Rollup merge of #139002 - cuviper:relnotes-1.86.0, r=BoxyUwU

Add release notes for 1.86.0

Closes #138795 (the draft)

cc ````@rust-lang/release````
````@rustbot```` ping relnotes-interest-group

Author: matthiaskrgr

RELEASES.md

@@ -1,3 +1,126 @@
+Version 1.86.0 (2025-04-03)
+==========================
+
+<a id="1.86.0-Language"></a>
+
+Language
+--------
+- [Stabilize upcasting trait objects to supertraits.](https://github.com/rust-lang/rust/pull/134367)
+- [Allow safe functions to be marked with the `#[target_feature]` attribute.](https://github.com/rust-lang/rust/pull/134090)
+- [The `missing_abi` lint now warns-by-default.](https://github.com/rust-lang/rust/pull/132397)
+- Rust now lints about double negations, to catch cases that might have intended to be a prefix decrement operator (`--x`) as written in other languages. This was previously a clippy lint, `clippy::double_neg`, and is [now available directly in Rust as `double_negations`.](https://github.com/rust-lang/rust/pull/126604)
+- [More pointers are now detected as definitely not-null based on their alignment in const eval.](https://github.com/rust-lang/rust/pull/133700)
+- [Empty `repr()` attribute applied to invalid items are now correctly rejected.](https://github.com/rust-lang/rust/pull/133925)
+- [Inner attributes `#![test]` and `#![rustfmt::skip]` are no longer accepted in more places than intended.](https://github.com/rust-lang/rust/pull/134276)
+
+<a id="1.86.0-Compiler"></a>
+
+Compiler
+--------
+- [Debug-assert that raw pointers are non-null on access.](https://github.com/rust-lang/rust/pull/134424)
+- [Change `-O` to mean `-C opt-level=3` instead of `-C opt-level=2` to match Cargo's defaults.](https://github.com/rust-lang/rust/pull/135439)
+- [Fix emission of `overflowing_literals` under certain macro environments.](https://github.com/rust-lang/rust/pull/136393)
+
+<a id="1.86.0-Platform-Support"></a>
+
+Platform Support
+----------------
+- [Replace `i686-unknown-redox` target with `i586-unknown-redox`.](https://github.com/rust-lang/rust/pull/136698)
+- [Increase baseline CPU of `i686-unknown-hurd-gnu` to Pentium 4.](https://github.com/rust-lang/rust/pull/136700)
+- New tier 3 targets:
+  - [`{aarch64-unknown,x86_64-pc}-nto-qnx710_iosock`](https://github.com/rust-lang/rust/pull/133631).
+    For supporting Neutrino QNX 7.1 with `io-socket` network stack.
+  - [`{aarch64-unknown,x86_64-pc}-nto-qnx800`](https://github.com/rust-lang/rust/pull/133631).
+    For supporting Neutrino QNX 8.0 (`no_std`-only).
+  - [`{x86_64,i686}-win7-windows-gnu`](https://github.com/rust-lang/rust/pull/134609).
+    Intended for backwards compatibility with Windows 7. `{x86_64,i686}-win7-windows-msvc` are the Windows MSVC counterparts that already exist as Tier 3 targets.
+  - [`amdgcn-amd-amdhsa`](https://github.com/rust-lang/rust/pull/134740).
+  - [`x86_64-pc-cygwin`](https://github.com/rust-lang/rust/pull/134999).
+  - [`{mips,mipsel}-mti-none-elf`](https://github.com/rust-lang/rust/pull/135074).
+    Initial bare-metal support.
+  - [`m68k-unknown-none-elf`](https://github.com/rust-lang/rust/pull/135085).
+  - [`armv7a-nuttx-{eabi,eabihf}`, `aarch64-unknown-nuttx`, and `thumbv7a-nuttx-{eabi,eabihf}`](https://github.com/rust-lang/rust/pull/135757).
+
+Refer to Rust's [platform support page][platform-support-doc]
+for more information on Rust's tiered platform support.
+
+<a id="1.86.0-Libraries"></a>
+
+Libraries
+---------
+- The type of `FromBytesWithNulError` in `CStr::from_bytes_with_nul(bytes: &[u8]) -> Result<&Self, FromBytesWithNulError>` was [changed from an opaque struct to an enum](https://github.com/rust-lang/rust/pull/134143), allowing users to examine why the conversion failed.
+- [Remove `RustcDecodable` and `RustcEncodable`.](https://github.com/rust-lang/rust/pull/134272)
+- [Deprecate libtest's `--logfile` option.](https://github.com/rust-lang/rust/pull/134283)
+- [On recent versions of Windows, `std::fs::remove_file` will now remove read-only files.](https://github.com/rust-lang/rust/pull/134679)
+
+<a id="1.86.0-Stabilized-APIs"></a>
+
+Stabilized APIs
+---------------
+
+- [`{float}::next_down`](https://doc.rust-lang.org/stable/std/primitive.f64.html#method.next_down)
+- [`{float}::next_up`](https://doc.rust-lang.org/stable/std/primitive.f64.html#method.next_up)
+- [`<[_]>::get_disjoint_mut`](https://doc.rust-lang.org/stable/std/primitive.slice.html#method.get_disjoint_mut)
+- [`<[_]>::get_disjoint_unchecked_mut`](https://doc.rust-lang.org/stable/std/primitive.slice.html#method.get_disjoint_unchecked_mut)
+- [`slice::GetDisjointMutError`](https://doc.rust-lang.org/stable/std/slice/enum.GetDisjointMutError.html)
+- [`HashMap::get_disjoint_mut`](https://doc.rust-lang.org/std/collections/hash_map/struct.HashMap.html#method.get_disjoint_mut)
+- [`HashMap::get_disjoint_unchecked_mut`](https://doc.rust-lang.org/std/collections/hash_map/struct.HashMap.html#method.get_disjoint_unchecked_mut)
+- [`NonZero::count_ones`](https://doc.rust-lang.org/stable/std/num/struct.NonZero.html#method.count_ones)
+- [`Vec::pop_if`](https://doc.rust-lang.org/std/vec/struct.Vec.html#method.pop_if)
+- [`sync::Once::wait`](https://doc.rust-lang.org/stable/std/sync/struct.Once.html#method.wait)
+- [`sync::Once::wait_force`](https://doc.rust-lang.org/stable/std/sync/struct.Once.html#method.wait_force)
+- [`sync::OnceLock::wait`](https://doc.rust-lang.org/stable/std/sync/struct.OnceLock.html#method.wait)
+
+These APIs are now stable in const contexts:
+
+- [`hint::black_box`](https://doc.rust-lang.org/stable/std/hint/fn.black_box.html)
+- [`io::Cursor::get_mut`](https://doc.rust-lang.org/stable/std/io/struct.Cursor.html#method.get_mut)
+- [`io::Cursor::set_position`](https://doc.rust-lang.org/stable/std/io/struct.Cursor.html#method.set_position)
+- [`str::is_char_boundary`](https://doc.rust-lang.org/stable/std/primitive.str.html#method.is_char_boundary)
+- [`str::split_at`](https://doc.rust-lang.org/stable/std/primitive.str.html#method.split_at)
+- [`str::split_at_checked`](https://doc.rust-lang.org/stable/std/primitive.str.html#method.split_at_checked)
+- [`str::split_at_mut`](https://doc.rust-lang.org/stable/std/primitive.str.html#method.split_at_mut)
+- [`str::split_at_mut_checked`](https://doc.rust-lang.org/stable/std/primitive.str.html#method.split_at_mut_checked)
+
+<a id="1.86.0-Cargo"></a>
+
+Cargo
+-----
+- [When merging, replace rather than combine configuration keys that refer to a program path and its arguments.](https://github.com/rust-lang/cargo/pull/15066/)
+- [Error if both `--package` and `--workspace` are passed but the requested package is missing.](https://github.com/rust-lang/cargo/pull/15071/) This was previously silently ignored, which was considered a bug since missing packages should be reported.
+- [Deprecate the token argument in `cargo login` to avoid shell history leaks.](https://github.com/rust-lang/cargo/pull/15057/)
+- [Simplify the implementation of `SourceID` comparisons.](https://github.com/rust-lang/cargo/pull/14980/) This may potentially change behavior if the canonicalized URL compares differently in alternative registries.
+
+<a id="1.86.0-Rustdoc"></a>
+
+Rustdoc
+-----
+- [Add a sans-serif font setting.](https://github.com/rust-lang/rust/pull/133636)
+
+<a id="1.86.0-Compatibility-Notes"></a>
+
+Compatibility Notes
+-------------------
+- [The `wasm_c_abi` future compatibility warning is now a hard error.](https://github.com/rust-lang/rust/pull/133951)
+  Users of `wasm-bindgen` should upgrade to at least version 0.2.89, otherwise compilation will fail.
+- [Remove long-deprecated no-op attributes `#![no_start]` and `#![crate_id]`.](https://github.com/rust-lang/rust/pull/134300)
+- [The future incompatibility lint `cenum_impl_drop_cast` has been made into a hard error.](https://github.com/rust-lang/rust/pull/135964) This means it is now an error to cast a field-less enum to an integer if the enum implements `Drop`.
+- [SSE2 is now required for "i686" 32-bit x86 hard-float targets; disabling it causes a warning that will become a hard error eventually.](https://github.com/rust-lang/rust/pull/137037)
+  To compile for pre-SSE2 32-bit x86, use a "i586" target instead.
+
+<a id="1.86.0-Internal-Changes"></a>
+
+Internal Changes
+----------------
+
+These changes do not affect any public interfaces of Rust, but they represent
+significant improvements to the performance or internals of rustc and related
+tools.
+
+- [Build the rustc on AArch64 Linux with ThinLTO + PGO.](https://github.com/rust-lang/rust/pull/133807)
+  The ARM 64-bit compiler (AArch64) on Linux is now optimized with ThinLTO and PGO, similar to the optimizations we have already performed for the x86-64 compiler on Linux. This should make it up to 30% faster.
+
+
 Version 1.85.1 (2025-03-18)
 ==========================