Stabilize `derive_default_enum`
This stabilizes `#![feature(derive_default_enum)]`, as proposed in [RFC 3107](https://github.com/rust-lang/rfcs/pull/3107) and tracked in #87517. In short, it permits you to `#[derive(Default)]` on `enum`s, indicating what the default should be by placing a `#[default]` attribute on the desired variant (which must be a unit variant in the interest of forward compatibility).
```````@rustbot``````` label +S-waiting-on-review +T-lang
Add SyncUnsafeCell.
This adds `SyncUnsafeCell`, which is just `UnsafeCell` except it implements `Sync`.
This was first proposed under the name `RacyUnsafeCell` here: https://github.com/rust-lang/rust/issues/53639#issuecomment-415515748 and here: https://github.com/rust-lang/rust/issues/53639#issuecomment-432741659 and here: https://github.com/rust-lang/rust/issues/53639#issuecomment-888435728
It allows you to create an UnsafeCell that is Sync without having to wrap it in a struct first (and then implement Sync for that struct).
E.g. `static X: SyncUnsafeCell<i32>`. Using a regular `UnsafeCell` as `static` is not possible, because it isn't `Sync`. We have a language workaround for it called `static mut`, but it's nice to be able to use the proper type for such unsafety instead.
It also makes implementing synchronization primitives based on unsafe cells slightly less verbose, because by using `SyncUnsafeCell` for `UnsafeCell`s that are shared between threads, you don't need a separate `impl<..> Sync for ..`. Using this type also clearly documents that the cell is expected to be accessed from multiple threads.
This is a continuation of #60109, which noted that while the ADX
intrinsics were stabilized, the corresponding target feature never was.
This PR follows the same general structure and stabilizes the ADX target
feature.
Constify `Index{,Mut}` for `[T]`, `str`, and `[T; N]`
Several panic functions were rewired (via `const_eval_select`) to simpler implementations that do not require formatting for compile-time usage.
r? ```@oli-obk```
Merge `#[deprecated]` and `#[rustc_deprecated]`
The first commit makes "reason" an alias for "note" in `#[rustc_deprecated]`, while still prohibiting it in `#[deprecated]`.
The second commit changes "suggestion" to not just be a feature of `#[rustc_deprecated]`. This is placed behind the new `deprecated_suggestion` feature. This needs a tracking issue; let me know if this PR will be approved and I can create one.
The third commit is what permits `#[deprecated]` to be used when `#![feature(staged_api)]` is enabled. This isn't yet used in stdlib (only tests), as it would require duplicating all deprecation attributes until a bootstrap occurs. I intend to submit a follow-up PR that replaces all uses and removes the remaining `#[rustc_deprecated]` code after the next bootstrap.
`@rustbot` label +T-libs-api +C-feature-request +A-attributes +S-waiting-on-review
Stabilize asm! and global_asm!
Tracking issue: #72016
It's been almost 2 years since the original [RFC](https://github.com/rust-lang/rfcs/pull/2850) was posted and we're finally ready to stabilize this feature!
The main changes in this PR are:
- Removing `asm!` and `global_asm!` from the prelude as per the decision in #87228.
- Stabilizing the `asm` and `global_asm` features.
- Removing the unstable book pages for `asm` and `global_asm`. The contents are moved to the [reference](https://github.com/rust-lang/reference/pull/1105) and [rust by example](https://github.com/rust-lang/rust-by-example/pull/1483).
- All links to these pages have been removed to satisfy the link checker. In a later PR these will be replaced with links to the reference or rust by example.
- Removing the automatic suggestion for using `llvm_asm!` instead of `asm!` if you're still using the old syntax, since it doesn't work anymore with `asm!` no longer being in the prelude. This only affects code that predates the old LLVM-style `asm!` being renamed to `llvm_asm!`.
- Updating `stdarch` and `compiler-builtins`.
- Updating all the tests.
r? `@joshtriplett`
They are also removed from the prelude as per the decision in
https://github.com/rust-lang/rust/issues/87228.
stdarch and compiler-builtins are updated to work with the new, stable
asm! and global_asm! macros.
Partially stabilize `duration_consts_2`
Methods that were only blocked on `const_panic` have been stabilized.
The remaining methods of `duration_consts_2` are all related to floats,
and as such have been placed behind the `duration_consts_float` feature
gate.
