Preserve nested DST padding in layout formulas - #3630
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Additional details and impacted files@@ Coverage Diff @@
## main #3630 +/- ##
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- Coverage 91.85% 91.50% -0.36%
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Files 20 20
Lines 6093 6477 +384
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+ Hits 5597 5927 +330
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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 C + round_up(r + nE, A), encoding A and r in one nonzero word. Carry that four-word layout formula through composition, padding, metadata inference, casts, projections, allocation, and split overlap checks. This is a smaller state-model alternative to #3630. Exhaustive reduced-width model checking matches #3630's core formula transforms and representability behavior, and the checked benchmark snapshots are byte-for-byte identical. Add regression coverage for compiler-accepted generic packed/aligned nesting, parsing, allocation, zeroing, projection, metadata plateaus, and dynamic padding. Add modular Kani proofs for the normal form, transforms, inverse validator, affine cast arithmetic, alignment, containment, the conservative dynamic-padding predicate, and both modern and MSRV unchecked-arithmetic implementations. The arithmetic proofs are conditional on the documented compiler-layout premise; regression and Miri coverage exercise the actual compiler layout and pointer paths. Closes #3617 *Authored by an AI agent acting on Josh Liebow-Feeser's behalf.* gherrit-pr-id: Ger2cetjqc3naucboffw4r4hal423gaa5
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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: v12 — Compare vs v11
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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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