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Rollup merge of #89726 - jkugelman:must-use-alloc-constructors, r=joshtriplett

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Add #[must_use] to alloc constructors

Added `#[must_use]`. to the various forms of `new`, `pin`, and `with_capacity` in the `alloc` crate. No extra explanations given as I couldn't think of anything useful to add.

I figure this deserves extra scrutiny compared to the other PRs I've done so far. In particular:

* The 4 `pin`/`pin_in` methods I touched. Are there legitimate use cases for pinning and not using the result? Pinning's a difficult concept I'm not very comfortable with.
* `Box`'s constructors. Do people ever create boxes just for the side effects... allocating or zeroing out memory?

Parent issue: #89692

r? ``@joshtriplett``
This commit is contained in:
Guillaume Gomez 2021-10-11 14:11:42 +02:00 • committed by GitHub
commit d7c9693401
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12 changed files with 40 additions and 2 deletions
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6
library/alloc/src/rc.rs
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@ -452,6 +452,7 @@ impl<T> Rc<T> {
/// ```
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "new_uninit", issue = "63291")]
#[must_use]
pub fn new_uninit() -> Rc<mem::MaybeUninit<T>> {
unsafe {
Rc::from_ptr(Rc::allocate_for_layout(
@ -484,6 +485,7 @@ impl<T> Rc<T> {
/// [zeroed]: mem::MaybeUninit::zeroed
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "new_uninit", issue = "63291")]
#[must_use]
pub fn new_zeroed() -> Rc<mem::MaybeUninit<T>> {
unsafe {
Rc::from_ptr(Rc::allocate_for_layout(
@ -587,6 +589,7 @@ impl<T> Rc<T> {
/// `value` will be pinned in memory and unable to be moved.
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "pin", since = "1.33.0")]
#[must_use]
pub fn pin(value: T) -> Pin<Rc<T>> {
unsafe { Pin::new_unchecked(Rc::new(value)) }
}
@ -658,6 +661,7 @@ impl<T> Rc<[T]> {
/// ```
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "new_uninit", issue = "63291")]
#[must_use]
pub fn new_uninit_slice(len: usize) -> Rc<[mem::MaybeUninit<T>]> {
unsafe { Rc::from_ptr(Rc::allocate_for_slice(len)) }
}
@ -684,6 +688,7 @@ impl<T> Rc<[T]> {
/// [zeroed]: mem::MaybeUninit::zeroed
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "new_uninit", issue = "63291")]
#[must_use]
pub fn new_zeroed_slice(len: usize) -> Rc<[mem::MaybeUninit<T>]> {
unsafe {
Rc::from_ptr(Rc::allocate_for_layout(
@ -2044,6 +2049,7 @@ impl<T> Weak<T> {
/// assert!(empty.upgrade().is_none());
/// ```
#[stable(feature = "downgraded_weak", since = "1.10.0")]
#[must_use]
pub fn new() -> Weak<T> {
Weak { ptr: NonNull::new(usize::MAX as *mut RcBox<T>).expect("MAX is not 0") }
}