Fix From<LocalWaker>
This is a follow-up to https://github.com/rust-lang/rust/pull/52640
Fixes `From<LocalWaker>` which is affected by the same accidental drop bug (unless I'm totally mistaken)
r? @cramertj
Rollup of bare_trait_objects PRs
All deny attributes were moved into bootstrap so they can be disabled with a line of config.
Warnings for external tools are allowed and it's up to the tool's maintainer to keep it warnings free.
r? @Mark-Simulacrum
cc @ljedrz @kennytm
std::ops::Try impl for std::task::Poll
I originally left out the `Try` impl for `Poll` because I was curious if we needed it, and @MajorBreakfast and I had discussed the potential for it to introduce confusion about exactly what control-flow was happening at different points. However, after porting a pretty significant chunk of Fuchsia over to futures 0.3, I discovered that I was *constantly* having to do repetitive matching on `Poll<Result<...>>` or `Poll<Option<Result<...>>>` in order to propagate errors correctly. `try_poll` (propagate `Poll::Ready(Err(..))`s) helped in some places, but it was far more common to need some form of conversion between `Result`, `Poll<Result<...>>`, and `Poll<Option<Result<...>>>`. The `Try` trait conveniently provides all of these conversions in addition to a more concise syntax (`?`), so I'd like to experiment with using these instead.
cc @seanmonstar
r? @aturon
Note: this change means that far more futures 0.1 code can work without significant changes since it papers over the fact that `Result` is no longer at the top-level when using `Stream` and `Future` (since it's now `Poll<Result<...>>` or `Poll<Option<Result<...>>>` instead of `Result<Poll<..>>` and `Result<Poll<Option<...>>>`).
Clarify what a task is
Currently we call two distinct concepts "task":
1. The top-level future that is polled until completion
2. The lightweight "thread" that is responsible for polling the top-level future. What additional data beside the future is stored in this type varies between different `Executor` implementations.
I'd prefer to return to the old formulation by @alexcrichton:
```rust
/// A handle to a "task", which represents a single lightweight "thread" of
/// execution driving a future to completion.
pub struct Task {
```
Source: [`task_impl/mod.rs` in futures-rs 0.1](1328fc9e8a/src/task_impl/mod.rs (L49-L50))
I think that this change will make it much easier to explain everything.
r? @aturon
@cramertj
Prefer `Option::map`/etc over `match` wherever it improves clarity
This isn't intended to change behavior anywhere. A lot of times statements like `match x { None => None, Some(y) => [...] }` can be rewritten using `Option::map` or `Option::and_then` in a way that preserves or improves clarity, so that's what I've done here.
I think it's particularly valuable to keep things in `libcore` and `libstd` pretty/idiomatic since it's not uncommon to follow the `[src]` links when browsing the rust-lang.org docs for std/core. If there's any concern about pushing style-based changes though, I'll happily back out the non-std/core commits here.
impl PartialEq+Eq for BuildHasherDefault
`BuildHasherDefault`is only one way of implementing `BuildHasher`. Clearly, every `BuildHasherDefault` for the same type `H` is identical, since it just uses `Default<H>` to construct `H`. In general, this is not true for every `BuildHasher`, so I think it is helpful to implement `PartialEq` and `Eq`.
Add unaligned volatile intrinsics
Surprisingly enough, it turns out that unaligned volatile loads are actually useful for certain (very niche) types of lock-free code. I included unaligned volatile stores for completeness, but I currently do not know of any use cases for them.
These are only exposed as intrinsics for now. If they turn out to be useful in practice, we can work towards stabilizing them.
r? @alexcrichton
Forget Waker when cloning LocalWaker
Since NonNull is Copy the inner field of the cloned Waker was copied for
use in the new LocalWaker, however this left Waker to be dropped. Which
means that when cloning LocalWaker would also erroneously call drop_raw.
This change forgets the Waker, rather then dropping it, leaving the
inner field to be used by the returned LocalWaker.
Closes#52629.
Implement rfc 1789: Conversions from `&mut T` to `&Cell<T>`
I'm surprised that RFC 1789 has not been implemented for several months. Tracking issue: https://github.com/rust-lang/rust/issues/43038
Please note: when I was writing tests for `&Cell<[i32]>`, I found it is not easy to get the length of the contained slice. So I designed a `get_with` method which might be useful for similar cases. This method is not designed in the RFC, and it certainly needs to be reviewed by core team. I think it has some connections with `Cell::update` https://github.com/rust-lang/rust/issues/50186 , which is also in design phase.
Since NonNull is Copy the inner field of the cloned Waker was copied for
use in the new LocalWaker, however this left Waker to be dropped. Which
means that when cloning LocalWaker would also erroneously call drop_raw.
This change forgets the Waker, rather then dropping it, leaving the
inner field to be used by the returned LocalWaker.
Closes#52629.
Document that Unique::empty() and NonNull::dangling() aren't sentinel values
The documentation of Unique::empty() and NonNull::dangling() could
potentially suggest that they work as sentinel values indicating a
not-yet-initialized pointer. However, they both declare a non-null
pointer equal to the alignment of the type, which could potentially
reference a valid value of that type (specifically, the first such valid
value in memory). Explicitly document that the return value of these
functions does not work as a sentinel value.
