Document that `ManuallyDrop`'s `Box` interaction has been fixed by WaffleLapkin · Pull Request #155750 · rust-lang/rust

WaffleLapkin · 2026-04-24T18:23:06Z

Both #150447 and #150446 has been merged in 1.96.0, fixing the unfortunate ManuallyDrop<Box<_>> behavior.

rustbot · 2026-04-24T18:23:10Z

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jhpratt · 2026-04-26T05:03:58Z

@bors r+ rollup

rust-bors · 2026-04-26T05:04:01Z

📌 Commit 8520b8e has been approved by jhpratt

It is now in the queue for this repository.

@RalfJung

…r=jhpratt Document that `ManuallyDrop`'s `Box` interaction has been fixed Both rust-lang#150447 and rust-lang#150446 has been merged in `1.96.0`, fixing the unfortunate `ManuallyDrop<Box<_>>` behavior. cc @RalfJung

Rollup of 2 pull requests Successful merges: - #155750 (Document that `ManuallyDrop`'s `Box` interaction has been fixed) - #155774 (std: maintain `CStringArray` null-termination even if `Vec::push` panics)

RalfJung · 2026-04-26T08:52:59Z

@bors r-

Uh no we can't yet make this a stable guarantee I don't think.

rust-bors · 2026-04-26T08:53:06Z

This pull request was unapproved.

This PR was contained in a rollup (#155807), which was unapproved.

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RalfJung · 2026-04-26T08:57:10Z

If we make this a stable guarantee then even if MaybeDangling ends up getting rejected, we are committing to having something like this in the language permanently. This should hence go through FCP, for both lang and libs-api I assume.

nia-e · 2026-04-28T17:36:50Z

This definitely requires signoff from lang, but if they are willing to preserve MaybeDangling or similar semantics into the future we're happy making the API guarantee on the libs-api side per today's meeting ^^

traviscross · 2026-04-29T15:48:14Z

Thanks @WaffleLapkin. Sounds right to me. This is a kind of partial stabilization of RFC 3336.

@rfcbot fcp merge libs-api

WaffleLapkin · 2026-06-15T13:26:49Z

@bors r=jhpratt rollup

rust-bors · 2026-06-15T13:26:52Z

📌 Commit 5afb1df has been approved by jhpratt

It is now in the queue for this repository.

@RalfJung

…r=jhpratt Document that `ManuallyDrop`'s `Box` interaction has been fixed Both rust-lang#150447 and rust-lang#150446 has been merged in `1.96.0`, fixing the unfortunate `ManuallyDrop<Box<_>>` behavior. cc @RalfJung

@RalfJung

…r=jhpratt Document that `ManuallyDrop`'s `Box` interaction has been fixed Both rust-lang#150447 and rust-lang#150446 has been merged in `1.96.0`, fixing the unfortunate `ManuallyDrop<Box<_>>` behavior. cc @RalfJung

Rollup of 13 pull requests Successful merges: - #152544 (Stabilize `int_format_into` feature) - #157507 (fixed: differentiation between uninitialized and possibly uninitialized) - #155750 (Document that `ManuallyDrop`'s `Box` interaction has been fixed) - #157075 (lower edition requirements for some async-closure test helpers) - #157627 (remove LLVM `va_end` calls) - #157660 (normalize instead of evaluating type const patterns) - #157692 (Don't emit `unused_parens` suggestion for proc-macro-synthesized parens around bounds) - #157908 (fix binding const argument to assoc type suggestion) - #157915 (scalable vecs size incl. num vecs + no sret for scalable vecs) - #157916 (Avoid ICE on invalid crate-level cfg_attr predicates) - #157919 (mention in the `extern "tail"` error that it's supported on x86) - #157920 (mailmap: add mu001999) - #157924 (Update books)

@RalfJung

Rollup merge of #155750 - WaffleLapkin:manually-drop-unbox, r=jhpratt Document that `ManuallyDrop`'s `Box` interaction has been fixed Both #150447 and #150446 has been merged in `1.96.0`, fixing the unfortunate `ManuallyDrop<Box<_>>` behavior. cc @RalfJung

theemathas · 2026-06-16T00:41:58Z

@traviscross See #155750 (comment)

traviscross · 2026-06-16T01:52:46Z

Thanks. I didn't see @WaffleLapkin's comment when readding the labels.

At the time that I applied the needs-reference-pr label, originally, it did not block merging (that happened later, as I now see, in #157798), so it was not my intention to block the merge by automated means.

It is my opinion that the Reference needs to be updated for this PR (though I'm not asking anyone else to do that). In fact, RFC 3336, the basis for this stabilization, describes Reference changes it requires. Specifically, we need to update Behavior Considered Undefined. Just as we have carve-outs for UnsafeCell<T>, we need certain carve-outs for ManuallyDrop<T> now. And we should add ManuallyDrop<T> to Special Types and Traits, just as we did for UnsafeCell<T>.

I'm going to add back both labels. This is for @rust-lang/lang-docs tracking.

traviscross · 2026-06-16T01:54:07Z

cc @rust-lang/fls

RalfJung · 2026-08-08T20:15:04Z

This should probably have included @rust-lang/opsem in the FCP... here's a retroactive ping, sorry for the lapse.

This MR contains the following updates: | Package | Type | Update | Change | |---|---|---|---| | [rust](https://github.com/rust-lang/rust) | tools | minor | `1.97.1` → `1.98.0` | MR created with the help of [el-capitano/tools/renovate-bot](https://gitlab.com/el-capitano/tools/renovate-bot). **Proposed changes to behavior should be submitted there as MRs.** --- ### Release Notes <details> <summary>rust-lang/rust (rust)</summary> ### [`v1.98.0`](https://github.com/rust-lang/rust/blob/HEAD/RELEASES.md#Version-1980-2026-08-20) [Compare Source](rust-lang/rust@1.97.1...1.98.0) \========================== <a id="1.98.0-Language"></a> ## Language - [Allow shortening lifetime of `&mut` when unsize-coercing, even in an invariant position.](rust-lang/rust#149219) For example, you can now coerce a `Cell<&'long mut i32>` to a `Cell<&'short mut dyn Send>`. Such shortenings were already previously allowed when coercing a `&mut` to a `&`, or coercing a `&` to a `&`. - [Add deny-by-default `invalid_runtime_symbol_definitions` lint and warn-by-default `suspicious_runtime_symbol_definitions` lint](rust-lang/rust#155521) - The lints currently specifically targets `core` runtime symbols like `memcmp`, `memset`, `strlen`, ... and is planned to be expanded in the next few releases. - [Add warn-by-default `c_void_returns` lint to check `core::ffi::c_void` as a return type](rust-lang/rust#156379) <a id="1.98.0-Platform-Support"></a> ## Platform Support - [Add `powerpc64-unknown-linux-gnuelfv2` as Tier 3](rust-lang/rust#144220) - [Add `aarch64-unknown-linux-pauthtest` as Tier 3 target](rust-lang/rust#155722) - [Promote `thumbv7a-none-eabi` to Tier 2](rust-lang/rust#155763) - [Promote `thumbv7a-none-eabihf` to Tier 2](rust-lang/rust#155763) - [Promote `thumbv7r-none-eabi` to Tier 2](rust-lang/rust#155763) - [Promote `thumbv7r-none-eabihf` to Tier 2](rust-lang/rust#155763) - [Promote `thumbv8r-none-eabihf` to Tier 2](rust-lang/rust#155763) Refer to Rust's [platform support page][platform-support-doc] for more information on Rust's tiered platform support. [platform-support-doc]: https://doc.rust-lang.org/rustc/platform-support.html <a id="1.98.0-Libraries"></a> ## Libraries - [Change `Location<'_>` lifetime to `'static` in `Panic[Hook]Info`](rust-lang/rust#146561) - [Document panic in `RangeInclusive::from(legacy::RangeInclusive)`](rust-lang/rust#155421) - [Document that `ManuallyDrop`'s `Box` interaction has been fixed](rust-lang/rust#155750) - [Stabilize LoongArch CRC Intrinsics](rust-lang/rust#156908) - [The `derive` macro is available at `{core,std}::derive`.](rust-lang/rust#154645) This was previously [unintentionally stabilized in 1.96](rust-lang/rust#159856), but is now [explicitly accepted](rust-lang/rust#154645) as a stabilized API. - Please note that the MSRV for `{core,std}::derive` will be 1.96, and not 1.98. <a id="1.98.0-Stabilized-APIs"></a> ## Stabilized APIs - [`str::substr_range`](https://doc.rust-lang.org/stable/std/primitive.str.html#method.substr_range) - [`[T]::subslice_range`](https://doc.rust-lang.org/stable/std/primitive.slice.html#method.subslice_range) - [`core::fmt::NumBuffer`](https://doc.rust-lang.org/stable/core/fmt/struct.NumBuffer.html) - [`<{integer}>::format_into`](https://doc.rust-lang.org/stable/core/primitive.usize.html#method.format_into) - [`Send/Sync for std::process::CommandArgs`](https://doc.rust-lang.org/stable/std/process/struct.CommandArgs.html#impl-Send-for-CommandArgs%3C'a%3E) - [`{fN}::algebraic_add`](https://doc.rust-lang.org/stable/core/primitive.f32.html#method.algebraic_add) - [`{fN}::algebraic_sub`](https://doc.rust-lang.org/stable/core/primitive.f32.html#method.algebraic_sub) - [`{fN}::algebraic_mul`](https://doc.rust-lang.org/stable/core/primitive.f32.html#method.algebraic_mul) - [`{fN}::algebraic_div`](https://doc.rust-lang.org/stable/core/primitive.f32.html#method.algebraic_div) - [`{fN}::algebraic_rem`](https://doc.rust-lang.org/stable/core/primitive.f32.html#method.algebraic_rem) - [`NonZero<{integer}>::from_str_radix`](https://doc.rust-lang.org/stable/core/num/struct.NonZero.html#method.from_str_radix-4) - [`String::from_utf16le`](https://doc.rust-lang.org/stable/std/string/struct.String.html#method.from_utf16le) - [`String::from_utf16le_lossy`](https://doc.rust-lang.org/stable/std/string/struct.String.html#method.from_utf16le_lossy) - [`String::from_utf16be`](https://doc.rust-lang.org/stable/std/string/struct.String.html#method.from_utf16be) - [`String::from_utf16be_lossy`](https://doc.rust-lang.org/stable/std/string/struct.String.html#method.from_utf16be_lossy) - [`[T]::strip_circumfix`](https://doc.rust-lang.org/stable/core/primitive.slice.html#method.strip_circumfix) - [`str::strip_circumfix`](https://doc.rust-lang.org/stable/core/primitive.str.html#method.strip_circumfix) - [`Atomic<T>::from_mut`](https://doc.rust-lang.org/stable/core/sync/atomic/struct.Atomic.html#method.from_mut) - [`Atomic<T>::get_mut_slice`](https://doc.rust-lang.org/stable/core/sync/atomic/struct.Atomic.html#method.get_mut_slice) - [`Atomic<T>::from_mut_slice`](https://doc.rust-lang.org/stable/core/sync/atomic/struct.Atomic.html#method.from_mut_slice) - [`std::range::legacy`](https://doc.rust-lang.org/stable/std/range/legacy/index.html) <a id="1.98.0-Compatibility-Notes"></a> ## Compatibility Notes - [If fully elided, lifetime bounds of trait object types may now resolve differently or even get rejected in very specific niche scenarios](rust-lang/rust#129543) - [Error in more cases of ambiguous imports](rust-lang/rust#145108) - [Switch the destructors implementation for thread locals on Windows to use Fiber Local Storage (FLS)](rust-lang/rust#148799) - [Convert some cases of the `ambiguous_glob_imports` lint into a hard error](rust-lang/rust#149195) - [Where-bounds of the form `Type = Type` and `Type == Type` are no longer syntactically allowed](rust-lang/rust#153513) - [Ensure Send/Sync is not implemented for std::env::Vars{,Os}](rust-lang/rust#155153) - [Fix that in some attributes, arguments were not properly rejected](rust-lang/rust#155193) - [`repr(transparent)` is now more strict about which fields have "trivial" layout and hence can be ignored: `repr(C)` types, types with private fields, and `#[non_exhaustive]` types are no longer considered "trivial"](rust-lang/rust#155299) - [Correctly check whether types have equal size in `transmute()` when some `repr` attributes are involved.](rust-lang/rust#155418) - [More characters are escaped when printing strings and chars](rust-lang/rust#155527) - [Implement fast path for `derive(PartialOrd)` when deriving `Ord`](rust-lang/rust#155598) This can break crates in practice where a type's PartialOrd and Ord impls were inconsistent with each other. - [Add temporary scope to `assert_eq` and `assert_ne`](rust-lang/rust#155739) - Closed a hole in the pattern matching [structural equality](https://doc.rust-lang.org/reference/patterns.html#constant-patterns) check, preventing cases where a match of a constant would be allowed, despite disagreeing with a manually written `PartialEq` implementation, when a `derive(PartialEq)` implementation for that type also exists. - [On Emscripten the WASM exception handling ABI is now unconditionally used](rust-lang/rust#156928) The `-Zemscripten-wasm-eh=false` flag to switch back to JS exceptions has been removed. - [The UNSAFE\_CODE lint is now consistently emitted for all unsafe attributes](rust-lang/rust#157201) - [Solaris: remove `File::lock` implementation, it has the wrong semantics (return "unsupported" instead)](rust-lang/rust#157509) - [Windows-gnu targets now specify baseline tools versions](rust-lang/rust#158020) - [rustfmt now discovers module files that are defined in `cfg_select!`](rust-lang/rust#158372) This may cause more code to be formatted which was previously ignored. </details> --- ### Configuration 📅 **Schedule**: (UTC) - Branch creation - At any time (no schedule defined) - Automerge - At any time (no schedule defined) 🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied. ♻ **Rebasing**: Whenever MR becomes conflicted, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this MR and you won't be reminded about this update again. --- - [ ] If you want to rebase/retry this MR, check this box --- This MR has been generated by [Mend Renovate](https://github.com/renovatebot/renovate).

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Rollup of 2 pull requests #155807

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Rollup of 8 pull requests #157925

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Add missing CSS for highlighting the labels rust-lang/triagebot#2435

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Rollup of 13 pull requests #157932

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Tracking Issue for MaybeDangling #118166

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