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>.
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>
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.
Relevant commit messages from squashed history in order:
Add initial version of ThinBox
update test to actually capture failure
swap to middle ptr impl based on matthieu-m's design
Fix stack overflow in debug impl
The previous version would take a `&ThinBox<T>` and deref it once, which
resulted in a no-op and the same type, which it would then print causing
an endless recursion. I've switched to calling `deref` by name to let
method resolution handle deref the correct number of times.
I've also updated the Drop impl for good measure since it seemed like it
could be falling prey to the same bug, and I'll be adding some tests to
verify that the drop is happening correctly.
add test to verify drop is behaving
add doc examples and remove unnecessary Pointee bounds
ThinBox: use NonNull
ThinBox: tests for size
Apply suggestions from code review
Co-authored-by: Alphyr <47725341+a1phyr@users.noreply.github.com>
use handle_alloc_error and fix drop signature
update niche and size tests
add cfg for allocating APIs
check null before calculating offset
add test for zst and trial usage
prevent optimizer induced ub in drop and cleanup metadata gathering
account for arbitrary size and alignment metadata
Thank you nika and thomcc!
Update library/alloc/src/boxed/thin.rs
Co-authored-by: Josh Triplett <josh@joshtriplett.org>
Update library/alloc/src/boxed/thin.rs
Co-authored-by: Josh Triplett <josh@joshtriplett.org>
