but it tracks up to the full depth of 6 while preparing it.

That means that these two doc comment both generate the same outline:

```rust
/// # First
/// ## Second
struct One;
/// ## First
/// ### Second
struct Two;
```

## Drawbacks

The biggest drawback is adding more stuff to the sidebar.

My crawl through docs.rs shows this to, surprisingly, be less of a problem than I thought. The manually-built tables of contents, and the pages with dozens of headers, usually seem to be modules or crates, not types (where extreme scrolling would become a problem, since they already have methods to deal with).

The best example of a type with many headers is [vec::Vec](https://doc.rust-lang.org/1.75.0/std/vec/struct.Vec.html), which still only has five headers, not dozens like [axum::extract](https://docs.rs/axum/0.7.4/axum/extract/index.html).

## Rationale and alternatives

### Why in the existing sidebar?

The method links and the top-doc header links have more in common with each other than either of them do with the "In [parent module]" links, and should go together.

### Why limited to two levels?

The sidebar is pretty narrow, and I don't want too much space used by indentation. Making the sidebar wider, while it has some upsides, also takes up more space on middling-sized screens or tiled WMs.

### Why not line wrap?

That behaves strangely when resizing.

## Prior art

### Doc generators that have TOC for headers

https://hexdocs.pm/phoenix/Phoenix.Controller.html is very close, in the sense that it also has header sections directly alongside functions and types.

Another example, referenced as part of the [early sidebar discussion](rust-lang#37856) that added methods, Ruby will show a table of contents in the sidebar (for example, on the [ARGF](https://docs.ruby-lang.org/en/master/ARGF.html) class). According to their changelog, [they added it in 2013](https://github.com/ruby/rdoc/blob/06137bde8ccc48cd502bc28178bcd8f2dfe37624/History.rdoc#400--2013-02-24-).

Haskell seems to mix text and functions even more freely than Elixir. For example, this [Naming conventions](https://hackage.haskell.org/package/base-4.19.0.0/docs/Control-Monad.html#g:3) is plain text, and is immediately followed by functions. And the [Pandoc top level](https://hackage.haskell.org/package/pandoc-3.1.11.1/docs/Text-Pandoc.html) has items split up by function, rather than by kind. Their TOC matches exactly with the contents of the page.

### Doc generators that don't have header TOC, but still have headers

Elm, interestingly enough, seems to have the same setup that Rust used to have: sibling navigation between modules, and no index within a single page. [They keep Haskell's habit of named sections with machine-generated type signatures](https://package.elm-lang.org/packages/elm/browser/latest/Browser-Dom), though.

[PHP](https://www.php.net/manual/en/book.datetime.php), like elm, also has a right-hand sidebar with sibling navigation. However, PHP has a single page for a single method, unlike Rust's page for an entire "class." So even though these pages have headers, it's never more than ten at most. And when they have guides, those guides are also multi-page.

## Unresolved questions

* Writing recommendations for anyone who wants to take advantage of this.
* Right now, it does not line wrap. That might be a bad idea: a lot of these are getting truncated.
* Split sidebars, which I [tried implementing](https://rust-lang.zulipchat.com/#narrow/stream/266220-t-rustdoc/topic/Table.20of.20contents), are not required. The TOC can be turned off, if it's really a problem. Implemented in rust-lang#120818, but needs more, separate, discussion.

## Future possibilities

I would like to do a better job of distinguishing global navigation from local navigation. Rustdoc has a pretty reasonable information architecture, if only we did a better job of communicating it.

This PR aims, mostly, to help doc authors help their users by writing docs that can be more effectively skimmed. But it doesn't do anything to make it easier to tell the TOC and the Module Nav apart.

Pkgsrc changes compared to rust182:
 * Remove patches related to rust-lang/rust#130110,
   which is now integrated upstream.
 * Remove patch to vendor/cc-1.0.79, now integrated in the current
   vendored cc crate.
 * Checksum updates.

TODO:
 * Cross-compilation fails ref.
   rust-lang/rust#133629

Upstream changes:

Version 1.83.0 (2024-11-28)
==========================

Language
--------
- [Stabilize `&mut`, `*mut`, `&Cell`, and `*const Cell` in const.]
  (rust-lang/rust#129195)
- [Allow creating references to statics in `const` initializers.]
  (rust-lang/rust#129759)
- [Implement raw lifetimes and labels (`'r#ident`).]
  (rust-lang/rust#126452)
- [Define behavior when atomic and non-atomic reads race.]
  (rust-lang/rust#128778)
- [Non-exhaustive structs may now be empty.]
  (rust-lang/rust#128934)
- [Disallow implicit coercions from places of type `!`]
  (rust-lang/rust#129392)
- [`const extern` functions can now be defined for other calling conventions.]
  (rust-lang/rust#129753)
- [Stabilize `expr_2021` macro fragment specifier in all editions.]
  (rust-lang/rust#129972)
- [The `non_local_definitions` lint now fires on less code and
  warns by default.]
  (rust-lang/rust#127117)

Compiler
--------
- [Deprecate unsound `-Csoft-float` flag.]
  (rust-lang/rust#129897)
- Add many new tier 3 targets:
    - [`aarch64_unknown_nto_qnx700`]
      (rust-lang/rust#127897)
    - [`arm64e-apple-tvos`]
      (rust-lang/rust#130614)
    - [`armv7-rtems-eabihf`]
      (rust-lang/rust#127021)
    - [`loongarch64-unknown-linux-ohos`]
      (rust-lang/rust#130750)
    - [`riscv32-wrs-vxworks` and `riscv64-wrs-vxworks`]
      (rust-lang/rust#130549)
    - [`riscv32{e|em|emc}-unknown-none-elf`]
      (rust-lang/rust#130555)
    - [`x86_64-unknown-hurd-gnu`]
      (rust-lang/rust#128345)
    - [`x86_64-unknown-trusty`]
      (rust-lang/rust#130453)

Refer to Rust's [platform support page][platform-support-doc]
for more information on Rust's tiered platform support.

Libraries
---------
- [Implement `PartialEq` for `ExitCode`.]
  (rust-lang/rust#127633)
- [Document that `catch_unwind` can deal with foreign exceptions
  without UB, although the exact behavior is unspecified.]
  (rust-lang/rust#128321)
- [Implement `Default` for `HashMap`/`HashSet` iterators that don't
  already have it.]
  (rust-lang/rust#128711)
- [Bump Unicode to version 16.0.0.]
  (rust-lang/rust#130183)
- [Change documentation of `ptr::add`/`sub` to not claim equivalence
  with `offset`.]
  (rust-lang/rust#130229).

Stabilized APIs
---------------

- [`BufRead::skip_until`]
  (https://doc.rust-lang.org/stable/std/io/trait.BufRead.html#method.skip_until)
- [`ControlFlow::break_value`]
  (https://doc.rust-lang.org/stable/core/ops/enum.ControlFlow.html#method.break_value)
- [`ControlFlow::continue_value`]
  (https://doc.rust-lang.org/stable/core/ops/enum.ControlFlow.html#method.continue_value)
- [`ControlFlow::map_break`]
  (https://doc.rust-lang.org/stable/core/ops/enum.ControlFlow.html#method.map_break)
- [`ControlFlow::map_continue`]
  (https://doc.rust-lang.org/stable/core/ops/enum.ControlFlow.html#method.map_continue)
- [`DebugList::finish_non_exhaustive`]
  (https://doc.rust-lang.org/stable/core/fmt/struct.DebugList.html#method.finish_non_exhaustive)
- [`DebugMap::finish_non_exhaustive`]
  (https://doc.rust-lang.org/stable/core/fmt/struct.DebugMap.html#method.finish_non_exhaustive)
- [`DebugSet::finish_non_exhaustive`]
  (https://doc.rust-lang.org/stable/core/fmt/struct.DebugSet.html#method.finish_non_exhaustive)
- [`DebugTuple::finish_non_exhaustive`]
  (https://doc.rust-lang.org/stable/core/fmt/struct.DebugTuple.html#method.finish_non_exhaustive)
- [`ErrorKind::ArgumentListTooLong`]
  (https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.ArgumentListTooLong)
- [`ErrorKind::Deadlock`]
  (https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.Deadlock)
- [`ErrorKind::DirectoryNotEmpty`]
  (https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.DirectoryNotEmpty)
- [`ErrorKind::ExecutableFileBusy`]
  (https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.ExecutableFileBusy)
- [`ErrorKind::FileTooLarge`]
  (https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.FileTooLarge)
- [`ErrorKind::HostUnreachable`]
  (https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.HostUnreachable)
- [`ErrorKind::IsADirectory`]
  (https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.IsADirectory)
- [`ErrorKind::NetworkDown`]
  (https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.NetworkDown)
- [`ErrorKind::NetworkUnreachable`]
  (https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.NetworkUnreachable)
- [`ErrorKind::NotADirectory`]
  (https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.NotADirectory)
- [`ErrorKind::NotSeekable`]
  (https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.NotSeekable)
- [`ErrorKind::ReadOnlyFilesystem`]
  (https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.ReadOnlyFilesystem)
- [`ErrorKind::ResourceBusy`]
  (https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.ResourceBusy)
- [`ErrorKind::StaleNetworkFileHandle`]
  (https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.StaleNetworkFileHandle)
- [`ErrorKind::StorageFull`]
  (https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.StorageFull)
- [`ErrorKind::TooManyLinks`]
  (https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.TooManyLinks)
- [`Option::get_or_insert_default`]
  (https://doc.rust-lang.org/stable/core/option/enum.Option.html#method.get_or_insert_default)
- [`Waker::data`]
  (https://doc.rust-lang.org/stable/core/task/struct.Waker.html#method.data)
- [`Waker::new`]
  (https://doc.rust-lang.org/stable/core/task/struct.Waker.html#method.new)
- [`Waker::vtable`]
  (https://doc.rust-lang.org/stable/core/task/struct.Waker.html#method.vtable)
- [`char::MIN`]
  (https://doc.rust-lang.org/stable/core/primitive.char.html#associatedconstant.MIN)
- [`hash_map::Entry::insert_entry`]
  (https://doc.rust-lang.org/stable/std/collections/hash_map/enum.Entry.html#method.insert_entry)
- [`hash_map::VacantEntry::insert_entry`]
  (https://doc.rust-lang.org/stable/std/collections/hash_map/struct.VacantEntry.html#method.insert_entry)

These APIs are now stable in const contexts:

- [`Cell::into_inner`]
  (https://doc.rust-lang.org/stable/core/cell/struct.Cell.html#method.into_inner)
- [`Duration::as_secs_f32`]
  (https://doc.rust-lang.org/stable/core/time/struct.Duration.html#method.as_secs_f32)
- [`Duration::as_secs_f64`]
  (https://doc.rust-lang.org/stable/core/time/struct.Duration.html#method.as_secs_f64)
- [`Duration::div_duration_f32`]
  (https://doc.rust-lang.org/stable/core/time/struct.Duration.html#method.div_duration_f32)
- [`Duration::div_duration_f64`]
  (https://doc.rust-lang.org/stable/core/time/struct.Duration.html#method.div_duration_f64)
- [`MaybeUninit::as_mut_ptr`]
  (https://doc.rust-lang.org/stable/core/mem/union.MaybeUninit.html#method.as_mut_ptr)
- [`NonNull::as_mut`]
  (https://doc.rust-lang.org/stable/core/ptr/struct.NonNull.html#method.as_mut)
- [`NonNull::copy_from`]
  (https://doc.rust-lang.org/stable/core/ptr/struct.NonNull.html#method.copy_from)
- [`NonNull::copy_from_nonoverlapping`]
  (https://doc.rust-lang.org/stable/core/ptr/struct.NonNull.html#method.copy_from_nonoverlapping)
- [`NonNull::copy_to`]
  (https://doc.rust-lang.org/stable/core/ptr/struct.NonNull.html#method.copy_to)
- [`NonNull::copy_to_nonoverlapping`]
  (https://doc.rust-lang.org/stable/core/ptr/struct.NonNull.html#method.copy_to_nonoverlapping)
- [`NonNull::slice_from_raw_parts`]
  (https://doc.rust-lang.org/stable/core/ptr/struct.NonNull.html#method.slice_from_raw_parts)
- [`NonNull::write`]
  (https://doc.rust-lang.org/stable/core/ptr/struct.NonNull.html#method.write)
- [`NonNull::write_bytes`]
  (https://doc.rust-lang.org/stable/core/ptr/struct.NonNull.html#method.write_bytes)
- [`NonNull::write_unaligned`]
  (https://doc.rust-lang.org/stable/core/ptr/struct.NonNull.html#method.write_unaligned)
- [`OnceCell::into_inner`]
  (https://doc.rust-lang.org/stable/core/cell/struct.OnceCell.html#method.into_inner)
- [`Option::as_mut`]
  (https://doc.rust-lang.org/stable/core/option/enum.Option.html#method.as_mut)
- [`Option::expect`]
  (https://doc.rust-lang.org/stable/core/option/enum.Option.html#method.expect)
- [`Option::replace`]
  (https://doc.rust-lang.org/stable/core/option/enum.Option.html#method.replace)
- [`Option::take`]
  (https://doc.rust-lang.org/stable/core/option/enum.Option.html#method.take)
- [`Option::unwrap`]
  (https://doc.rust-lang.org/stable/core/option/enum.Option.html#method.unwrap)
- [`Option::unwrap_unchecked`]
  (https://doc.rust-lang.org/stable/core/option/enum.Option.html#method.unwrap_unchecked)
- [`Option::<&_>::copied`]
  (https://doc.rust-lang.org/stable/core/option/enum.Option.html#method.copied)
- [`Option::<&mut _>::copied`]
  (https://doc.rust-lang.org/stable/core/option/enum.Option.html#method.copied-1)
- [`Option::<Option<_>>::flatten`]
  (https://doc.rust-lang.org/stable/core/option/enum.Option.html#method.flatten)
- [`Option::<Result<_, _>>::transpose`]
  (https://doc.rust-lang.org/stable/core/option/enum.Option.html#method.transpose)
- [`RefCell::into_inner`]
  (https://doc.rust-lang.org/stable/core/cell/struct.RefCell.html#method.into_inner)
- [`Result::as_mut`]
  (https://doc.rust-lang.org/stable/core/result/enum.Result.html#method.as_mut)
- [`Result::<&_, _>::copied`]
  (https://doc.rust-lang.org/stable/core/result/enum.Result.html#method.copied)
- [`Result::<&mut _, _>::copied`]
  (https://doc.rust-lang.org/stable/core/result/enum.Result.html#method.copied-1)
- [`Result::<Option<_>, _>::transpose`]
  (https://doc.rust-lang.org/stable/core/result/enum.Result.html#method.transpose)
- [`UnsafeCell::get_mut`]
  (https://doc.rust-lang.org/stable/core/cell/struct.UnsafeCell.html#method.get_mut)
- [`UnsafeCell::into_inner`]
  (https://doc.rust-lang.org/stable/core/cell/struct.UnsafeCell.html#method.into_inner)
- [`array::from_mut`]
  (https://doc.rust-lang.org/stable/core/array/fn.from_mut.html)
- [`char::encode_utf8`]
  (https://doc.rust-lang.org/stable/core/primitive.char.html#method.encode_utf8)
- [`{float}::classify`]
  (https://doc.rust-lang.org/stable/core/primitive.f64.html#method.classify)
- [`{float}::is_finite`]
  (https://doc.rust-lang.org/stable/core/primitive.f64.html#method.is_finite)
- [`{float}::is_infinite`]
  (https://doc.rust-lang.org/stable/core/primitive.f64.html#method.is_infinite)
- [`{float}::is_nan`]
  (https://doc.rust-lang.org/stable/core/primitive.f64.html#method.is_nan)
- [`{float}::is_normal`]
  (https://doc.rust-lang.org/stable/core/primitive.f64.html#method.is_normal)
- [`{float}::is_sign_negative`]
  (https://doc.rust-lang.org/stable/core/primitive.f64.html#method.is_sign_negative)
- [`{float}::is_sign_positive`]
  (https://doc.rust-lang.org/stable/core/primitive.f64.html#method.is_sign_positive)
- [`{float}::is_subnormal`]
  (https://doc.rust-lang.org/stable/core/primitive.f64.html#method.is_subnormal)
- [`{float}::from_bits`]
  (https://doc.rust-lang.org/stable/core/primitive.f64.html#method.from_bits)
- [`{float}::from_be_bytes`]
  (https://doc.rust-lang.org/stable/core/primitive.f64.html#method.from_be_bytes)
- [`{float}::from_le_bytes`]
  (https://doc.rust-lang.org/stable/core/primitive.f64.html#method.from_le_bytes)
- [`{float}::from_ne_bytes`]
  (https://doc.rust-lang.org/stable/core/primitive.f64.html#method.from_ne_bytes)
- [`{float}::to_bits`]
  (https://doc.rust-lang.org/stable/core/primitive.f64.html#method.to_bits)
- [`{float}::to_be_bytes`]
  (https://doc.rust-lang.org/stable/core/primitive.f64.html#method.to_be_bytes)
- [`{float}::to_le_bytes`]
  (https://doc.rust-lang.org/stable/core/primitive.f64.html#method.to_le_bytes)
- [`{float}::to_ne_bytes`]
  (https://doc.rust-lang.org/stable/core/primitive.f64.html#method.to_ne_bytes)
- [`mem::replace`]
  (https://doc.rust-lang.org/stable/core/mem/fn.replace.html)
- [`ptr::replace`]
  (https://doc.rust-lang.org/stable/core/ptr/fn.replace.html)
- [`ptr::slice_from_raw_parts_mut`]
  (https://doc.rust-lang.org/stable/core/ptr/fn.slice_from_raw_parts_mut.html)
- [`ptr::write`]
  (https://doc.rust-lang.org/stable/core/ptr/fn.write.html)
- [`ptr::write_unaligned`]
  (https://doc.rust-lang.org/stable/core/ptr/fn.write_unaligned.html)
- [`<*const _>::copy_to`]
  (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.copy_to)
- [`<*const _>::copy_to_nonoverlapping`]
  (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.copy_to_nonoverlapping)
- [`<*mut _>::copy_from`]
  (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.copy_from)
- [`<*mut _>::copy_from_nonoverlapping`]
  (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.copy_from_nonoverlapping)
- [`<*mut _>::copy_to`]
  (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.copy_to-1)
- [`<*mut _>::copy_to_nonoverlapping`]
  (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.copy_to_nonoverlapping-1)
- [`<*mut _>::write`]
  (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.write)
- [`<*mut _>::write_bytes`]
  (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.write_bytes)
- [`<*mut _>::write_unaligned`]
  (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.write_unaligned)
- [`slice::from_mut`]
  (https://doc.rust-lang.org/stable/core/slice/fn.from_mut.html)
- [`slice::from_raw_parts_mut`]
  (https://doc.rust-lang.org/stable/core/slice/fn.from_raw_parts_mut.html)
- [`<[_]>::first_mut`]
  (https://doc.rust-lang.org/stable/core/primitive.slice.html#method.first_mut)
- [`<[_]>::last_mut`]
  (https://doc.rust-lang.org/stable/core/primitive.slice.html#method.last_mut)
- [`<[_]>::first_chunk_mut`]
  (https://doc.rust-lang.org/stable/core/primitive.slice.html#method.first_chunk_mut)
- [`<[_]>::last_chunk_mut`]
  (https://doc.rust-lang.org/stable/core/primitive.slice.html#method.last_chunk_mut)
- [`<[_]>::split_at_mut`]
  (https://doc.rust-lang.org/stable/core/primitive.slice.html#method.split_at_mut)
- [`<[_]>::split_at_mut_checked`]
  (https://doc.rust-lang.org/stable/core/primitive.slice.html#method.split_at_mut_checked)
- [`<[_]>::split_at_mut_unchecked`]
  (https://doc.rust-lang.org/stable/core/primitive.slice.html#method.split_at_mut_unchecked)
- [`<[_]>::split_first_mut`]
  (https://doc.rust-lang.org/stable/core/primitive.slice.html#method.split_first_mut)
- [`<[_]>::split_last_mut`]
  (https://doc.rust-lang.org/stable/core/primitive.slice.html#method.split_last_mut)
- [`<[_]>::split_first_chunk_mut`]
  (https://doc.rust-lang.org/stable/core/primitive.slice.html#method.split_first_chunk_mut)
- [`<[_]>::split_last_chunk_mut`]
  (https://doc.rust-lang.org/stable/core/primitive.slice.html#method.split_last_chunk_mut)
- [`str::as_bytes_mut`]
  (https://doc.rust-lang.org/stable/core/primitive.str.html#method.as_bytes_mut)
- [`str::as_mut_ptr`]
  (https://doc.rust-lang.org/stable/core/primitive.str.html#method.as_mut_ptr)
- [`str::from_utf8_unchecked_mut`]
  (https://doc.rust-lang.org/stable/core/str/fn.from_utf8_unchecked_mut.html)

Cargo
-----
- [Introduced a new `CARGO_MANIFEST_PATH` environment variable,
  similar to `CARGO_MANIFEST_DIR` but pointing directly to the manifest
  file.]
  (rust-lang/cargo#14404)
- [Added `package.autolib` to the manifest, allowing `[lib]`
  auto-discovery to be disabled.]
  (rust-lang/cargo#14591)
- [Declare support level for each crate in Cargo's Charter / crate docs.]
  (rust-lang/cargo#14600)
- [Declare new Intentional Artifacts as 'small' changes.]
  (rust-lang/cargo#14599)

Rustdoc
-------

- [The sidebar / hamburger menu table of contents now includes the
  `# headers` from the main item's doc comment]
  (rust-lang/rust#120736). This is similar
  to a third-party feature provided by the rustdoc-search-enhancements
  browser extension.

Compatibility Notes
-------------------
- [Warn against function pointers using unsupported ABI strings.]
  (rust-lang/rust#128784)
- [Check well-formedness of the source type's signature in fn
  pointer casts.]
  (rust-lang/rust#129021) This partly closes
  a soundness hole that comes when casting a function item to
  function pointer
- [Use equality instead of subtyping when resolving type dependent paths.]
  (rust-lang/rust#129073)
- Linking on macOS now correctly includes Rust's default deployment
  target. Due to a linker bug, you might have to pass
  `MACOSX_DEPLOYMENT_TARGET` or fix your `#[link]` attributes to
  point to the correct frameworks. See
  <rust-lang/rust#129369>.
- [Rust will now correctly raise an error for `repr(Rust)` written
  on non-`struct`/`enum`/`union` items, since it previous did not
  have any effect.]
  (rust-lang/rust#129422)
- The future incompatibility lint `deprecated_cfg_attr_crate_type_name`
  [has been made into a hard error]
  (rust-lang/rust#129670). It was used to
  deny usage of `#![crate_type]` and `#![crate_name]` attributes in
  `#![cfg_attr]`, which required a hack in the compiler to be able
  to change the used crate type and crate name after cfg expansion.
  Users can use `--crate-type` instead of `#![cfg_attr(..., crate_type
  = "...")]` and `--crate-name` instead of `#![cfg_attr(...,
  crate_name = "...")]` when running `rustc`/`cargo rustc` on the
  command line.  Use of those two attributes outside of `#![cfg_attr]`
  continue to be fully supported.

- Until now, paths into the sysroot were always prefixed with
  `/rustc/$hash` in diagnostics, codegen, backtrace, e.g.
    ```
    thread 'main' panicked at 'hello world', map-panic.rs:2:50
    stack backtrace:
       0: std::panicking::begin_panic
                 at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/panicking.rs:616:12
       1: map_panic::main::{{closure}}
                 at ./map-panic.rs:2:50
       2: core::option::Option<T>::map
                 at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/core/src/option.rs:929:29
       3: map_panic::main
                 at ./map-panic.rs:2:30
       4: core::ops::function::FnOnce::call_once
                 at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/core/src/ops/function.rs:248:5
    note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
    ```
  [RFC 3127 said]
  (https://rust-lang.github.io/rfcs/3127-trim-paths.html#changing-handling-of-sysroot-path-in-rustc)
  > We want to change this behaviour such that, when `rust-src`
    source files can be discovered, the virtual path is discarded
    and therefore the local path will be embedded, unless there is
    a `--remap-path-prefix` that causes this local path to be remapped
    in the usual way.

    [#129687](rust-lang/rust#129687)
    implements this behaviour, when `rust-src` is present at compile
    time, `rustc` replaces `/rustc/$hash` with a real path into
    the local `rust-src` component with best effort.  To sanitize
    this, users must explicitly supply `--remap-path-prefix=<path
    to rust-src>=foo` or not have the `rust-src` component installed.
- The allow-by-default `missing_docs` lint used to disable itself
  when invoked through `rustc --test`/`cargo test`, resulting in
  `#[expect(missing_docs)]` emitting false positives due to the
  expectation being wrongly unfulfilled. This behavior [has now been
  removed]
  (rust-lang/rust#130025), which allows
  `#[expect(missing_docs)]` to be fulfilled in all scenarios, but
  will also report new `missing_docs` diagnostics for publicly
  reachable `#[cfg(test)]` items, [integration test]
  (https://doc.rust-lang.org/cargo/reference/cargo-targets.html#integration-tests)
  crate-level documentation, and publicly reachable items in
  integration tests.
- [The `armv8r-none-eabihf` target now uses the Armv8-R required
  set of floating-point features.]
  (rust-lang/rust#130295)
- [Fix a soundness bug where rustc wouldn't detect unconstrained
  higher-ranked lifetimes in a `dyn Trait`'s associated types that
  occur due to supertraits.]
  (rust-lang/rust#130367)
- [Update the minimum external LLVM version to 18.]
  (rust-lang/rust#130487)
- [Remove `aarch64-fuchsia` and `x86_64-fuchsia` target aliases in
  favor of `aarch64-unknown-fuchsia` and `x86_64-unknown-fuchsia`
  respectively.]
  (rust-lang/rust#130657)
- [The ABI-level exception class of a Rust panic is now encoded
  with native-endian bytes, so it is legible in hex dumps.]
  (rust-lang/rust#130897)
- [Visual Studio 2013 is no longer supported for MSVC targets.]
  (rust-lang/rust#131070)
- [The sysroot no longer contains the `std` dynamic library in its
  top-level `lib/` dir.]
  (rust-lang/rust#131188)