stabilize union with 'ManuallyDrop' fields and 'impl Drop for Union'
As [discussed by @SimonSapin and @withoutboats](https://github.com/rust-lang/rust/issues/55149#issuecomment-634692020), this PR proposes to stabilize parts of the `untagged_union` feature gate:
* It will be possible to have a union with field type `ManuallyDrop<T>` for any `T`.
* While at it I propose we also stabilize `impl Drop for Union`; to my knowledge, there are no open concerns around this feature.
In the RFC discussion, we also talked about allowing `&mut T` as another non-`Copy` non-dropping type, but that felt to me like an overly specific exception so I figured we'd wait if there is actually any use for such a special case.
Some things remain unstable and still require the `untagged_union` feature gate:
* Union with fields that do not drop, are not `Copy`, and are not `ManuallyDrop<_>`. The reason to not stabilize this is to avoid semver concerns around libraries adding `Drop` implementations later. (This is already not fully semver compatible as, to my knowledge, the borrow checker will exploit the non-dropping nature of any type, but it seems prudent to avoid further increasing the amount of trouble adding an `impl Drop` can cause.)
Due to this, quite a few tests still need the `untagged_union` feature, but I think the ones where I could remove the feature flag provide good test coverage for the stable part.
Cc @rust-lang/lang
Cleanup cloudabi mutexes and condvars
This gets rid of lots of unnecessary unsafety.
All the AtomicU32s were wrapped in UnsafeCell or UnsafeCell<MaybeUninit>, and raw pointers were used to get to the AtomicU32 inside. This change cleans that up by using AtomicU32 directly.
Also replaces a UnsafeCell<u32> by a safer Cell<u32>.
@rustbot modify labels: +C-cleanup
Static mutex is static
StaticMutex is only ever used with as a static (as the name already suggests). So it doesn't have to be generic over a lifetime, but can simply assume 'static.
This 'static lifetime guarantees the object is never moved, so this is no longer a manually checked requirement for unsafe calls to lock().
@rustbot modify labels: +T-libs +A-concurrency +C-cleanup
For backtrace, use StaticMutex instead of a raw sys Mutex.
The code used the very unsafe `sys::mutex::Mutex` directly, and built its own unlock-on-drop wrapper around it. The StaticMutex wrapper already provides that and is easier to use safely.
@rustbot modify labels: +T-libs +C-cleanup
Use futex-based thread-parker for Wasm32.
This uses the existing `sys_common/thread_parker/futex.rs` futex-based thread parker (that was already used for Linux) for wasm32 as well (if the wasm32 atomics target feature is enabled, which is not the case by default).
Wasm32 provides the basic futex operations as instructions: https://webassembly.github.io/threads/syntax/instructions.html
These are now exposed from `sys::futex::{futex_wait, futex_wake}`, just like on Linux. So, `thread_parker/futex.rs` stays completely unmodified.
Refactor io/buffered.rs into submodules
This pull request splits `BufWriter`, `BufReader`, `LineWriter`, and `LineWriterShim` (along with their associated tests) into separate submodules. It contains no functional changes. This change is being made in anticipation of adding another type of buffered writer which can be switched between line- and block-buffering mode.
Part of a series of pull requests resolving #60673.
Add `str::{Split,RSplit,SplitN,RSplitN,SplitTerminator,RSplitTerminator,SplitInclusive}::as_str` methods
tl;dr this allows viewing unyelded part of str-split-iterators, like so:
```rust
let mut split = "Mary had a little lamb".split(' ');
assert_eq!(split.as_str(), "Mary had a little lamb");
split.next();
assert_eq!(split.as_str(), "had a little lamb");
split.by_ref().for_each(drop);
assert_eq!(split.as_str(), "");
```
--------------
This PR adds semi-identical `as_str` methods to most str-split-iterators with signatures like `&'_ Split<'a, P: Pattern<'a>> -> &'a str` (Note: output `&str` lifetime is bound to the `'a`, not the `'_`). The methods are similar to [`Chars::as_str`]
`SplitInclusive::as_str` is under `"str_split_inclusive_as_str"` feature gate, all other methods are under `"str_split_as_str"` feature gate.
Before this PR you had to sum `len`s of all yielded parts or collect into `String` to emulate `as_str`.
[`Chars::as_str`]: https://doc.rust-lang.org/core/str/struct.Chars.html#method.as_str
StaticMutex is only ever used with as a static (as the name already
suggests). So it doesn't have to be generic over a lifetime, but can
simply assume 'static.
This 'static lifetime guarantees the object is never moved, so this is
no longer a manually checked requirement for unsafe calls to lock().
The comment said it's UB to call lock() while it is locked. That'd be
quite a useless Mutex. :) It was supposed to say 'locked by the same
thread', not just 'locked'.
Replace absolute paths with relative ones
Modern compilers allow reaching external crates
like std or core via relative paths in modules
outside of lib.rs and main.rs.
Remove unsafety from sys/unsupported and add deny(unsafe_op_in_unsafe_fn).
Replacing `UnsafeCell`s by a `Cell`s simplifies things and makes the mutex and rwlock implementations safe. Other than that, only unsafety in strlen() contained unsafe code.
@rustbot modify labels: +F-unsafe-block-in-unsafe-fn +C-cleanup
Stabilize slice_partition_at_index
This stabilizes slice_partition_at_index, including renaming `partition_at_index*` -> `select_nth_unstable*`.
Closes#55300
r? `@Amanieu`
