Revert `Vec::spare_capacity_mut` impl to prevent pointers invalidation
The implementation was changed in #79015.
Later it was [pointed out](https://github.com/rust-lang/rust/issues/81944#issuecomment-782849785) that the implementation invalidates pointers to the buffer (initialized elements) by creating a unique reference to the buffer. This PR reverts the implementation.
r? ```@RalfJung```
Discovered this kind of issue in an unrelated library.
The author copied the tests from here and AFAIK, there are no tests for this particular case.
Signed-off-by: Hanif Bin Ariffin <hanif.ariffin.4326@gmail.com>
Optimize Vec::retain
Use `copy_non_overlapping` instead of `swap` to reduce memory writes, like what we've done in #44355 and `String::retain`.
#48065 already tried to do this optimization but it is reverted in #67300 due to bad codegen of `DrainFilter::drop`.
This PR re-implement the drop-then-move approach. I did a [benchmark](https://gist.github.com/oxalica/3360eec9376f22533fcecff02798b698) on small-no-drop, small-need-drop, large-no-drop elements with different predicate functions. It turns out that the new implementation is >20% faster in average for almost all cases. Only 2/24 cases are slower by 3% and 5%. See the link above for more detail.
I think regression in may-panic cases is due to drop-guard preventing some optimization. If it's permitted to leak elements when predicate function of element's `drop` panic, the new implementation should be almost always faster than current one.
I'm not sure if we should leak on panic, since there is indeed an issue (#52267) complains about it before.
add `Vec::extend_from_within` method under `vec_extend_from_within` feature gate
Implement <https://github.com/rust-lang/rfcs/pull/2714>
### tl;dr
This PR adds a `extend_from_within` method to `Vec` which allows copying elements from a range to the end:
```rust
#![feature(vec_extend_from_within)]
let mut vec = vec![0, 1, 2, 3, 4];
vec.extend_from_within(2..);
assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4]);
vec.extend_from_within(..2);
assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1]);
vec.extend_from_within(4..8);
assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1, 4, 2, 3, 4]);
```
### Implementation notes
Originally I've copied `@Shnatsel's` [implementation](690742a0de/src/lib.rs (L74)) with some minor changes to support other ranges:
```rust
pub fn append_from_within<R>(&mut self, src: R)
where
T: Copy,
R: RangeBounds<usize>,
{
let len = self.len();
let Range { start, end } = src.assert_len(len);;
let count = end - start;
self.reserve(count);
unsafe {
// This is safe because `reserve()` above succeeded,
// so `self.len() + count` did not overflow usize
ptr::copy_nonoverlapping(
self.get_unchecked(src.start),
self.as_mut_ptr().add(len),
count,
);
self.set_len(len + count);
}
}
```
But then I've realized that this duplicates most of the code from (private) `Vec::append_elements`, so I've used it instead.
Then I've applied `@KodrAus` suggestions from https://github.com/rust-lang/rust/pull/79015#issuecomment-727200852.
Implement <https://github.com/rust-lang/rfcs/pull/2714>, changes from the RFC:
- Rename the method `append_from_within` => `extend_from_within`
- Loose :Copy bound => :Clone
- Specialize in case of :Copy
This commit also adds `Vec::split_at_spare` private method and use it to implement
`Vec::spare_capacity_mut` and `Vec::extend_from_within`. This method returns 2
slices - initialized elements (same as `&mut vec[..]`) and uninitialized but
allocated space (same as `vec.spare_capacity_mut()`).
The return of the GroupBy and GroupByMut iterators on slice
According to https://github.com/rust-lang/rfcs/pull/2477#issuecomment-742034372, I am opening this PR again, this time I implemented it in safe Rust only, it is therefore much easier to read and is completely safe.
This PR proposes to add two new methods to the slice, the `group_by` and `group_by_mut`. These two methods provide a way to iterate over non-overlapping sub-slices of a base slice that are separated by the predicate given by the user (e.g. `Partial::eq`, `|a, b| a.abs() < b.abs()`).
```rust
let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
let mut iter = slice.group_by(|a, b| a == b);
assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
assert_eq!(iter.next(), Some(&[3, 3][..]));
assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
assert_eq!(iter.next(), None);
```
[An RFC](https://github.com/rust-lang/rfcs/pull/2477) was open 2 years ago but wasn't necessary.
Move Vec UI tests to unit tests when possible
Helps with #76268.
I'm moving the tests using `Vec` or `VecDeque`.
````@rustbot```` modify labels: A-testsuite C-cleanup T-libs
Add PartialEq impls for Vec <-> slice
This is a follow-up to #71660 and rust-lang/rfcs#2917 to add two more missing vec/slice PartialEq impls:
```
impl<A, B> PartialEq<[B]> for Vec<A> where A: PartialEq<B> { .. }
impl<A, B> PartialEq<Vec<B>> for [A] where A: PartialEq<B> { .. }
```
Since this is insta-stable, it should go through the `@rust-lang/libs` FCP process. Note that I used version 1.47.0 for the `stable` attribute because I assume this will not merge before the 1.46.0 branch is cut next week.
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
Fix liballoc test suite for Miri
Mostly, fix the regression introduced by https://github.com/rust-lang/rust/pull/75207 that caused slices (i.e., references) to be created to invalid memory or memory that has aliasing pointers that we want to keep valid. @dylni this changes the type of `check_range` to only require the length, not the full reference to the slice, which indeed is all the information this function requires.
Also reduce the size of a test introduced in https://github.com/rust-lang/rust/pull/70793 to make it not take 3 minutes in Miri.
This makes https://github.com/RalfJung/miri-test-libstd work again.
