The main `arbitrary_self_types` feature gate will shortly be reused for
a new version of arbitrary self types which we are amending per [this
RFC](https://github.com/rust-lang/rfcs/blob/master/text/3519-arbitrary-self-types-v2.md).
The main amendments are:
* _do_ support `self` types which can't safely implement `Deref`
* do _not_ support generic `self` types
* do _not_ support raw pointers as `self` types.
This PR relates to the last of those bullet points: this strips pointer
support from the current `arbitrary_self_types` feature.
We expect this to cause some amount of breakage for crates using this
unstable feature to allow raw pointer self types. If that's the case, we
want to know about it, and we want crate authors to know of the upcoming
changes.
For now, this can be resolved by adding the new
`arbitrary_self_types_pointers` feature to such crates. If we determine
that use of raw pointers as self types is common, then we may maintain
that as an unstable feature even if we come to stabilize the rest of the
`arbitrary_self_types` support in future. If we don't hear that this PR
is causing breakage, then perhaps we don't need it at all, even behind
an unstable feature gate.
[Tracking issue](https://github.com/rust-lang/rust/issues/44874)
This is [step 4 of the plan outlined here](https://github.com/rust-lang/rust/issues/44874#issuecomment-2122179688)
Retroactively feature gate `ConstArgKind::Path`
This puts the lowering introduced by #125915 under a feature gate until we fix the regressions introduced by it. Alternative to whole sale reverting the PR since it didn't seem like a very clean revert and I think this is generally a step in the right direction and don't want to get stuck landing and reverting the PR over and over :)
cc #129137 ``@camelid,`` tests taken from there. beta is branching soon so I think it makes sense to not try and rush that fix through since it wont have much time to bake and if it has issues we can't simply revert it on beta.
Fixes#128016
Stabilize opaque type precise capturing (RFC 3617)
This PR partially stabilizes opaque type *precise capturing*, which was specified in [RFC 3617](https://github.com/rust-lang/rfcs/pull/3617), and whose syntax was amended by FCP in [#125836](https://github.com/rust-lang/rust/issues/125836).
This feature, as stabilized here, gives us a way to explicitly specify the generic lifetime parameters that an RPIT-like opaque type captures. This solves the problem of overcapturing, for lifetime parameters in these opaque types, and will allow the Lifetime Capture Rules 2024 ([RFC 3498](https://github.com/rust-lang/rfcs/pull/3498)) to be fully stabilized for RPIT in Rust 2024.
### What are we stabilizing?
This PR stabilizes the use of a `use<'a, T>` bound in return-position impl Trait opaque types. Such a bound fully specifies the set of generic parameters captured by the RPIT opaque type, entirely overriding the implicit default behavior. E.g.:
```rust
fn does_not_capture<'a, 'b>() -> impl Sized + use<'a> {}
// ~~~~~~~~~~~~~~~~~~~~
// This RPIT opaque type does not capture `'b`.
```
The way we would suggest thinking of `impl Trait` types *without* an explicit `use<..>` bound is that the `use<..>` bound has been *elided*, and that the bound is filled in automatically by the compiler according to the edition-specific capture rules.
All non-`'static` lifetime parameters, named (i.e. non-APIT) type parameters, and const parameters in scope are valid to name, including an elided lifetime if such a lifetime would also be valid in an outlives bound, e.g.:
```rust
fn elided(x: &u8) -> impl Sized + use<'_> { x }
```
Lifetimes must be listed before type and const parameters, but otherwise the ordering is not relevant to the `use<..>` bound. Captured parameters may not be duplicated. For now, only one `use<..>` bound may appear in a bounds list. It may appear anywhere within the bounds list.
### How does this differ from the RFC?
This stabilization differs from the RFC in one respect: the RFC originally specified `use<'a, T>` as syntactically part of the RPIT type itself, e.g.:
```rust
fn capture<'a>() -> impl use<'a> Sized {}
```
However, settling on the final syntax was left as an open question. T-lang later decided via FCP in [#125836](https://github.com/rust-lang/rust/issues/125836) to treat `use<..>` as a syntactic bound instead, e.g.:
```rust
fn capture<'a>() -> impl Sized + use<'a> {}
```
### What aren't we stabilizing?
The key goal of this PR is to stabilize the parts of *precise capturing* that are needed to enable the migration to Rust 2024.
There are some capabilities of *precise capturing* that the RFC specifies but that we're not stabilizing here, as these require further work on the type system. We hope to lift these limitations later.
The limitations that are part of this PR were specified in the [RFC's stabilization strategy](https://rust-lang.github.io/rfcs/3617-precise-capturing.html#stabilization-strategy).
#### Not capturing type or const parameters
The RFC addresses the overcapturing of type and const parameters; that is, it allows for them to not be captured in opaque types. We're not stabilizing that in this PR. Since all in scope generic type and const parameters are implicitly captured in all editions, this is not needed for the migration to Rust 2024.
For now, when using `use<..>`, all in scope type and const parameters must be nameable (i.e., APIT cannot be used) and included as arguments. For example, this is an error because `T` is in scope and not included as an argument:
```rust
fn test<T>() -> impl Sized + use<> {}
//~^ ERROR `impl Trait` must mention all type parameters in scope in `use<...>`
```
This is due to certain current limitations in the type system related to how generic parameters are represented as captured (i.e. bivariance) and how inference operates.
We hope to relax this in the future, and this stabilization is forward compatible with doing so.
#### Precise capturing for return-position impl Trait **in trait** (RPITIT)
The RFC specifies precise capturing for RPITIT. We're not stabilizing that in this PR. Since RPITIT already adheres to the Lifetime Capture Rules 2024, this isn't needed for the migration to Rust 2024.
The effect of this is that the anonymous associated types created by RPITITs must continue to capture all of the lifetime parameters in scope, e.g.:
```rust
trait Foo<'a> {
fn test() -> impl Sized + use<Self>;
//~^ ERROR `use<...>` precise capturing syntax is currently not allowed in return-position `impl Trait` in traits
}
```
To allow this involves a meaningful amount of type system work related to adding variance to GATs or reworking how generics are represented in RPITITs. We plan to do this work separately from the stabilization. See:
- https://github.com/rust-lang/rust/pull/124029
Supporting precise capturing for RPITIT will also require us to implement a new algorithm for detecting refining capture behavior. This may involve looking through type parameters to detect cases where the impl Trait type in an implementation captures fewer lifetimes than the corresponding RPITIT in the trait definition, e.g.:
```rust
trait Foo {
fn rpit() -> impl Sized + use<Self>;
}
impl<'a> Foo for &'a () {
// This is "refining" due to not capturing `'a` which
// is implied by the trait's `use<Self>`.
fn rpit() -> impl Sized + use<>;
// This is not "refining".
fn rpit() -> impl Sized + use<'a>;
}
```
This stabilization is forward compatible with adding support for this later.
### The technical details
This bound is purely syntactical and does not lower to a [`Clause`](https://doc.rust-lang.org/1.79.0/nightly-rustc/rustc_middle/ty/type.ClauseKind.html) in the type system. For the purposes of the type system (and for the types team's curiosity regarding this stabilization), we have no current need to represent this as a `ClauseKind`.
Since opaques already capture a variable set of lifetimes depending on edition and their syntactical position (e.g. RPIT vs RPITIT), a `use<..>` bound is just a way to explicitly rather than implicitly specify that set of lifetimes, and this only affects opaque type lowering from AST to HIR.
### FCP plan
While there's much discussion of the type system here, the feature in this PR is implemented internally as a transformation that happens before lowering to the type system layer. We already support impl Trait types partially capturing the in scope lifetimes; we just currently only expose that implicitly.
So, in my (errs's) view as a types team member, there's nothing for types to weigh in on here with respect to the implementation being stabilized, and I'd suggest a lang-only proposed FCP (though we'll of course CC the team below).
### Authorship and acknowledgments
This stabilization report was coauthored by compiler-errors and TC.
TC would like to acknowledge the outstanding and speedy work that compiler-errors has done to make this feature happen.
compiler-errors thanks TC for authoring the RFC, for all of his involvement in this feature's development, and pushing the Rust 2024 edition forward.
### Open items
We're doing some things in parallel here. In signaling the intention to stabilize, we want to uncover any latent issues so we can be sure they get addressed. We want to give the maximum time for discussion here to happen by starting it while other remaining miscellaneous work proceeds. That work includes:
- [x] Look into `syn` support.
- https://github.com/dtolnay/syn/issues/1677
- https://github.com/dtolnay/syn/pull/1707
- [x] Look into `rustfmt` support.
- https://github.com/rust-lang/rust/pull/126754
- [x] Look into `rust-analyzer` support.
- https://github.com/rust-lang/rust-analyzer/issues/17598
- https://github.com/rust-lang/rust-analyzer/pull/17676
- [x] Look into `rustdoc` support.
- https://github.com/rust-lang/rust/issues/127228
- https://github.com/rust-lang/rust/pull/127632
- https://github.com/rust-lang/rust/pull/127658
- [x] Suggest this feature to RfL (a known nightly user).
- [x] Add a chapter to the edition guide.
- https://github.com/rust-lang/edition-guide/pull/316
- [x] Update the Reference.
- https://github.com/rust-lang/reference/pull/1577
### (Selected) implementation history
* https://github.com/rust-lang/rfcs/pull/3498
* https://github.com/rust-lang/rfcs/pull/3617
* https://github.com/rust-lang/rust/pull/123468
* https://github.com/rust-lang/rust/issues/125836
* https://github.com/rust-lang/rust/pull/126049
* https://github.com/rust-lang/rust/pull/126753Closes#123432.
cc `@rust-lang/lang` `@rust-lang/types`
`@rustbot` labels +T-lang +I-lang-nominated +A-impl-trait +F-precise_capturing
Tracking:
- https://github.com/rust-lang/rust/issues/123432
----
For the compiler reviewer, I'll leave some inline comments about diagnostics fallout :^)
r? compiler
Stabilize `unsafe_attributes`
# Stabilization report
## Summary
This is a tracking issue for the RFC 3325: unsafe attributes
We are stabilizing `#![feature(unsafe_attributes)]`, which makes certain attributes considered 'unsafe', meaning that they must be surrounded by an `unsafe(...)`, as in `#[unsafe(no_mangle)]`.
RFC: rust-lang/rfcs#3325
Tracking issue: #123757
## What is stabilized
### Summary of stabilization
Certain attributes will now be designated as unsafe attributes, namely, `no_mangle`, `export_name`, and `link_section` (stable only), and these attributes will need to be called by surrounding them in `unsafe(...)` syntax. On editions prior to 2024, this is simply an edition lint, but it will become a hard error in 2024. This also works in `cfg_attr`, but `unsafe` is not allowed for any other attributes, including proc-macros ones.
```rust
#[unsafe(no_mangle)]
fn a() {}
#[cfg_attr(any(), unsafe(export_name = "c"))]
fn b() {}
```
For a table showing the attributes that were considered to be included in the list to require unsafe, and subsequent reasoning about why each such attribute was or was not included, see [this comment here](https://github.com/rust-lang/rust/pull/124214#issuecomment-2124753464)
## Tests
The relevant tests are in `tests/ui/rust-2024/unsafe-attributes` and `tests/ui/attributes/unsafe`.
derive(SmartPointer): register helper attributes
Fix#128888
This PR enables built-in macros to register helper attributes, if any, to support correct name resolution in the correct lexical scope under the macros.
Also, `#[pointee]` is moved into the scope under `derive(SmartPointer)`.
cc `@Darksonn` `@davidtwco`
turn `invalid_type_param_default` into a `FutureReleaseErrorReportInDeps`
`````@rust-lang/types````` I assume the plan is still to disallow this? It has been a future-compat lint for a long time, seems ripe to go for hard error.
However, turns out that outright removing it right now would lead to [tons of crater regressions](https://github.com/rust-lang/rust/pull/127655#issuecomment-2228285460), so for now this PR just makes this future-compat lint show up in cargo's reports, so people are warned when they use a dependency that is affected by this.
Fixes https://github.com/rust-lang/rust/issues/27336 by removing the feature gate (so there's no way to silence the lint even on nightly)
CC https://github.com/rust-lang/rust/issues/36887
Assert that all attributes are actually checked via `CheckAttrVisitor` and aren't accidentally usable on completely unrelated HIR nodes
``@oli-obk's`` #128444 with unreachable case removed to avoid that PR bitrotting away.
Based on #128402.
This PR will make adding a new attribute ICE on any use of that attribute unless it gets a handler added in `rustc_passes::CheckAttrVisitor`.
r? ``@nnethercote`` (since you were the reviewer of the original PR)
rustc_target: add known safe s390x target features
This pull request adds known safe target features for s390x (aka IBM Z systems).
Currently, these features are unstable since stabilizing the target features requires submitting proposals.
The `vector` feature was added in IBM Z13 (`arch11`), and this is a SIMD feature for the newer IBM Z systems.
The `backchain` attribute is the IBM Z way of adding frame pointers like unwinding capabilities (the "frame-pointer" switch on IBM Z and IBM POWER platforms will add _emulated_ frame pointers to the binary, which profilers can't use for unwinding the stack).
Both attributes can be applied at the LLVM module or function levels. However, the `backchain` attribute has to be enabled for all the functions in the call stack to get a successful unwind process.
Remove lang feature for type ascription (since it's a lib feature now)
It's not necessary since it's a library feature now, via the type ascription macro. We can't (and shouldn't) register it as a removed feature since I think that would give "this feature has been removed" errors even for people using the macro (well, I'm pretty sure, though I didn't check).
r? `@Nilstrieb`
Add AMX target-features and `x86_amx_intrinsics` feature flag
This is an effort towards #126622. This adds support for all 5 target-features for `AMX`, and introduces the feature flag `x86_amx_intrinsics`, which would gate these target-features and the yet-to-be-implemented amx intrinsics in stdarch.
Remove the unstable `extern "wasm"` ABI (`wasm_abi` feature tracked
in #83788).
As discussed in https://github.com/rust-lang/rust/pull/127513#issuecomment-2220410679
and following, this ABI is a failed experiment that did not end
up being used for anything. Keeping support for this ABI in LLVM 19
would require us to switch wasm targets to the `experimental-mv`
ABI, which we do not want to do.
It should be noted that `Abi::Wasm` was internally used for two
things: The `-Z wasm-c-abi=legacy` ABI that is still used by
default on some wasm targets, and the `extern "wasm"` ABI. Despite
both being `Abi::Wasm` internally, they were not the same. An
explicit `extern "wasm"` additionally enabled the `+multivalue`
feature.
I've opted to remove `Abi::Wasm` in this patch entirely, instead
of keeping it as an ABI with only internal usage. Both
`-Z wasm-c-abi` variants are now treated as part of the normal
C ABI, just with different different treatment in
adjust_for_foreign_abi.
Match ergonomics 2024: Implement TC's match ergonomics proposal
Under gate `ref_pat_eat_one_layer_2024_structural`. Enabling `ref_pat_eat_one_layer_2024` at the same time allows the union of what the individual gates allow. `@traviscross`
r? `@Nadrieril`
cc https://github.com/rust-lang/rust/issues/123076
`@rustbot` label A-edition-2024 A-patterns
patchable-function-entry: Add unstable compiler flag and attribute
Tracking issue: #123115
Add the -Z patchable-function-entry compiler flag and the #[patchable_function_entry(prefix_nops = m, entry_nops = n)] attribute.
Rebased and adjusted the canditate implementation to match changes in the RFC.
