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Stabilize maybe_uninit_write_slice #148048

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Stabilize maybe_uninit_write_slice #148048

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15 changes: 5 additions & 10 deletions library/core/src/mem/maybe_uninit.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1122,7 +1122,6 @@ impl<T> [MaybeUninit<T>] {
/// # Examples
///
/// ```
/// #![feature(maybe_uninit_write_slice)]
/// use std::mem::MaybeUninit;
///
/// let mut dst = [MaybeUninit::uninit(); 32];
Expand All @@ -1134,8 +1133,6 @@ impl<T> [MaybeUninit<T>] {
/// ```
///
/// ```
/// #![feature(maybe_uninit_write_slice)]
///
/// let mut vec = Vec::with_capacity(32);
/// let src = [0; 16];
///
Expand All @@ -1151,7 +1148,8 @@ impl<T> [MaybeUninit<T>] {
/// ```
///
/// [`write_clone_of_slice`]: slice::write_clone_of_slice
#[unstable(feature = "maybe_uninit_write_slice", issue = "79995")]
#[stable(feature = "maybe_uninit_write_slice", since = "CURRENT_RUSTC_VERSION")]
#[rustc_const_stable(feature = "maybe_uninit_write_slice", since = "CURRENT_RUSTC_VERSION")]
pub const fn write_copy_of_slice(&mut self, src: &[T]) -> &mut [T]
where
T: Copy,
Expand Down Expand Up @@ -1182,7 +1180,6 @@ impl<T> [MaybeUninit<T>] {
/// # Examples
///
/// ```
/// #![feature(maybe_uninit_write_slice)]
/// use std::mem::MaybeUninit;
///
/// let mut dst = [const { MaybeUninit::uninit() }; 5];
Expand All @@ -1197,8 +1194,6 @@ impl<T> [MaybeUninit<T>] {
/// ```
///
/// ```
/// #![feature(maybe_uninit_write_slice)]
///
/// let mut vec = Vec::with_capacity(32);
/// let src = ["rust", "is", "a", "pretty", "cool", "language"].map(|s| s.to_string());
///
Expand All @@ -1214,7 +1209,7 @@ impl<T> [MaybeUninit<T>] {
/// ```
///
/// [`write_copy_of_slice`]: slice::write_copy_of_slice
#[unstable(feature = "maybe_uninit_write_slice", issue = "79995")]
#[stable(feature = "maybe_uninit_write_slice", since = "CURRENT_RUSTC_VERSION")]
pub fn write_clone_of_slice(&mut self, src: &[T]) -> &mut [T]
where
T: Clone,
Expand Down Expand Up @@ -1409,7 +1404,7 @@ impl<T> [MaybeUninit<T>] {
/// # Examples
///
/// ```
/// #![feature(maybe_uninit_as_bytes, maybe_uninit_write_slice, maybe_uninit_slice)]
/// #![feature(maybe_uninit_as_bytes, maybe_uninit_slice)]
/// use std::mem::MaybeUninit;
///
/// let uninit = [MaybeUninit::new(0x1234u16), MaybeUninit::new(0x5678u16)];
Expand All @@ -1436,7 +1431,7 @@ impl<T> [MaybeUninit<T>] {
/// # Examples
///
/// ```
/// #![feature(maybe_uninit_as_bytes, maybe_uninit_write_slice, maybe_uninit_slice)]
/// #![feature(maybe_uninit_as_bytes, maybe_uninit_slice)]
/// use std::mem::MaybeUninit;
///
/// let mut uninit = [MaybeUninit::<u16>::uninit(), MaybeUninit::<u16>::uninit()];
Expand Down
1 change: 0 additions & 1 deletion library/coretests/tests/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -81,7 +81,6 @@
#![feature(lazy_get)]
#![feature(maybe_uninit_fill)]
#![feature(maybe_uninit_uninit_array_transpose)]
#![feature(maybe_uninit_write_slice)]
#![feature(min_specialization)]
#![feature(never_type)]
#![feature(next_index)]
Expand Down
3 changes: 3 additions & 0 deletions library/proc_macro/Cargo.toml
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Expand Up @@ -14,3 +14,6 @@ rustc-literal-escaper = { version = "0.0.5", features = ["rustc-dep-of-std"] }
[features]
default = ["rustc-dep-of-std"]
rustc-dep-of-std = []

[lints.rust]
unexpected_cfgs = { level = "warn", check-cfg = ['cfg(bootstrap)'] }
2 changes: 1 addition & 1 deletion library/proc_macro/src/lib.rs
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Expand Up @@ -22,7 +22,7 @@
#![feature(staged_api)]
#![feature(allow_internal_unstable)]
#![feature(decl_macro)]
#![feature(maybe_uninit_write_slice)]
#![cfg_attr(bootstrap, feature(maybe_uninit_write_slice))]
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@clarfonthey clarfonthey Nov 5, 2025

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Is this actually required? I thought we stopped needing most of these after the latest bootstrap reworks…

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@thaliaarchi thaliaarchi Nov 5, 2025 •
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It appears necessary. With that line removed:

error[E0658]: use of unstable library feature `maybe_uninit_write_slice`
   --> compiler/rustc_proc_macro/../../library/proc_macro/src/bridge/arena.rs:105:27
    |
105 |         let bytes = alloc.write_copy_of_slice(string.as_bytes());
    |                           ^^^^^^^^^^^^^^^^^^^

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@clarfonthey clarfonthey Nov 5, 2025

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Hmm, that's extra strange considering the weird relative library path, but it is what it is. Thanks for verifying.

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@thaliaarchi thaliaarchi Nov 5, 2025

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@jieyouxu Is this behavior expected?

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@jieyouxu jieyouxu Nov 5, 2025

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Yes, proc-macros can be one of those special cases, because see

rust/compiler/rustc_proc_macro/Cargo.toml

Lines 1 to 5 in 6e41e61

# We need to use a separate crate including library/proc_macro as opposed to a
# direct path dependency on library/proc_macro because doing the latter will
# cause two copies of libproc_macro.rlib to end up in the sysroot, breaking
# proc-macro crates. In addition it confuses the workspace_members function of
# bootstrap.

So I believe library/proc_macro can still need cfg-bootstrap bits, but other parts of library should (generally) not need it anymore.

#![feature(negative_impls)]
#![feature(panic_can_unwind)]
#![feature(restricted_std)]
Expand Down
1 change: 0 additions & 1 deletion library/std/src/lib.rs
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Expand Up @@ -351,7 +351,6 @@
#![feature(ip)]
#![feature(lazy_get)]
#![feature(maybe_uninit_slice)]
#![feature(maybe_uninit_write_slice)]
#![feature(panic_can_unwind)]
#![feature(panic_internals)]
#![feature(pin_coerce_unsized_trait)]
Expand Down
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