AIKIDO-2026-439418

TL;DR

ArrayVec::extend_from_iter, used by extend(), collect(), and FromIterator, skips writing each element for zero-sized types but still increments the vector length. For a zero-sized type that implements Drop, the moved element is dropped once when the loop iteration ends and again later when the ArrayVec is dropped or cleared. This double drop is undefined behavior that any safe caller can trigger by extending an ArrayVec with such elements. The fix calls mem::forget on the element in the zero-sized case so it is dropped exactly once.