stabilize new Range type and iterator

[pitaj]

For #125687
Stabilizes core::range::Range and core::range::RangeIter, newly stable API:

// in core::range

pub struct Range<Idx> {
    pub start: Idx,
    pub end: Idx,
}

impl<Idx: fmt::Debug> fmt::Debug for Range<Idx> { /* ... */ }

impl<Idx: PartialOrd<Idx>> Range<Idx> {
    pub const fn contains<U>(&self, item: &U) -> bool
    where
        Idx: [const] PartialOrd<U>,
        U: ?Sized + [const] PartialOrd<Idx>;

    pub const fn is_empty(&self) -> bool
    where
        Idx: [const] PartialOrd;
}

impl<Idx: Step> Range<Idx> {
    pub fn iter(&self) -> RangeIter<Idx>;
}

impl<T> const RangeBounds<T> for Range<T> { /* ... */ }
impl<T> const RangeBounds<T> for Range<&T> { /* ... */ }

impl<T> const From<Range<T>> for legacy::Range<T> { /* ... */ }
impl<T> const From<legacy::Range<T>> for Range<T> { /* ... */ }

pub struct RangeIter<A>(/* ... */);

// `RangeIter::remainder` not stabilized

impl<A: Step> Iterator for RangeIter<A> {
    type Item = A;
    /* ... */
}

impl<A: Step> DoubleEndedIterator for RangeIter<A> { /* ... */ }
impl<A: Step> FusedIterator for RangeIter<A> { }
impl<A: Step> IntoIterator for Range<A> {
    type Item = A;
    type IntoIter = RangeIter<A>;
    /* ... */
}

impl ExactSizeIterator for RangeIter<u8> { }
impl ExactSizeIterator for RangeIter<i8> { }

unsafe impl<T> const SliceIndex<[T]> for range::Range<usize> {
    type Output = [T];
    /* ... */
}
unsafe impl const SliceIndex<str> for range::Range<usize> {
    type Output = str;
    /* ... */
}

Updates docs to reflect stabilization (removed "experimental")

[pitaj]

r? @tgross35

[rustbot]

tgross35 is currently at their maximum review capacity.
They may take a while to respond.

[tgross35]

Woohoo, last one!

Double checked that API matches the existing Range. One nit on the comment then r=me

View changes since this review

[tgross35]

Put cfg(bootstrap) in the comment here because (aiui) that's what the release team greps for when they do cfg cleanup with bootstrap bumps.

[tgross35]

huh 🤔

[tgross35]

Ah this comes from #154577, I assume you did --bless locally. Could you drop changes to these files? Otherwise this will conflict once that one merges.

I assume tests will still pass given that PR says we're not testing this bit.

[tgross35]

Thanks!

@bors r+

[rust-bors]

📌 Commit 620e92f has been approved by tgross35

It is now in the queue for this repository.