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Add #[must_use] to alloc functions that would leak memory #90427

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merged 1 commit into from
Oct 31, 2021

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jkugelman
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As requested by @joshtriplett.

Please do go ahead and add the ones whose only legitimate use for ignoring the return value is leaking memory. (In a separate PR please.) I think it's sufficiently error-prone to call something like alloc and ignore the result that it's legitimate to require let _ = for that.

I added realloc myself. Clippy ignored it because of its mut argument.

alloc/src/alloc.rs:123:1   alloc   unsafe fn realloc(ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8;

Parent issue: #89692

r? @joshtriplett

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Oct 31, 2021
@joshtriplett joshtriplett added the relnotes Marks issues that should be documented in the release notes of the next release. label Oct 31, 2021
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@bors r+

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bors commented Oct 31, 2021

📌 Commit 42e0282 has been approved by joshtriplett

@bors 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-review Status: Awaiting review from the assignee but also interested parties. labels Oct 31, 2021
bors added a commit to rust-lang-ci/rust that referenced this pull request Oct 31, 2021
…askrgr

Rollup of 8 pull requests

Successful merges:

 - rust-lang#89446 (Add paragraph to ControlFlow docs to menion it works with the ? operator (rust-lang#88715))
 - rust-lang#89677 (Stabilize `is_symlink()` for `Metadata` and `Path`)
 - rust-lang#89833 (Add #[must_use] to Rc::downgrade)
 - rust-lang#89835 (Add #[must_use] to expensive computations)
 - rust-lang#89839 (Add #[must_use] to mem/ptr functions)
 - rust-lang#89897 (Add #[must_use] to remaining core functions)
 - rust-lang#89951 (Stabilize `option_result_unwrap_unchecked`)
 - rust-lang#90427 (Add #[must_use] to alloc functions that would leak memory)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit ff6d8ec into rust-lang:master Oct 31, 2021
@rustbot rustbot added this to the 1.58.0 milestone Oct 31, 2021
@jkugelman jkugelman deleted the must-use-alloc-leak branch October 31, 2021 14:38
@@ -804,6 +804,7 @@ impl<T: ?Sized> Arc<T> {
/// let x_ptr = Arc::into_raw(x);
/// assert_eq!(unsafe { &*x_ptr }, "hello");
/// ```
#[must_use = "losing the pointer will leak memory"]
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This one feels like it could lead to false positives. This is Arc, so you can get the data back via another instance.

not sure if it happens in practice though. I think I used that once to simulate
increment_strong_count? Not sure.

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6 participants