Preserve nested DST padding in layout formulas - #3630
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## main #3630 +/- ##
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- Coverage 91.85% 91.18% -0.68%
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Files 20 20
Lines 6093 6443 +350
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+ Hits 5597 5875 +278
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| // SAFETY: By invariant on `self`, the size of `T` with this | ||
| // metadata is no larger than `isize::MAX`, and thus cannot | ||
| // overflow `usize`. | ||
| None => unsafe { core::hint::unreachable_unchecked() }, |
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BLOCKING: This newly introduced unreachable_unchecked call is an unsafe block, but its safety comment lacks the versioned standard-library citation and quotation required by the repository's unsafe-review policy. Because reaching this arm is undefined behavior, add the relevant unreachable_unchecked safety text—for example, // [1] Per https://doc.rust-lang.org/1.92.0/std/hint/fn.unreachable_unchecked.html#safety: Reaching this function is Undefined Behavior.—and explicitly connect the MetadataOf and KnownLayout invariants to why size_for_metadata cannot return None.
AGENTS.md reference: zerocopy/AGENTS.md:L19-L23
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DstLayout flattened a nested slice DST's trailing-padding operation into the alignment of its packed outer container. That could understate the Rust object size, causing safe parsers and allocators to construct references and boxes whose referents extended beyond their backing storage. Represent slice-DST sizes as a normalized prefix plus an independently rounded inner size. Carry that formula through composition, padding, metadata inference, casts, projections, allocation, and split overlap checks. Add regressions for the reported 8-byte-versus-10-byte packed layout, parsing, allocation, zeroing, projection, metadata plateaus, and dynamic padding. Closes #3617 *Authored by an AI agent acting on Josh Liebow-Feeser's behalf.* gherrit-pr-id: Gxauzb34ce7e537xqailxsfsyzknfjcnl
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DstLayout flattened a nested slice DST's trailing-padding operation into the
alignment of its packed outer container. That could understate the Rust object
size, causing safe parsers and allocators to construct references and boxes
whose referents extended beyond their backing storage.
Represent slice-DST sizes as a normalized prefix plus an independently rounded
inner size. Carry that formula through composition, padding, metadata
inference, casts, projections, allocation, and split overlap checks. Add
regressions for the reported 8-byte-versus-10-byte packed layout, parsing,
allocation, zeroing, projection, metadata plateaus, and dynamic padding.
Closes #3617
Authored by an AI agent acting on Josh Liebow-Feeser's behalf.
Latest Update: v6 — Compare vs v5
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git fetch origin refs/heads/Gxauzb34ce7e537xqailxsfsyzknfjcnl && git checkout -b pr-Gxauzb34ce7e537xqailxsfsyzknfjcnl FETCH_HEADCheckout
git fetch origin refs/heads/Gxauzb34ce7e537xqailxsfsyzknfjcnl && git checkout FETCH_HEADCherry Pick
git fetch origin refs/heads/Gxauzb34ce7e537xqailxsfsyzknfjcnl && git cherry-pick FETCH_HEADPull
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