Implement Debug for MaybeUninit #65013
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cc @RalfJung |
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No objections from my side; this is mostly a T-libs question IMO. |
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Updated labels accordingly :) |
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Ping from triage: @withoutboats could you review this? |
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@rfcbot fcp merge I think it makes sense to me that this wouldn't need a |
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Team member @sfackler has proposed to merge this. The next step is review by the rest of the tagged team members: No concerns currently listed. Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up! See this document for info about what commands tagged team members can give me. |
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Precedent: UnsafeCell implements Debug even though it can't actually display the value.
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🔔 This is now entering its final comment period, as per the review above. 🔔 |
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Is this intended to be insta-stable, or was that an oversight? |
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@programmerjake there is no such thing as an unstable trait impl. The libs team reviewed this and decided to stabilize. |
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@bors r+ |
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📌 Commit 8fad66b has been approved by |
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Implement Debug for MaybeUninit
Precedent: `UnsafeCell` implements `Debug` even though it can't actually display the value. I noticed this omission while writing the following:
```
#[derive(Debug)]
pub struct SliceInitializer<'a, T> {
marker: PhantomData<&'a mut T>,
uninit: &'a mut [MaybeUninit<T>],
written: usize,
}
```
...which currently unergonomically fails to compile.
`UnsafeCell` does require `T: Debug`. Because of things like the above I think it'd be better to leave that requirement off. In fact, I'd also suggest removing that requirement for `UnsafeCell` too, which again I noticed in some low-level real world code.
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☀️ Test successful - checks-azure |
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Version 1.41.0 (2020-01-30)
===========================
Language
--------
- [You can now pass type parameters to foreign items when implementing
traits.][65879] E.g. You can now write `impl<T> From<Foo> for Vec<T> {}`.
- [You can now arbitrarily nest receiver types in the `self` position.][64325] E.g. you can
now write `fn foo(self: Box<Box<Self>>) {}`. Previously only `Self`, `&Self`,
`&mut Self`, `Arc<Self>`, `Rc<Self>`, and `Box<Self>` were allowed.
- [You can now use any valid identifier in a `format_args` macro.][66847]
Previously identifiers starting with an underscore were not allowed.
- [Visibility modifiers (e.g. `pub`) are now syntactically allowed on trait items and
enum variants.][66183] These are still rejected semantically, but
can be seen and parsed by procedural macros and conditional compilation.
Compiler
--------
- [Rustc will now warn if you have unused loop `'label`s.][66325]
- [Removed support for the `i686-unknown-dragonfly` target.][67255]
- [Added tier 3 support\* for the `riscv64gc-unknown-linux-gnu` target.][66661]
- [You can now pass an arguments file passing the `@path` syntax
to rustc.][66172] Note that the format differs somewhat from what is
found in other tooling; please see [the documentation][argfile-docs] for
more information.
- [You can now provide `--extern` flag without a path, indicating that it is
available from the search path or specified with an `-L` flag.][64882]
\* Refer to Rust's [platform support page][forge-platform-support] for more
information on Rust's tiered platform support.
[argfile-docs]: https://doc.rust-lang.org/nightly/rustc/command-line-arguments.html#path-load-command-line-flags-from-a-path
Libraries
---------
- [The `core::panic` module is now stable.][66771] It was already stable
through `std`.
- [`NonZero*` numerics now implement `From<NonZero*>` if it's a smaller integer
width.][66277] E.g. `NonZeroU16` now implements `From<NonZeroU8>`.
- [`MaybeUninit<T>` now implements `fmt::Debug`.][65013]
Stabilized APIs
---------------
- [`Result::map_or`]
- [`Result::map_or_else`]
- [`std::rc::Weak::weak_count`]
- [`std::rc::Weak::strong_count`]
- [`std::sync::Weak::weak_count`]
- [`std::sync::Weak::strong_count`]
Cargo
-----
- [Cargo will now document all the private items for binary crates
by default.][cargo/7593]
- [`cargo-install` will now reinstall the package if it detects that it is out
of date.][cargo/7560]
- [Cargo.lock now uses a more git friendly format that should help to reduce
merge conflicts.][cargo/7579]
- [You can now override specific dependencies's build settings][cargo/7591] E.g.
`[profile.dev.overrides.image] opt-level = 2` sets the `image` crate's
optimisation level to `2` for debug builds. You can also use
`[profile.<profile>.build_overrides]` to override build scripts and
their dependencies.
Misc
----
- [You can now specify `edition` in documentation code blocks to compile the block
for that edition.][66238] E.g. `edition2018` tells rustdoc that the code sample
should be compiled the 2018 edition of Rust.
- [You can now provide custom themes to rustdoc with `--theme`, and check the
current theme with `--check-theme`.][54733]
- [You can use `#[cfg(doc)]` to compile an item when building documentation.][61351]
Compatibility Notes
-------------------
- [As previously announced 1.41.0 will be the last tier 1 release for 32-bit
Apple targets.][apple-32bit-drop] This means that the source code is still
available to build, but the targets are no longer being tested and release
binaries for those platforms will no longer be distributed by the Rust project.
Please refer to the linked blog post for more information.
[54733]: rust-lang/rust#54733
[61351]: rust-lang/rust#61351
[67255]: rust-lang/rust#67255
[66661]: rust-lang/rust#66661
[66771]: rust-lang/rust#66771
[66847]: rust-lang/rust#66847
[66238]: rust-lang/rust#66238
[66277]: rust-lang/rust#66277
[66325]: rust-lang/rust#66325
[66172]: rust-lang/rust#66172
[66183]: rust-lang/rust#66183
[65879]: rust-lang/rust#65879
[65013]: rust-lang/rust#65013
[64882]: rust-lang/rust#64882
[64325]: rust-lang/rust#64325
[cargo/7560]: rust-lang/cargo#7560
[cargo/7579]: rust-lang/cargo#7579
[cargo/7591]: rust-lang/cargo#7591
[cargo/7593]: rust-lang/cargo#7593
[`Result::map_or_else`]: https://doc.rust-lang.org/std/result/enum.Result.html#method.map_or_else
[`Result::map_or`]: https://doc.rust-lang.org/std/result/enum.Result.html#method.map_or
[`std::rc::Weak::weak_count`]: https://doc.rust-lang.org/std/rc/struct.Weak.html#method.weak_count
[`std::rc::Weak::strong_count`]: https://doc.rust-lang.org/std/rc/struct.Weak.html#method.strong_count
[`std::sync::Weak::weak_count`]: https://doc.rust-lang.org/std/sync/struct.Weak.html#method.weak_count
[`std::sync::Weak::strong_count`]: https://doc.rust-lang.org/std/sync/struct.Weak.html#method.strong_count
[apple-32bit-drop]: https://blog.rust-lang.org/2020/01/03/reducing-support-for-32-bit-apple-targets.html
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Remove `T: Debug` bound on UnsafeCell Debug impl Prior art: rust-lang#65013
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Remove `T: Debug` bound on UnsafeCell Debug impl Prior art: rust-lang#65013
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Precedent:
UnsafeCellimplementsDebugeven though it can't actually display the value. I noticed this omission while writing the following:...which currently unergonomically fails to compile.
UnsafeCelldoes requireT: Debug. Because of things like the above I think it'd be better to leave that requirement off. In fact, I'd also suggest removing that requirement forUnsafeCelltoo, which again I noticed in some low-level real world code.