Draft release notes for 1.93

[BoxyUwU]

NOTE: Use the 📝 links to edit those that have a relnotes-tracking-issue,
and they will be updated when we regenerate the notes periodically (manually).

---

Version 1.93 (2026-01-22)

Language

• Add new function_casts_as_integer lint
  📝
• Add future-incompatibility warning for ... function parameters without a pattern outside of extern blocks
  📝
• Stabilize s390x vector target feature and is_s390x_feature_detected! macro
  📝
• Stabilize declaration of c-style variadic functions for the system ABI
  📝
• Emit error when using some keyword as a cfg predicate
  📝
• Future compat warning for repr(C) enums whose discriminant values do not fit into a c_int or c_uint
  📝
• Forward-compatibility warning against ignoring repr(C) types as part of repr(transparent)
  📝
• Stabilize asm_cfg
  📝
• Make deref_nullptr deny by default instead of warn
  📝
• During const-evaluation, support copying pointers byte-for-byte
  📝
• Add const_item_interior_mutations lint to warn against calls which mutates an interior mutable const-items
  📝
• LUB coercions now correctly handle function item types, and functions with differing safeties
  📝
• Allow const items that contain mutable references to static (which is very unsafe, but not always UB)
  📝

Compiler

• Stabilize -Zno-jump-tables as -Cjump-tables=bool
  📝
• Promote riscv64a23-unknown-linux-gnu to Tier 2 (without host tools)
  📝

Platform Support

Refer to Rust's platform support page
for more information on Rust's tiered platform support.

Libraries

• Allow the global allocator to use thread-local storage and std::thread::current()
  📝
• Stabilize char_max_len
• Make BTree::append not update existing keys when appending an entry which already exists
  📝
• Don't require T: RefUnwindSafe for vec::IntoIter<T>: UnwindSafe
  📝

Stabilized APIs

• String::into_raw_parts
• Vec::into_raw_parts
  📝
• <[T]>::as_array
• <[T]>::as_array_mut
• <*const [T]>::as_array
• <*mut [T]>::as_array_mut
  📝
• VecDeque::pop_front_if
• VecDeque::pop_back_if
  📝
• Duration::from_nanos_u128
  📝

These previously stable APIs are now stable in const contexts:

Cargo

• Enable CARGO_CFG_DEBUG_ASSERTIONS in build scripts based on profile
• feat(tree): Support long forms for --format variables
• clean: Add --workspace support

Rustdoc

• Remove #![doc(document_private_items)]
  📝
• Include attribute and derive macros in search filters for "macros"
  📝
• Include extern crates in search filters for import
  📝
• validate usage of crate-level doc attributes. This means if any of html_favicon_url, html_logo_url, html_playground_url, issue_tracker_base_url, or html_no_source either has a missing value, an unexpected value, or a value of the wrong type, rustdoc will emit the deny-by-default lint rustdoc::invalid_doc_attributes.
  📝

Compatibility Notes

• Introduce pin_v2 into the builtin attributes namespace
  📝
• Update bundled musl to 1.2.5
  📝
• On Emscripten, the unwinding ABI used when compiling with panic=unwind was changed from the JS exception handling ABI to the wasm exception handling ABI. If linking C/C++ object files with Rust objects, -fwasm-exceptions must be passed to the linker now. On nightly Rust, it is possible to get the old behavior with -Zwasm-emscripten-eh=false -Zbuild-std, but it will be removed in a future release.
  📝
• Error when test attribute is applied to structs
  📝

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.

Other

[BoxyUwU]

@rustbot ping relnotes-interest-group

[rustbot]

Hi relnotes-interest-group, this issue/PR could use some help in reviewing /
adjusting release notes. Could you take a look if available? Thanks <3

cc @alex-semenyuk @jieyouxu @joshtriplett @Kobzol @lcnr @traviscross

[pthariensflame]

Suggestion:

 ## Libraries
 
 * [Allow the global allocator to use thread-local storage and std::thread::current()](https://github.com/rust-lang/rust/pull/144465)
   [📝](https://github.com/rust-lang/rust/issues/145110)
-* [Stabilize `char_max_len`](https://github.com/rust-lang/rust/pull/145610/)
 * [Make `BTree::append` not update existing keys when appending an entry which already exists](https://github.com/rust-lang/rust/pull/145628)
   [📝](https://github.com/rust-lang/rust/issues/145889)
 * [Don't require `T: RefUnwindSafe` for `vec::IntoIter<T>: UnwindSafe`](https://github.com/rust-lang/rust/pull/145665)
   [📝](https://github.com/rust-lang/rust/issues/148111)
 
 ## Stabilized APIs
 
 * [`String::into_raw_parts`](https://doc.rust-lang.org/beta/std/string/struct.String.html#method.into_raw_parts)
 * [`Vec::into_raw_parts`](https://doc.rust-lang.org/beta/std/vec/struct.Vec.html#method.into_raw_parts)
   [📝](https://github.com/rust-lang/rust/issues/148824)
 * [`<[T]>::as_array`](https://doc.rust-lang.org/beta/std/primitive.slice.html#method.as_array)
 * [`<[T]>::as_array_mut`](https://doc.rust-lang.org/beta/std/primitive.slice.html#method.as_mut_array)
 * [`<*const [T]>::as_array`](https://doc.rust-lang.org/beta/std/primitive.pointer.html#method.as_array)
 * [`<*mut [T]>::as_array_mut`](https://doc.rust-lang.org/beta/std/primitive.pointer.html#method.as_mut_array)
   [📝](https://github.com/rust-lang/rust/issues/148582)
 * [`VecDeque::pop_front_if`](https://doc.rust-lang.org/beta/std/collections/struct.VecDeque.html#method.pop_front_if)
 * [`VecDeque::pop_back_if`](https://doc.rust-lang.org/beta/std/collections/struct.VecDeque.html#method.pop_back_if)
   [📝](https://github.com/rust-lang/rust/issues/148107)
 * `Duration::from_nanos_u128`
   [📝](https://github.com/rust-lang/rust/issues/148583)
+* [`char::MAX_LEN_UTF8`](https://doc.rust-lang.org/beta/std/primitive.char.html#associatedconstant.MAX_LEN_UTF8)
+* [`char::MAX_LEN_UTF16`](https://doc.rust-lang.org/beta/std/primitive.char.html#associatedconstant.MAX_LEN_UTF16)
+  [📝](https://github.com/rust-lang/rust/pull/145610/)

These previously stable APIs are now stable in const contexts:

[BoxyUwU]

Release notes have been converted into a PR: #151230