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Document requirements for unsized {Rc,Arc}::from_raw #120449

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Feb 15, 2024

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@udoprog udoprog commented Jan 28, 2024

This seems to be implied due to these types supporting operation-less unsized coercions. Taken together with the established behavior of a wide to thin pointer cast it would enable unsafe downcasting of these containers.

Note that the term "data pointer" is adopted from rust-lang/rfcs#3559

See also this internals thread.

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@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Jan 28, 2024
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@udoprog udoprog force-pushed the document-unsized-rc-arc-from-raw branch from e64211f to 57e0dea Compare January 28, 2024 14:57
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@udoprog udoprog force-pushed the document-unsized-rc-arc-from-raw branch from ef55c61 to bdbbf04 Compare January 28, 2024 17:25
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@rustbot rustbot added the T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. label Feb 11, 2024
@rustbot rustbot assigned m-ou-se and unassigned joshtriplett Feb 11, 2024
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m-ou-se commented Feb 15, 2024

@bors r+ rollup

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bors commented Feb 15, 2024

📌 Commit bdbbf04 has been approved by m-ou-se

It is now in the queue for this repository.

@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 Feb 15, 2024
bors added a commit to rust-lang-ci/rust that referenced this pull request Feb 15, 2024
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Rollup of 8 pull requests

Successful merges:

 - rust-lang#120449 (Document requirements for unsized {Rc,Arc}::from_raw)
 - rust-lang#120505 (Fix BTreeMap's Cursor::remove_{next,prev})
 - rust-lang#120672 (std::thread update freebsd stack guard handling.)
 - rust-lang#121088 (Implicitly enable evex512 if avx512 is enabled)
 - rust-lang#121104 (Ignore unsized types when trying to determine the size of the original type)
 - rust-lang#121107 (Fix msg for verbose suggestions with confusable capitalization)
 - rust-lang#121113 (Continue compilation even if inherent impl checks fail)
 - rust-lang#121120 (Add `ErrorGuaranteed` to `ast::LitKind::Err`, `token::LitKind::Err`.)

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@bors bors merged commit 9fdab38 into rust-lang:master Feb 15, 2024
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@rustbot rustbot added this to the 1.78.0 milestone Feb 15, 2024
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request Feb 15, 2024
Rollup merge of rust-lang#120449 - udoprog:document-unsized-rc-arc-from-raw, r=m-ou-se

Document requirements for unsized {Rc,Arc}::from_raw

This seems to be implied due to these types supporting operation-less unsized coercions. Taken together with the [established behavior of a wide to thin pointer cast](rust-lang/reference#1451) it would enable unsafe downcasting of these containers.

Note that the term "data pointer" is adopted from rust-lang/rfcs#3559

See also this [internals thread](https://internals.rust-lang.org/t/can-unsafe-smart-pointer-downcasts-be-correct/20229/2).
@udoprog udoprog deleted the document-unsized-rc-arc-from-raw branch February 15, 2024 21:24
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