Rust 1.79: what's new, what was stabilized

• Update the minimum external LLVM to 17.
• [RustcEncodable and RustcDecodable are soft-destabilized, to be removed
• [The wasm_c_abi future-incompatibility lint will warn about use of the
• Check return types of function types for well-formedness

Language

• Stabilize inline const {} expressions.
• Prevent opaque types being instantiated twice with different regions within the same function.
• Stabilize WebAssembly target features that are in phase 4 and 5.
• Add the redundant_lifetimes lint to detect lifetimes which are semantically redundant.
• Stabilize the unnameable_types lint for public types that can't be named.
• [Enable debuginfo in macros, and stabilize -C collapse-macro-debuginfo and #[collapse_debuginfo].](https://github.com/rust-lang/rust/pull/120845/)
• Propagate temporary lifetime extension into if and match expressions.
• Restrict promotion of const fn calls.
• Warn against refining impls of crate-private traits with refining_impl_trait lint.
• Stabilize associated type bounds (RFC 2289).
• Stabilize importing main from other modules or crates.
• Check return types of function types for well-formedness
• Rework impl Trait lifetime inference
• Change inductive trait solver cycles to be ambiguous

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Compiler

• Define -C strip to only affect binaries, not artifacts like .pdb.
• Stabilize -Crelro-level for controlling runtime link hardening.
• Stabilize checking of cfg names and values at compile-time with --check-cfg. *Note that this only stabilizes the compiler part, the Cargo part is still unstable in this release.*
• Add aarch64-apple-visionos and aarch64-apple-visionos-sim tier 3 targets.
• Add riscv32ima-unknown-none-elf tier 3 target.
• Promote several Windows targets to tier 2: aarch64-pc-windows-gnullvm, i686-pc-windows-gnullvm, and x86_64-pc-windows-gnullvm.

Refer to Rust's [platform support page][platform-support-doc] for more information on Rust's tiered platform support.

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Libraries

• Implement FromIterator for (impl Default + Extend, impl Default + Extend).
• Implement {Div,Rem}Assign<NonZero<X>> on X.
• Document overrides of clone_from() in core/std.
• Link MSVC default lib in core.
• Caution against using transmute between pointers and integers.
• Enable frame pointers for the standard library.

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Stabilized APIs

• {integer}::unchecked_add
• {integer}::unchecked_mul
• {integer}::unchecked_sub
• [<[T]>::split_at_unchecked](https://doc.rust-lang.org/stable/core/primitive.slice.html#method.split_at_unchecked)
• [<[T]>::split_at_mut_unchecked](https://doc.rust-lang.org/stable/core/primitive.slice.html#method.split_at_mut_unchecked)
• [<[u8]>::utf8_chunks](https://doc.rust-lang.org/stable/core/primitive.slice.html#method.utf8_chunks)
• str::Utf8Chunks
• str::Utf8Chunk
• <*const T>::is_aligned
• <*mut T>::is_aligned
• NonNull::is_aligned
• [<*const [T]>::len](https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.len)
• [<*mut [T]>::len](https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.len-1)
• [<*const [T]>::is_empty](https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.is_empty)
• [<*mut [T]>::is_empty](https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.is_empty-1)
• [NonNull::<[T]>::is_empty](https://doc.rust-lang.org/stable/core/ptr/struct.NonNull.html#method.is_empty)
• CStr::count_bytes
• io::Error::downcast
• num::NonZero<T>
• path::absolute
• proc_macro::Literal::byte_character
• proc_macro::Literal::c_string

These APIs are now stable in const contexts:

• Atomic*::into_inner
• io::Cursor::new
• io::Cursor::get_ref
• io::Cursor::position
• io::empty
• io::repeat
• io::sink
• panic::Location::caller
• panic::Location::file
• panic::Location::line
• panic::Location::column

<a id="1.79.0-Cargo"></a>

Cargo

• Prevent dashes in lib.name, always normalizing to _.
• Stabilize MSRV-aware version requirement selection in cargo add.
• Switch to using gitoxide by default for listing files.

<a id="1.79.0-Rustdoc"></a>

Rustdoc

• Always display stability version even if it's the same as the containing item.
• Show a single search result for items with multiple paths.
• Support typing / in docs to begin a search.

<a id="1.79.0-Misc"></a>

Misc

<a id="1.79.0-Compatibility-Notes"></a>

Compatibility Notes

• Update the minimum external LLVM to 17.
• RustcEncodable and RustcDecodable are soft-destabilized, to be removed from the prelude in next edition.
• The wasm_c_abi future-incompatibility lint will warn about use of the non-spec-compliant C ABI. Use wasm-bindgen v0.2.88 to generate forward-compatible bindings.
• Check return types of function types for well-formedness