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Rollup merge of #118890 - Amanieu:allocator-lifetime, r=Mark-Simulacrum

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Clarify the lifetimes of allocations returned by the `Allocator` trait

The previous definition (accidentally) disallowed the implementation of stack-based allocators whose memory would become invalid once the lifetime of the allocator type ended.

This also ensures the validity of the following blanket implementation:
```rust
impl<A: Allocator> Allocator for &'_ A {}
```
This commit is contained in:
Oli Scherer 2024-02-14 11:53:38 +01:00 • committed by GitHub
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1 changed files with 8 additions and 2 deletions
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10
library/core/src/alloc/mod.rs
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@ -95,8 +95,10 @@ impl fmt::Display for AllocError {
/// # Safety
///
/// * Memory blocks returned from an allocator that are [*currently allocated*] must point to
/// valid memory and retain their validity while they are [*currently allocated*] and at
/// least one of the instance and all of its clones has not been dropped.
/// valid memory and retain their validity while they are [*currently allocated*] and the shorter
/// of:
/// - the borrow-checker lifetime of the allocator type itself.
/// - as long as at least one of the instance and all of its clones has not been dropped.
///
/// * copying, cloning, or moving the allocator must not invalidate memory blocks returned from this
/// allocator. A copied or cloned allocator must behave like the same allocator, and
@ -114,6 +116,10 @@ pub unsafe trait Allocator {
/// The returned block may have a larger size than specified by `layout.size()`, and may or may
/// not have its contents initialized.
///
/// The returned block of memory remains valid as long as it is [*currently allocated*] and the shorter of:
/// - the borrow-checker lifetime of the allocator type itself.
/// - as long as at the allocator and all its clones has not been dropped.
///
/// # Errors
///
/// Returning `Err` indicates that either memory is exhausted or `layout` does not meet