Implement Debug for MaybeUninit #65013

petertodd · 2019-10-02T17:48:41Z

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.

rust-highfive · 2019-10-02T17:48:45Z

r? @withoutboats

(rust_highfive has picked a reviewer for you, use r? to override)

Centril · 2019-10-02T21:32:26Z

cc @RalfJung

src/libcore/mem/maybe_uninit.rs

RalfJung · 2019-10-03T01:55:58Z

No objections from my side; this is mostly a T-libs question IMO.

Centril · 2019-10-03T01:58:08Z

Updated labels accordingly :)

JohnTitor · 2019-10-27T09:00:28Z

Ping from triage: @withoutboats could you review this?

sfackler · 2019-11-07T13:41:27Z

@rfcbot fcp merge

I think it makes sense to me that this wouldn't need a T: Debug bound since there's no way we could ever actually display the T, but let's go through an FCP round to make sure people agree.

rfcbot · 2019-11-07T13:41:28Z

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.

src/libcore/mem/maybe_uninit.rs

Precedent: UnsafeCell implements Debug even though it can't actually display the value.

rfcbot · 2019-11-21T08:12:24Z

🔔 This is now entering its final comment period, as per the review above. 🔔

programmerjake · 2019-11-27T20:53:55Z

Is this intended to be insta-stable, or was that an oversight?

dtolnay · 2019-11-27T20:57:41Z

@programmerjake there is no such thing as an unstable trait impl. The libs team reviewed this and decided to stabilize.

sfackler · 2019-11-28T03:10:38Z

@bors r+

bors · 2019-11-28T03:10:40Z

📌 Commit 8fad66b has been approved by sfackler

bors · 2019-11-28T03:41:34Z

⌛ Testing commit 8fad66b with merge 96ad8e5...

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.

bors · 2019-11-28T06:58:54Z

☀️ Test successful - checks-azure
Approved by: sfackler
Pushing 96ad8e5 to master...

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

Remove `T: Debug` bound on UnsafeCell Debug impl Prior art: rust-lang#65013

rust-highfive assigned withoutboats Oct 2, 2019

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Oct 2, 2019

petertodd force-pushed the 2019-maybeuninit-debug branch from 9aab81b to 5fefbd1 Compare October 2, 2019 17:50

Centril reviewed Oct 2, 2019

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src/libcore/mem/maybe_uninit.rs Outdated Show resolved Hide resolved

Centril added T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. needs-fcp This change is insta-stable, so needs a completed FCP to proceed. labels Oct 3, 2019

Centril added this to the 1.40 milestone Oct 3, 2019

Centril added the relnotes Marks issues that should be documented in the release notes of the next release. label Oct 3, 2019

Centril modified the milestones: 1.40, 1.41 Nov 7, 2019

rfcbot added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Nov 7, 2019

Centril reviewed Nov 7, 2019

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src/libcore/mem/maybe_uninit.rs Outdated Show resolved Hide resolved

Implement Debug for MaybeUninit

8fad66b

Precedent: UnsafeCell implements Debug even though it can't actually display the value.

petertodd force-pushed the 2019-maybeuninit-debug branch from edfd0fa to 8fad66b Compare November 7, 2019 13:51

rfcbot added final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. and removed proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. labels Nov 21, 2019

bors removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Nov 28, 2019

bors added the S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. label Nov 28, 2019

bors added the merged-by-bors This PR was explicitly merged by bors. label Nov 28, 2019

bors merged commit 8fad66b into rust-lang:master Nov 28, 2019

petertodd deleted the 2019-maybeuninit-debug branch November 28, 2019 07:00

rfcbot added finished-final-comment-period The final comment period is finished for this PR / Issue. and removed final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. labels Dec 1, 2019

exrook mentioned this pull request Mar 31, 2021

Remove T: Debug bound on UnsafeCell Debug impl #83707

Merged

Dylan-DPC-zz pushed a commit to Dylan-DPC-zz/rust that referenced this pull request Apr 12, 2021

Rollup merge of rust-lang#83707 - exrook:unsafecell, r=m-ou-se

abb93d3

Remove `T: Debug` bound on UnsafeCell Debug impl Prior art: rust-lang#65013

Dylan-DPC-zz pushed a commit to Dylan-DPC-zz/rust that referenced this pull request Apr 13, 2021

Rollup merge of rust-lang#83707 - exrook:unsafecell, r=m-ou-se

1cc4b6d

Remove `T: Debug` bound on UnsafeCell Debug impl Prior art: rust-lang#65013

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Implement Debug for MaybeUninit #65013

Implement Debug for MaybeUninit #65013

petertodd commented Oct 2, 2019

rust-highfive commented Oct 2, 2019

Centril commented Oct 2, 2019

RalfJung commented Oct 3, 2019

Centril commented Oct 3, 2019

JohnTitor commented Oct 27, 2019

sfackler commented Nov 7, 2019

rfcbot commented Nov 7, 2019 •

edited by withoutboats

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rfcbot commented Nov 21, 2019

programmerjake commented Nov 27, 2019

dtolnay commented Nov 27, 2019

sfackler commented Nov 28, 2019

bors commented Nov 28, 2019

bors commented Nov 28, 2019

bors commented Nov 28, 2019

Implement Debug for MaybeUninit #65013

Implement Debug for MaybeUninit #65013

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petertodd commented Oct 2, 2019

rust-highfive commented Oct 2, 2019

Centril commented Oct 2, 2019

RalfJung commented Oct 3, 2019

Centril commented Oct 3, 2019

JohnTitor commented Oct 27, 2019

sfackler commented Nov 7, 2019

rfcbot commented Nov 7, 2019 • edited by withoutboats Loading

rfcbot commented Nov 21, 2019

programmerjake commented Nov 27, 2019

dtolnay commented Nov 27, 2019

sfackler commented Nov 28, 2019

bors commented Nov 28, 2019

bors commented Nov 28, 2019

bors commented Nov 28, 2019

rfcbot commented Nov 7, 2019 •

edited by withoutboats

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