Implement allow-by-default `multiple_supertrait_upcastable` lint
The lint detects when an object-safe trait has multiple supertraits.
Enabled in libcore and liballoc as they are low-level enough that many embedded programs will use them.
r? `@nikomatsakis`
Test leaking of BinaryHeap Drain iterators
Add test cases about forgetting the `BinaryHeap::Drain` iterator, and slightly fortifies some other test cases.
Consists of separate commits that I don't think are relevant on their own (but I'll happily turn these into more PRs if desired).
The lint "clippy::uninlined_format_args" recommends inline
variables in format strings. Fix two places in the docs that do
not do this. I noticed this because I copy/pasted one example in
to my project, then noticed this lint error. This fixes:
error: variables can be used directly in the `format!` string
--> src/main.rs:30:22
|
30 | let string = format!("{:.*}", decimals, magnitude);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: variables can be used directly in the `format!` string
--> src/main.rs:39:2
|
39 | write!(&mut io::stdout(), "{}", args).unwrap();
Send `VecDeque::from_iter` via `Vec::from_iter`
Since it's O(1) to convert between them now, might as well reuse the logic.
Mostly for the various specializations it does, but might also save some monomorphization work if, say, people collect slice iterators into both `Vec`s and `VecDeque`s.
improve doc of into_boxed_slice and impl From<Vec<T>> for Box<[T]>
Improves description of `into_boxed_slice`, and adds example to `impl From<Vec<T>> for Box<[T]>`.
Fixes#98908
Since it's O(1) to convert between them now, might as well reuse the logic.
Mostly for the various specializations it does, but might also save some monomorphization work if, say, people collect slice iterators into both `Vec`s and `VecDeque`s.
Update VecDeque implementation to use head+len instead of head+tail
(See #99805)
This changes `alloc::collections::VecDeque`'s internal representation from using head and tail indices to using a head index and a length field. It has a few advantages over the current design:
* It allows the buffer to be of length 0, which means the `VecDeque::new` new longer has to allocate and could be changed to a `const fn`
* It allows the `VecDeque` to fill the buffer completely, unlike the old implementation, which always had to leave a free space
* It removes the restriction for the size to be a power of two, allowing it to properly `shrink_to_fit`, unlike the old `VecDeque`
* The above points also combine to allow the `Vec<T> -> VecDeque<T>` conversion to be very cheap and guaranteed O(1). I mention this in the `From<Vec<T>>` impl, but it's not a strong guarantee just yet, as that would likely need some form of API change proposal.
All the tests seem to pass for the new `VecDeque`, with some slight adjustments.
r? `@scottmcm`
Stop peeling the last iteration of the loop in `Vec::resize_with`
`resize_with` uses the `ExtendWith` code that peels the last iteration:
341d8b8a2c/library/alloc/src/vec/mod.rs (L2525-L2529)
But that's kinda weird for `ExtendFunc` because it does the same thing on the last iteration anyway:
341d8b8a2c/library/alloc/src/vec/mod.rs (L2494-L2502)
So this just has it use the normal `extend`-from-`TrustedLen` code instead.
r? `@ghost`
Clarify and restrict when `{Arc,Rc}::get_unchecked_mut` is allowed.
(Tracking issue for `{Arc,Rc}::get_unchecked_mut`: #63292)
(I'm using `Rc` in this comment, but it applies for `Arc` all the same).
As currently documented, `Rc::get_unchecked_mut` can lead to unsoundness when multiple `Rc`/`Weak` pointers to the same allocation exist. The current documentation only requires that other `Rc`/`Weak` pointers to the same allocation "must not be dereferenced for the duration of the returned borrow". This can lead to unsoundness in (at least) two ways: variance, and `Rc<str>`/`Rc<[u8]>` aliasing. ([playground link](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=d7e2d091c389f463d121630ab0a37320)).
This PR changes the documentation of `Rc::get_unchecked_mut` to restrict usage to when all `Rc<T>`/`Weak<T>` have the exact same `T` (including lifetimes). I believe this is sufficient to prevent unsoundness, while still allowing `get_unchecked_mut` to be called on an aliased `Rc` as long as the safety contract is upheld by the caller.
## Alternatives
* A less strict, but still sound alternative would be to say that the caller must only write values which are valid for all aliased `Rc`/`Weak` inner types. (This was [mentioned](https://github.com/rust-lang/rust/issues/63292#issuecomment-568284090) in the tracking issue). This may be too complicated to clearly express in the documentation.
* A more strict alternative would be to say that there must not be any aliased `Rc`/`Weak` pointers, i.e. it is required that get_mut would return `Some(_)`. (This was also mentioned in the tracking issue). There is at least one codebase that this would cause to become unsound ([here](be5a164d77/src/memtable.rs (L166)), where additional locking is used to ensure unique access to an aliased `Rc<T>`; I saw this because it was linked on the tracking issue).
This moves the stable sort implementation to the core::slice::sort module. By
virtue of being in core it can't access `Vec`. The two `Vec` used by merge sort,
`buf` and `runs`, are modelled as custom types that implement the very limited
required `Vec` interface with the help of provided allocation and free
functions. This is done to allow future re-use of functions and logic between
stable and unstable sort. Such as `insert_head`.
`VecDeque::resize` should re-use the buffer in the passed-in element
Today it always copies it for *every* appended element, but one of those clones is avoidable.
This adds `iter::repeat_n` (https://github.com/rust-lang/rust/issues/104434) as the primitive needed to do this. If this PR is acceptable, I'll also use this in `Vec` rather than its custom `ExtendElement` type & infrastructure that is harder to share between multiple different containers:
101e1822c3/library/alloc/src/vec/mod.rs (L2479-L2492)
Attempt to reuse `Vec<T>` backing storage for `Rc/Arc<[T]>`
If a `Vec<T>` has sufficient capacity to store the inner `RcBox<[T]>`, we can just reuse the existing allocation and shift the elements up, instead of making a new allocation.
run alloc benchmarks in Miri and fix UB
Miri since recently has a "fake monotonic clock" that works even with isolation. Its measurements are not very meaningful but it means we can run these benches and check them for UB.
And that's a good thing since there was UB here: fixes https://github.com/rust-lang/rust/issues/104096.
r? ``@thomcc``
disable btree size tests on Miri
Seems fine not to run these in Miri, they can't have UB anyway. And this lets us do layout randomization in Miri.
r? ``@thomcc``
The new implementation doesn't use weak lang items and instead changes
`#[alloc_error_handler]` to an attribute macro just like
`#[global_allocator]`.
The attribute will generate the `__rg_oom` function which is called by
the compiler-generated `__rust_alloc_error_handler`. If no `__rg_oom`
function is defined in any crate then the compiler shim will call
`__rdl_oom` in the alloc crate which will simply panic.
This also fixes link errors with `-C link-dead-code` with
`default_alloc_error_handler`: `__rg_oom` was previously defined in the
alloc crate and would attempt to reference the `oom` lang item, even if
it didn't exist. This worked as long as `__rg_oom` was excluded from
linking since it was not called.
This is a prerequisite for the stabilization of
`default_alloc_error_handler` (#102318).
Remove redundant lifetime bound from `impl Borrow for Cow`
The lifetime bound `B::Owned: 'a` is redundant and doesn't make a difference,
because `Cow<'a, B>` comes with an implicit `B: 'a`, and associated types
will outlive lifetimes outlived by the `Self` type (and all the trait's
generic parameters, of which there are none in this case), so the implicit `B: 'a`
implies `B::Owned: 'a` anyway.
The explicit lifetime bound here does however [end up in documentation](https://doc.rust-lang.org/std/borrow/enum.Cow.html#impl-Borrow%3CB%3E),
and that's confusing in my opinion, so let's remove it ^^
_(Documentation right now, compare to `AsRef`, too:)_
Adjust argument type for mutable with_metadata_of (#75091)
The method takes two pointer arguments: one `self` supplying the pointer value, and a second pointer supplying the metadata.
The new parameter type more clearly reflects the actual requirements. The provenance of the metadata parameter is disregarded completely. Using a mutable pointer in the call site can be coerced to a const pointer while the reverse is not true.
In some cases, the current parameter type can thus lead to a very slightly confusing additional cast. [Example](cad93775eb).
```rust
// Manually taking an unsized object from a `ManuallyDrop` into another allocation.
let val: &core::mem::ManuallyDrop<T> = …;
let ptr = val as *const _ as *mut T;
let ptr = uninit.as_ptr().with_metadata_of(ptr);
```
This could then instead be simplified to:
```rust
// Manually taking an unsized object from a `ManuallyDrop` into another allocation.
let val: &core::mem::ManuallyDrop<T> = …;
let ptr = uninit.as_ptr().with_metadata_of(&**val);
```
Tracking issue: https://github.com/rust-lang/rust/issues/75091
``@dtolnay`` you're reviewed #95249, would you mind chiming in?
Remove incorrect comment in `Vec::drain`
r? ``@scottmcm``
Turns out this comment wasn't correct for 6 years, since #34951, which switched from using `slice::IterMut` into using `slice::Iter`.
Add `Box<[T; N]>: TryFrom<Vec<T>>`
We have `[T; N]: TryFrom<Vec<T>>` (#76310) and `Box<[T; N]>: TryFrom<Box<[T]>>`, but not this combination.
`vec.into_boxed_slice().try_into()` isn't quite a replacement for this, as that'll reallocate unnecessarily in the error case.
**Insta-stable, so needs an FCP**
(I tried to make this work with `, A`, but that's disallowed because of `#[fundamental]` https://github.com/rust-lang/rust/issues/29635#issuecomment-1247598385)
Detect and reject out-of-range integers in format string literals
Until now out-of-range integers in format string literals were silently ignored. They wrapped around to zero at usize::MAX, producing unexpected results.
When using debug builds of rustc, such integers in format string literals even cause an 'attempt to add with overflow' panic in rustc.
Fix this by producing an error diagnostic for integers in format string literals which do not fit into usize.
Fixes#102528
