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@@ -19,32 +19,55 @@ If you'd like to help us out by testing future releases, you might consider upda | |
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| ## What's in 1.84.0 stable | ||
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| ### Cargo can use toolchain version for library version selection | ||
| ### Cargo considers Rust versions for dependency version selection | ||
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| 1.84.0 stabilizes the minimum supported Rust version (MSRV) aware resolver, | ||
| which uses the declared [minimum supported Rust version](https://doc.rust-lang.org/cargo/reference/rust-version.html) from | ||
| dependencies, if available, to improve package version selection. Rust version | ||
| aware selection allows library authors to easily adopt newer Rust versions | ||
| while allowing consumers of the library to automatically use old versions | ||
| if they need compatibility with older toolchains. | ||
| which prefers dependency versions compatible with the project's declared | ||
| [MSRV](https://doc.rust-lang.org/cargo/reference/rust-version.html). | ||
| With MSRV-aware version selection, the toil is reduced for maintainers to | ||
| support older toolchains by not needing to manually select older versions for | ||
| each dependency. | ||
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| Library authors should take the MSRV-aware resolver into account when deciding | ||
| You can opt-in to the MSRV-aware resolver via [`.cargo/config.toml`](https://doc.rust-lang.org/cargo/reference/config.html#resolverincompatible-rust-versions): | ||
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| ```toml | ||
| [resolver] | ||
| incompatible-rust-versions = "fallback" | ||
| ``` | ||
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| Then when adding a dependency: | ||
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| ```console | ||
| $ cargo add clap | ||
| Updating crates.io index | ||
| warning: ignoring [email protected] (which requires rustc 1.74) to maintain demo's rust-version of 1.60 | ||
| Adding clap v4.0.32 to dependencies | ||
| Updating crates.io index | ||
| Locking 33 packages to latest Rust 1.60 compatible versions | ||
| Adding clap v4.0.32 (available: v4.5.23, requires Rust 1.74) | ||
| ``` | ||
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| When [verifying the latest dependencies in CI](https://doc.rust-lang.org/cargo/guide/continuous-integration.html#verifying-latest-dependencies), you can override this: | ||
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| ```console | ||
| $ CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS=allow cargo update | ||
| Updating crates.io index | ||
| Locking 12 packages to latest compatible versions | ||
| Updating clap v4.0.32 -> v4.5.23 | ||
| ``` | ||
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| You can also opt-in by setting [`package.resolver = "3"`](https://doc.rust-lang.org/cargo/reference/resolver.html#resolver-versions) in the Cargo.toml manifest file though that will require raising your MSRV to 1.84. The new resolver will be enabled by default for projects using the 2024 edition | ||
| (which will stabilize in 1.85). | ||
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| This gives library authors more flexibility when deciding | ||
| their policy on adopting new Rust toolchain features. Previously, a library | ||
| adopting features from a new Rust toolchain would force downstream users of | ||
| that library who have an older Rust version to either upgrade their toolchain | ||
| or manually select an old version of the library compatible with their | ||
| toolchain (and avoid running `cargo update`). Now, those users will be able to | ||
| automatically use older library versions compatible with their older toolchain. | ||
| In the future, we expect this to provide more flexibility for library authors | ||
| to select their preferred support strategy for Rust versions, with the toolchain | ||
| helping users on older toolchains avoid breakage. | ||
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| The new resolver will be enabled by default with the 2024 edition (expected to | ||
| stabilize in 1.85), but can be enabled as of 1.84 by setting | ||
| [`package.resolver = "3"`](https://doc.rust-lang.org/cargo/reference/resolver.html#resolver-versions) in the Cargo.toml manifest file, or | ||
| [`resolver.incompatible-rust-versions = "fallback"`](https://doc.rust-lang.org/cargo/reference/config.html#resolverincompatible-rust-versions) in the Cargo configuration file. | ||
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| Read [the documentation](https://doc.rust-lang.org/cargo/reference/resolver.html#rust-version) for more details. | ||
| See the [documentation](https://doc.rust-lang.org/cargo/reference/rust-version.html#setting-and-updating-rust-version) for more considerations when deciding on an MSRV policy. | ||
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| ### Migration to a new trait solver begins | ||
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@@ -54,7 +77,7 @@ component of Rust's type system. It is not only responsible for checking | |
| whether trait-bounds - e.g. `Vec<T>: Clone` - hold, but is also used by many | ||
| other parts of the type system, such as normalization - figuring out the | ||
| underlying type of `<Vec<T> as IntoIterator>::Item` - and equating types | ||
| (checking whether T and U are the same). | ||
| (checking whether `T` and `U` are the same). | ||
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| In 1.84, the new solver is used for checking coherence of trait impls. At a | ||
| high level, coherence is responsible for ensuring that there is at most one | ||
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| where impls do *not* overlap, allowing more code to be written in some cases. | ||
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| For more details, see a [previous blog post](https://blog.rust-lang.org/inside-rust/2024/12/04/trait-system-refactor-initiative.html) | ||
| and the [stabilization report](https://github.com/rust-lang/rust/pull/130654) | ||
| and the [stabilization report](https://github.com/rust-lang/rust/pull/130654). | ||
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| [Crater]: https://github.com/rust-lang/crater/ | ||
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| ### Strict provenance APIs | ||
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| In Rust, [pointers are not simply an “integer” or | ||
| “address”](https://rust-lang.github.io/rfcs/3559-rust-has-provenance.html). For | ||
| instance, it’s uncontroversial to say that a Use After Free is clearly | ||
| Undefined Behavior, even if you “get lucky” and the freed memory gets | ||
| reallocated before your read/write. It is also uncontroversial that writing | ||
| through a pointer derived from an `&i32` reference is Undefined Behavior, even | ||
| In Rust, [pointers are not simply an "integer" or | ||
| "address"](https://rust-lang.github.io/rfcs/3559-rust-has-provenance.html). For | ||
| instance, a "use after free" is undefined behavior even if you "get lucky" and the freed memory gets | ||
| reallocated before your read/write. As another example, writing | ||
| through a pointer derived from an `&i32` reference is undefined behavior, even | ||
| if writing to the same address via a different pointer is legal. The underlying | ||
| pattern here is that *the way a pointer is computed matters*, not just the | ||
| address that results from this computation. For this reason, we say that | ||
| pointers have **provenance**: to fully characterize pointer-related Undefined | ||
| Behavior in Rust, we have to know not only the address the pointer points to, | ||
| pointers have **provenance**: to fully characterize pointer-related undefined | ||
| behavior in Rust, we have to know not only the address the pointer points to, | ||
| but also track which other pointer(s) it is "derived from". | ||
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| Most of the time, programmers do not need to worry much about provenance, and | ||
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@@ -106,7 +128,48 @@ For more details, see the standard library [documentation on provenance](https:/ | |
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| ### Stabilized APIs | ||
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| TODO, relnotes still in-progress for this section | ||
| - [`Ipv6Addr::is_unique_local`](https://doc.rust-lang.org/stable/core/net/struct.Ipv6Addr.html#method.is_unique_local) | ||
| - [`Ipv6Addr::is_unicast_link_local`](https://doc.rust-lang.org/stable/core/net/struct.Ipv6Addr.html#method.is_unicast_link_local) | ||
| - [`core::ptr::with_exposed_provenance`](https://doc.rust-lang.org/stable/core/ptr/fn.with_exposed_provenance.html) | ||
| - [`core::ptr::with_exposed_provenance_mut`](https://doc.rust-lang.org/stable/core/ptr/fn.with_exposed_provenance_mut.html) | ||
| - [`<ptr>::addr`](https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.addr) | ||
| - [`<ptr>::expose_provenance`](https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.expose_provenance) | ||
| - [`<ptr>::with_addr`](https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.with_addr) | ||
| - [`<ptr>::map_addr`](https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.map_addr) | ||
| - [`<int>::isqrt`](https://doc.rust-lang.org/stable/core/primitive.i32.html#method.isqrt) | ||
| - [`<int>::checked_isqrt`](https://doc.rust-lang.org/stable/core/primitive.i32.html#method.checked_isqrt) | ||
| - [`<uint>::isqrt`](https://doc.rust-lang.org/stable/core/primitive.u32.html#method.isqrt) | ||
| - [`NonZero::isqrt`](https://doc.rust-lang.org/stable/core/num/struct.NonZero.html#impl-NonZero%3Cu128%3E/method.isqrt) | ||
| - [`core::ptr::without_provenance`](https://doc.rust-lang.org/stable/core/ptr/fn.without_provenance.html) | ||
| - [`core::ptr::without_provenance_mut`](https://doc.rust-lang.org/stable/core/ptr/fn.without_provenance_mut.html) | ||
| - [`core::ptr::dangling`](https://doc.rust-lang.org/stable/core/ptr/fn.dangling.html) | ||
| - [`core::ptr::dangling_mut`](https://doc.rust-lang.org/stable/core/ptr/fn.dangling_mut.html) | ||
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| These APIs are now stable in const contexts | ||
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| - [`AtomicBool::from_ptr`](https://doc.rust-lang.org/stable/core/sync/atomic/struct.AtomicBool.html#method.from_ptr) | ||
| - [`AtomicPtr::from_ptr`](https://doc.rust-lang.org/stable/core/sync/atomic/struct.AtomicPtr.html#method.from_ptr) | ||
| - [`AtomicU8::from_ptr`](https://doc.rust-lang.org/stable/core/sync/atomic/struct.AtomicU8.html#method.from_ptr) | ||
| - [`AtomicU16::from_ptr`](https://doc.rust-lang.org/stable/core/sync/atomic/struct.AtomicU16.html#method.from_ptr) | ||
| - [`AtomicU32::from_ptr`](https://doc.rust-lang.org/stable/core/sync/atomic/struct.AtomicU32.html#method.from_ptr) | ||
| - [`AtomicU64::from_ptr`](https://doc.rust-lang.org/stable/core/sync/atomic/struct.AtomicU64.html#method.from_ptr) | ||
| - [`AtomicUsize::from_ptr`](https://doc.rust-lang.org/stable/core/sync/atomic/struct.AtomicUsize.html#method.from_ptr) | ||
| - [`AtomicI8::from_ptr`](https://doc.rust-lang.org/stable/core/sync/atomic/struct.AtomicI8.html#method.from_ptr) | ||
| - [`AtomicI16::from_ptr`](https://doc.rust-lang.org/stable/core/sync/atomic/struct.AtomicI16.html#method.from_ptr) | ||
| - [`AtomicI32::from_ptr`](https://doc.rust-lang.org/stable/core/sync/atomic/struct.AtomicI32.html#method.from_ptr) | ||
| - [`AtomicI64::from_ptr`](https://doc.rust-lang.org/stable/core/sync/atomic/struct.AtomicI64.html#method.from_ptr) | ||
| - [`AtomicIsize::from_ptr`](https://doc.rust-lang.org/stable/core/sync/atomic/struct.AtomicIsize.html#method.from_ptr) | ||
| - [`<ptr>::is_null`](https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.is_null-1) | ||
| - [`<ptr>::as_ref`](https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.as_ref-1) | ||
| - [`<ptr>::as_mut`](https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.as_mut) | ||
| - [`Pin::new`](https://doc.rust-lang.org/stable/core/pin/struct.Pin.html#method.new) | ||
| - [`Pin::new_unchecked`](https://doc.rust-lang.org/stable/core/pin/struct.Pin.html#method.new_unchecked) | ||
| - [`Pin::get_ref`](https://doc.rust-lang.org/stable/core/pin/struct.Pin.html#method.get_ref) | ||
| - [`Pin::into_ref`](https://doc.rust-lang.org/stable/core/pin/struct.Pin.html#method.into_ref) | ||
| - [`Pin::get_mut`](https://doc.rust-lang.org/stable/core/pin/struct.Pin.html#method.get_mut) | ||
| - [`Pin::get_unchecked_mut`](https://doc.rust-lang.org/stable/core/pin/struct.Pin.html#method.get_unchecked_mut) | ||
| - [`Pin::static_ref`](https://doc.rust-lang.org/stable/core/pin/struct.Pin.html#method.static_ref) | ||
| - [`Pin::static_mut`](https://doc.rust-lang.org/stable/core/pin/struct.Pin.html#method.static_mut) | ||
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| ### Other changes | ||
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