Make `std::mem::needs_drop` accept `?Sized` #97675

nvzqz · 2022-06-03T07:31:00Z

This change attempts to make needs_drop work with types like [u8] and str.

This enables code in types like Arc<T> that was not possible before, such as #97676.

rust-highfive · 2022-06-03T07:31:03Z

Some changes occured to rustc_codegen_cranelift

cc @bjorn3

Some changes occured to rustc_codegen_gcc

cc @antoyo

Hey! It looks like you've submitted a new PR for the library teams!

If this PR contains changes to any rust-lang/rust public library APIs then please comment with r? rust-lang/libs-api @rustbot label +T-libs-api -T-libs to request review from a libs-api team reviewer. If you're unsure where your change falls no worries, just leave it as is and the reviewer will take a look and make a decision to forward on if necessary.

Examples of T-libs-api changes:

Stabilizing library features
Introducing insta-stable changes such as new implementations of existing stable traits on existing stable types
Introducing new or changing existing unstable library APIs (excluding permanently unstable features / features without a tracking issue)
Changing public documentation in ways that create new stability guarantees
Changing observable runtime behavior of library APIs

rust-highfive · 2022-06-03T07:31:04Z

r? @oli-obk

(rust-highfive has picked a reviewer for you, use r? to override)

oli-obk · 2022-06-03T08:02:06Z

The compiler's implementation already supported this. This is solely a libs-api decision on whether to expose it to users, as the change is insta-stable

r? rust-lang/libs-api

oli-obk · 2022-06-03T08:02:28Z

@rustbot label +T-libs-api -T-libs

dtolnay · 2022-06-03T10:13:36Z

@rust-lang/libs-api:
@rfcbot fcp merge

I don't foresee this causing problems. needs_drop is defined as being allowed to be implemented conservatively, so in the worst case making it return true for "weird" unsized types would be okay.

rust/library/core/src/mem/mod.rs

Lines 536 to 540 in 3a90bed

    
           /// This is purely an optimization hint, and may be implemented conservatively: 
        
           /// it may return `true` for types that don't actually need to be dropped. 
        
           /// As such always returning `true` would be a valid implementation of 
        
           /// this function. However if this function actually returns `false`, then you 
        
           /// can be certain dropping `T` has no side effect.

rfcbot · 2022-06-03T10:13:37Z

Team member @dtolnay 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.

compiler/rustc_codegen_cranelift/example/mini_core_hello_world.rs

bjorn3 · 2022-06-03T10:17:27Z

I think this change can be feature gated by introducing a new unstable function with the relaxed bound and merging it back in again once it is stabilized.

clarfonthey · 2022-06-03T23:21:12Z

I think this change can be feature gated by introducing a new unstable function with the relaxed bound and merging it back in again once it is stabilized.

I believe this path would be changing it on the intrinsic without changing it on the mem export, then later also changing the mem export after confidence has built up.

rfcbot · 2022-06-06T14:34:08Z

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

rfcbot · 2022-06-16T14:37:10Z

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

dtolnay · 2022-06-16T15:44:05Z

@bors r+

bors · 2022-06-16T15:44:07Z

📌 Commit 24b1b7c has been approved by dtolnay

Rollup of 5 pull requests Successful merges: - rust-lang#97377 (Do not suggest adding semicolon/changing delimiters for macros in item position that originates in macros) - rust-lang#97675 (Make `std::mem::needs_drop` accept `?Sized`) - rust-lang#98118 (Test NLL fix of bad lifetime inference for reference captured in closure.) - rust-lang#98166 (Add rustdoc-json regression test for rust-lang#98009) - rust-lang#98169 (Keyword docs: Link to wikipedia article for dynamic dispatch) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup

Make `std::mem::needs_drop` accept `?Sized` This change attempts to make `needs_drop` work with types like `[u8]` and `str`. This enables code in types like `Arc<T>` that was not possible before, such as rust-lang#97676.

Pkgsrc changes: * Adjust patches as needed & checksum updates. Upstream changes: Version 1.63.0 (2022-08-11) ========================== Language -------- - [Remove migrate borrowck mode for pre-NLL errors.][95565] - [Modify MIR building to drop repeat expressions with length zero.][95953] - [Remove label/lifetime shadowing warnings.][96296] - [Allow explicit generic arguments in the presence of `impl Trait` args.] [96868] - [Make `cenum_impl_drop_cast` warnings deny-by-default.][97652] - [Prevent unwinding when `-C panic=abort` is used regardless of declared ABI.][96959] - [lub: don't bail out due to empty binders.][97867] Compiler -------- - [Stabilize the `bundle` native library modifier,][95818] also removing the deprecated `static-nobundle` linking kind. - [Add Apple WatchOS compile targets\*.][95243] - [Add a Windows application manifest to rustc-main.][96737] \* Refer to Rust's [platform support page][platform-support-doc] for more information on Rust's tiered platform support. Libraries --------- - [Implement `Copy`, `Clone`, `PartialEq` and `Eq` for `core::fmt::Alignment`.][94530] - [Extend `ptr::null` and `null_mut` to all thin (including extern) types.][94954] - [`impl Read and Write for VecDeque<u8>`.][95632] - [STD support for the Nintendo 3DS.][95897] - [Make write/print macros eagerly drop temporaries.][96455] - [Implement internal traits that enable `[OsStr]::join`.][96881] - [Implement `Hash` for `core::alloc::Layout`.][97034] - [Add capacity documentation for `OsString`.][97202] - [Put a bound on collection misbehavior.][97316] - [Make `std::mem::needs_drop` accept `?Sized`.][97675] - [`impl Termination for Infallible` and then make the `Result` impls of `Termination` more generic.][97803] - [Document Rust's stance on `/proc/self/mem`.][97837] Stabilized APIs --------------- - [`array::from_fn`] - [`Box::into_pin`] - [`BinaryHeap::try_reserve`] - [`BinaryHeap::try_reserve_exact`] - [`OsString::try_reserve`] - [`OsString::try_reserve_exact`] - [`PathBuf::try_reserve`] - [`PathBuf::try_reserve_exact`] - [`Path::try_exists`] - [`Ref::filter_map`] - [`RefMut::filter_map`] - [`NonNull::<[T]>::len`][`NonNull::<slice>::len`] - [`ToOwned::clone_into`] - [`Ipv6Addr::to_ipv4_mapped`] - [`unix::io::AsFd`] - [`unix::io::BorrowedFd<'fd>`] - [`unix::io::OwnedFd`] - [`windows::io::AsHandle`] - [`windows::io::BorrowedHandle<'handle>`] - [`windows::io::OwnedHandle`] - [`windows::io::HandleOrInvalid`] - [`windows::io::HandleOrNull`] - [`windows::io::InvalidHandleError`] - [`windows::io::NullHandleError`] - [`windows::io::AsSocket`] - [`windows::io::BorrowedSocket<'handle>`] - [`windows::io::OwnedSocket`] - [`thread::scope`] - [`thread::Scope`] - [`thread::ScopedJoinHandle`] These APIs are now usable in const contexts: - [`array::from_ref`] - [`slice::from_ref`] - [`intrinsics::copy`] - [`intrinsics::copy_nonoverlapping`] - [`<*const T>::copy_to`] - [`<*const T>::copy_to_nonoverlapping`] - [`<*mut T>::copy_to`] - [`<*mut T>::copy_to_nonoverlapping`] - [`<*mut T>::copy_from`] - [`<*mut T>::copy_from_nonoverlapping`] - [`str::from_utf8`] - [`Utf8Error::error_len`] - [`Utf8Error::valid_up_to`] - [`Condvar::new`] - [`Mutex::new`] - [`RwLock::new`] Cargo ----- - [Stabilize the `--config path` command-line argument.][cargo/10755] - [Expose rust-version in the environment as `CARGO_PKG_RUST_VERSION`.][cargo/10713] Compatibility Notes ------------------- - [`#[link]` attributes are now checked more strictly,][96885] which may introduce errors for invalid attribute arguments that were previously ignored. Internal Changes ---------------- These changes provide no direct user facing benefits, but represent significant improvements to the internals and overall performance of rustc and related tools. - [Prepare Rust for LLVM opaque pointers.][94214] [94214]: rust-lang/rust#94214 [94530]: rust-lang/rust#94530 [94954]: rust-lang/rust#94954 [95243]: rust-lang/rust#95243 [95565]: rust-lang/rust#95565 [95632]: rust-lang/rust#95632 [95818]: rust-lang/rust#95818 [95897]: rust-lang/rust#95897 [95953]: rust-lang/rust#95953 [96296]: rust-lang/rust#96296 [96455]: rust-lang/rust#96455 [96737]: rust-lang/rust#96737 [96868]: rust-lang/rust#96868 [96881]: rust-lang/rust#96881 [96885]: rust-lang/rust#96885 [96959]: rust-lang/rust#96959 [97034]: rust-lang/rust#97034 [97202]: rust-lang/rust#97202 [97316]: rust-lang/rust#97316 [97652]: rust-lang/rust#97652 [97675]: rust-lang/rust#97675 [97803]: rust-lang/rust#97803 [97837]: rust-lang/rust#97837 [97867]: rust-lang/rust#97867 [cargo/10713]: rust-lang/cargo#10713 [cargo/10755]: rust-lang/cargo#10755 [`array::from_fn`]: https://doc.rust-lang.org/stable/std/array/fn.from_fn.html [`Box::into_pin`]: https://doc.rust-lang.org/stable/std/boxed/struct.Box.html#method.into_pin [`BinaryHeap::try_reserve_exact`]: https://doc.rust-lang.org/stable/alloc/collections/binary_heap/struct.BinaryHeap.html#method.try_reserve_exact [`BinaryHeap::try_reserve`]: https://doc.rust-lang.org/stable/std/collections/struct.BinaryHeap.html#method.try_reserve [`OsString::try_reserve`]: https://doc.rust-lang.org/stable/std/ffi/struct.OsString.html#method.try_reserve [`OsString::try_reserve_exact`]: https://doc.rust-lang.org/stable/std/ffi/struct.OsString.html#method.try_reserve_exact [`PathBuf::try_reserve`]: https://doc.rust-lang.org/stable/std/path/struct.PathBuf.html#method.try_reserve [`PathBuf::try_reserve_exact`]: https://doc.rust-lang.org/stable/std/path/struct.PathBuf.html#method.try_reserve_exact [`Path::try_exists`]: https://doc.rust-lang.org/stable/std/path/struct.Path.html#method.try_exists [`Ref::filter_map`]: https://doc.rust-lang.org/stable/std/cell/struct.Ref.html#method.filter_map [`RefMut::filter_map`]: https://doc.rust-lang.org/stable/std/cell/struct.RefMut.html#method.filter_map [`NonNull::<slice>::len`]: https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.len [`ToOwned::clone_into`]: https://doc.rust-lang.org/stable/std/borrow/trait.ToOwned.html#method.clone_into [`Ipv6Addr::to_ipv4_mapped`]: https://doc.rust-lang.org/stable/std/net/struct.Ipv6Addr.html#method.to_ipv4_mapped [`unix::io::AsFd`]: https://doc.rust-lang.org/stable/std/os/unix/io/trait.AsFd.html [`unix::io::BorrowedFd<'fd>`]: https://doc.rust-lang.org/stable/std/os/unix/io/struct.BorrowedFd.html [`unix::io::OwnedFd`]: https://doc.rust-lang.org/stable/std/os/unix/io/struct.OwnedFd.html [`windows::io::AsHandle`]: https://doc.rust-lang.org/stable/std/os/windows/io/trait.AsHandle.html [`windows::io::BorrowedHandle<'handle>`]: https://doc.rust-lang.org/stable/std/os/windows/io/struct.BorrowedHandle.html [`windows::io::OwnedHandle`]: https://doc.rust-lang.org/stable/std/os/windows/io/struct.OwnedHandle.html [`windows::io::HandleOrInvalid`]: https://doc.rust-lang.org/stable/std/os/windows/io/struct.HandleOrInvalid.html [`windows::io::HandleOrNull`]: https://doc.rust-lang.org/stable/std/os/windows/io/struct.HandleOrNull.html [`windows::io::InvalidHandleError`]: https://doc.rust-lang.org/stable/std/os/windows/io/struct.InvalidHandleError.html [`windows::io::NullHandleError`]: https://doc.rust-lang.org/stable/std/os/windows/io/struct.NullHandleError.html [`windows::io::AsSocket`]: https://doc.rust-lang.org/stable/std/os/windows/io/trait.AsSocket.html [`windows::io::BorrowedSocket<'handle>`]: https://doc.rust-lang.org/stable/std/os/windows/io/struct.BorrowedSocket.html [`windows::io::OwnedSocket`]: https://doc.rust-lang.org/stable/std/os/windows/io/struct.OwnedSocket.html [`thread::scope`]: https://doc.rust-lang.org/stable/std/thread/fn.scope.html [`thread::Scope`]: https://doc.rust-lang.org/stable/std/thread/struct.Scope.html [`thread::ScopedJoinHandle`]: https://doc.rust-lang.org/stable/std/thread/struct.ScopedJoinHandle.html [`array::from_ref`]: https://doc.rust-lang.org/stable/std/array/fn.from_ref.html [`slice::from_ref`]: https://doc.rust-lang.org/stable/std/slice/fn.from_ref.html [`intrinsics::copy`]: https://doc.rust-lang.org/stable/std/intrinsics/fn.copy.html [`intrinsics::copy_nonoverlapping`]: https://doc.rust-lang.org/stable/std/intrinsics/fn.copy_nonoverlapping.html [`<*const T>::copy_to`]: https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.copy_to [`<*const T>::copy_to_nonoverlapping`]: https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.copy_to_nonoverlapping [`<*mut T>::copy_to`]: https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.copy_to-1 [`<*mut T>::copy_to_nonoverlapping`]: https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.copy_to_nonoverlapping-1 [`<*mut T>::copy_from`]: https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.copy_from [`<*mut T>::copy_from_nonoverlapping`]: https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.copy_from_nonoverlapping [`str::from_utf8`]: https://doc.rust-lang.org/stable/std/str/fn.from_utf8.html [`Utf8Error::error_len`]: https://doc.rust-lang.org/stable/std/str/struct.Utf8Error.html#method.error_len [`Utf8Error::valid_up_to`]: https://doc.rust-lang.org/stable/std/str/struct.Utf8Error.html#method.valid_up_to [`Condvar::new`]: https://doc.rust-lang.org/stable/std/sync/struct.Condvar.html#method.new [`Mutex::new`]: https://doc.rust-lang.org/stable/std/sync/struct.Mutex.html#method.new [`RwLock::new`]: https://doc.rust-lang.org/stable/std/sync/struct.RwLock.html#method.new

Make `std::mem::needs_drop` accept `?Sized` This change attempts to make `needs_drop` work with types like `[u8]` and `str`. This enables code in types like `Arc<T>` that was not possible before, such as rust-lang#97676.

Make std::mem::needs_drop accept ?Sized

fd38f66

rust-highfive assigned oli-obk Jun 3, 2022

rustbot added T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Jun 3, 2022

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jun 3, 2022

nvzqz mentioned this pull request Jun 3, 2022

Inline Arc and Rc dealloc for T: !Drop #97676

Closed

rust-highfive assigned dtolnay and unassigned oli-obk Jun 3, 2022

rustbot added T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. and removed T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Jun 3, 2022

dtolnay added needs-fcp This change is insta-stable, so needs a completed FCP to proceed. and removed T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jun 3, 2022

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 Jun 3, 2022

bjorn3 reviewed Jun 3, 2022

View reviewed changes

compiler/rustc_codegen_cranelift/example/mini_core_hello_world.rs Show resolved Hide resolved

Fix unsized field order

24b1b7c

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 Jun 6, 2022

apiraino removed the to-announce Announce this issue on triage meeting label Jun 16, 2022

dtolnay approved these changes Jun 16, 2022

View reviewed changes

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 16, 2022

JohnTitor mentioned this pull request Jun 16, 2022

Rollup of 5 pull requests #98181

Merged

bors merged commit cf68fd7 into rust-lang:master Jun 17, 2022

rustbot added this to the 1.63.0 milestone Jun 17, 2022

nvzqz deleted the unsized-needs-drop branch June 17, 2022 02:33

rust-timer mentioned this pull request Mar 8, 2023

Rollup of 7 pull requests #108877

Merged

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Make `std::mem::needs_drop` accept `?Sized` #97675

Make `std::mem::needs_drop` accept `?Sized` #97675

nvzqz commented Jun 3, 2022 •

edited

Loading

rust-highfive commented Jun 3, 2022

rust-highfive commented Jun 3, 2022

oli-obk commented Jun 3, 2022

oli-obk commented Jun 3, 2022

dtolnay commented Jun 3, 2022

rfcbot commented Jun 3, 2022 •

edited by m-ou-se

Loading

bjorn3 commented Jun 3, 2022

clarfonthey commented Jun 3, 2022

rfcbot commented Jun 6, 2022

rfcbot commented Jun 16, 2022

dtolnay commented Jun 16, 2022

bors commented Jun 16, 2022

Make std::mem::needs_drop accept ?Sized #97675

Make std::mem::needs_drop accept ?Sized #97675

Conversation

nvzqz commented Jun 3, 2022 • edited Loading

rust-highfive commented Jun 3, 2022

rust-highfive commented Jun 3, 2022

oli-obk commented Jun 3, 2022

oli-obk commented Jun 3, 2022

dtolnay commented Jun 3, 2022

rfcbot commented Jun 3, 2022 • edited by m-ou-se Loading

bjorn3 commented Jun 3, 2022

clarfonthey commented Jun 3, 2022

rfcbot commented Jun 6, 2022

rfcbot commented Jun 16, 2022

dtolnay commented Jun 16, 2022

bors commented Jun 16, 2022

Make `std::mem::needs_drop` accept `?Sized` #97675

Make `std::mem::needs_drop` accept `?Sized` #97675

nvzqz commented Jun 3, 2022 •

edited

Loading

rfcbot commented Jun 3, 2022 •

edited by m-ou-se

Loading