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Rollup merge of #140483 - baumanj:patch-1, r=workingjubilee

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Comment on `Rc` abort-guard strategy without naming unrelated fn

`wrapped_add` is used, not `checked_add`, so avoid mentioning specific fn calls that may vary slightly based on "whatever produces the best code" and focus on things that will remain constant into the future.
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Jacob Pratt 2025-05-07 00:29:22 +00:00 • committed by GitHub
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10
library/alloc/src/rc.rs
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@ -3536,11 +3536,11 @@ impl<T> Default for Weak<T> {
}
}
// NOTE: We checked_add here to deal with mem::forget safely. In particular
// if you mem::forget Rcs (or Weaks), the ref-count can overflow, and then
// you can free the allocation while outstanding Rcs (or Weaks) exist.
// We abort because this is such a degenerate scenario that we don't care about
// what happens -- no real program should ever experience this.
// NOTE: If you mem::forget Rcs (or Weaks), drop is skipped and the ref-count
// is not decremented, meaning the ref-count can overflow, and then you can
// free the allocation while outstanding Rcs (or Weaks) exist, which would be
// unsound. We abort because this is such a degenerate scenario that we don't
// care about what happens -- no real program should ever experience this.
//
// This should have negligible overhead since you don't actually need to
// clone these much in Rust thanks to ownership and move-semantics.