Announce Rust 1.91.0 stable release

content/Rust-1.91.0.md

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+path = "2025/10/30/Rust-1.91.0"
+title = "Announcing Rust 1.91.0"
+authors = ["The Rust Release Team"]
+aliases = ["releases/1.91.0"]
+
+[extra]
+release = true
++++
+
+The Rust team is happy to announce a new version of Rust, 1.91.0. Rust is a programming language empowering everyone to build reliable and efficient software.
+
+If you have a previous version of Rust installed via `rustup`, you can get 1.91.0 with:
+
+```console
+$ rustup update stable
+```
+
+If you don't have it already, you can [get `rustup`](https://www.rust-lang.org/install.html) from the appropriate page on our website, and check out the [detailed release notes for 1.91.0](https://doc.rust-lang.org/stable/releases.html#version-1910-2025-10-30).
+
+If you'd like to help us out by testing future releases, you might consider updating locally to use the beta channel (`rustup default beta`) or the nightly channel (`rustup default nightly`). Please [report](https://github.com/rust-lang/rust/issues/new/choose) any bugs you might come across!
+
+## What's in 1.91.0 stable
+
+### `aarch64-pc-windows-msvc` is now a Tier 1 platform
+
+The Rust compiler supports [a wide variety of targets][platform-support], but
+the Rust Team can't provide the same level of support for all of them. To
+clearly mark how supported each target is, we use a tiering system:
+
+* Tier 3 targets are technically supported by the compiler, but we don't check
+  whether their code build or passes the tests, and we don't provide any
+  prebuilt binaries as part of our releases.
+* Tier 2 targets are guaranteed to build and we provide prebuilt binaries, but
+  we don't execute the test suite on those platforms: the produced binaries
+  might not work or might have bugs.
+* Tier 1 targets provide the highest support guarantee, and we run the full
+  suite on those platforms for every change merged in the compiler. Prebuilt
+  binaries are also available.
+
+Rust 1.91.0 promotes the `aarch64-pc-windows-msvc` target to Tier 1 support,
+bringing our highest guarantees to users of 64-bit ARM systems running Windows.
+
+### Add lint against dangling raw pointers from local variables
+
+While Rust's borrow checking prevents dangling references from being returned, it doesn't
+track raw pointers. With this release, we are adding a warn-by-default lint on raw
+pointers to local variables being returned from functions. For example, code like this:
+
+```rust
+fn f() -> *const u8 {
+    let x = 0;
+    &x
+}
+```
+
+will now produce a lint:
+
+```
+warning: a dangling pointer will be produced because the local variable `x` will be dropped
+ --> src/lib.rs:3:5
+  |
+1 | fn f() -> *const u8 {
+  |           --------- return type of the function is `*const u8`
+2 |     let x = 0;
+  |         - `x` is part the function and will be dropped at the end of the function
+3 |     &x
+  |     ^^
+  |
+  = note: pointers do not have a lifetime; after returning, the `u8` will be deallocated
+    at the end of the function because nothing is referencing it as far as the type system is
+    concerned
+  = note: `#[warn(dangling_pointers_from_locals)]` on by default
+```
+
+Note that the code above is not unsafe, as it itself doesn't perform any dangerous
+operations. Only dereferencing the raw pointer after the function returns would be
+unsafe. We expect future releases of Rust to add more functionality helping authors
+to safely interact with raw pointers, and with unsafe code more generally.
+
+### Stabilized APIs
+
+- [`Path::file_prefix`](https://doc.rust-lang.org/stable/std/path/struct.Path.html#method.file_prefix)
+- [`AtomicPtr::fetch_ptr_add`](https://doc.rust-lang.org/stable/std/sync/atomic/struct.AtomicPtr.html#method.fetch_ptr_add)
+- [`AtomicPtr::fetch_ptr_sub`](https://doc.rust-lang.org/stable/std/sync/atomic/struct.AtomicPtr.html#method.fetch_ptr_sub)
+- [`AtomicPtr::fetch_byte_add`](https://doc.rust-lang.org/stable/std/sync/atomic/struct.AtomicPtr.html#method.fetch_byte_add)
+- [`AtomicPtr::fetch_byte_sub`](https://doc.rust-lang.org/stable/std/sync/atomic/struct.AtomicPtr.html#method.fetch_byte_sub)
+- [`AtomicPtr::fetch_or`](https://doc.rust-lang.org/stable/std/sync/atomic/struct.AtomicPtr.html#method.fetch_or)
+- [`AtomicPtr::fetch_and`](https://doc.rust-lang.org/stable/std/sync/atomic/struct.AtomicPtr.html#method.fetch_and)
+- [`AtomicPtr::fetch_xor`](https://doc.rust-lang.org/stable/std/sync/atomic/struct.AtomicPtr.html#method.fetch_xor)
+- [`{integer}::strict_add`](https://doc.rust-lang.org/stable/std/primitive.u32.html#method.strict_add)
+- [`{integer}::strict_sub`](https://doc.rust-lang.org/stable/std/primitive.u32.html#method.strict_sub)
+- [`{integer}::strict_mul`](https://doc.rust-lang.org/stable/std/primitive.u32.html#method.strict_mul)
+- [`{integer}::strict_div`](https://doc.rust-lang.org/stable/std/primitive.i32.html#method.strict_div)
+- [`{integer}::strict_div_euclid`](https://doc.rust-lang.org/stable/std/primitive.i32.html#method.strict_div_euclid)
+- [`{integer}::strict_rem`](https://doc.rust-lang.org/stable/std/primitive.i32.html#method.strict_rem)
+- [`{integer}::strict_rem_euclid`](https://doc.rust-lang.org/stable/std/primitive.i32.html#method.strict_rem_euclid)
+- [`{integer}::strict_neg`](https://doc.rust-lang.org/stable/std/primitive.u32.html#method.strict_neg)
+- [`{integer}::strict_shl`](https://doc.rust-lang.org/stable/std/primitive.u32.html#method.strict_shl)
+- [`{integer}::strict_shr`](https://doc.rust-lang.org/stable/std/primitive.u32.html#method.strict_shr)
+- [`{integer}::strict_pow`](https://doc.rust-lang.org/stable/std/primitive.u32.html#method.strict_pow)
+- [`i{N}::strict_add_unsigned`](https://doc.rust-lang.org/stable/std/primitive.i32.html#method.strict_add_unsigned)
+- [`i{N}::strict_sub_unsigned`](https://doc.rust-lang.org/stable/std/primitive.i32.html#method.strict_sub_unsigned)
+- [`i{N}::strict_abs`](https://doc.rust-lang.org/stable/std/primitive.i32.html#method.strict_abs)
+- [`u{N}::strict_add_signed`](https://doc.rust-lang.org/stable/std/primitive.u32.html#method.strict_add_signed)
+- [`u{N}::strict_sub_signed`](https://doc.rust-lang.org/stable/std/primitive.u32.html#method.strict_sub_signed)
+- [`PanicHookInfo::payload_as_str`](https://doc.rust-lang.org/stable/std/panic/struct.PanicHookInfo.html#method.payload_as_str)
+- [`core::iter::chain`](https://doc.rust-lang.org/stable/core/iter/fn.chain.html)
+- [`u{N}::checked_signed_diff`](https://doc.rust-lang.org/stable/std/primitive.u16.html#method.checked_signed_diff)
+- [`core::array::repeat`](https://doc.rust-lang.org/stable/core/array/fn.repeat.html)
+- [`PathBuf::add_extension`](https://doc.rust-lang.org/stable/std/path/struct.PathBuf.html#method.add_extension)
+- [`PathBuf::with_added_extension`](https://doc.rust-lang.org/stable/std/path/struct.PathBuf.html#method.with_added_extension)
+- [`Duration::from_mins`](https://doc.rust-lang.org/stable/std/time/struct.Duration.html#method.from_mins)
+- [`Duration::from_hours`](https://doc.rust-lang.org/stable/std/time/struct.Duration.html#method.from_hours)
+- [`impl PartialEq<str> for PathBuf`](https://doc.rust-lang.org/stable/std/path/struct.PathBuf.html#impl-PartialEq%3Cstr%3E-for-PathBuf)
+- [`impl PartialEq<String> for PathBuf`](https://doc.rust-lang.org/stable/std/path/struct.PathBuf.html#impl-PartialEq%3CString%3E-for-PathBuf)
+- [`impl PartialEq<str> for Path`](https://doc.rust-lang.org/stable/std/path/struct.Path.html#impl-PartialEq%3Cstr%3E-for-Path)
+- [`impl PartialEq<String> for Path`](https://doc.rust-lang.org/stable/std/path/struct.Path.html#impl-PartialEq%3CString%3E-for-Path)
+- [`impl PartialEq<PathBuf> for String`](https://doc.rust-lang.org/stable/std/string/struct.String.html#impl-PartialEq%3CPathBuf%3E-for-String)
+- [`impl PartialEq<Path> for String`](https://doc.rust-lang.org/stable/std/string/struct.String.html#impl-PartialEq%3CPath%3E-for-String)
+- [`impl PartialEq<PathBuf> for str`](https://doc.rust-lang.org/stable/std/primitive.str.html#impl-PartialEq%3CPathBuf%3E-for-str)
+- [`impl PartialEq<Path> for str`](https://doc.rust-lang.org/stable/std/primitive.str.html#impl-PartialEq%3CPath%3E-for-str)
+- [`Ipv4Addr::from_octets`](https://doc.rust-lang.org/stable/std/net/struct.Ipv4Addr.html#method.from_octets)
+- [`Ipv6Addr::from_octets`](https://doc.rust-lang.org/stable/std/net/struct.Ipv6Addr.html#method.from_octets)
+- [`Ipv6Addr::from_segments`](https://doc.rust-lang.org/stable/std/net/struct.Ipv6Addr.html#method.from_segments)
+- [`impl<T> Default for Pin<Box<T>> where Box<T>: Default, T: ?Sized`](https://doc.rust-lang.org/stable/std/default/trait.Default.html#impl-Default-for-Pin%3CBox%3CT%3E%3E)
+- [`impl<T> Default for Pin<Rc<T>> where Rc<T>: Default, T: ?Sized`](https://doc.rust-lang.org/stable/std/default/trait.Default.html#impl-Default-for-Pin%3CRc%3CT%3E%3E)
+- [`impl<T> Default for Pin<Arc<T>> where Arc<T>: Default, T: ?Sized`](https://doc.rust-lang.org/stable/std/default/trait.Default.html#impl-Default-for-Pin%3CArc%3CT%3E%3E)
+- [`Cell::as_array_of_cells`](https://doc.rust-lang.org/stable/std/cell/struct.Cell.html#method.as_array_of_cells)
+- [`u{N}::carrying_add`](https://doc.rust-lang.org/stable/std/primitive.u64.html#method.carrying_add)
+- [`u{N}::borrowing_sub`](https://doc.rust-lang.org/stable/std/primitive.u64.html#method.borrowing_sub)
+- [`u{N}::carrying_mul`](https://doc.rust-lang.org/stable/std/primitive.u64.html#method.carrying_mul)
+- [`u{N}::carrying_mul_add`](https://doc.rust-lang.org/stable/std/primitive.u64.html#method.carrying_mul_add)
+- [`BTreeMap::extract_if`](https://doc.rust-lang.org/stable/std/collections/struct.BTreeMap.html#method.extract_if)
+- [`BTreeSet::extract_if`](https://doc.rust-lang.org/stable/std/collections/struct.BTreeSet.html#method.extract_if)
+- [`impl Debug for windows::ffi::EncodeWide<'_>`](https://doc.rust-lang.org/stable/std/os/windows/ffi/struct.EncodeWide.html#impl-Debug-for-EncodeWide%3C'_%3E)
+- [`str::ceil_char_boundary`](https://doc.rust-lang.org/stable/std/primitive.str.html#method.ceil_char_boundary)
+- [`str::floor_char_boundary`](https://doc.rust-lang.org/stable/std/primitive.str.html#method.floor_char_boundary)
+- [`impl Sum for Saturating<u{N}>`](https://doc.rust-lang.org/stable/std/num/struct.Saturating.html#impl-Sum-for-Saturating%3Cu32%3E)
+- [`impl Sum<&Self> for Saturating<u{N}>`](https://doc.rust-lang.org/stable/std/num/struct.Saturating.html#impl-Sum%3C%26Saturating%3Cu32%3E%3E-for-Saturating%3Cu32%3E)
+- [`impl Product for Saturating<u{N}>`](https://doc.rust-lang.org/stable/std/num/struct.Saturating.html#impl-Product-for-Saturating%3Cu32%3E)
+- [`impl Product<&Self> for Saturating<u{N}>`](https://doc.rust-lang.org/stable/std/num/struct.Saturating.html#impl-Product%3C%26Saturating%3Cu32%3E%3E-for-Saturating%3Cu32%3E)
+
+These previously stable APIs are now stable in const contexts:
+
+- [`<[T; N]>::each_ref`](https://doc.rust-lang.org/stable/std/primitive.array.html#method.each_ref)
+- [`<[T; N]>::each_mut`](https://doc.rust-lang.org/stable/std/primitive.array.html#method.each_mut)
+- [`OsString::new`](https://doc.rust-lang.org/stable/std/ffi/struct.OsString.html#method.new)
+- [`PathBuf::new`](https://doc.rust-lang.org/stable/std/path/struct.PathBuf.html#method.new)
+- [`TypeId::of`](https://doc.rust-lang.org/stable/std/any/struct.TypeId.html#method.of)
+- [`ptr::with_exposed_provenance`](https://doc.rust-lang.org/stable/std/ptr/fn.with_exposed_provenance.html)
+- [`ptr::with_exposed_provenance_mut`](https://doc.rust-lang.org/stable/std/ptr/fn.with_exposed_provenance_mut.html)
+
+### Platform Support
+
+- [Promote `aarch64-pc-windows-msvc` to Tier 1](https://github.com/rust-lang/rust/pull/145682)
+- [Promote `aarch64-pc-windows-gnullvm` and `x86_64-pc-windows-gnullvm` to Tier 2 with host tools.](https://github.com/rust-lang/rust/pull/143031)
+  Note: llvm-tools and MSI installers are missing but will be added in future releases.
+
+Refer to Rust’s [platform support page][platform-support] for more information on Rust’s tiered platform support.
+
+### Other changes
+
+Check out everything that changed in [Rust](https://github.com/rust-lang/rust/releases/tag/1.91.0), [Cargo](https://doc.rust-lang.org/nightly/cargo/CHANGELOG.html#cargo-191-2025-10-30), and [Clippy](https://github.com/rust-lang/rust-clippy/blob/master/CHANGELOG.md#rust-191).
+
+## Contributors to 1.91.0
+
+Many people came together to create Rust 1.91.0. We couldn't have done it without all of you. [Thanks!](https://thanks.rust-lang.org/rust/1.91.0/)
+
+[platform-support]: https://doc.rust-lang.org/rustc/platform-support.html