Add shift_remove family to IndexMap/IndexSet - #685
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swap_remove is O(1) but perturbs the position of the last element, which isn't acceptable when callers need remaining entries to keep their relative insertion order after a removal. This mirrors the upstream indexmap crate's shift_remove/shift_remove_entry API (O(n), shifts entries down via Vec::remove and fixes up the hash table's index pointers) adapted to heapless's fixed-capacity, no_std CoreMap/Pos representation. Fixes rust-embedded#678
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Summary
swap_removeis O(1) but perturbs map/set order by moving the last element into the removed slot. This adds order-preserving removal, mirroring theindexmapcrate'sshift_removeAPI:IndexMap::shift_remove/shift_remove_entry/shift_remove_indexOccupiedEntry::shift_remove/shift_remove_entryIndexSet::shift_removeImplementation:
CoreMap::shift_remove_foundremoves the entry withVec::remove(order-preserving shift) instead ofswap_remove_unchecked, then walks theindicesrobin-hood table decrementing everyPoswhose index pointed past the removed slot, then runs the existingbackward_shift_after_removalto restore the probe-distance invariant. O(n) instead ofswap_remove's O(1), same as upstreamindexmap.remove/swap_remove/remove_entry/swap_remove_entryare untouched.Fixes #678
Test plan
cargo buildcargo test --lib(251 passed, including 5 newshift_removetests covering order preservation onIndexMap,OccupiedEntry,shift_remove_index, andIndexSet)cargo test --doc index_map(31 passed, including new doctests)cargo clippy --libclean (repo deniesclippy::undocumented_unsafe_blocks)cargo fmt --checkclean