[multi-vector] Verify Standard won't overflow in its constructor.

[Mark Hildebrand (hildebrandmw)]

Move the check that:

1. nrows * ncols will not overflow
2. nrows * ncols * std::mem::size_of::<T>() will not exceed isize::MAX

into the constructor Standard::new(). This allows the calculation of the number of elements and allocation sizes to be performed with safely with reckless abandon in implementation code as we no longer need to worry about overflow. The constructor Standard::new() can now return an error, which is slightly less ergonomic, but I think the improved safety in the implementation is worth it.

[Copilot]

Pull request overview

This PR hardens the multi_vector::Standard matrix representation by moving overflow/size validation into Standard::new(), so downstream element-count and allocation-size computations can rely on a checked constructor invariant.

Changes:

• Change Standard::new(nrows, ncols) to return Result<Standard<T>, Overflow> and validate element-count overflow and isize::MAX allocation bounds.
• Make Standard::num_elements() infallible (usize) and remove the SliceError::Overflow path.
• Update docs/tests/compile-fail fixtures to handle the new fallible constructor and add targeted overflow tests.

Reviewed changes

Copilot reviewed 24 out of 24 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
diskann-quantization/src/multi_vector/matrix.rs	Implements fallible Standard::new with overflow checks, adds Overflow error, updates num_elements and tests.
diskann-quantization/src/multi_vector/mod.rs	Updates doctest examples and re-exports the new Overflow type.
diskann-quantization/src/multi_vector/distance/simple.rs	Updates doctest/test helpers to unwrap the now-fallible Standard::new.
diskann-quantization/src/multi_vector/distance/mod.rs	Updates module-level doctest examples to unwrap Standard::new.
diskann-quantization/src/minmax/multi/mod.rs	Updates doctest examples to unwrap Standard::new.
diskann-quantization/src/minmax/multi/meta.rs	Updates tests to unwrap Standard::new when building MatRef.
diskann-quantization/src/minmax/multi/max_sim.rs	Updates tests to unwrap Standard::<f32>::new.
diskann-quantization/tests/compile-fail/multi/matref_rows.rs	Updates compile-fail fixture to unwrap Standard::new.
diskann-quantization/tests/compile-fail/multi/matref_get_row.rs	Updates compile-fail fixture to unwrap Standard::new.
diskann-quantization/tests/compile-fail/multi/matmut_rows_mut.rs	Updates compile-fail fixture to unwrap Standard::new.
diskann-quantization/tests/compile-fail/multi/matmut_rows.rs	Updates compile-fail fixture to unwrap Standard::new.
diskann-quantization/tests/compile-fail/multi/matmut_reborrow_mut.rs	Updates compile-fail fixture to unwrap Standard::new.
diskann-quantization/tests/compile-fail/multi/matmut_reborrow.rs	Updates compile-fail fixture to unwrap Standard::new.
diskann-quantization/tests/compile-fail/multi/matmut_get_row_mut.rs	Updates compile-fail fixture to unwrap Standard::new.
diskann-quantization/tests/compile-fail/multi/matmut_get_row.rs	Updates compile-fail fixture to unwrap Standard::new.
diskann-quantization/tests/compile-fail/multi/matmut_as_view_borrows.rs	Updates compile-fail fixture to unwrap Standard::new.
diskann-quantization/tests/compile-fail/multi/mat_rows_mut.rs	Updates compile-fail fixture to unwrap Standard::new.
diskann-quantization/tests/compile-fail/multi/mat_rows.rs	Updates compile-fail fixture to unwrap Standard::new.
diskann-quantization/tests/compile-fail/multi/mat_reborrow_mut.rs	Updates compile-fail fixture to unwrap Standard::new.
diskann-quantization/tests/compile-fail/multi/mat_reborrow.rs	Updates compile-fail fixture to unwrap Standard::new.
diskann-quantization/tests/compile-fail/multi/mat_get_row_mut.rs	Updates compile-fail fixture to unwrap Standard::new.
diskann-quantization/tests/compile-fail/multi/mat_get_row.rs	Updates compile-fail fixture to unwrap Standard::new.
diskann-quantization/tests/compile-fail/multi/mat_as_view_mut.rs	Updates compile-fail fixture to unwrap Standard::new.
diskann-quantization/tests/compile-fail/multi/mat_as_view.rs	Updates compile-fail fixture to unwrap Standard::new.

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[Codecov Comments Bot (codecov-commenter)]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.00%. Comparing base (e873811) to head (8a662c4).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #757 +/- ##
=======================================
Coverage 88.99% 89.00% =======================================
Files 428 428 Lines 78235 78291 +56 =======================================
+ Hits 69627 69680 +53 - Misses 8608 8611 +3 

Flag	Coverage Δ
miri	89.00% <100.00%> (+<0.01%)	⬆️
unittests	89.00% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
diskann-quantization/src/minmax/multi/max_sim.rs	98.06% <100.00%> (ø)
diskann-quantization/src/minmax/multi/meta.rs	97.66% <100.00%> (+0.03%)	⬆️
...n-quantization/src/multi_vector/distance/simple.rs	98.43% <100.00%> (ø)
diskann-quantization/src/multi_vector/matrix.rs	97.30% <100.00%> (-0.85%)	⬇️

... and 1 file with indirect coverage changes

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[Copilot]

Mark Hildebrand (@hildebrandmw) I've opened a new pull request, #758, to work on those changes. Once the pull request is ready, I'll request review from you.

[Mark Hildebrand (hildebrandmw)]

Mark Hildebrand (@hildebrandmw) I've opened a new pull request, #758, to work on those changes. Once the pull request is ready, I'll request review from you.

Ugh - that's not what I meant to happen 😞.

[Aditya Krishnan (arkrishn94)]

Makes sense