Stabilize `std::{rc,sync}::Weak::{weak_count, strong_count}`
* Original PR: #56696
* Tracking issue: #57977Closes: #57977
Supporting comments:
> Although these were added for testing, it is occasionally useful to have a way to probe optimistically for whether a weak pointer has become dangling, without actually taking the overhead of manipulating atomics. Are there any plans to stabilize this?
_Originally posted by @bdonlan in https://github.com/rust-lang/rust/issues/57977#issuecomment-516970921_
> Having this stabilized would help. Currently, the only way to check if a weak pointer has become dangling is to call `upgrade`, which is by far expensive.
_Originally posted by @glebpom in https://github.com/rust-lang/rust/issues/57977#issuecomment-526934709_
Not sure if stabilizing these warrants a full RFC, so throwing this out here as a start for now.
Note: per CONTRIBUTING.md, I ran the tidy checks, but they seem to be failing on unchanged files (primarily in `src/stdsimd`).
Restore original implementation of Vec::retain
This PR reverts #48065, which aimed to optimize `Vec::retain` by making use of `Vec::drain_filter`. Unfortunately at that time, `drain_filter` was unsound.
The soundness hole in `Vec::drain_filter` was fixed in #61224 by guaranteeing that cleanup logic runs via a nested `Drop`, even in the event of a panic. Implementing this nested drop affects codegen (apparently?) and results in slower code.
Fixes#65970
This PR reverts #48065, which aimed to optimize `Vec::retain` by
making use of `Vec::drain_filter`. Unfortunately at that time,
`drain_filter` was unsound.
The soundness hole in `Vec::drain_filter` was fixed in #61224 by
guaranteeing that cleanup logic runs via a nested `Drop`, even in
the event of a panic. Implementing this nested drop affects codegen
(apparently?) and results in slower code.
Fixes#65970
Require stable/unstable annotations for the constness of all stable fns with a const modifier
r? @RalfJung @Centril
Every `#[stable]` const fn now needs either a `#[rustc_const_unstable]` attribute or a `#[rustc_const_stable]` attribute. You can't silently stabilize the constness of a function anymore.
LinkedList: drop remaining items when drop panics
https://github.com/rust-lang/rust/pull/67235, but for `LinkedList`, which has the same issue.
I've also copied over the other drop-related tests from `VecDeque` since AFAICT `LinkedList` didn't have any.
Match `VecDeque::extend` to `Vec::extend_desugared`
Currently, `VecDeque::extend` [does not reserve at all](https://github.com/rust-lang/rust/pull/65069#discussion_r333166522). This implementation still runs a check every iteration of the loop, but should reallocate at most once for the common cases where the `size_hint` lower bound is exact. Further optimizations in the future could improve this for some common cases, but given the complexity of the `Vec::extend` implementation it's not immediately clear that this would be worthwhile.
weak-into-raw: Clarify some details in Safety
Clarify it is OK to pass a pointer that never owned a weak count (one
from Weak::new) back into it as it was created from it. Relates to
discussion in #60728.
@CAD97 Do you want to have a look at the new docs?
Clarify it is OK to pass a pointer that never owned a weak count (one
from Weak::new) back into it as it was created from it. Relates to
discussion in #60728.
Layout::pad_to_align is infallible
As per [this comment](https://github.com/rust-lang/rust/issues/55724#issuecomment-441421651) (cc @glandium).
> Per eb981a1/src/libcore/alloc.rs (L63-L65), `layout.size()` is always <= `usize::MAX - (layout.align() - 1)`.
>
> Which means:
>
> * The maximum value `layout.size()` can have is already aligned for `layout.align()` (`layout.align()` being a power of two, `usize::MAX - (layout.align() - 1)` is a multiple of `layout.align()`)
> * Incidentally, any value smaller than that maximum value will align at most to that maximum value.
>
> IOW, `pad_to_align` can not return `Err(LayoutErr)`, except for the layout not respecting its invariants, but we shouldn't care about that.
This PR makes `pad_to_align` return `Layout` directly, representing the fact that it cannot fail.
Format liballoc with rustfmt
Same strategy as #66691 -- as with my previous formatting PRs, I am avoiding causing merge conflicts in other PRs by only touches those files that are not involved in any currently open PR. Files that appear in new PRs between when this PR is opened and when it makes it to the top of the bors queue will be reverted from this PR.
The list of files involved in open PRs is determined by querying GitHub's GraphQL API [with this script](https://gist.github.com/dtolnay/aa9c34993dc051a4f344d1b10e4487e8).
With the list of files from the script in outstanding_files, the relevant commands were:
```
$ find src/liballoc -name '*.rs' \
| xargs rustfmt --edition=2018 --unstable-features --skip-children
$ rg liballoc outstanding_files | xargs git checkout --
```
To confirm no funny business:
```
$ git checkout $THIS_COMMIT^
$ git show --pretty= --name-only $THIS_COMMIT \
| xargs rustfmt --edition=2018 --unstable-features --skip-children
$ git diff $THIS_COMMIT # there should be no difference
```
r? @Dylan-DPC
Miri: run panic-catching tests in liballoc
I also converted two tests from using `thread::spawn(...).join()` just for catching panics, to `catch_panic`, so that Miri can run them.
impl TrustedLen for vec::Drain
The iterator methods just forward to `slice::Iter`, which is `TrustedLen`.
This can probably be applied to other `Drain` structs as well.
Fix shrink_to panic documentation
While the potential for panicking is already documented for the
`Vec::shrink_to` method, it is not clearly labeled with the usual
`# Panics` heading.
r? @steveklabnik
alloc: Add new_zeroed() versions like new_uninit().
MaybeUninit has both uninit() and zeroed(), it seems reasonable to have the same
surface on Box/Rc/Arc.
Needs tests.
cc #63291
introduce benchmarks of HashSet operations
To avoid goofs such as corrected by #66280, I added benchmarks of binary HashSet operations.
Due to the fact x.py keeps recompiling the whole shebang (or at least a big part of it) whenever you touch the test code, and because piling up all tests in one file does not strike me as future proof, I tried moving the hash benches to the separate place they are for liballoc/collections/btree. But it turns out that, in a cleaned checkout, x.py still recompiles the whole shebang whenever you touch the test code (PS or when you add or delete any irrelevant file). So I'm not going to add more tests, and I doubt others will, and these tests have proven their point already, so this PR is kind of pointless
Scope format! temporaries
This places the temporaries that `format!` generates to refer to its arguments (through `&dyn Trait`) in a short-lived scope surrounding just the invocation of `format!`. This enables `format!` to be used in generators without the temporaries preventing the generator from being `Send` (due to `dyn Trait` not being `Sync`).
See rust-lang/rust#64477 for details.
