Add doc alias for iterator fold
fold is known in python and javascript as reduce,
not sure about inject but it was written in doc there.
This was my first confusion when coming into rust, I somehow cannot find where is reduce, sometimes I still forget that it is known as `fold`.
Remove `#[rustc_allow_const_fn_ptr]` and add `#![feature(const_fn_fn_ptr_basics)]`
`rustc_allow_const_fn_ptr` was a hack to work around the lack of an escape hatch for the "min `const fn`" checks in const-stable functions. Now that we have co-opted `allow_internal_unstable` for this purpose, we no longer need a bespoke attribute.
Now this functionality is gated under `const_fn_fn_ptr_basics` (how concise!), and `#[allow_internal_unstable(const_fn_fn_ptr_basics)]` replaces `#[rustc_allow_const_fn_ptr]`. `const_fn_fn_ptr_basics` allows function pointer types to appear in the arguments and locals of a `const fn` as well as function pointer casts to be performed inside a `const fn`. Both of these were allowed in constants and statics already. Notably, this does **not** allow users to invoke function pointers in a const context. Presumably, we will use a nicer name for that (`const_fn_ptr`?).
r? @oli-obk
UI to unit test for those using Cell/RefCell/UnsafeCell
Helps with #76268.
I'm working on all files using `Cell` and moving them to unit tests when possible.
r? @matklad
Add missing definitions required by the sparc-unknown-linux-gnu target
This PR adds a few missing definitions required by sparc-unknown-linux-target which were discovered during build tests.
This fixes https://github.com/rust-lang/wg-cargo-std-aware/issues/53
Now users will be able to do:
```
cargo build -Zbuild-std=core -Zbuild-std-features=compiler-builtins-mem
```
and correctly get the Rust implemenations for `memcpy` and friends.
Signed-off-by: Joe Richey <joerichey@google.com>
The syscalls returning a new file descriptors generally use
lowest-numbered file descriptor not currently opened, without any
exceptions for those corresponding to the standard streams.
Previously when any of standard streams has been closed before starting
the application, operations on std::io::{stderr,stdin,stdout} objects
were likely to operate on other logically unrelated file resources
opened afterwards.
Avoid the issue by reopening the standard streams when they are closed.
This was a hack to work around the lack of an escape hatch for the "min
`const fn`" checks in const-stable functions. Now that we have co-opted
`allow_internal_unstable` for this purpose, we no longer need the
bespoke attribute.
Previously, `BTreeMap` tried to link to `crate::collections`, intending
for the link to go to `std/collections/index.html`. But `BTreeMap` is
defined in `alloc`, so after the fix in the previous commit, the links
instead went to `alloc/collections/index.html`, which has almost no
information.
This changes it to link to `index.html`, which only works when viewing
from `std::collections::BTreeMap`, the most common place to visit the
docs. Fixing it to work from anywhere would require the docs for
`std::collections` to be duplicated in `alloc::collections`, which in
turn would require HashMap to be `alloc` for intra-doc links to work
(https://github.com/rust-lang/rust/issues/74481).
update stdarch submodule
This commit update the src/stdarch submodule, we primarily want to include [https://github.com/rust-lang/stdarch/pull/918](url) which provides prefetch hints for aarch64. This PR could deliver ~20% performance gain on our aarch64 server in Filecoin. Wish this could be used as soon as possible.
Thanks.
The thread local LOCAL_STDOUT and LOCAL_STDERR are only used by the test
crate to capture output from tests when running them in the same process
in differen threads. However, every program will check these variables
on every print, even outside of testing.
This involves allocating a thread local key, and registering a thread
local destructor. This can be somewhat expensive.
This change keeps a global flag (LOCAL_STREAMS) which will be set to
true when either of these local streams is used. (So, effectively only
in test and benchmark runs.) When this flag is off, these thread locals
are not even looked at and therefore will not be initialized on the
first output on every thread, which also means no thread local
destructors will be registered.
The (unsafe) Mutex from sys_common had a rather complicated interface.
You were supposed to call init() manually, unless you could guarantee it
was neither moved nor used reentrantly.
Calling `destroy()` was also optional, although it was unclear if 1)
resources might be leaked or not, and 2) if destroy() should only be
called when `init()` was called.
This allowed for a number of interesting (confusing?) different ways to
use this Mutex, all captured in a single type.
In practice, this type was only ever used in two ways:
1. As a static variable. In this case, neither init() nor destroy() are
called. The variable is never moved, and it is never used
reentrantly. It is only ever locked using the LockGuard, never with
raw_lock.
2. As a Boxed variable. In this case, both init() and destroy() are
called, it will be moved and possibly used reentrantly.
No other combinations are used anywhere in `std`.
This change simplifies things by splitting this Mutex type into
two types matching the two use cases: StaticMutex and MovableMutex.
The interface of both new types is now both safer and simpler. The first
one does not call nor expose init/destroy, and the second one calls
those automatically in its new() and Drop functions. Also, the locking
functions of MovableMutex are no longer unsafe.
Remove std::io::lazy::Lazy in favour of SyncOnceCell
The (internal) std::io::lazy::Lazy was used to lazily initialize the stdout and stdin buffers (and mutexes). It uses atexit() to register a destructor to flush the streams on exit, and mark the streams as 'closed'. Using the stream afterwards would result in a panic.
Stdout uses a LineWriter which contains a BufWriter that will flush the buffer on drop. This one is important to be executed during shutdown, to make sure no buffered output is lost. It also forbids access to stdout afterwards, since the buffer is already flushed and gone.
Stdin uses a BufReader, which does not implement Drop. It simply forgets any previously read data that was not read from the buffer yet. This means that in the case of stdin, the atexit() function's only effect is making stdin inaccessible to the program, such that later accesses result in a panic. This is uncessary, as it'd have been safe to access stdin during shutdown of the program.
---
This change removes the entire io::lazy module in favour of SyncOnceCell. SyncOnceCell's fast path is much faster (a single atomic operation) than locking a sys_common::Mutex on every access like Lazy did.
However, SyncOnceCell does not use atexit() to drop the contained object during shutdown.
As noted above, this is not a problem for stdin. It simply means stdin is now usable during shutdown.
The atexit() call for stdout is moved to the stdio module. Unlike the now-removed Lazy struct, SyncOnceCell does not have a 'gone and unusable' state that panics. Instead of adding this again, this simply replaces the buffer with one with zero capacity. This effectively flushes the old buffer *and* makes any writes afterwards pass through directly without touching a buffer, making print!() available during shutdown without panicking.
---
In addition, because the contents of the SyncOnceCell are no longer dropped, we can now use `&'static` instead of `Arc` in `Stdout` and `Stdin`. This also saves two levels of indirection in `stdin()` and `stdout()`, since Lazy effectively stored a `Box<Arc<T>>`, and SyncOnceCell stores the `T` directly.
Rust vec bench import specific rand::RngCore
Using `RngCore` import for side effects is clearer than `*` which may bring it unnecessary more stuff than needed, it is also more explicit doing so.
@pickfire change `LEN = 16384` (and pos) and `once` instead of `[0].iter()` after this.
@rustbot modify labels: +C-cleanup +A-testsuite
Add `#![feature(const_fn_floating_point_arithmetic)]`
cc #76618
This is a template for splitting up `const_fn` into granular feature gates. I think this will make it easier, both for us and for users, to track stabilization of each individual feature. We don't *have* to do this, however. We could also keep stabilizing things out from under `const_fn`.
cc @rust-lang/wg-const-eval
r? @oli-obk
Explicitly document the size guarantees that Option makes.
Triggered by a discussion on wg-unsafe-code-guidelines about which layouts of `Option<T>` one can guarantee are optimised to a single pointer.
CC @RalfJung
