allow unions with mutable references and tuples of allowed types #97995

RalfJung · 2022-06-11T14:54:26Z

We currently allow shared references in unions, but not mutable references. That seems somewhat inconsistent. So let's allow all references, and while we are at it, let's make sure the set of allowed types is closed under tuples.

This will need T-lang FCP (at least).

Then remove the tagged_unions feature, since we do not plan to stabilize any more of it.
Closes #55149

rust-highfive · 2022-06-11T14:54:29Z

r? @petrochenkov

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

RalfJung · 2022-06-11T14:56:57Z

compiler/rustc_passes/src/stability.rs

+                ) -> bool {
+                    // We don't just accept all !needs_drop fields, due to semver concerns.
+                    match ty.kind() {
+                        ty::TyKind::Ref(..) => true, // references never drop (even mutable refs, which are non-Copy and hence fail the later check)


I noticed that is_trivially_pure_clone_copy is, for some reason, careful around references and raw pointers:

rust/compiler/rustc_middle/src/ty/sty.rs

Line 2340 in 90db033

ty::Ref(_, _, hir::Mutability::Not) | ty::RawPtr(..) => false,

Not sure if that should be a concern here.

at least mutable references can't be cloned or copied, so it makes sense.

Hm, the comment on that calls out custom metadata ("Thin pointers & thin shared references are pure-clone-copy, but for anything with custom metadata it might be more complicated."), which I think makes sense for Copy/Clone -- we might eventually support having metadata be !Copy, I guess. But here we really care about !Drop, not !Copy, and I can't ever see &T/&mut T/*const/*mut gaining any kind of drop impl, so I think we're OK here.

That check is just an optimization though. It could be adjusted once we do have custom metadata.

We already guarantee on stable that all raw ptrs can be duplicated.

we might eventually support having metadata be !Copy, I guess

Not to my understanding, at least not for simply ?Sized (you would need even more opt-outs).

Soveu · 2022-06-11T19:14:05Z

Could we allow also to place unions inside unions? For example this code doesn't compile, because U1 is not Copy.

union U1 {
    a: (),
}

union U2 {
    b: U1,
}

RalfJung · 2022-06-11T19:34:10Z

unions can implement Drop like all other types, so there is no good reason to special-case them.

Soveu · 2022-06-11T20:24:20Z

Good point, and what about arrays? They are a special case of a tuple ([T; 3] == (T, T, T)).

We could also allow slices, so that we don't print E0658 (!Copy types in unions are unstable),
just E0277 (unsized values not allowed in unions).

RalfJung · 2022-06-12T00:18:25Z

Arrays are a bit tricky because of the size 0 case. So I figured I'd start with what is simple an obvious.

joshtriplett · 2022-06-13T07:52:42Z

@rfcbot merge

rfcbot · 2022-06-13T07:52:43Z

Team member @joshtriplett 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.

scottmcm · 2022-06-14T17:19:04Z

Easy +1 on &mut, given that it supports & already.

It's not clear to me that tuples are quite so obvious -- especially if zero-length arrays are non-obvious (#97995 (comment)) then wouldn't zero-length tuples also be non-obvious?

nikomatsakis · 2022-06-14T17:24:03Z

@rfcbot reviewed

nikomatsakis · 2022-06-14T17:34:50Z

Hey @RalfJung -- we were discussing in the @rust-lang/lang meeting today and we had a question.

It seems like we could trivially permit [T; N] so long as T is permitted. (We might later want to add a rule to permit [T; 0] in any situation.) Do you foresee potential complications with that, and -- if so -- what are they? (Or is it just annoying to implement?)

RalfJung · 2022-06-19T16:32:36Z

It seems like we could trivially permit [T; N] so long as T is permitted. (We might later want to add a rule to permit [T; 0] in any situation.) Do you foresee potential complications with that, and -- if so -- what are they? (Or is it just annoying to implement?)

My concern was that I am not sure whether [T; 0] is always Copy, so we need to be very careful here to avoid regressing existing code. But it looks like empty arrays are not always Copy, in which case ignoring the length and just recursing to the field type is I think always correct.

RalfJung · 2022-06-19T16:57:25Z

It seems like we could trivially permit [T; N] so long as T is permitted.

I have now implemented this.

scottmcm · 2022-06-19T23:34:09Z

@rfcbot reviewed

rfcbot · 2022-06-19T23:34:19Z

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

rustbot · 2022-07-13T22:30:16Z

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

RalfJung · 2022-07-13T22:30:27Z

@bors r=Mark-Simulacrum rollup=never

bors · 2022-07-13T22:30:28Z

📌 Commit e43a0de62a6dbe0fab34b59baa0da0453dc29ac3 has been approved by Mark-Simulacrum

It is now in the queue for this repository.

RalfJung · 2022-07-13T22:32:43Z

@bors r=Mark-Simulacrum

bors · 2022-07-13T22:32:44Z

📌 Commit 07fe988 has been approved by Mark-Simulacrum

It is now in the queue for this repository.

bors · 2022-07-13T23:42:08Z

⌛ Testing commit 07fe988 with merge cbb07c2...

bors · 2022-07-14T02:22:43Z

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing cbb07c2 to master...

rust-highfive · 2022-07-14T02:23:11Z

📣 Toolstate changed by #97995!

Tested on commit cbb07c2.
Direct link to PR: #97995

💔 miri on windows: test-pass → test-fail (cc @RalfJung @oli-obk).
💔 miri on linux: test-pass → test-fail (cc @RalfJung @oli-obk).

@RalfJung

Tested on commit rust-lang/rust@cbb07c2. Direct link to PR: <rust-lang/rust#97995> 💔 miri on windows: test-pass → test-fail (cc @RalfJung @oli-obk). 💔 miri on linux: test-pass → test-fail (cc @RalfJung @oli-obk).

rust-timer · 2022-07-14T04:08:20Z

Finished benchmarking commit (cbb07c2): comparison url.

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

Primary benchmarks: no relevant changes found
Secondary benchmarks: mixed results

	mean¹	max	count²
Regressions 😿 (primary)	N/A	N/A	0
Regressions 😿 (secondary)	9.1%	9.1%	1
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	-3.1%	-3.1%	1
All 😿🎉 (primary)	N/A	N/A	0

Cycles

Results

Primary benchmarks: 😿 relevant regression found
Secondary benchmarks: 🎉 relevant improvement found

	mean¹	max	count²
Regressions 😿 (primary)	2.0%	2.0%	1
Regressions 😿 (secondary)	N/A	N/A	0
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	-3.4%	-3.4%	1
All 😿🎉 (primary)	2.0%	2.0%	1

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

@rustbot label: -perf-regression

the arithmetic mean of the percent change ↩ ↩²
number of relevant changes ↩ ↩²

ehuss · 2022-07-16T18:47:00Z

@RalfJung Would you mind posting a PR to the reference to update it for this change? IIUC, this expands the list of allowed fields to Copy, ManuallyDrop, &mut, and tuples containing any combination of those? I'm not sure if there is a term to succinctly refer to what those types are, but there are severally places that could use updating I think:

Unions and drop
this sentence which refers to that collection.
this sentence in the type chapter which also refers to that collection.

Unions with `impl Copy` and `ManuallyDrop` fields have been stabilized by [rust-lang/rust#77547][1] back in 2020, making enabling the feature already unnecessary for us. A few more field types have been added to the allowlist later by [rust-lang/rust#97995][2], which also removed the feature as there was no intent to stabilize more field types. [1]: rust-lang/rust#77547 [2]: rust-lang/rust#97995

a-hosani

Thank you

Pkgsrc changes: * Add patch to fix vendor/kqueue issue (on 32-bit hosts) * Adjust other patches & line numbers * Version bumps & checksum changes. Upstream changes: Version 1.64.0 (2022-09-22) =========================== Language -------- - [Unions with mutable references or tuples of allowed types are now allowed](rust-lang/rust#97995) - It is now considered valid to deallocate memory pointed to by a shared reference `&T` [if every byte in `T` is inside an `UnsafeCell`](rust-lang/rust#98017) - Unused tuple struct fields are now warned against in an allow-by-default lint, [`unused_tuple_struct_fields`] (rust-lang/rust#95977), similar to the existing warning for unused struct fields. This lint will become warn-by-default in the future. Compiler -------- - [Add Nintendo Switch as tier 3 target] (rust-lang/rust#88991) - Refer to Rust's [platform support page][platform-support-doc] for more information on Rust's tiered platform support. - [Only compile `#[used]` as llvm.compiler.used for ELF targets] (rust-lang/rust#93718) - [Add the `--diagnostic-width` compiler flag to define the terminal width.] (rust-lang/rust#95635) - [Add support for link-flavor `rust-lld` for iOS, tvOS and watchOS] (rust-lang/rust#98771) Libraries --------- - [Remove restrictions on compare-exchange memory ordering.] (rust-lang/rust#98383) - You can now `write!` or `writeln!` into an `OsString`: [Implement `fmt::Write` for `OsString`](rust-lang/rust#97915) - [Make RwLockReadGuard covariant] (rust-lang/rust#96820) - [Implement `FusedIterator` for `std::net::[Into]Incoming`] (rust-lang/rust#97300) - [`impl<T: AsRawFd> AsRawFd for {Arc,Box}<T>`] (rust-lang/rust#97437) - [`ptr::copy` and `ptr::swap` are doing untyped copies] (rust-lang/rust#97712) - [Add cgroupv1 support to `available_parallelism`] (rust-lang/rust#97925) - [Mitigate many incorrect uses of `mem::uninitialized`] (rust-lang/rust#99182) Stabilized APIs --------------- - [`future::IntoFuture`] (https://doc.rust-lang.org/stable/std/future/trait.IntoFuture.html) - [`future::poll_fn`] (https://doc.rust-lang.org/stable/std/future/fn.poll_fn.html) - [`task::ready!`] (https://doc.rust-lang.org/stable/std/task/macro.ready.html) - [`num::NonZero*::checked_mul`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroUsize.html#method.checked_mul) - [`num::NonZero*::checked_pow`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroUsize.html#method.checked_pow) - [`num::NonZero*::saturating_mul`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroUsize.html#method.saturating_mul) - [`num::NonZero*::saturating_pow`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroUsize.html#method.saturating_pow) - [`num::NonZeroI*::abs`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroIsize.html#method.abs) - [`num::NonZeroI*::checked_abs`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroIsize.html#method.checked_abs) - [`num::NonZeroI*::overflowing_abs`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroIsize.html#method.overflowing_abs) - [`num::NonZeroI*::saturating_abs`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroIsize.html#method.saturating_abs) - [`num::NonZeroI*::unsigned_abs`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroIsize.html#method.unsigned_abs) - [`num::NonZeroI*::wrapping_abs`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroIsize.html#method.wrapping_abs) - [`num::NonZeroU*::checked_add`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroUsize.html#method.checked_add) - [`num::NonZeroU*::checked_next_power_of_two`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroUsize.html#method.checked_next_power_of_two) - [`num::NonZeroU*::saturating_add`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroUsize.html#method.saturating_add) - [`os::unix::process::CommandExt::process_group`] (https://doc.rust-lang.org/stable/std/os/unix/process/trait.CommandExt.html#tymethod.process_group) - [`os::windows::fs::FileTypeExt::is_symlink_dir`] (https://doc.rust-lang.org/stable/std/os/windows/fs/trait.FileTypeExt.html#tymethod.is_symlink_dir) - [`os::windows::fs::FileTypeExt::is_symlink_file`] (https://doc.rust-lang.org/stable/std/os/windows/fs/trait.FileTypeExt.html#tymethod.is_symlink_file) These types were previously stable in `std::ffi`, but are now also available in `core` and `alloc`: - [`core::ffi::CStr`] (https://doc.rust-lang.org/stable/core/ffi/struct.CStr.html) - [`core::ffi::FromBytesWithNulError`] (https://doc.rust-lang.org/stable/core/ffi/struct.FromBytesWithNulError.html) - [`alloc::ffi::CString`] (https://doc.rust-lang.org/stable/alloc/ffi/struct.CString.html) - [`alloc::ffi::FromVecWithNulError`] (https://doc.rust-lang.org/stable/alloc/ffi/struct.FromVecWithNulError.html) - [`alloc::ffi::IntoStringError`] (https://doc.rust-lang.org/stable/alloc/ffi/struct.IntoStringError.html) - [`alloc::ffi::NulError`] (https://doc.rust-lang.org/stable/alloc/ffi/struct.NulError.html) These types were previously stable in `std::os::raw`, but are now also available in `core::ffi` and `std::ffi`: - [`ffi::c_char`] (https://doc.rust-lang.org/stable/std/ffi/type.c_char.html) - [`ffi::c_double`] (https://doc.rust-lang.org/stable/std/ffi/type.c_double.html) - [`ffi::c_float`] (https://doc.rust-lang.org/stable/std/ffi/type.c_float.html) - [`ffi::c_int`] (https://doc.rust-lang.org/stable/std/ffi/type.c_int.html) - [`ffi::c_long`] (https://doc.rust-lang.org/stable/std/ffi/type.c_long.html) - [`ffi::c_longlong`] (https://doc.rust-lang.org/stable/std/ffi/type.c_longlong.html) - [`ffi::c_schar`] (https://doc.rust-lang.org/stable/std/ffi/type.c_schar.html) - [`ffi::c_short`] (https://doc.rust-lang.org/stable/std/ffi/type.c_short.html) - [`ffi::c_uchar`] (https://doc.rust-lang.org/stable/std/ffi/type.c_uchar.html) - [`ffi::c_uint`] (https://doc.rust-lang.org/stable/std/ffi/type.c_uint.html) - [`ffi::c_ulong`] (https://doc.rust-lang.org/stable/std/ffi/type.c_ulong.html) - [`ffi::c_ulonglong`] (https://doc.rust-lang.org/stable/std/ffi/type.c_ulonglong.html) - [`ffi::c_ushort`] (https://doc.rust-lang.org/stable/std/ffi/type.c_ushort.html) These APIs are now usable in const contexts: - [`slice::from_raw_parts`] (https://doc.rust-lang.org/stable/core/slice/fn.from_raw_parts.html) Cargo ----- - [Packages can now inherit settings from the workspace so that the settings can be centralized in one place.] (rust-lang/cargo#10859) See [`workspace.package`](https://doc.rust-lang.org/nightly/cargo/reference/workspaces.html#the-workspacepackage-table) and [`workspace.dependencies`](https://doc.rust-lang.org/nightly/cargo/reference/workspaces.html#the-workspacedependencies-table) for more details on how to define these common settings. - [Cargo commands can now accept multiple `--target` flags to build for multiple targets at once] (rust-lang/cargo#10766), and the [`build.target`](https://doc.rust-lang.org/nightly/cargo/reference/config.html#buildtarget) config option may now take an array of multiple targets. - [The `--jobs` argument can now take a negative number to count backwards from the max CPUs.] (rust-lang/cargo#10844) - [`cargo add` will now update `Cargo.lock`.] (rust-lang/cargo#10902) - [Added](rust-lang/cargo#10838) the [`--crate-type`](https://doc.rust-lang.org/nightly/cargo/commands/cargo-rustc.html#option-cargo-rustc---crate-type) flag to `cargo rustc` to override the crate type. - [Significantly improved the performance fetching git dependencies from GitHub when using a hash in the `rev` field.] (rust-lang/cargo#10079) Misc ---- - [The `rust-analyzer` rustup component is now available on the stable channel.] (rust-lang/rust#98640) Compatibility Notes ------------------- - The minimum required versions for all `-linux-gnu` targets are now at least kernel 3.2 and glibc 2.17, for targets that previously supported older versions: [Increase the minimum linux-gnu versions](rust-lang/rust#95026) - [Network primitives are now implemented with the ideal Rust layout, not the C system layout] (rust-lang/rust#78802). This can cause problems when transmuting the types. - [Add assertion that `transmute_copy`'s `U` is not larger than `T`] (rust-lang/rust#98839) - [A soundness bug in `BTreeMap` was fixed] (rust-lang/rust#99413) that allowed data it was borrowing to be dropped before the container. - [The Drop behavior of C-like enums cast to ints has changed] (rust-lang/rust#96862). These are already discouraged by a compiler warning. - [Relate late-bound closure lifetimes to parent fn in NLL] (rust-lang/rust#98835) - [Errors at const-eval time are now in future incompatibility reports] (rust-lang/rust#97743) - On the `thumbv6m-none-eabi` target, some incorrect `asm!` statements were erroneously accepted if they used the high registers (r8 to r14) as an input/output operand. [This is no longer accepted] (rust-lang/rust#99155). - [`impl Trait` was accidentally accepted as the associated type value of return-position `impl Trait`] (rust-lang/rust#97346), without fulfilling all the trait bounds of that associated type, as long as the hidden type satisfies said bounds. This has been fixed. Internal Changes ---------------- These changes do not affect any public interfaces of Rust, but they represent significant improvements to the performance or internals of rustc and related tools. - Windows builds now use profile-guided optimization, providing 10-20% improvements to compiler performance: [Utilize PGO for windows x64 rustc dist builds] (rust-lang/rust#96978) - [Stop keeping metadata in memory before writing it to disk] (rust-lang/rust#96544) - [compiletest: strip debuginfo by default for mode=ui] (rust-lang/rust#98140) - Many improvements to generated code for derives, including performance improvements: - [Don't use match-destructuring for derived ops on structs.] (rust-lang/rust#98446) - [Many small deriving cleanups] (rust-lang/rust#98741) - [More derive output improvements] (rust-lang/rust#98758) - [Clarify deriving code](rust-lang/rust#98915) - [Final derive output improvements] (rust-lang/rust#99046) - [Stop injecting `#[allow(unused_qualifications)]` in generated `derive` implementations](rust-lang/rust#99485) - [Improve `derive(Debug)`](rust-lang/rust#98190) - [Bump to clap 3](rust-lang/rust#98213) - [fully move dropck to mir](rust-lang/rust#98641) - [Optimize `Vec::insert` for the case where `index == len`.] (rust-lang/rust#98755) - [Convert rust-analyzer to an in-tree tool] (rust-lang/rust#99603)

Pkgsrc changes: * This package now contains rust-analyzer, so implicitly conflicts with that pkgsrc package. The same goes for the rust-src package. * Add NetBSD/arm6 port * Add unfinished NetBSD/mipsel port * Revert the use of the internal LLVM, should now build with the new pkgsrc LLVM (15). * Add depndence on compat80 for sparc64 to fix the build * Adapt patches * Add CHECK_INTERPRETER_SKIP for a few (mostly unused) files. (A proper fix may come later.) Upstream changes: Version 1.64.0 (2022-09-22) =========================== Language -------- - [Unions with mutable references or tuples of allowed types are now allowed](rust-lang/rust#97995) - It is now considered valid to deallocate memory pointed to by a shared reference `&T` [if every byte in `T` is inside an `UnsafeCell`](rust-lang/rust#98017) - Unused tuple struct fields are now warned against in an allow-by-default lint, [`unused_tuple_struct_fields`] (rust-lang/rust#95977), similar to the existing warning for unused struct fields. This lint will become warn-by-default in the future. Compiler -------- - [Add Nintendo Switch as tier 3 target] (rust-lang/rust#88991) - Refer to Rust's [platform support page][platform-support-doc] for more information on Rust's tiered platform support. - [Only compile `#[used]` as llvm.compiler.used for ELF targets] (rust-lang/rust#93718) - [Add the `--diagnostic-width` compiler flag to define the terminal width.] (rust-lang/rust#95635) - [Add support for link-flavor `rust-lld` for iOS, tvOS and watchOS] (rust-lang/rust#98771) Libraries --------- - [Remove restrictions on compare-exchange memory ordering.] (rust-lang/rust#98383) - You can now `write!` or `writeln!` into an `OsString`: [Implement `fmt::Write` for `OsString`](rust-lang/rust#97915) - [Make RwLockReadGuard covariant] (rust-lang/rust#96820) - [Implement `FusedIterator` for `std::net::[Into]Incoming`] (rust-lang/rust#97300) - [`impl<T: AsRawFd> AsRawFd for {Arc,Box}<T>`] (rust-lang/rust#97437) - [`ptr::copy` and `ptr::swap` are doing untyped copies] (rust-lang/rust#97712) - [Add cgroupv1 support to `available_parallelism`] (rust-lang/rust#97925) - [Mitigate many incorrect uses of `mem::uninitialized`] (rust-lang/rust#99182) Stabilized APIs --------------- - [`future::IntoFuture`] (https://doc.rust-lang.org/stable/std/future/trait.IntoFuture.html) - [`future::poll_fn`] (https://doc.rust-lang.org/stable/std/future/fn.poll_fn.html) - [`task::ready!`] (https://doc.rust-lang.org/stable/std/task/macro.ready.html) - [`num::NonZero*::checked_mul`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroUsize.html#method.checked_mul) - [`num::NonZero*::checked_pow`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroUsize.html#method.checked_pow) - [`num::NonZero*::saturating_mul`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroUsize.html#method.saturating_mul) - [`num::NonZero*::saturating_pow`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroUsize.html#method.saturating_pow) - [`num::NonZeroI*::abs`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroIsize.html#method.abs) - [`num::NonZeroI*::checked_abs`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroIsize.html#method.checked_abs) - [`num::NonZeroI*::overflowing_abs`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroIsize.html#method.overflowing_abs) - [`num::NonZeroI*::saturating_abs`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroIsize.html#method.saturating_abs) - [`num::NonZeroI*::unsigned_abs`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroIsize.html#method.unsigned_abs) - [`num::NonZeroI*::wrapping_abs`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroIsize.html#method.wrapping_abs) - [`num::NonZeroU*::checked_add`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroUsize.html#method.checked_add) - [`num::NonZeroU*::checked_next_power_of_two`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroUsize.html#method.checked_next_power_of_two) - [`num::NonZeroU*::saturating_add`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroUsize.html#method.saturating_add) - [`os::unix::process::CommandExt::process_group`] (https://doc.rust-lang.org/stable/std/os/unix/process/trait.CommandExt.html#tymethod.process_group) - [`os::windows::fs::FileTypeExt::is_symlink_dir`] (https://doc.rust-lang.org/stable/std/os/windows/fs/trait.FileTypeExt.html#tymethod.is_symlink_dir) - [`os::windows::fs::FileTypeExt::is_symlink_file`] (https://doc.rust-lang.org/stable/std/os/windows/fs/trait.FileTypeExt.html#tymethod.is_symlink_file) These types were previously stable in `std::ffi`, but are now also available in `core` and `alloc`: - [`core::ffi::CStr`] (https://doc.rust-lang.org/stable/core/ffi/struct.CStr.html) - [`core::ffi::FromBytesWithNulError`] (https://doc.rust-lang.org/stable/core/ffi/struct.FromBytesWithNulError.html) - [`alloc::ffi::CString`] (https://doc.rust-lang.org/stable/alloc/ffi/struct.CString.html) - [`alloc::ffi::FromVecWithNulError`] (https://doc.rust-lang.org/stable/alloc/ffi/struct.FromVecWithNulError.html) - [`alloc::ffi::IntoStringError`] (https://doc.rust-lang.org/stable/alloc/ffi/struct.IntoStringError.html) - [`alloc::ffi::NulError`] (https://doc.rust-lang.org/stable/alloc/ffi/struct.NulError.html) These types were previously stable in `std::os::raw`, but are now also available in `core::ffi` and `std::ffi`: - [`ffi::c_char`] (https://doc.rust-lang.org/stable/std/ffi/type.c_char.html) - [`ffi::c_double`] (https://doc.rust-lang.org/stable/std/ffi/type.c_double.html) - [`ffi::c_float`] (https://doc.rust-lang.org/stable/std/ffi/type.c_float.html) - [`ffi::c_int`] (https://doc.rust-lang.org/stable/std/ffi/type.c_int.html) - [`ffi::c_long`] (https://doc.rust-lang.org/stable/std/ffi/type.c_long.html) - [`ffi::c_longlong`] (https://doc.rust-lang.org/stable/std/ffi/type.c_longlong.html) - [`ffi::c_schar`] (https://doc.rust-lang.org/stable/std/ffi/type.c_schar.html) - [`ffi::c_short`] (https://doc.rust-lang.org/stable/std/ffi/type.c_short.html) - [`ffi::c_uchar`] (https://doc.rust-lang.org/stable/std/ffi/type.c_uchar.html) - [`ffi::c_uint`] (https://doc.rust-lang.org/stable/std/ffi/type.c_uint.html) - [`ffi::c_ulong`] (https://doc.rust-lang.org/stable/std/ffi/type.c_ulong.html) - [`ffi::c_ulonglong`] (https://doc.rust-lang.org/stable/std/ffi/type.c_ulonglong.html) - [`ffi::c_ushort`] (https://doc.rust-lang.org/stable/std/ffi/type.c_ushort.html) These APIs are now usable in const contexts: - [`slice::from_raw_parts`] (https://doc.rust-lang.org/stable/core/slice/fn.from_raw_parts.html) Cargo ----- - [Packages can now inherit settings from the workspace so that the settings can be centralized in one place.] (rust-lang/cargo#10859) See [`workspace.package`](https://doc.rust-lang.org/nightly/cargo/reference/workspaces.html#the-workspacepackage-table) and [`workspace.dependencies`](https://doc.rust-lang.org/nightly/cargo/reference/workspaces.html#the-workspacedependencies-table) for more details on how to define these common settings. - [Cargo commands can now accept multiple `--target` flags to build for multiple targets at once] (rust-lang/cargo#10766), and the [`build.target`](https://doc.rust-lang.org/nightly/cargo/reference/config.html#buildtarget) config option may now take an array of multiple targets. - [The `--jobs` argument can now take a negative number to count backwards from the max CPUs.] (rust-lang/cargo#10844) - [`cargo add` will now update `Cargo.lock`.] (rust-lang/cargo#10902) - [Added](rust-lang/cargo#10838) the [`--crate-type`](https://doc.rust-lang.org/nightly/cargo/commands/cargo-rustc.html#option-cargo-rustc---crate-type) flag to `cargo rustc` to override the crate type. - [Significantly improved the performance fetching git dependencies from GitHub when using a hash in the `rev` field.] (rust-lang/cargo#10079) Misc ---- - [The `rust-analyzer` rustup component is now available on the stable channel.] (rust-lang/rust#98640) Compatibility Notes ------------------- - The minimum required versions for all `-linux-gnu` targets are now at least kernel 3.2 and glibc 2.17, for targets that previously supported older versions: [Increase the minimum linux-gnu versions](rust-lang/rust#95026) - [Network primitives are now implemented with the ideal Rust layout, not the C system layout] (rust-lang/rust#78802). This can cause problems when transmuting the types. - [Add assertion that `transmute_copy`'s `U` is not larger than `T`] (rust-lang/rust#98839) - [A soundness bug in `BTreeMap` was fixed] (rust-lang/rust#99413) that allowed data it was borrowing to be dropped before the container. - [The Drop behavior of C-like enums cast to ints has changed] (rust-lang/rust#96862). These are already discouraged by a compiler warning. - [Relate late-bound closure lifetimes to parent fn in NLL] (rust-lang/rust#98835) - [Errors at const-eval time are now in future incompatibility reports] (rust-lang/rust#97743) - On the `thumbv6m-none-eabi` target, some incorrect `asm!` statements were erroneously accepted if they used the high registers (r8 to r14) as an input/output operand. [This is no longer accepted] (rust-lang/rust#99155). - [`impl Trait` was accidentally accepted as the associated type value of return-position `impl Trait`] (rust-lang/rust#97346), without fulfilling all the trait bounds of that associated type, as long as the hidden type satisfies said bounds. This has been fixed. Internal Changes ---------------- These changes do not affect any public interfaces of Rust, but they represent significant improvements to the performance or internals of rustc and related tools. - Windows builds now use profile-guided optimization, providing 10-20% improvements to compiler performance: [Utilize PGO for windows x64 rustc dist builds] (rust-lang/rust#96978) - [Stop keeping metadata in memory before writing it to disk] (rust-lang/rust#96544) - [compiletest: strip debuginfo by default for mode=ui] (rust-lang/rust#98140) - Many improvements to generated code for derives, including performance improvements: - [Don't use match-destructuring for derived ops on structs.] (rust-lang/rust#98446) - [Many small deriving cleanups] (rust-lang/rust#98741) - [More derive output improvements] (rust-lang/rust#98758) - [Clarify deriving code](rust-lang/rust#98915) - [Final derive output improvements] (rust-lang/rust#99046) - [Stop injecting `#[allow(unused_qualifications)]` in generated `derive` implementations](rust-lang/rust#99485) - [Improve `derive(Debug)`](rust-lang/rust#98190) - [Bump to clap 3](rust-lang/rust#98213) - [fully move dropck to mir](rust-lang/rust#98641) - [Optimize `Vec::insert` for the case where `index == len`.] (rust-lang/rust#98755) - [Convert rust-analyzer to an in-tree tool] (rust-lang/rust#99603)

rust-highfive assigned petrochenkov Jun 11, 2022

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Tracking issue for RFC 2514, "Union initialization and Drop" #55149

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RalfJung commented Jun 11, 2022

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petrochenkov added S-waiting-on-team Status: Awaiting decision from the relevant subteam (see the T-<team> label). and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 12, 2022

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assigning to a union field can never drop now

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RalfJung force-pushed the union-more-nodrop branch from 7a24f8e to e43a0de Compare July 13, 2022 22:30

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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jul 13, 2022

add array tests, cleanup, tidy, and bless

07fe988

RalfJung force-pushed the union-more-nodrop branch from e43a0de to 07fe988 Compare July 13, 2022 22:32

bors added the merged-by-bors This PR was explicitly merged by bors. label Jul 14, 2022

bors merged commit cbb07c2 into rust-lang:master Jul 14, 2022

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miri no longer builds after rust-lang/rust#97995 #99224

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RalfJung deleted the union-more-nodrop branch July 14, 2022 02:43

RalfJung mentioned this pull request Jul 17, 2022

update union field type rules rust-lang/reference#1238

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carbotaniuman mentioned this pull request Jul 17, 2022

(nightly) internal compiler error: union fields that need dropping should be impossible #99375

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Stabilize THIR unsafeck #117673

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allow unions with mutable references and tuples of allowed types #97995

allow unions with mutable references and tuples of allowed types #97995

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allow unions with mutable references and tuples of allowed types #97995

allow unions with mutable references and tuples of allowed types #97995

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