Rust 1.83.0 release notes

Language

Compiler

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

Libraries

Stabilized APIs

These APIs are now stable in const contexts:

Cargo

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

Rustdoc

The sidebar / hamburger menu table of contents now includes the # headers from the main item's doc comment. 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.
Check well-formedness of the source type's signature in fn pointer casts. 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.
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 https://github.com/rust-lang/rust/pull/129369.
Rust will now correctly raise an error for repr(Rust) written on non-struct/enum/union items, since it previously did not have any effect.
The future incompatibility lint deprecated_cfg_attr_crate_type_name has been made into a hard error. 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

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 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, 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 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.
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.
Update the minimum external LLVM version to 18.
Remove aarch64-fuchsia and x86_64-fuchsia target aliases in favor of aarch64-unknown-fuchsia and x86_64-unknown-fuchsia respectively.
The ABI-level exception class of a Rust panic is now encoded with native-endian bytes, so it is legible in hex dumps.
Visual Studio 2013 is no longer supported for MSVC targets.
The sysroot no longer contains the std dynamic library in its top-level lib/ dir.