Tracking issue for release notes of #133349: Stabilize the 2024 edition

[rustbot]

This issue tracks the release notes text for #133349.

Steps

• Proposed text is drafted by PR author (or team) making the noteworthy change.
• Issue is nominated for release team review of clarity for wider audience.
• Release team includes text in release notes/blog posts.

Release notes text

The responsible team for the underlying change should edit this section to replace the automatically generated link with a succinct description of what changed, drawing upon text proposed by the author (either in discussion or through direct editing).

# Language
- [The 2024 Edition is now stable.](https://github.com/rust-lang/rust/pull/133349)
  See [the edition guide](https://doc.rust-lang.org/nightly/edition-guide/rust-2024/index.html) for more details.

Tip

Use the previous releases categories to help choose which one(s) to use.
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Release blog section

If the change is notable enough for inclusion in the blog post, the responsible team should add content to this section.
Otherwise leave it empty.

### Rust 2024

We are excited to announce that the Rust 2024 Edition is now stable!
Editions are a mechanism for opt-in changes that may otherwise pose a backwards compatibility risk. See [the edition guide](https://doc.rust-lang.org/edition-guide/editions/index.html) for details on how this is achieved, and detailed instructions on how to migrate.

This is the largest edition we have released. The [edition guide](https://doc.rust-lang.org/edition-guide/rust-2024/index.html) contains detailed information about each change, but as a summary, here are all the changes:

- Language
  - [RPIT lifetime capture rules](https://doc.rust-lang.org/edition-guide/rust-2024/rpit-lifetime-capture.html) — Changes the default impl trait `use<..>` capturing.
  - [`if let` temporary scope](https://doc.rust-lang.org/edition-guide/rust-2024/temporary-if-let-scope.html) — Changes the scope of temporaries for `if let` expressions.
  - [Tail expression temporary scope](https://doc.rust-lang.org/edition-guide/rust-2024/temporary-tail-expr-scope.html) — Changes the scope of temporaries for the tail expression in a block.
  - [Match ergonomics reservations](https://doc.rust-lang.org/edition-guide/rust-2024/match-ergonomics.html) — New restrictions on pattern binding modes.
  - [Unsafe `extern` blocks](https://doc.rust-lang.org/edition-guide/rust-2024/unsafe-extern.html) — `extern` blocks now require the `unsafe` keyword.
  - [Unsafe attributes](https://doc.rust-lang.org/edition-guide/rust-2024/unsafe-attributes.html) — The `export_name`, `link_section`, and `no_mangle` attributes must now be marked as `unsafe`.
  - [`unsafe_op_in_unsafe_fn` warning](https://doc.rust-lang.org/edition-guide/rust-2024/unsafe-op-in-unsafe-fn.html) — The [`unsafe_op_in_unsafe_fn`](https://doc.rust-lang.org/rustc/lints/listing/allowed-by-default.html#unsafe-op-in-unsafe-fn) lint now warns by default, requiring explicit `unsafe {}` blocks in `unsafe` functions.
  - [Disallow references to `static mut`](https://doc.rust-lang.org/edition-guide/rust-2024/static-mut-references.html) — References to `static mut` items now generate a deny-by-default error.
  - [Never type fallback change](https://doc.rust-lang.org/edition-guide/rust-2024/never-type-fallback.html) — Changes to how the never type `!` coerces, and changes the [`never_type_fallback_flowing_into_unsafe`](https://doc.rust-lang.org/rustc/lints/listing/warn-by-default.html#never-type-fallback-flowing-into-unsafe) lint level to "deny".  
  - [Macro fragment specifiers](https://doc.rust-lang.org/edition-guide/rust-2024/macro-fragment-specifiers.html) — The `expr` macro fragment specifier in `macro_rules!` macros now also matches `const` and `_` expressions.
  - [Missing macro fragment specifiers](https://doc.rust-lang.org/edition-guide/rust-2024/missing-macro-fragment-specifiers.html) — The [`missing_fragment_specifier`](https://doc.rust-lang.org/rustc/lints/listing/deny-by-default.html#missing-fragment-specifier) lint is now a hard error, rejecting macro meta variables without a fragment specifier kind.
  - [`gen` keyword](https://doc.rust-lang.org/edition-guide/rust-2024/gen-keyword.html) — Reserves the `gen` keyword in anticipation of adding generator blocks in the future.
  - [Reserved syntax](https://doc.rust-lang.org/edition-guide/rust-2024/reserved-syntax.html) — Reserves `#"foo"#` style strings and `##` tokens in anticipation of changing how guarded string literals may change in the future.
- Standard library
  - [Changes to the prelude](https://doc.rust-lang.org/edition-guide/rust-2024/prelude.html) — Adds `Future` and `IntoFuture` to the prelude.
  - [Add `IntoIterator` for `Box<[T]>`](https://doc.rust-lang.org/edition-guide/rust-2024/intoiterator-box-slice.html) — Changes how iterators work with boxed slices.
  - [Newly unsafe functions](https://doc.rust-lang.org/edition-guide/rust-2024/newly-unsafe-functions.html) — `std::env::set_var`, `std::env::remove_var`, and `std::os::unix::process::CommandExt::before_exec` are now unsafe functions.
- Cargo
  - [Cargo: Rust-version aware resolver](https://doc.rust-lang.org/edition-guide/rust-2024/cargo-resolver.html) — Changes the default dependency resolver behavior to consider the `rust-version` field.
  - [Cargo: Table and key name consistency](https://doc.rust-lang.org/edition-guide/rust-2024/cargo-table-key-names.html) — Removes some outdated `Cargo.toml` keys.
  - [Cargo: Reject unused inherited default-features](https://doc.rust-lang.org/edition-guide/rust-2024/cargo-inherited-default-features.html) — Changes how `default-features = false` works with inherited workspace dependencies.
- Rustdoc
  - [Rustdoc combined tests](https://doc.rust-lang.org/edition-guide/rust-2024/rustdoc-doctests.html) — Doctests are now combined into a single executable, significantly improving performance.
  - [Rustdoc nested `include!` change](https://doc.rust-lang.org/edition-guide/rust-2024/rustdoc-nested-includes.html) — Changes to the relative path behavior of nested `include!` files.
- Rustfmt
  - [Rustfmt: Style edition](https://doc.rust-lang.org/edition-guide/rust-2024/rustfmt-style-edition.html) — Introduces the concept of "style editions", which allow you to independently control the formatting edition from the Rust edition.
  - [Rustfmt: Formatting fixes](https://doc.rust-lang.org/edition-guide/rust-2024/rustfmt-formatting-fixes.html) — A large number of fixes to formatting various situations.
  - [Rustfmt: Combine all delimited exprs as last argument](https://doc.rust-lang.org/edition-guide/rust-2024/rustfmt-overflow-delimited-expr.html) — Changes to multi-line expressions as the last argument.
  - [Rustfmt: Raw identifier sorting](https://doc.rust-lang.org/edition-guide/rust-2024/rustfmt-raw-identifier-sorting.html) — Changes to how `r#foo` identifiers are sorted.
  - [Rustfmt: Version sorting](https://doc.rust-lang.org/edition-guide/rust-2024/rustfmt-version-sorting.html) — Changes to how identifiers that contain integers are sorted.

#### Migrating to 2024

The guide includes migration instructions for all new features, and in general
[transitioning an existing project to a new edition](https://doc.rust-lang.org/edition-guide/editions/transitioning-an-existing-project-to-a-new-edition.html).
In many cases `cargo fix` can automate the necessary changes. You may even
find that no changes in your code are needed at all for 2024!

*Many* people came together to create this edition. We'd like to thank them all for their hard work!

<!-- consider a similar thanks thread like https://github.com/rust-lang/rust/issues/88623? -->

cc @ehuss, @traviscross -- origin issue/PR authors and assignees for starting to draft text