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Github Fix overflowing length in Vec<ZST> to VecDeque by cuviper · Pull Re...
source link: https://github.com/rust-lang/rust/pull/83244
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Vec can hold up to usize::MAX ZST items, but VecDeque has a lower
limit to keep its raw capacity as a power of two, so we should check
that in From<Vec<T>> for VecDeque<T>. We can also simplify the
capacity check for the remaining non-ZST case.
Before this fix, the new test would fail on the length:
thread 'collections::vec_deque::tests::test_from_vec_zst_overflow' panicked at 'assertion failed: `(left == right)`
left: `0`,
right: `9223372036854775808`', library/alloc/src/collections/vec_deque/tests.rs:474:5
note: panic did not contain expected string
panic message: `"assertion failed: `(left == right)`\n left: `0`,\n right: `9223372036854775808`"`,
expected substring: `"capacity overflow"`
That was a result of len() using a mask & (size - 1) with the
improper length. Now we do get a "capacity overflow" panic as soon as
that VecDeque::from(vec) is attempted.
Fixes #80167.
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