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A successful advance is now signalled by returning `0` and other values now represent the remaining number
of steps that couldn't be advanced as opposed to the amount of steps that have been advanced during a partial advance_by.
This simplifies adapters a bit, replacing some `match`/`if` with arithmetic. Whether this is beneficial overall depends
on whether `advance_by` is mostly used as a building-block for other iterator methods and adapters or whether
we also see uses by users where `Result` might be more useful.
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Global implements Default so we can use that as bound for all allocators
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This way one can `mem::take()` them out of structs or #[derive(Default)] on structs containing them.
These changes will be insta-stable.
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Signed-off-by: Alex Saveau <saveau.alexandre@gmail.com>
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Fix in-place collection leak when remaining element destructor panic
Fixes #101628
cc `@the8472`
I went for the drop guard route, placing it immediately before the `forget_allocation_drop_remaining` call and after the comment, as to signal they are closely related.
I also updated the test to check for the leak, though the only change really needed was removing the leak clean up for miri since now that's no longer leaked.
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There's a bunch of these checks because of special handing for ZSTs in various unsafe implementations of stuff.
This lets them be `T::IS_ZST` instead of `mem::size_of::<T>() == 0` every time, making them both more readable and more terse.
*Not* proposed for stabilization at this time. Would be `pub(crate)` except `alloc` wants to use it too.
(And while it doesn't matter now, if we ever get something like 85836 making it a const can help codegen be simpler.)
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...replacing `.cast().wrapping_offset().cast()` & similar code.
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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_
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```
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.
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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
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6 | use core::marker::{PhantomData, Unsize};
| ^^^^^^
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= note: `#[warn(unused_imports)]` on by default
warning: unused import: `from_fn`
--> library/alloc/src/string.rs:51:18
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51 | use core::iter::{from_fn, FusedIterator};
| ^^^^^^^
warning: unused import: `core::ops::Deref`
--> library/alloc/src/vec/into_iter.rs:12:5
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12 | use core::ops::Deref;
| ^^^^^^^^^^^^^^^^
warning: associated function `shrink` is never used
--> library/alloc/src/raw_vec.rs:424:8
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424 | fn shrink(&mut self, cap: usize) -> Result<(), TryReserveError> {
| ^^^^^^
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= 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
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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>
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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.
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jhorstmann:fix-double-drop-of-allocator-in-vec-into-iter, r=oli-obk
Fix double drop of allocator in IntoIter impl of Vec
Fixes #95269
The `drop` impl of `IntoIter` reconstructs a `RawVec` from `buf`, `cap` and `alloc`, when that `RawVec` is dropped it also drops the allocator. To avoid dropping the allocator twice we wrap it in `ManuallyDrop` in the `InttoIter` struct.
Note this is my first contribution to the standard library, so I might be missing some details or a better way to solve this.
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Some things like the unwinders and system APIs are not fully conformant,
this only covers a lot of low-hanging fruit.
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Co-authored-by: Daniel Henry-Mantilla <daniel.henry.mantilla@gmail.com>
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Correctly handle supertraits for min_specialization
Supertraits of specialization markers could circumvent checks for
min_specialization. Elaborating predicates prevents this.
r? ````@nikomatsakis````
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Removes the implementations that depend on the user-definable trait `Copy`.
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This method on the Iterator trait is doc(hidden), and about half of
implementations were doc(hidden). This adds the attribute to the
remaining implementations.
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For certain sorts of systems, programming, it's deemed essential that
all allocation failures be explicitly handled where they occur. For
example, see Linus Torvald's opinion in [1]. Merely not calling global
panic handlers, or always `try_reserving` first (for vectors), is not
deemed good enough, because the mere presence of the global OOM handlers
is burdens static analysis.
One option for these projects to use rust would just be to skip `alloc`,
rolling their own allocation abstractions. But this would, in my
opinion be a real shame. `alloc` has a few `try_*` methods already, and
we could easily have more. Features like custom allocator support also
demonstrate and existing to support diverse use-cases with the same
abstractions.
A natural way to add such a feature flag would a Cargo feature, but
there are currently uncertainties around how std library crate's Cargo
features may or not be stable, so to avoid any risk of stabilizing by
mistake we are going with a more low-level "raw cfg" token, which
cannot be interacted with via Cargo alone.
Note also that since there is no notion of "default cfg tokens" outside
of Cargo features, we have to invert the condition from
`global_oom_handling` to to `not(no_global_oom_handling)`. This breaks
the monotonicity that would be important for a Cargo feature (i.e.
turning on more features should never break compatibility), but it
doesn't matter for raw cfg tokens which are not intended to be
"constraint solved" by Cargo or anything else.
To support this use-case we create a new feature, "global-oom-handling",
on by default, and put the global OOM handler infra and everything else
it that depends on it behind it. By default, nothing is changed, but
users concerned about global handling can make sure it is disabled, and
be confident that all OOM handling is local and explicit.
For this first iteration, non-flat collections are outright disabled.
`Vec` and `String` don't yet have `try_*` allocation methods, but are
kept anyways since they can be oom-safely created "from parts", and we
hope to add those `try_` methods in the future.
[1]: https://lore.kernel.org/lkml/CAHk-=wh_sNLoz84AUUzuqXEsYH35u=8HV3vK-jbRbJ_B-JjGrg@mail.gmail.com/
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The `may_have_side_effect` is an implementation detail of `TrustedRandomAccess`
trait. It describes if obtaining an iterator element may have side effects. It
is currently implemented as an associated function.
Turn `may_have_side_effect` into an associated constant. This makes the
value immediately available to the optimizer.
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