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r=Mark-Simulacrum
Remove memory leaks in doctests in `core`, `alloc`, and `std`
cc `@RalfJung` https://github.com/rust-lang/rust/issues/126067 https://github.com/rust-lang/miri/issues/3670
Should be no actual *documentation* changes[^1], all added/modified lines in the doctests are hidden with `#`,
This PR splits the existing memory leaks in doctests in `core`, `alloc`, and `std` into two general categories:
1. "Non-focused" memory leaks that are incidental to the thing being documented, and/or are easy to remove, i.e. they are only there because preventing the leak would make the doctest less clear and/or concise.
- These doctests simply have a comment like `# // Prevent leaks for Miri.` above the added line that removes the memory leak.
- [^2]Some of these would perhaps be better as part of the public documentation part of the doctest, to clarify that a memory leak can happen if it is not otherwise mentioned explicitly in the documentation (specifically the ones in `(A)Rc::increment_strong_count(_in)`).
2. "Focused" memory leaks that are intentional and documented, and/or are possibly fragile to remove.
- These doctests have a `# // FIXME` comment above the line that removes the memory leak, with a note that once `-Zmiri-disable-leak-check` can be applied at test granularity, these tests should be "un-unleakified" and have `-Zmiri-disable-leak-check` enabled.
- Some of these are possibly fragile (e.g. unleaking the result of `Vec::leak`) and thus should definitely not be made part of the documentation.
This should be all of the leaks currently in `core` and `alloc`. I only found one leak in `std`, and it was in the first category (excluding the modules `@RalfJung` mentioned in https://github.com/rust-lang/rust/issues/126067 , and reducing the number of iterations of [one test](https://github.com/rust-lang/rust/blob/master/library/std/src/sync/once_lock.rs#L49-L94) from 1000 to 10)
[^1]: assuming [^2] is not added
[^2]: backlink
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If/when `-Zmiri-disable-leak-check` is able to be used at test-granularity, it should applied to these tests instead of unleaking.
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The rules for casting `*mut X<dyn A>` -> `*mut Y<dyn B>` are as follows:
- If `B` has a principal
- `A` must have exactly the same principal (including generics)
- Auto traits of `B` must be a subset of autotraits in `A`
Note that `X<_>` and `Y<_>` can be identity, or arbitrary structs with last field being the dyn type.
The lifetime of the trait object itself (`dyn ... + 'a`) is not checked.
This prevents a few soundness issues with `#![feature(arbitrary_self_types)]` and trait upcasting.
Namely, these checks make sure that vtable is always valid for the pointee.
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Co-authored-by: ltdk <usr@ltdk.xyz>
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Box<[T]> implements FromIterator<T> using Vec<T> + into_boxed_slice().
Add analogous FromIterator implementations for Box<str>
matching the current implementations for String.
Remove the Global allocator requirement for FromIterator<Box<str>> too.
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Document overrides of `clone_from()` in core/std
As mentioned in https://github.com/rust-lang/rust/pull/96979#discussion_r1379502413
Specifically, when an override doesn't just forward to an inner type, document the behavior and that it's preferred over simply assigning a clone of source. Also, change instances where the second parameter is "other" to "source".
I reused some of the wording over and over for similar impls, but I'm not sure that the wording is actually *good*. Would appreciate feedback about that.
Also, now some of these seem to provide pretty specific guarantees about behavior (e.g. will reuse the exact same allocation iff the len is the same), but I was basing it off of the docs for [`Box::clone_from`](https://doc.rust-lang.org/1.75.0/std/boxed/struct.Box.html#method.clone_from-1) - I'm not sure if providing those strong guarantees is actually good or not.
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Specifically, when an override doesn't just forward to an inner type,
document the behavior and that it's preferred over simply assigning
a clone of source. Also, change instances where the second parameter is
"other" to "source".
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Remove useless `'static` bounds on `Box` allocator
#79327 added `'static` bounds to the allocator parameter for various `Box` + `Pin` APIs to ensure soundness. But it was a bit overzealous, some of the bounds aren't actually needed.
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`std::error::Error` -> Trait Implementations: lifetimes consistency improvement
This cleans up `std::error::Error` trait implementations lifetime inconsistency (`'static` -> `'a`)
**Reasoning:**
Trait implementations for `std::error::Error`, like:
`impl From<&str> for Box<dyn Error + 'static, Global>`
`impl<'a> From<&str> for Box<dyn Error + Sync + Send + 'a, Global>`
use different lifetime annotations misleadingly implying using different life annotations here is a conscious, nonaccidental decision.
[(Related forum discussion here)](https://users.rust-lang.org/t/confusing-std-error-source-code/97011/5?u=wiktor)
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#79327 added `'static` bounds to the allocator parameter
for various `Box` + `Pin` APIs to ensure soundness.
But it was a bit overzealous, some of the bounds aren't
actually needed.
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Signed-off-by: Bugen Zhao <i@bugenzhao.com>
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Co-authored-by: David Tolnay <dtolnay@gmail.com>
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Fix `unused_must_use` warning for `Box::from_raw`
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Issue #27732 was closed as a duplicate of #18598.
Signed-off-by: Anders Kaseorg <andersk@mit.edu>
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Make the Box one-liner more descriptive
I would like to avoid a definition that relies on itself.
r? `@GuillaumeGomez`
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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)
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We have `[T; N]: TryFrom<Vec<T>>` and `Box<[T; N]>: TryFrom<Box<[T]>>`, but not the 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**
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