Make unreachable_unchecked a const fn
This PR makes `std::hint::unreachable_unchecked` a const fn so we can use it inside a const function.
r? @RalfJung
Fixes#53188.
Add lazy initialization primitives to std
Follow-up to #68198
Current RFC: https://github.com/rust-lang/rfcs/pull/2788
Rebased and fixed up a few of the dangling comments. Some notes carried over from the previous PR:
- [ ] Naming. I'm ok to just roll with the `Sync` prefix like `SyncLazy` for now, but [have a personal preference for `Atomic`](https://github.com/rust-lang/rfcs/pull/2788#issuecomment-574466983) like `AtomicLazy`.
- [x] [Poisoning](https://github.com/rust-lang/rfcs/pull/2788#discussion_r366725768). It seems like there's [some regret around poisoning in other `std::sync` types that we might want to just avoid upfront for `std::lazy`, especially if that would align with a future `std::mutex` that doesn't poison](https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/parking_lot.3A.3AMutex.20in.20std/near/190331199). Personally, if we're adding these types to `std::lazy` instead of `std::sync`, I'd be on-board with not worrying about poisoning in `std::lazy`, and potentially deprecating `std::sync::Once` and `lazy_static` in favour of `std::lazy` down the track if it's possible, rather than attempting to replicate their behavior. cc @Amanieu @sfackler.
- [ ] [Consider making`SyncOnceCell::get` blocking](https://github.com/matklad/once_cell/pull/92). There doesn't seem to be consensus in the linked PR on whether or not that's strictly better than the non-blocking variant.
In general, none of these seem to be really blocking an initial unstable merge, so we could possibly kick off a FCP if y'all are happy?
cc @matklad @pitdicker have I missed anything, or were there any other considerations that have come up since we last looked at this?
Make some Option methods const
Tracking issue: #67441
Constantify the following methods of `Option`:
- `as_ref`
- `is_some`
- `is_none`
- `iter` (not sure about this one, but it is possible, and will be useful when const traits are a thing)
cc @rust-lang/wg-const-eval @rust-lang/libs
Bump version to 1.47
This also bumps to a more recent rustfmt version, just to keep us relatively up to date (though almost nothing has changed in rustfmt we use beyond bumps to the parser infra). No formatting changes as a result of this.
r? @pietroalbini
This commit refactors the initial implementation to fit into std and
makes some other changes:
- use MaybeUninit internally in SyncOnceCell
- correctly impl Drop for lazy::Once
- port Lazy::take from once_cell from: https://github.com/matklad/once_cell/pull/100
Co-Authored-By: Paul Dicker <pitdicker@users.noreply.github.com>
add (unchecked) indexing methods to raw (and NonNull) slices
This complements the existing (unstable) `len` method. Unfortunately, for non-null slices, we cannot call this method `as_ptr` as that overlaps with the existing method of the same name.
If this looks reasonable to accept, I propose to reuse the https://github.com/rust-lang/rust/issues/71146 tracking issue and rename the feature get to `slice_ptr_methods` or so.
Cc @SimonSapin
Fixes https://github.com/rust-lang/rust/issues/60639
Deny unsafe ops in unsafe fns in libcore
After `liballoc`, It's time for `libcore` :D
I planned to do this bit by bit to avoid having a big chunk of diffs, so to make reviews easier, and to make the unsafe blocks narrower and take the time to document them properly.
r? @nikomatsakis cc @RalfJung
Make `likely` and `unlikely` const, gated by feature `const_unlikely`
This PR also contains a fix to allow `#[allow_internal_unstable]` to work properly with `#[rustc_const_unstable]`.
cc @RalfJung @nagisa
r? @oli-obk
Stabilize `#![feature(const_if_match)]`
Quoting from the [stabilization report](https://github.com/rust-lang/rust/issues/49146#issuecomment-616301045):
> `if` and `match` expressions as well as the short-circuiting logic operators `&&` and `||` will become legal in all [const contexts](https://doc.rust-lang.org/reference/const_eval.html#const-context). A const context is any of the following:
>
> - The initializer of a `const`, `static`, `static mut` or enum discriminant.
> - The body of a `const fn`.
> - The value of a const generic (nightly only).
> - The length of an array type (`[u8; 3]`) or an array repeat expression (`[0u8; 3]`).
>
> Furthermore, the short-circuiting logic operators will no longer be lowered to their bitwise equivalents (`&` and `|` respectively) in `const` and `static` initializers (see #57175). As a result, `let` bindings can be used alongside short-circuiting logic in those initializers.
Resolves#49146.
Ideally, we would resolve 🐳#66753 before this lands on stable, so it might be worth pushing this back a release. Also, this means we should get the process started for #52000, otherwise people will have no recourse except recursion for iterative `const fn`.
r? @oli-obk
They used to be covered by `optin_builtin_traits` but negative impls
are now applicable to all traits, not just auto traits.
This also adds docs in the unstable book for the current state of auto traits.
This commit introduces 2 methods - `Option::zip` and `Option::zip_with` with
respective signatures:
- zip: `(Option<T>, Option<U>) -> Option<(T, U)>`
- zip_with: `(Option<T>, Option<U>, (T, U) -> R) -> Option<R>`
Both are under the feature gate "option_zip".
I'm not sure about the name "zip", maybe we can find a better name for this.
(I would prefer `union` for example, but this is a keyword :( )
--------------------------------------------------------------------------------
Recently in a russian rust begginers telegram chat a newbie asked (translated):
> Are there any methods for these conversions:
>
> 1. `(Option<A>, Option<B>) -> Option<(A, B)>`
> 2. `Vec<Option<T>> -> Option<Vec<T>>`
>
> ?
While second (2.) is clearly `vec.into_iter().collect::<Option<Vec<_>>()`, the
first one isn't that clear.
I couldn't find anything similar in the `core` and I've come to this solution:
```rust
let tuple: (Option<A>, Option<B>) = ...;
let res: Option<(A, B)> = tuple.0.and_then(|a| tuple.1.map(|b| (a, b)));
```
However this solution isn't "nice" (same for just `match`/`if let`), so I thought
that this functionality should be in `core`.
make `mem::discriminant` const
implements #69821, which could be used as a tracking issue for `const_discriminant`.
Should this be added to the meta tracking issue #57563?
@Lokathor
Stabilize const for integer {to,from}_{be,le,ne}_bytes methods
All of these functions can be implemented simply and naturally as const functions, e.g. `u32::from_le_bytes` can be implemented as
```rust
(bytes[0] as u32)
| (bytes[1] as u32) << 8
| (bytes[2] as u32) << 16
| (bytes[3] as u32) << 24
```
So stabilizing the constness will not expose that internally they are implemented using transmute which is not const in stable.
Remove spotlight
I had a few comments saying that this feature was at best misunderstood or not even used so I decided to organize a poll about on [twitter](https://twitter.com/imperioworld_/status/1232769353503956994). After 87 votes, the result is very clear: it's not useful. Considering the amount of code we have just to run it, I think it's definitely worth it to remove it.
r? @kinnison
cc @ollie27
