On later stages, the feature is already stable.
Result of running:
rg -l "feature.let_else" compiler/ src/librustdoc/ library/ | xargs sed -s -i "s#\\[feature.let_else#\\[cfg_attr\\(bootstrap, feature\\(let_else\\)#"
Implement internal `IsZero` for Wrapping and Saturating for `Vec` optimizations
This implements the `IsZero` trait for the `Wrapping` and `Saturating` types so that users of these types can get the improved performance from the specialization of creating a `Vec` from a single element repeated when it has a zero bit pattern (example `vec![0_i32; 500]`, or after this PR `vec![Wrapping(0_i32); 500]`)
CC #60978
Fix a bunch of typo
This PR will fix some typos detected by [typos].
I only picked the ones I was sure were spelling errors to fix, mostly in
the comments.
[typos]: https://github.com/crate-ci/typos
This PR will fix some typos detected by [typos].
I only picked the ones I was sure were spelling errors to fix, mostly in
the comments.
[typos]: https://github.com/crate-ci/typos
Add `vec::Drain{,Filter}::keep_rest`
This PR adds `keep_rest` methods to `vec::Drain` and `vec::DrainFilter` under `drain_keep_rest` feature gate:
```rust
// mod alloc::vec
impl<T, A: Allocator> Drain<'_, T, A> {
pub fn keep_rest(self);
}
impl<T, F, A: Allocator> DrainFilter<'_, T, F, A>
where
F: FnMut(&mut T) -> bool,
{
pub fn keep_rest(self);
}
```
Both these methods cancel draining of elements that were not yet yielded from the iterators. While this needs more testing & documentation, I want at least start the discussion. This may be a potential way out of the "should `DrainFilter` exhaust itself on drop?" argument.
Make use of `[wrapping_]byte_{add,sub}`
These new methods trivially replace old `.cast().wrapping_offset().cast()` & similar code.
Note that [`arith_offset`](https://doc.rust-lang.org/std/intrinsics/fn.arith_offset.html) and `wrapping_offset` are the same thing.
r? ``@scottmcm``
_split off from #100746_
Box::from(slice): Clarify that contents are copied
A colleague mentioned that they interpreted the old text
as saying that only the pointer and the length are copied.
Add a clause so it is more clear that the pointed to contents
are also copied.
In Rust for Linux we are using these to make `alloc` a bit
more modular.
A `run-make-fulldeps` test is added for each of them, so that
enabling each of them independently is kept in a compilable state.
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
BTree: evaluate static type-related check at compile time
`assert`s like the ones replaced here would only go off when you run the right test cases, if the code were ever incorrectly changed such that rhey would trigger. But [inspired on a nice forum question](https://users.rust-lang.org/t/compile-time-const-generic-parameter-check/69202), they can be checked at compile time.
Extra documentation for new formatting feature
Documentation of this feature was added in #90473 and released in Rust 1.58. However, high traffic macros did not receive new examples. Namely `println!()` and `format!()`.
The doc comments included in Rust are super important to the community- especially newcomers. I have met several other newbies like myself who are unaware of this recent (well about 7 months old now) update to the language allowing for convenient intra-string identifiers.
Bringing small examples of this feature to the doc comments of `println!()` and `format!()` would be helpful to everyone learning the language.
[Blog Post Announcing Feature](https://blog.rust-lang.org/2022/01/13/Rust-1.58.0.html)
[Feature PR](https://github.com/rust-lang/rust/pull/90473) - includes several instances of documentation of the feature- minus the macros in question for this PR
*This is my first time contributing to a project this large. Feedback would mean the world to me 😄*
---
*Recreated; I violated the [No-Merge Policy](https://rustc-dev-guide.rust-lang.org/git.html#no-merge-policy)*
Move Error trait into core
This PR moves the error trait from the standard library into a new unstable `error` module within the core library. The goal of this PR is to help unify error reporting across the std and no_std ecosystems, as well as open the door to integrating the error trait into the panic reporting system when reporting panics whose source is an errors (such as via `expect`).
This PR is a rewrite of https://github.com/rust-lang/rust/pull/90328 using new compiler features that have been added to support error in core.
Add guarantee that Vec::default() does not alloc
Currently `Vec::new()` is guaranteed to not allocate until elements are pushed onto the `Vec`, but such a guarantee is missing for `Vec`'s implementation of `Default::default`.
This adds such a guarantee for `Vec::default()` to the API reference.
See also [this discussion on URLO](https://users.rust-lang.org/t/guarantee-that-vec-default-does-not-allocate/79903).
Use pointer `is_aligned*` methods
This PR replaces some manual alignment checks with calls to `pointer::{is_aligned, is_aligned_to}` and removes a useless pointer cast.
r? `@scottmcm`
_split off from #100746_
Guarantee `try_reserve` preserves the contents on error
Update doc comments to make the guarantee explicit. However, some
implementations does not have the statement though.
* `HashMap`, `HashSet`: require guarantees on hashbrown side.
* `PathBuf`: simply redirecting to `OsString`.
Fixes#99606.
Currently `Vec::new()` is guaranteed to not allocate until elements are
pushed onto the `Vec`, but such a guarantee is missing for `Vec`'s
implementation of `Default::default`. This adds such a guarantee for
`Vec::default()` to the API reference.
Add tests that check `Vec::retain` predicate execution order.
This behaviour is documented for `Vec::retain` which means that there is code that rely on that but there weren't tests about that.
Std module docs improvements
My primary goal is to create a cleaner separation between primitive types and primitive type helper modules (fixes#92777). I also changed a few header lines in other top-level std modules (seen at https://doc.rust-lang.org/std/) for consistency.
Some conventions used/established:
* "The \`Box\<T>` type for heap allocation." - if a module mainly provides a single type, name it and summarize its purpose in the module header
* "Utilities for the _ primitive type." - this wording is used for the header of helper modules
* Documentation for primitive types themselves are removed from helper modules
* provided-by-core functionality of primitive types is documented in the primitive type instead of the helper module (such as the "Iteration" section in the slice docs)
I wonder if some content in `std::ptr` should be in `pointer` but I did not address this.
Replace most uses of `pointer::offset` with `add` and `sub`
As PR title says, it replaces `pointer::offset` in compiler and standard library with `pointer::add` and `pointer::sub`. This generally makes code cleaner, easier to grasp and removes (or, well, hides) integer casts.
This is generally trivially correct, `.offset(-constant)` is just `.sub(constant)`, `.offset(usized as isize)` is just `.add(usized)`, etc. However in some cases we need to be careful with signs of things.
r? ````@scottmcm````
_split off from #100746_
Make some docs nicer wrt pointer offsets
This PR replaces `pointer::offset` with `pointer::add` and similarly `.cast().wrapping_add().cast()` with `.wrapping_byte_add()` **in docs**.
r? ``````@scottmcm``````
_split off from #100746_
Expose `Utf8Lossy` as `Utf8Chunks`
This PR changes the feature for `Utf8Lossy` from `str_internals` to `utf8_lossy` and improves the API. This is done to eventually expose the API as stable.
Proposal: rust-lang/libs-team#54
Tracking Issue: #99543
Update doc comments to make the guarantee explicit. However, some
implementations does not have the statement though.
* `HashMap`, `HashSet`: require guarantees on hashbrown side.
* `PathBuf`: simply redirecting to `OsString`.
Fixes#99606.
Optimized vec::IntoIter::next_chunk impl
```
x86_64v1, default
test vec::bench_next_chunk ... bench: 696 ns/iter (+/- 22)
x86_64v1, pr
test vec::bench_next_chunk ... bench: 309 ns/iter (+/- 4)
znver2, default
test vec::bench_next_chunk ... bench: 17,272 ns/iter (+/- 117)
znver2, pr
test vec::bench_next_chunk ... bench: 211 ns/iter (+/- 3)
```
On znver2 the default impl seems to be slow due to different inlining decisions. It goes through `core::array::iter_next_chunk`
which has a deep call tree.
codegen: use new {re,de,}allocator annotations in llvm
This obviates the patch that teaches LLVM internals about
_rust_{re,de}alloc functions by putting annotations directly in the IR
for the optimizer.
The sole test change is required to anchor FileCheck to the body of the
`box_uninitialized` method, so it doesn't see the `allocalign` on
`__rust_alloc` and get mad about the string `alloca` showing up. Since I
was there anyway, I added some checks on the attributes to prove the
right attributes got set.
r? `@nikic`
```
test vec::bench_next_chunk ... bench: 696 ns/iter (+/- 22)
x86_64v1, pr
test vec::bench_next_chunk ... bench: 309 ns/iter (+/- 4)
znver2, default
test vec::bench_next_chunk ... bench: 17,272 ns/iter (+/- 117)
znver2, pr
test vec::bench_next_chunk ... bench: 211 ns/iter (+/- 3)
```
The znver2 default impl seems to be slow due to inlining decisions. It goes through `core::array::iter_next_chunk`
which has a deeper call tree.
This obviates the patch that teaches LLVM internals about
_rust_{re,de}alloc functions by putting annotations directly in the IR
for the optimizer.
The sole test change is required to anchor FileCheck to the body of the
`box_uninitialized` method, so it doesn't see the `allocalign` on
`__rust_alloc` and get mad about the string `alloca` showing up. Since I
was there anyway, I added some checks on the attributes to prove the
right attributes got set.
While we're here, we also emit allocator attributes on
__rust_alloc_zeroed. This should allow LLVM to perform more
optimizations for zeroed blocks, and probably fixes#90032. [This
comment](https://github.com/rust-lang/rust/issues/24194#issuecomment-308791157)
mentions "weird UB-like behaviour with bitvec iterators in
rustc_data_structures" so we may need to back this change out if things
go wrong.
The new test cases require LLVM 15, so we copy them into LLVM
14-supporting versions, which we can delete when we drop LLVM 14.
correct the output of a `capacity` method example
The output of this example in std::alloc is different from which shown in the comment. I have tested it on both Linux and Windows.
* Implement IsZero trait for tuples up to 8 IsZero elements;
* Implement IsZero for u8/i8, leading to implementation of it for arrays of them too;
* Add more codegen tests for this optimization.
* Lower size of array for IsZero trait because it fails to inline checks
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,
and that's confusing in my opinion, so let's remove it ^^
A colleague mentioned that they interpreted the old text
as saying that only the pointer and the length are copied.
Add a clause so it is more clear that the pointed to contents
are also copied.
add missing null ptr check in alloc example
`alloc` can return null on OOM, if I understood correctly. So we should never just deref a pointer we get from `alloc`.
Borrow Vec<T, A> as [T]
Hello all,
When `Vec` was parametrized with `A`, the `Borrow` impls were omitted and currently `Vec<T, A>` can't be borrowed as `[T]`. This PR fixes that.
This was probably missed, because the `Borrow` impls are in a different file - `src/alloc/slice.rs`.
We briefly discussed this here: https://github.com/rust-lang/wg-allocators/issues/96 and I was told to go ahead and make a PR :)
I tested this by building the toolchain and building my code that needed the `Borrow` impl against it, but let me know if I should add any tests to this PR.
Stabilize `core::ffi::CStr`, `alloc::ffi::CString`, and friends
Stabilize the `core_c_str` and `alloc_c_string` feature gates.
Change `std::ffi` to re-export these types rather than creating type
aliases, since they now have matching stability.
Stabilize the `core_c_str` and `alloc_c_string` feature gates.
Change `std::ffi` to re-export these types rather than creating type
aliases, since they now have matching stability.
Stabilize `core::ffi:c_*` and rexport in `std::ffi`
This only stabilizes the base types, not the non-zero variants, since
those have their own separate tracking issue and have not gone through
FCP to stabilize.
This only stabilizes the base types, not the non-zero variants, since
those have their own separate tracking issue and have not gone through
FCP to stabilize.
In particular, be clear that it is sound to specify memory not
originating from a previous `Vec` allocation. That is already suggested
in other parts of the documentation about zero-alloc conversions to Box<[T]>.
Incorporate a constraint from `slice::from_raw_parts` that was missing
but needs to be fulfilled, since a `Vec` can be converted into a slice.
Enforce that layout size fits in isize in Layout
As it turns out, enforcing this _in APIs that already enforce `usize` overflow_ is fairly trivial. `Layout::from_size_align_unchecked` continues to "allow" sizes which (when rounded up) would overflow `isize`, but these are now declared as library UB for `Layout`, meaning that consumers of `Layout` no longer have to check this before making an allocation.
(Note that this is "immediate library UB;" IOW it is valid for a future release to make this immediate "language UB," and there is an extant patch to do so, to allow Miri to catch this misuse.)
See also #95252, [Zulip discussion](https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/Layout.20Isn't.20Enforcing.20The.20isize.3A.3AMAX.20Rule).
Fixes https://github.com/rust-lang/rust/issues/95334
Some relevant quotes:
`@eddyb,` https://github.com/rust-lang/rust/pull/95252#issuecomment-1078513769
> [B]ecause of the non-trivial presence of both of these among code published on e.g. crates.io:
>
> 1. **`Layout` "producers" / `GlobalAlloc` "users"**: smart pointers (including `alloc::rc` copies with small tweaks), collections, etc.
> 2. **`Layout` "consumers" / `GlobalAlloc` "providers"**: perhaps fewer of these, but anything built on top of OS APIs like `mmap` will expose `> isize::MAX` allocations (on 32-bit hosts) if they lack extra checks
>
> IMO the only responsible option is to enforce the `isize::MAX` limit in `Layout`, which:
>
> * makes `Layout` _sound_ in terms of only ever allowing allocations where `(alloc_base_ptr: *mut u8).offset(size)` is never UB
> * frees both "producers" and "consumers" of `Layout` from manually reimplementing the checks
> * manual checks can be risky, e.g. if the final size passed to the allocator isn't the one being checked
> * this applies retroactively, fixing the overall soundness of existing code with zero transition period or _any_ changes required from users (as long as going through `Layout` is mandatory, making a "choke point")
>
>
> Feel free to quote this comment onto any relevant issue, I might not be able to keep track of developments.
`@Gankra,` https://github.com/rust-lang/rust/pull/95252#issuecomment-1078556371
> As someone who spent way too much time optimizing libcollections checks for this stuff and tried to splatter docs about it everywhere on the belief that it was a reasonable thing for people to manually take care of: I concede the point, it is not reasonable. I am wholy spiritually defeated by the fact that _liballoc_ of all places is getting this stuff wrong. This isn't throwing shade at the folks who implemented these Rc features, but rather a statement of how impractical it is to expect anyone out in the wider ecosystem to enforce them if _some of the most audited rust code in the library that defines the very notion of allocating memory_ can't even reliably do it.
>
> We need the nuclear option of Layout enforcing this rule. Code that breaks this rule is _deeply_ broken and any "regressions" from changing Layout's contract is a _correctness_ fix. Anyone who disagrees and is sufficiently motivated can go around our backs but the standard library should 100% refuse to enable them.
cc also `@RalfJung` `@rust-lang/wg-allocators.` Even though this technically supersedes #95252, those potential failure points should almost certainly still get nicer panics than just "unwrap failed" (which they would get by this PR).
It might additionally be worth recommending to users of the `Layout` API that they should ideally use `.and_then`/`?` to complete the entire layout calculation, and then `panic!` from a single location at the end of `Layout` manipulation, to reduce the overhead of the checks and optimizations preserving the exact location of each `panic` which are conceptually just one failure: allocation too big.
Probably deserves a T-lang and/or T-libs-api FCP (this technically solidifies the [objects must be no larger than `isize::MAX`](https://rust-lang.github.io/unsafe-code-guidelines/layout/scalars.html#isize-and-usize) rule further, and the UCG document says this hasn't been RFCd) and a crater run. Ideally, no code exists that will start failing with this addition; if it does, it was _likely_ (but not certainly) causing UB.
Changes the raw_vec allocation path, thus deserves a perf run as well.
I suggest hiding whitespace-only changes in the diff view.
Optimize `Vec::insert` for the case where `index == len`.
By skipping the call to `copy` with a zero length. This makes it closer
to `push`.
I did this recently for `SmallVec`
(https://github.com/servo/rust-smallvec/pull/282) and it was a big perf win in
one case. Although I don't have a specific use case in mind, it seems
worth doing it for `Vec` as well.
Things to note:
- In the `index < len` case, the number of conditions checked is
unchanged.
- In the `index == len` case, the number of conditions checked increases
by one, but the more expensive zero-length copy is avoided.
- In the `index > len` case the code now reserves space for the extra
element before panicking. This seems like an unimportant change.
r? `@cuviper`
Make `ThinBox<T>` covariant in `T`
Just like `Box<T>`, we want `ThinBox<T>` to be covariant in `T`, but the
projection in `WithHeader<<T as Pointee>::Metadata>` was making it
invariant. This is now hidden as `WithOpaqueHeader`, which we type-cast
whenever the real `WithHeader<H>` type is needed.
Fixes the problem noted in <https://github.com/rust-lang/rust/issues/92791#issuecomment-1104636249>.
By skipping the call to `copy` with a zero length. This makes it closer
to `push`.
I did this recently for `SmallVec`
(https://github.com/servo/rust-smallvec/pull/282) and it was a big perf win in
one case. Although I don't have a specific use case in mind, it seems
worth doing it for `Vec` as well.
Things to note:
- In the `index < len` case, the number of conditions checked is
unchanged.
- In the `index == len` case, the number of conditions checked increases
by one, but the more expensive zero-length copy is avoided.
- In the `index > len` case the code now reserves space for the extra
element before panicking. This seems like an unimportant change.
Rust 1.62.0 introduced a couple new `unused_imports` warnings
in `no_global_oom_handling` builds, making a total of 5 warnings:
```txt
warning: unused import: `Unsize`
--> library/alloc/src/boxed/thin.rs:6:33
|
6 | use core::marker::{PhantomData, Unsize};
| ^^^^^^
|
= note: `#[warn(unused_imports)]` on by default
warning: unused import: `from_fn`
--> library/alloc/src/string.rs:51:18
|
51 | use core::iter::{from_fn, FusedIterator};
| ^^^^^^^
warning: unused import: `core::ops::Deref`
--> library/alloc/src/vec/into_iter.rs:12:5
|
12 | use core::ops::Deref;
| ^^^^^^^^^^^^^^^^
warning: associated function `shrink` is never used
--> library/alloc/src/raw_vec.rs:424:8
|
424 | fn shrink(&mut self, cap: usize) -> Result<(), TryReserveError> {
| ^^^^^^
|
= note: `#[warn(dead_code)]` on by default
warning: associated function `forget_remaining_elements` is never used
--> library/alloc/src/vec/into_iter.rs:126:19
|
126 | pub(crate) fn forget_remaining_elements(&mut self) {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
```
This patch cleans them so that projects compiling `alloc` without
infallible allocations do not see the warnings. It also enables
the use of `-Dwarnings`.
The couple `dead_code` ones may be reverted when some fallible
allocation support starts using them.
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Implement `Send` and `Sync` for `ThinBox<T>`
Just like `Box<T>`, `ThinBox<T>` owns its data on the heap, so it should
implement `Send` and `Sync` when `T` does.
This extends tracking issue #92791.
Just like `Box<T>`, we want `ThinBox<T>` to be covariant in `T`, but the
projection in `WithHeader<<T as Pointee>::Metadata>` was making it
invariant. This is now hidden as `WithOpaqueHeader`, which we type-cast
whenever the real `WithHeader<H>` type is needed.
Fix `panic` message for `BTreeSet`'s `range` API and document `panic` cases
Currently, the `panic` cases for [`BTreeSet`'s `range` API](https://doc.rust-lang.org/std/collections/struct.BTreeSet.html#method.range) are undocumented and produce a slightly wrong `panic` message (says `BTreeMap` instead of `BTreeSet`).
Panic case 1 code:
```rust
use std::collections::BTreeSet;
use std::ops::Bound::Excluded;
fn main() {
let mut set = BTreeSet::new();
set.insert(3);
set.insert(5);
set.insert(8);
for &elem in set.range((Excluded(&3), Excluded(&3))) {
println!("{elem}");
}
}
```
Panic case 1 message:
```
thread 'main' panicked at 'range start and end are equal and excluded in BTreeMap', /rustc/fe5b13d681f25ee6474be29d748c65adcd91f69e/library/alloc/src/collections/btree/search.rs:105:17
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```
Panic case 2 code:
```rust
use std::collections::BTreeSet;
use std::ops::Bound::Included;
fn main() {
let mut set = BTreeSet::new();
set.insert(3);
set.insert(5);
set.insert(8);
for &elem in set.range((Included(&8), Included(&3))) {
println!("{elem}");
}
}
```
Panic case 2:
```
thread 'main' panicked at 'range start is greater than range end in BTreeMap', /rustc/fe5b13d681f25ee6474be29d748c65adcd91f69e/library/alloc/src/collections/btree/search.rs:110:17
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```
This PR fixes the output messages to say `BTreeSet`, adds the relevant unit tests, and updates the documentation for the API.
clarify Arc::clone overflow check comment
I had to read this twice to realize that this is explaining that the code is technically unsound, so move that into a dedicated paragraph and make the wording a bit more explicit.
Fix documentation for `with_capacity` and `reserve` families of methods
Fixes#95614
Documentation for the following methods
- `with_capacity`
- `with_capacity_in`
- `with_capacity_and_hasher`
- `reserve`
- `reserve_exact`
- `try_reserve`
- `try_reserve_exact`
was inconsistent and often not entirely correct where they existed on the following types
- `Vec`
- `VecDeque`
- `String`
- `OsString`
- `PathBuf`
- `BinaryHeap`
- `HashSet`
- `HashMap`
- `BufWriter`
- `LineWriter`
since the allocator is allowed to allocate more than the requested capacity in all such cases, and will frequently "allocate" much more in the case of zero-sized types (I also checked `BufReader`, but there the docs appear to be accurate as it appears to actually allocate the exact capacity).
Some effort was made to make the documentation more consistent between types as well.
Documentation for the following methods
with_capacity
with_capacity_in
with_capacity_and_hasher
reserve
reserve_exact
try_reserve
try_reserve_exact
was inconsistent and often not entirely correct where they existed on the following types
Vec
VecDeque
String
OsString
PathBuf
BinaryHeap
HashSet
HashMap
BufWriter
LineWriter
since the allocator is allowed to allocate more than the requested capacity in all such cases, and will frequently "allocate" much more in the case of zero-sized types (I also checked BufReader, but there the docs appear to be accurate as it appears to actually allocate the exact capacity).
Some effort was made to make the documentation more consistent between types as well.
Fix with_capacity* methods for Vec
Fix *reserve* methods for Vec
Fix docs for *reserve* methods of VecDeque
Fix docs for String::with_capacity
Fix docs for *reserve* methods of String
Fix docs for OsString::with_capacity
Fix docs for *reserve* methods on OsString
Fix docs for with_capacity* methods on HashSet
Fix docs for *reserve methods of HashSet
Fix docs for with_capacity* methods of HashMap
Fix docs for *reserve methods on HashMap
Fix expect messages about OOM in doctests
Fix docs for BinaryHeap::with_capacity
Fix docs for *reserve* methods of BinaryHeap
Fix typos
Fix docs for with_capacity on BufWriter and LineWriter
Fix consistent use of `hasher` between `HashMap` and `HashSet`
Fix warning in doc test
Add test for capacity of vec with ZST
Fix doc test error
Add VecDeque::extend from TrustedLen specialization
Continuation of #95904
Inspired by how [`VecDeque::copy_slice` works](c08b235a5c/library/alloc/src/collections/vec_deque/mod.rs (L437-L454)).
## Benchmarks
Before
```
test vec_deque::bench_extend_chained_bytes ... bench: 1,026 ns/iter (+/- 17)
test vec_deque::bench_extend_chained_trustedlen ... bench: 1,024 ns/iter (+/- 40)
test vec_deque::bench_extend_trustedlen ... bench: 637 ns/iter (+/- 693)
```
After
```
test vec_deque::bench_extend_chained_bytes ... bench: 828 ns/iter (+/- 24)
test vec_deque::bench_extend_chained_trustedlen ... bench: 25 ns/iter (+/- 1)
test vec_deque::bench_extend_trustedlen ... bench: 21 ns/iter (+/- 0)
```
## Why do it this way
https://rust.godbolt.org/z/15qY1fMYh
The Compiler Explorer example shows how "just" removing the capacity check, like the [`Vec` `TrustedLen` specialization](c08b235a5c/library/alloc/src/vec/spec_extend.rs (L22-L58)) does, wouldn't have been enough for `VecDeque`. `wrap_add` would still have greatly limited what LLVM could do while optimizing.
---
r? `@the8472`
btree: avoid forcing the allocator to be a reference
The previous code forces the actual allocator used to be some `&A`. This generalizes the code to allow any `A: Copy`. If people truly want to use a reference, they can use `&A` themselves.
Fixes https://github.com/rust-lang/rust/issues/98176
Entry and_modify doc
This PR modifies the documentation for [HashMap](https://doc.rust-lang.org/std/collections/struct.HashMap.html#) and [BTreeMap](https://doc.rust-lang.org/std/collections/struct.BTreeMap.html#) by introducing examples for `and_modify`. `and_modify` is a function that tends to give more idiomatic rust code when dealing with these data structures -- yet it lacked examples and was hidden away. This PR adds that and addresses #98122.
I've made some choices which I tried to explain in my commits. This is my first time contributing to rust, so hopefully, I made the right choices.
Updated the btree's documentation to include two references to
add_modify.
The first is when the `Entry` API is mentioned at the beginning. With
the same reasoning as HashMap's documentation, I thought it would best
to keep `attack`, but show the `mana` example.
The second is with the `entry` function that is used for the `Entry`
API. The code example was a perfect use for `add_modify`, which is why
it was changed to reflect that.
BTreeSet: avoid intermediate sorting when collecting sorted iterators
As [pointed out by droundy](https://users.rust-lang.org/t/question-about-btreeset-implementation/76427), an obvious optimization is to skip the first step introduced by #88448 (creation of a vector and sorting) and it's easy to do so for btree's own iterators. Also, exploit `from` in the examples.
Remove migrate borrowck mode
Closes#58781Closes#43234
# Stabilization proposal
This PR proposes the stabilization of `#![feature(nll)]` and the removal of `-Z borrowck`. Current borrow checking behavior of item bodies is currently done by first infering regions *lexically* and reporting any errors during HIR type checking. If there *are* any errors, then MIR borrowck (NLL) never occurs. If there *aren't* any errors, then MIR borrowck happens and any errors there would be reported. This PR removes the lexical region check of item bodies entirely and only uses MIR borrowck. Because MIR borrowck could never *not* be run for a compiled program, this should not break any programs. It does, however, change diagnostics significantly and allows a slightly larger set of programs to compile.
Tracking issue: #43234
RFC: https://github.com/rust-lang/rfcs/blob/master/text/2094-nll.md
Version: 1.63 (2022-06-30 => beta, 2022-08-11 => stable).
## Motivation
Over time, the Rust borrow checker has become "smarter" and thus allowed more programs to compile. There have been three different implementations: AST borrowck, MIR borrowck, and polonius (well, in progress). Additionally, there is the "lexical region resolver", which (roughly) solves the constraints generated through HIR typeck. It is not a full borrow checker, but does emit some errors.
The AST borrowck was the original implementation of the borrow checker and was part of the initially stabilized Rust 1.0. In mid 2017, work began to implement the current MIR borrow checker and that effort ompleted by the end of 2017, for the most part. During 2018, efforts were made to migrate away from the AST borrow checker to the MIR borrow checker - eventually culminating into "migrate" mode - where HIR typeck with lexical region resolving following by MIR borrow checking - being active by default in the 2018 edition.
In early 2019, migrate mode was turned on by default in the 2015 edition as well, but with MIR borrowck errors emitted as warnings. By late 2019, these warnings were upgraded to full errors. This was followed by the complete removal of the AST borrow checker.
In the period since, various errors emitted by the MIR borrow checker have been improved to the point that they are mostly the same or better than those emitted by the lexical region resolver.
While there do remain some degradations in errors (tracked under the [NLL-diagnostics tag](https://github.com/rust-lang/rust/issues?q=is%3Aopen+is%3Aissue+label%3ANLL-diagnostics), those are sufficiently small and rare enough that increased flexibility of MIR borrow check-only is now a worthwhile tradeoff.
## What is stabilized
As said previously, this does not fundamentally change the landscape of accepted programs. However, there are a [few](https://github.com/rust-lang/rust/issues?q=is%3Aopen+is%3Aissue+label%3ANLL-fixed-by-NLL) cases where programs can compile under `feature(nll)`, but not otherwise.
There are two notable patterns that are "fixed" by this stabilization. First, the `scoped_threads` feature, which is a continutation of a pre-1.0 API, can sometimes emit a [weird lifetime error](https://github.com/rust-lang/rust/issues/95527) without NLL. Second, actually seen in the standard library. In the `Extend` impl for `HashMap`, there is an implied bound of `K: 'a` that is available with NLL on but not without - this is utilized in the impl.
As mentioned before, there are a large number of diagnostic differences. Most of them are better, but some are worse. None are serious or happen often enough to need to block this PR. The biggest change is the loss of error code for a number of lifetime errors in favor of more general "lifetime may not live long enough" error. While this may *seem* bad, the former error codes were just attempts to somewhat-arbitrarily bin together lifetime errors of the same type; however, on paper, they end up being roughly the same with roughly the same kinds of solutions.
## What isn't stabilized
This PR does not completely remove the lexical region resolver. In the future, it may be possible to remove that (while still keeping HIR typeck) or to remove it together with HIR typeck.
## Tests
Many test outputs get updated by this PR. However, there are number of tests specifically geared towards NLL under `src/test/ui/nll`
## History
* On 2017-07-14, [tracking issue opened](https://github.com/rust-lang/rust/issues/43234)
* On 2017-07-20, [initial empty MIR pass added](https://github.com/rust-lang/rust/pull/43271)
* On 2017-08-29, [RFC opened](https://github.com/rust-lang/rfcs/pull/2094)
* On 2017-11-16, [Integrate MIR type-checker with NLL](https://github.com/rust-lang/rust/pull/45825)
* On 2017-12-20, [NLL feature complete](https://github.com/rust-lang/rust/pull/46862)
* On 2018-07-07, [Don't run AST borrowck on mir mode](https://github.com/rust-lang/rust/pull/52083)
* On 2018-07-27, [Add migrate mode](https://github.com/rust-lang/rust/pull/52681)
* On 2019-04-22, [Enable migrate mode on 2015 edition](https://github.com/rust-lang/rust/pull/59114)
* On 2019-08-26, [Don't downgrade errors on 2015 edition](https://github.com/rust-lang/rust/pull/64221)
* On 2019-08-27, [Remove AST borrowck](https://github.com/rust-lang/rust/pull/64790)
Avoid zero-sized allocs in ThinBox if T and H are both ZSTs.
This was surprisingly tricky, and took longer to get right than expected. `ThinBox` is a surprisingly subtle piece of code. That said, in the end, a lot of this was due to overthinking[^overthink] -- ultimately the fix ended up fairly clean and simple.
[^overthink]: Honestly, for a while I was convinced this couldn't be done without allocations or runtime branches in these cases, but that's obviously untrue.
Anyway, as a result of spending all that time debugging, I've extended the tests quite a bit, and also added more debug assertions. Many of these helped for subtle bugs I made in the middle (for example, the alloc/drop tracking is because I ended up double-dropping the value in the case where both were ZSTs), they're arguably a bit of overkill at this point, although I imagine they could help in the future too.
Anyway, these tests cover a wide range of size/align cases, nd fully pass under miri[^1]. They also do some smoke-check asserting that the value has the correct alignment, although in practice it's totally within the compiler's rights to delete these assertions since we'd have already done UB if they get hit. They have more boilerplate than they really need, but it's not *too* bad on a per-test basis.
A notable absence from testing is atypical header types, but at the moment it's impossible to manually implement `Pointee`. It would be really nice to have testing here, since it's not 100% obvious to me that the aligned read/write we use for `H` are correct in the face of arbitrary combinations of `size_of::<H>()`, `align_of::<H>()`, and `align_of::<T>()`. (That said, I spent a while thinking through it and am *pretty* sure it's fine -- I'd just feel... better if we could test some cases for non-ZST headers which have unequal and align).
[^1]: Or at least, they pass under miri if I copy the code and tests into a new crate and run miri on it (after making it less stdlibified).
Fixes#96485.
I'd request review ``@yaahc,`` but I believe you're taking some time away from reviews, so I'll request from the previous PR's reviewer (I think that the context helps, even if the actual change didn't end up being bad here).
r? ``@joshtriplett``
Improve documentation for constructors of pinned `Box`es
Adds a cross-references between `Box::pin` and `Box::into_pin` (and other related methods, i.e. the equivalent `From` implementation, and the unstable `pin_in` method), in particular now that `into_pin` [was stabilized](https://github.com/rust-lang/rust/pull/97397). The main goal is to further improve visibility of the fact that `Box<T> -> Pin<Box<T>>` conversion exits in the first place, and that `Box::pin(x)` is – essentially – just a convenience function for `Box::into_pin(Box::new(x))`
The motivating context why I think this is important is even experienced Rust users overlooking the existence this kind of conversion, [e.g. in this thread on IRLO](https://internals.rust-lang.org/t/pre-rfc-function-variants/16732/7?u=steffahn); and also the fact that that discussion brought up that there would be a bunch of Box-construction methods "missing" such as e.g. methods with fallible allocation a la "`Box::try_pin`", and similar; while those are in fact *not* necessary, because you can use `Box::into_pin(Box::try_new(x)?)` instead.
I have *not* included explicit mention of methods (e.g. `try_new`) in the docs of stable methods (e.g. `into_pin`). (Referring to unstable API in stable API docs would be bad style IMO.) Stable examples I have in mind with the statement "constructing a (pinned) Box in a different way than with `Box::new`" are things like cloning a `Box`, or `Box::from_raw`. If/when `try_new` would get stabilized, it would become a very good concrete example use-case of `Box::into_pin` IMO.
Add #[rustc_box] and use it inside alloc
This commit adds an alternative content boxing syntax, and uses it inside alloc.
```Rust
#![feature(box_syntax)]
fn foo() {
let foo = box bar;
}
```
is equivalent to
```Rust
#![feature(rustc_attrs)]
fn foo() {
let foo = #[rustc_box] Box::new(bar);
}
```
The usage inside the very performance relevant code in
liballoc is the only remaining relevant usage of box syntax
in the compiler (outside of tests, which are comparatively easy to port).
box syntax was originally designed to be used by all Rust
developers. This introduces a replacement syntax more tailored
to only being used inside the Rust compiler, and with it,
lays the groundwork for eventually removing box syntax.
[Earlier work](https://github.com/rust-lang/rust/pull/87781#issuecomment-894714878) by `@nbdd0121` to lower `Box::new` to `box` during THIR -> MIR building ran into borrow checker problems, requiring the lowering to be adjusted in a way that led to [performance regressions](https://github.com/rust-lang/rust/pull/87781#issuecomment-894872367). The proposed change in this PR lowers `#[rustc_box] Box::new` -> `box` in the AST -> HIR lowering step, which is way earlier in the compiler, and thus should cause less issues both performance wise as well as regarding type inference/borrow checking/etc. Hopefully, future work can move the lowering further back in the compiler, as long as there are no performance regressions.
Tweak insert docs
For `{Hash, BTree}Map::insert`, I always have to take a few extra seconds to think about the slight weirdness about the fact that if we "did not" insert (which "sounds" false), we return true, and if we "did" insert, (which "sounds" true), we return false.
This tweaks the doc comments for the `insert` methods of those types (as well as what looks like a rustc internal data structure that I found just by searching the codebase for "If the set did") to first use the "Returns whether _something_" pattern used in e.g. `remove`, where we say that `remove` "returns whether the value was present".
alloc: remove repeated word in comment
Linux's `checkpatch.pl` reports:
```txt
#42544: FILE: rust/alloc/vec/mod.rs:2692:
WARNING: Possible repeated word: 'to'
+ // - Elements are :Copy so it's OK to to copy them, without doing
```
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Put a bound on collection misbehavior
As currently written, when a logic error occurs in a collection's trait parameters, this allows *completely arbitrary* misbehavior, so long as it does not cause undefined behavior in std. However, because the extent of misbehavior is not specified, it is allowed for *any* code in std to start misbehaving in arbitrary ways which are not formally UB; consider the theoretical example of a global which gets set on an observed logic error. Because the misbehavior is only bound by not resulting in UB from safe APIs and the crate-level encapsulation boundary of all of std, this makes writing user unsafe code that utilizes std theoretically impossible, as it now relies on undocumented QOI (quality of implementation) that unrelated parts of std cannot be caused to misbehave by a misuse of std::collections APIs.
In practice, this is a nonconcern, because std has reasonable QOI and an implementation that takes advantage of this freedom is essentially a malicious implementation and only compliant by the most langauage-lawyer reading of the documentation.
To close this hole, we just add a small clause to the existing logic error paragraph that ensures that any misbehavior is limited to the collection which observed the logic error, making it more plausible to prove the soundness of user unsafe code.
This is not meant to be formal; a formal refinement would likely need to mention that values derived from the collection can also misbehave after a logic error is observed, as well as define what it means to "observe" a logic error in the first place. This fix errs on the side of informality in order to close the hole without complicating a normal reading which can assume a reasonable nonmalicious QOI.
See also [discussion on IRLO][1].
[1]: https://internals.rust-lang.org/t/using-std-collections-and-unsafe-anything-can-happen/16640
r? rust-lang/libs-api ```@rustbot``` label +T-libs-api -T-libs
This technically adds a new guarantee to the documentation, though I argue as written it's one already implicitly provided.
Clarify the guarantees of Vec::as_ptr and Vec::as_mut_ptr when there's no allocation
Currently the documentation says they return a pointer to the vector's buffer, which has the implied precondition that the vector allocated some memory. However `Vec`'s documentation also specifies that it won't always allocate, so it's unclear whether the pointer returned is valid in that case. Of course you won't be able to read/write actual bytes to/from it since the capacity is 0, but there's an exception: zero sized read/writes. They are still valid as long as the pointer is not null and the memory it points to wasn't deallocated, but `Vec::as_ptr` and `Vec::as_mut_ptr` don't specify that's not the case. This PR thus specifies they are actually valid for zero sized reads since `Vec` is implemented to hold a dangling pointer in those cases, which is neither null nor was deallocated.
Linux's `checkpatch.pl` reports:
```txt
#42544: FILE: rust/alloc/vec/mod.rs:2692:
WARNING: Possible repeated word: 'to'
+ // - Elements are :Copy so it's OK to to copy them, without doing
```
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Document the current aliasing rules for `Box<T>`.
Currently, `Box<T>` gets `noalias`, meaning it has the same rules as `&mut T`. This is sparsely documented, even though it can have quite a big impact on unsafe code using box. Therefore, these rules are documented here, with a big warning that they are not normative and subject to change, since we have not yet committed to an aliasing model and the state of `Box<T>` is especially uncertain.
If you have any suggestions and improvements, make sure to leave them here. This is mostly intended to inform people about what is currently going on (to prevent misunderstandings such as [Jon Gjengset's Box aliasing](https://www.youtube.com/watch?v=EY7Wi9fV5bk)).
This is supposed to _only document current UB_ and not add any new guarantees or rules.
refactor: VecDeques Iter fields to private
Made the fields of VecDeque's Iter private by creating a Iter::new(...) function to create a new instance of Iter and migrating usage to use Iter::new(...).
improve format impl for literals
The basic idea of this change can be seen here https://godbolt.org/z/MT37cWoe1.
Updates the format impl to have a fast path for string literals and the default path for regular format args.
This change will allow `format!("string literal")` to be used interchangably with `"string literal".to_owned()`.
This would be relevant in the case of `f!"string literal"` being legal (https://github.com/rust-lang/rfcs/pull/3267) in which case it would be the easiest way to create owned strings from literals, while also being just as efficient as any other impl
Use Box::new() instead of box syntax in library tests
The tests inside `library/*` have no reason to use `box` syntax as they have 0 performance relevance. Therefore, we can safely remove them (instead of having to use alternatives like the one in #97293).
Finish bumping stage0
It looks like the last time had left some remaining cfg's -- which made me think
that the stage0 bump was actually successful. This brings us to a released 1.62
beta though.
This now brings us to cfg-clean, with the exception of check-cfg-features in bootstrap;
I'd prefer to leave that for a separate PR at this time since it's likely to be more tricky.
cc https://github.com/rust-lang/rust/pull/97147#issuecomment-1132845061
r? `@pietroalbini`
Remove impossible panic note from `Vec::append`
Neither the number of elements in a vector can overflow a `usize`, nor
can the amount of elements in two vectors.
It looks like the last time had left some remaining cfg's -- which made me think
that the stage0 bump was actually successful. This brings us to a released 1.62
beta though.
Currently, `Box<T>` gets `noalias`, meaning it has
the same rules as `&mut T`. This is
sparsely documented, even though it can have quite
a big impact on unsafe code using box. Therefore,
these rules are documented here, with a big warning
that they are not normative and subject to change,
since we have not yet committed to an aliasing model
and the state of `Box<T>` is especially uncertain.
improve case conversion happy path
Someone shared the source code for [Go's string case conversion](19156a5474/src/strings/strings.go (L558-L616)).
It features a hot path for ascii-only strings (although I assume for reasons specific to go, they've opted for a read safe hot loop).
I've borrowed these ideas and also kept our existing code to provide a fast path + seamless utf-8 correct path fallback.
(Naive) Benchmarks can be found here https://github.com/conradludgate/case-conv
For the cases where non-ascii is found near the start, the performance of this algorithm does fall back to original speeds and has not had any measurable speed loss
As currently written, when a logic error occurs in a collection's trait
parameters, this allows *completely arbitrary* misbehavior, so long as
it does not cause undefined behavior in std. However, because the extent
of misbehavior is not specified, it is allowed for *any* code in std to
start misbehaving in arbitrary ways which are not formally UB; consider
the theoretical example of a global which gets set on an observed logic
error. Because the misbehavior is only bound by not resulting in UB from
safe APIs and the crate-level encapsulation boundary of all of std, this
makes writing user unsafe code that utilizes std theoretically
impossible, as it now relies on undocumented QOI that unrelated parts of
std cannot be caused to misbehave by a misuse of std::collections APIs.
In practice, this is a nonconcern, because std has reasonable QOI and an
implementation that takes advantage of this freedom is essentially a
malicious implementation and only compliant by the most langauage-lawyer
reading of the documentation.
To close this hole, we just add a small clause to the existing logic
error paragraph that ensures that any misbehavior is limited to the
collection which observed the logic error, making it more plausible to
prove the soundness of user unsafe code.
This is not meant to be formal; a formal refinement would likely need to
mention that values derived from the collection can also misbehave after a
logic error is observed, as well as define what it means to "observe" a
logic error in the first place. This fix errs on the side of informality
in order to close the hole without complicating a normal reading which
can assume a reasonable nonmalicious QOI.
See also [discussion on IRLO][1].
[1]: https://internals.rust-lang.org/t/using-std-collections-and-unsafe-anything-can-happen/16640
Clarify slice and Vec iteration order
While already being inferable from the doc examples, it wasn't fully specified. This is the only logical way to do a slice iterator, so I think this should be uncontroversial. It also improves the `Vec::into_iter` example to better show the order and that the iterator returns owned values.
Improve codegen of String::retain method
This pull-request improve the codegen of the `String::retain` method.
Using `unwrap_unchecked` helps the optimizer to not generate a panicking path that will never be taken for valid UTF-8 like string.
Using `encode_utf8` saves us from an expensive call to `memcpy`, as the optimizer is unable to realize that `ch_len <= 4` and so can generate much better assembly code.
https://rust.godbolt.org/z/z73ohenfc
Remove libstd's calls to `C-unwind` foreign functions
Remove all libstd and its dependencies' usage of `extern "C-unwind"`.
This is a prerequiste of a WIP PR which will forbid libraries calling `extern "C-unwind"` functions to be compiled in `-Cpanic=unwind` and linked against `panic_abort` (this restriction is necessary to address soundness bug #96926).
Cargo will ensure all crates are compiled with the same `-Cpanic` but the std is only compiled `-Cpanic=unwind` but needs the ability to be linked into `-Cpanic=abort`.
Currently there are two places where `C-unwind` is used in libstd:
* `__rust_start_panic` is used for interfacing to the panic runtime. This could be `extern "Rust"`
* `_{rdl,rg}_oom`: a shim `__rust_alloc_error_handler` will be generated by codegen to call into one of these; they can also be `extern "Rust"` (in fact, the generated shim is used as `extern "Rust"`, so I am not even sure why these are not, probably because they used to `extern "C"` and was changed to `extern "C-unwind"` when we allow alloc error hooks to unwind, but they really should just be using Rust ABI).
For dependencies, there is only one `extern "C-unwind"` function call, in `unwind` crate. This can be expressed as a re-export.
More dicussions can be seen in the Zulip thread: https://rust-lang.zulipchat.com/#narrow/stream/210922-project-ffi-unwind/topic/soundness.20in.20mixed.20panic.20mode
`@rustbot` label: T-libs F-c_unwind
Use default alloc_error_handler for hermit
Hermit now properly separates kernel from userspace.
Applications for hermit can now use Rust's default `alloc_error_handler` instead of calling the kernel's `__rg_oom`.
CC: ``@stlankes``
Add `sub_ptr` on pointers (the `usize` version of `offset_from`)
We have `add`/`sub` which are the `usize` versions of `offset`, this adds the `usize` equivalent of `offset_from`. Like how `.add(d)` replaced a whole bunch of `.offset(d as isize)`, you can see from the changes here that it's fairly common that code actually knows the order between the pointers and *wants* a `usize`, not an `isize`.
As a bonus, this can do `sub nuw`+`udiv exact`, rather than `sub`+`sdiv exact`, which can be optimized slightly better because it doesn't have to worry about negatives. That's why the slice iterators weren't using `offset_from`, though I haven't updated that code in this PR because slices are so perf-critical that I'll do it as its own change.
This is an intrinsic, like `offset_from`, so that it can eventually be allowed in CTFE. It also allows checking the extra safety condition -- see the test confirming that CTFE catches it if you pass the pointers in the wrong order.
Like we have `add`/`sub` which are the `usize` version of `offset`, this adds the `usize` equivalent of `offset_from`. Like how `.add(d)` replaced a whole bunch of `.offset(d as isize)`, you can see from the changes here that it's fairly common that code actually knows the order between the pointers and *wants* a `usize`, not an `isize`.
As a bonus, this can do `sub nuw`+`udiv exact`, rather than `sub`+`sdiv exact`, which can be optimized slightly better because it doesn't have to worry about negatives. That's why the slice iterators weren't using `offset_from`, though I haven't updated that code in this PR because slices are so perf-critical that I'll do it as its own change.
This is an intrinsic, like `offset_from`, so that it can eventually be allowed in CTFE. It also allows checking the extra safety condition -- see the test confirming that CTFE catches it if you pass the pointers in the wrong order.
Implement a lint to warn about unused macro rules
This implements a new lint to warn about unused macro rules (arms/matchers), similar to the `unused_macros` lint added by #41907 that warns about entire macros.
```rust
macro_rules! unused_empty {
(hello) => { println!("Hello, world!") };
() => { println!("empty") }; //~ ERROR: 1st rule of macro `unused_empty` is never used
}
fn main() {
unused_empty!(hello);
}
```
Builds upon #96149 and #96156.
Fixes#73576
Warn on unused `#[doc(hidden)]` attributes on trait impl items
[Zulip conversation](https://rust-lang.zulipchat.com/#narrow/stream/266220-rustdoc/topic/.E2.9C.94.20Validy.20checks.20for.20.60.23.5Bdoc.28hidden.29.5D.60).
Whether an associated item in a trait impl is shown or hidden in the documentation entirely depends on the corresponding item in the trait declaration. Rustdoc completely ignores `#[doc(hidden)]` attributes on impl items. No error or warning is emitted:
```rust
pub trait Tr { fn f(); }
pub struct Ty;
impl Tr for Ty { #[doc(hidden)] fn f() {} }
// ^^^^^^^^^^^^^^ ignored by rustdoc and currently
// no error or warning issued
```
This may lead users to the wrong belief that the attribute has an effect. In fact, several such cases are found in the standard library (I've removed all of them in this PR).
There does not seem to exist any incentive to allow this in the future either: Impl'ing a trait for a type means the type *fully* conforms to its API. Users can add `#[doc(hidden)]` to the whole impl if they want to hide the implementation or add the attribute to the corresponding associated item in the trait declaration to hide the specific item. Hiding an implementation of an associated item does not make much sense: The associated item can still be found on the trait page.
This PR emits the warn-by-default lint `unused_attribute` for this case with a future-incompat warning.
`@rustbot` label T-compiler T-rustdoc A-lint
Remove `#[rustc_deprecated]`
This removes `#[rustc_deprecated]` and introduces diagnostics to help users to the right direction (that being `#[deprecated]`). All uses of `#[rustc_deprecated]` have been converted. CI is expected to fail initially; this requires #95958, which includes converting `stdarch`.
I plan on following up in a short while (maybe a bootstrap cycle?) removing the diagnostics, as they're only intended to be short-term.
Add a dedicated length-prefixing method to `Hasher`
This accomplishes two main goals:
- Make it clear who is responsible for prefix-freedom, including how they should do it
- Make it feasible for a `Hasher` that *doesn't* care about Hash-DoS resistance to get better performance by not hashing lengths
This does not change rustc-hash, since that's in an external crate, but that could potentially use it in future.
Fixes#94026
r? rust-lang/libs
---
The core of this change is the following two new methods on `Hasher`:
```rust
pub trait Hasher {
/// Writes a length prefix into this hasher, as part of being prefix-free.
///
/// If you're implementing [`Hash`] for a custom collection, call this before
/// writing its contents to this `Hasher`. That way
/// `(collection![1, 2, 3], collection![4, 5])` and
/// `(collection![1, 2], collection![3, 4, 5])` will provide different
/// sequences of values to the `Hasher`
///
/// The `impl<T> Hash for [T]` includes a call to this method, so if you're
/// hashing a slice (or array or vector) via its `Hash::hash` method,
/// you should **not** call this yourself.
///
/// This method is only for providing domain separation. If you want to
/// hash a `usize` that represents part of the *data*, then it's important
/// that you pass it to [`Hasher::write_usize`] instead of to this method.
///
/// # Examples
///
/// ```
/// #![feature(hasher_prefixfree_extras)]
/// # // Stubs to make the `impl` below pass the compiler
/// # struct MyCollection<T>(Option<T>);
/// # impl<T> MyCollection<T> {
/// # fn len(&self) -> usize { todo!() }
/// # }
/// # impl<'a, T> IntoIterator for &'a MyCollection<T> {
/// # type Item = T;
/// # type IntoIter = std::iter::Empty<T>;
/// # fn into_iter(self) -> Self::IntoIter { todo!() }
/// # }
///
/// use std:#️⃣:{Hash, Hasher};
/// impl<T: Hash> Hash for MyCollection<T> {
/// fn hash<H: Hasher>(&self, state: &mut H) {
/// state.write_length_prefix(self.len());
/// for elt in self {
/// elt.hash(state);
/// }
/// }
/// }
/// ```
///
/// # Note to Implementers
///
/// If you've decided that your `Hasher` is willing to be susceptible to
/// Hash-DoS attacks, then you might consider skipping hashing some or all
/// of the `len` provided in the name of increased performance.
#[inline]
#[unstable(feature = "hasher_prefixfree_extras", issue = "88888888")]
fn write_length_prefix(&mut self, len: usize) {
self.write_usize(len);
}
/// Writes a single `str` into this hasher.
///
/// If you're implementing [`Hash`], you generally do not need to call this,
/// as the `impl Hash for str` does, so you can just use that.
///
/// This includes the domain separator for prefix-freedom, so you should
/// **not** call `Self::write_length_prefix` before calling this.
///
/// # Note to Implementers
///
/// The default implementation of this method includes a call to
/// [`Self::write_length_prefix`], so if your implementation of `Hasher`
/// doesn't care about prefix-freedom and you've thus overridden
/// that method to do nothing, there's no need to override this one.
///
/// This method is available to be overridden separately from the others
/// as `str` being UTF-8 means that it never contains `0xFF` bytes, which
/// can be used to provide prefix-freedom cheaper than hashing a length.
///
/// For example, if your `Hasher` works byte-by-byte (perhaps by accumulating
/// them into a buffer), then you can hash the bytes of the `str` followed
/// by a single `0xFF` byte.
///
/// If your `Hasher` works in chunks, you can also do this by being careful
/// about how you pad partial chunks. If the chunks are padded with `0x00`
/// bytes then just hashing an extra `0xFF` byte doesn't necessarily
/// provide prefix-freedom, as `"ab"` and `"ab\u{0}"` would likely hash
/// the same sequence of chunks. But if you pad with `0xFF` bytes instead,
/// ensuring at least one padding byte, then it can often provide
/// prefix-freedom cheaper than hashing the length would.
#[inline]
#[unstable(feature = "hasher_prefixfree_extras", issue = "88888888")]
fn write_str(&mut self, s: &str) {
self.write_length_prefix(s.len());
self.write(s.as_bytes());
}
}
```
With updates to the `Hash` implementations for slices and containers to call `write_length_prefix` instead of `write_usize`.
`write_str` defaults to using `write_length_prefix` since, as was pointed out in the issue, the `write_u8(0xFF)` approach is insufficient for hashers that work in chunks, as those would hash `"a\u{0}"` and `"a"` to the same thing. But since `SipHash` works byte-wise (there's an internal buffer to accumulate bytes until a full chunk is available) it overrides `write_str` to continue to use the add-non-UTF-8-byte approach.
---
Compatibility:
Because the default implementation of `write_length_prefix` calls `write_usize`, the changed hash implementation for slices will do the same thing the old one did on existing `Hasher`s.
This accomplishes two main goals:
- Make it clear who is responsible for prefix-freedom, including how they should do it
- Make it feasible for a `Hasher` that *doesn't* care about Hash-DoS resistance to get better performance by not hashing lengths
This does not change rustc-hash, since that's in an external crate, but that could potentially use it in future.
Avoid using `rand::thread_rng` in the stdlib benchmarks.
This is kind of an anti-pattern because it introduces extra nondeterminism for no real reason. In thread_rng's case this comes both from the random seed and also from the reseeding operations it does, which occasionally does syscalls (which adds additional nondeterminism). The impact of this would be pretty small in most cases, but it's a good practice to avoid (particularly because avoiding it was not hard).
Anyway, several of our benchmarks already did the right thing here anyway, so the change was pretty easy and mostly just applying it more universally. That said, the stdlib benchmarks aren't particularly stable (nor is our benchmark framework particularly great), so arguably this doesn't matter that much in practice.
~~Anyway, this also bumps the `rand` dev-dependency to 0.8, since it had fallen somewhat out of date.~~ Nevermind, too much of a headache.
Tweak the vec-calloc runtime check to only apply to shortish-arrays
r? `@Mark-Simulacrum`
`@nbdd0121` pointed out in https://github.com/rust-lang/rust/pull/95362#issuecomment-1114085395 that LLVM currently doesn't constant-fold the `IsZero` check for long arrays, so that seems like a reasonable justification for limiting it.
It appears that it's based on length, not byte size, (https://godbolt.org/z/4s48Y81dP), so that's what I used in the PR. Maybe it's a ["the number of inlining shall be three"](https://youtu.be/s4wnuiCwTGU?t=320) sort of situation.
Certainly there's more that could be done here -- that generated code that checks long arrays byte-by-byte is highly suboptimal, for example -- but this is an easy, low-risk tweak.
