This adds new optional methods on `Extend`: `extend_one` add a single
element to the collection, and `extend_reserve` pre-allocates space for
the predicted number of incoming elements. These are used in `Iterator`
for `partition` and `unzip` as they shuffle elements one-at-a-time into
their respective collections.
Use min_specialization in liballoc
- Remove a type parameter from `[A]RcFromIter`.
- Remove an implementation of `[A]RcFromIter` that didn't actually
specialize anything.
- Remove unused implementation of `IsZero` for `Option<&mut T>`.
- Change specializations of `[A]RcEqIdent` to use a marker trait version
of `Eq`.
- Remove `BTreeClone`. I couldn't find a way to make this work with
`min_specialization`.
- Add `rustc_unsafe_specialization_marker` to `Copy` and `TrustedLen`.
After this only libcore is the only standard library crate using `feature(specialization)`.
cc #31844
- Remove a type parameter from `[A]RcFromIter`.
- Remove an implementation of `[A]RcFromIter` that didn't actually
specialize anything.
- Remove unused implementation of `IsZero` for `Option<&mut T>`.
- Change specializations of `[A]RcEqIdent` to use a marker trait version
of `Eq`.
- Remove `BTreeClone`. I couldn't find a way to make this work with
`min_specialization`.
- Add `rustc_unsafe_specialization_marker` to `Copy` and `TrustedLen`.
Rollup of 7 pull requests
Successful merges:
- #69041 (proc_macro: Stabilize `Span::resolved_at` and `Span::located_at`)
- #69813 (Implement BitOr and BitOrAssign for the NonZero integer types)
- #70712 (stabilize BTreeMap::remove_entry)
- #71168 (Deprecate `{Box,Rc,Arc}::into_raw_non_null`)
- #71544 (Replace filter_map().next() calls with find_map())
- #71545 (Fix comment in docstring example for Error::kind)
- #71548 (Add missing Send and Sync impls for linked list Cursor and CursorMut.)
Failed merges:
r? @ghost
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.
Currently, constructing a waker requires calling the unsafe
`Waker::from_raw` API. This API requires the user to manually construct
a vtable for the waker themself - which is both cumbersome and very
error prone. This API would provide an ergonomic, straightforward and
guaranteed memory-safe way of constructing a waker.
It has been our longstanding intention that the `Waker` type essentially
function as an `Arc<dyn Wake>`, with a `Wake` trait as defined here. Two
considerations prevented the original API from being shipped as simply
an `Arc<dyn Wake>`:
- We want to support futures on embedded systems, which may not have an
allocator, and in optimized executors for which this API may not be
best-suited. Therefore, we have always explicitly supported the
maximally-flexible (but also memory-unsafe) `RawWaker` API, and
`Waker` has always lived in libcore.
- Because `Waker` lives in libcore and `Arc` lives in liballoc, it has
not been feasible to provide a constructor for `Waker` from `Arc<dyn
Wake>`.
Therefore, the Wake trait was left out of the initial version of the
task waker API.
However, as Rust 1.41, it is possible under the more flexible orphan
rules to implement `From<Arc<W>> for Waker where W: Wake` in liballoc.
Therefore, we can now define this constructor even though `Waker` lives
in libcore.
This PR adds these APIs:
- A `Wake` trait, which contains two methods
- A required method `wake`, which is called by `Waker::wake`
- A provided method `wake_by_ref`, which is called by
`Waker::wake_by_ref` and which implementors can override if they
can optimize this use case.
- An implementation of `From<Arc<W>> for Waker where W: Wake + Send +
Sync + 'static`
- A similar implementation of `From<Arc<W>> for RawWaker`.
The memory fences used previously in Arc implementation are not properly
understood by ThreadSanitizer as synchronization primitives. This had
unfortunate effect where running any non-trivial program compiled with
`-Z sanitizer=thread` would result in numerous false positives.
Replace acquire fences with acquire loads when using ThreadSanitizer to
address the issue.
Split non-CAS atomic support off into target_has_atomic_load_store
This PR implements my proposed changes in https://github.com/rust-lang/rust/issues/32976#issuecomment-518542029 by removing `target_has_atomic = "cas"` and splitting `target_has_atomic` into two separate `cfg`s:
* `target_has_atomic = 8/16/32/64/128`: This indicates the largest width that the target can atomically CAS (which implies support for all atomic operations).
* ` target_has_atomic_load_store = 8/16/32/64/128`: This indicates the largest width that the target can support loading or storing atomically (but may not support CAS).
cc #32976
r? @alexcrichton
… and add a separately-unstable field to force non-exhaustive matching
(`#[non_exhaustive]` is no implemented yet on enum variants)
so that we have the option to later expose the allocator’s error value.
CC https://github.com/rust-lang/wg-allocators/issues/23
Turn `INCOMPLETE_FEATURES` into lint
We do this because it is annoying to see the warning when building rustc and because this is better from a "separation of concerns" POV.
The drawback to this change is that this will respect `--cap-lints`.
Also note that this is not a buffered lint so if there are fatal parser errors then the lint will not trigger.
r? @varkor
Add `impl<T> FromIterator<T> for Arc/Rc<[T]>`
Add implementations of `FromIterator<T> for Arc/Rc<[T]>` with symmetrical logic.
This also takes advantage of specialization in the case of iterators with known length (`TrustedLen`) to elide the final allocation/copying from a `Vec<T>` into `Rc<[T]>` because we can allocate the space for the `Rc<[T]>` directly when the size is known. This is the primary motivation and why this is to be preferred over `iter.collect::<Vec<_>>().into(): Rc<[T]>`.
Moreover, this PR does some refactoring in some places.
r? @RalfJung for the code
cc @alexcrichton from T-libs
