Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 78 insertions, 0 deletions

diff --git a/library/core/src/iter/traits/marker.rs b/library/core/src/iter/traits/marker.rs
new file mode 100644
index 000000000..da7537457
--- /dev/null
+++ b/library/core/src/iter/traits/marker.rs
@@ -0,0 +1,78 @@
+use crate::iter::Step;
+
+/// An iterator that always continues to yield `None` when exhausted.
+///
+/// Calling next on a fused iterator that has returned `None` once is guaranteed
+/// to return [`None`] again. This trait should be implemented by all iterators
+/// that behave this way because it allows optimizing [`Iterator::fuse()`].
+///
+/// Note: In general, you should not use `FusedIterator` in generic bounds if
+/// you need a fused iterator. Instead, you should just call [`Iterator::fuse()`]
+/// on the iterator. If the iterator is already fused, the additional [`Fuse`]
+/// wrapper will be a no-op with no performance penalty.
+///
+/// [`Fuse`]: crate::iter::Fuse
+#[stable(feature = "fused", since = "1.26.0")]
+#[rustc_unsafe_specialization_marker]
+pub trait FusedIterator: Iterator {}
+
+#[stable(feature = "fused", since = "1.26.0")]
+impl<I: FusedIterator + ?Sized> FusedIterator for &mut I {}
+
+/// An iterator that reports an accurate length using size_hint.
+///
+/// The iterator reports a size hint where it is either exact
+/// (lower bound is equal to upper bound), or the upper bound is [`None`].
+/// The upper bound must only be [`None`] if the actual iterator length is
+/// larger than [`usize::MAX`]. In that case, the lower bound must be
+/// [`usize::MAX`], resulting in an [`Iterator::size_hint()`] of
+/// `(usize::MAX, None)`.
+///
+/// The iterator must produce exactly the number of elements it reported
+/// or diverge before reaching the end.
+///
+/// # Safety
+///
+/// This trait must only be implemented when the contract is upheld. Consumers
+/// of this trait must inspect [`Iterator::size_hint()`]’s upper bound.
+#[unstable(feature = "trusted_len", issue = "37572")]
+#[rustc_unsafe_specialization_marker]
+pub unsafe trait TrustedLen: Iterator {}
+
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<I: TrustedLen + ?Sized> TrustedLen for &mut I {}
+
+/// An iterator that when yielding an item will have taken at least one element
+/// from its underlying [`SourceIter`].
+///
+/// Calling any method that advances the iterator, e.g.  [`next()`] or [`try_fold()`],
+/// guarantees that for each step at least one value of the iterator's underlying source
+/// has been moved out and the result of the iterator chain could be inserted
+/// in its place, assuming structural constraints of the source allow such an insertion.
+/// In other words this trait indicates that an iterator pipeline can be collected in place.
+///
+/// The primary use of this trait is in-place iteration. Refer to the [`vec::in_place_collect`]
+/// module documentation for more information.
+///
+/// [`vec::in_place_collect`]: ../../../../alloc/vec/in_place_collect/index.html
+/// [`SourceIter`]: crate::iter::SourceIter
+/// [`next()`]: Iterator::next
+/// [`try_fold()`]: Iterator::try_fold
+#[unstable(issue = "none", feature = "inplace_iteration")]
+#[doc(hidden)]
+pub unsafe trait InPlaceIterable: Iterator {}
+
+/// A type that upholds all invariants of [`Step`].
+///
+/// The invariants of [`Step::steps_between()`] are a superset of the invariants
+/// of [`TrustedLen`]. As such, [`TrustedLen`] is implemented for all range
+/// types with the same generic type argument.
+///
+/// # Safety
+///
+/// The implementation of [`Step`] for the given type must guarantee all
+/// invariants of all methods are upheld. See the [`Step`] trait's documentation
+/// for details. Consumers are free to rely on the invariants in unsafe code.
+#[unstable(feature = "trusted_step", issue = "85731")]
+#[rustc_specialization_trait]
+pub unsafe trait TrustedStep: Step {}