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Diffstat (limited to 'vendor/itertools/src/next_array.rs')
| -rw-r--r-- | vendor/itertools/src/next_array.rs | 269 |
1 files changed, 0 insertions, 269 deletions
diff --git a/vendor/itertools/src/next_array.rs b/vendor/itertools/src/next_array.rs deleted file mode 100644 index 86480b19..00000000 --- a/vendor/itertools/src/next_array.rs +++ /dev/null @@ -1,269 +0,0 @@ -use core::mem::{self, MaybeUninit}; - -/// An array of at most `N` elements. -struct ArrayBuilder<T, const N: usize> { - /// The (possibly uninitialized) elements of the `ArrayBuilder`. - /// - /// # Safety - /// - /// The elements of `arr[..len]` are valid `T`s. - arr: [MaybeUninit<T>; N], - - /// The number of leading elements of `arr` that are valid `T`s, len <= N. - len: usize, -} - -impl<T, const N: usize> ArrayBuilder<T, N> { - /// Initializes a new, empty `ArrayBuilder`. - pub fn new() -> Self { - // SAFETY: The safety invariant of `arr` trivially holds for `len = 0`. - Self { - arr: [(); N].map(|_| MaybeUninit::uninit()), - len: 0, - } - } - - /// Pushes `value` onto the end of the array. - /// - /// # Panics - /// - /// This panics if `self.len >= N`. - #[inline(always)] - pub fn push(&mut self, value: T) { - // PANICS: This will panic if `self.len >= N`. - let place = &mut self.arr[self.len]; - // SAFETY: The safety invariant of `self.arr` applies to elements at - // indices `0..self.len` — not to the element at `self.len`. Writing to - // the element at index `self.len` therefore does not violate the safety - // invariant of `self.arr`. Even if this line panics, we have not - // created any intermediate invalid state. - *place = MaybeUninit::new(value); - // Lemma: `self.len < N`. By invariant, `self.len <= N`. Above, we index - // into `self.arr`, which has size `N`, at index `self.len`. If `self.len == N` - // at that point, that index would be out-of-bounds, and the index - // operation would panic. Thus, `self.len != N`, and since `self.len <= N`, - // that means that `self.len < N`. - // - // PANICS: Since `self.len < N`, and since `N <= usize::MAX`, - // `self.len + 1 <= usize::MAX`, and so `self.len += 1` will not - // overflow. Overflow is the only panic condition of `+=`. - // - // SAFETY: - // - We are required to uphold the invariant that `self.len <= N`. - // Since, by the preceding lemma, `self.len < N` at this point in the - // code, `self.len += 1` results in `self.len <= N`. - // - We are required to uphold the invariant that `self.arr[..self.len]` - // are valid instances of `T`. Since this invariant already held when - // this method was called, and since we only increment `self.len` - // by 1 here, we only need to prove that the element at - // `self.arr[self.len]` (using the value of `self.len` before incrementing) - // is valid. Above, we construct `place` to point to `self.arr[self.len]`, - // and then initialize `*place` to `MaybeUninit::new(value)`, which is - // a valid `T` by construction. - self.len += 1; - } - - /// Consumes the elements in the `ArrayBuilder` and returns them as an array - /// `[T; N]`. - /// - /// If `self.len() < N`, this returns `None`. - pub fn take(&mut self) -> Option<[T; N]> { - if self.len == N { - // SAFETY: Decreasing the value of `self.len` cannot violate the - // safety invariant on `self.arr`. - self.len = 0; - - // SAFETY: Since `self.len` is 0, `self.arr` may safely contain - // uninitialized elements. - let arr = mem::replace(&mut self.arr, [(); N].map(|_| MaybeUninit::uninit())); - - Some(arr.map(|v| { - // SAFETY: We know that all elements of `arr` are valid because - // we checked that `len == N`. - unsafe { v.assume_init() } - })) - } else { - None - } - } -} - -impl<T, const N: usize> AsMut<[T]> for ArrayBuilder<T, N> { - fn as_mut(&mut self) -> &mut [T] { - let valid = &mut self.arr[..self.len]; - // SAFETY: By invariant on `self.arr`, the elements of `self.arr` at - // indices `0..self.len` are in a valid state. Since `valid` references - // only these elements, the safety precondition of - // `slice_assume_init_mut` is satisfied. - unsafe { slice_assume_init_mut(valid) } - } -} - -impl<T, const N: usize> Drop for ArrayBuilder<T, N> { - // We provide a non-trivial `Drop` impl, because the trivial impl would be a - // no-op; `MaybeUninit<T>` has no innate awareness of its own validity, and - // so it can only forget its contents. By leveraging the safety invariant of - // `self.arr`, we do know which elements of `self.arr` are valid, and can - // selectively run their destructors. - fn drop(&mut self) { - // SAFETY: - // - by invariant on `&mut [T]`, `self.as_mut()` is: - // - valid for reads and writes - // - properly aligned - // - non-null - // - the dropped `T` are valid for dropping; they do not have any - // additional library invariants that we've violated - // - no other pointers to `valid` exist (since we're in the context of - // `drop`) - unsafe { core::ptr::drop_in_place(self.as_mut()) } - } -} - -/// Assuming all the elements are initialized, get a mutable slice to them. -/// -/// # Safety -/// -/// The caller guarantees that the elements `T` referenced by `slice` are in a -/// valid state. -unsafe fn slice_assume_init_mut<T>(slice: &mut [MaybeUninit<T>]) -> &mut [T] { - // SAFETY: Casting `&mut [MaybeUninit<T>]` to `&mut [T]` is sound, because - // `MaybeUninit<T>` is guaranteed to have the same size, alignment and ABI - // as `T`, and because the caller has guaranteed that `slice` is in the - // valid state. - unsafe { &mut *(slice as *mut [MaybeUninit<T>] as *mut [T]) } -} - -/// Equivalent to `it.next_array()`. -pub(crate) fn next_array<I, const N: usize>(it: &mut I) -> Option<[I::Item; N]> -where - I: Iterator, -{ - let mut builder = ArrayBuilder::new(); - for _ in 0..N { - builder.push(it.next()?); - } - builder.take() -} - -#[cfg(test)] -mod test { - use super::ArrayBuilder; - - #[test] - fn zero_len_take() { - let mut builder = ArrayBuilder::<(), 0>::new(); - let taken = builder.take(); - assert_eq!(taken, Some([(); 0])); - } - - #[test] - #[should_panic] - fn zero_len_push() { - let mut builder = ArrayBuilder::<(), 0>::new(); - builder.push(()); - } - - #[test] - fn push_4() { - let mut builder = ArrayBuilder::<(), 4>::new(); - assert_eq!(builder.take(), None); - - builder.push(()); - assert_eq!(builder.take(), None); - - builder.push(()); - assert_eq!(builder.take(), None); - - builder.push(()); - assert_eq!(builder.take(), None); - - builder.push(()); - assert_eq!(builder.take(), Some([(); 4])); - } - - #[test] - fn tracked_drop() { - use std::panic::{catch_unwind, AssertUnwindSafe}; - use std::sync::atomic::{AtomicU16, Ordering}; - - static DROPPED: AtomicU16 = AtomicU16::new(0); - - #[derive(Debug, PartialEq)] - struct TrackedDrop; - - impl Drop for TrackedDrop { - fn drop(&mut self) { - DROPPED.fetch_add(1, Ordering::Relaxed); - } - } - - { - let builder = ArrayBuilder::<TrackedDrop, 0>::new(); - assert_eq!(DROPPED.load(Ordering::Relaxed), 0); - drop(builder); - assert_eq!(DROPPED.load(Ordering::Relaxed), 0); - } - - { - let mut builder = ArrayBuilder::<TrackedDrop, 2>::new(); - builder.push(TrackedDrop); - assert_eq!(builder.take(), None); - assert_eq!(DROPPED.load(Ordering::Relaxed), 0); - drop(builder); - assert_eq!(DROPPED.swap(0, Ordering::Relaxed), 1); - } - - { - let mut builder = ArrayBuilder::<TrackedDrop, 2>::new(); - builder.push(TrackedDrop); - builder.push(TrackedDrop); - assert!(matches!(builder.take(), Some(_))); - assert_eq!(DROPPED.swap(0, Ordering::Relaxed), 2); - drop(builder); - assert_eq!(DROPPED.load(Ordering::Relaxed), 0); - } - - { - let mut builder = ArrayBuilder::<TrackedDrop, 2>::new(); - - builder.push(TrackedDrop); - builder.push(TrackedDrop); - - assert!(catch_unwind(AssertUnwindSafe(|| { - builder.push(TrackedDrop); - })) - .is_err()); - - assert_eq!(DROPPED.load(Ordering::Relaxed), 1); - - drop(builder); - - assert_eq!(DROPPED.swap(0, Ordering::Relaxed), 3); - } - - { - let mut builder = ArrayBuilder::<TrackedDrop, 2>::new(); - - builder.push(TrackedDrop); - builder.push(TrackedDrop); - - assert!(catch_unwind(AssertUnwindSafe(|| { - builder.push(TrackedDrop); - })) - .is_err()); - - assert_eq!(DROPPED.load(Ordering::Relaxed), 1); - - assert!(matches!(builder.take(), Some(_))); - - assert_eq!(DROPPED.load(Ordering::Relaxed), 3); - - builder.push(TrackedDrop); - builder.push(TrackedDrop); - - assert!(matches!(builder.take(), Some(_))); - - assert_eq!(DROPPED.swap(0, Ordering::Relaxed), 5); - } - } -} |
