Auto merge of #151891 - jhpratt:rollup-cG0AjgK, r=jhpratt

Rollup of 5 pull requests

Successful merges:

 - #143650 (core: add Option::get_or_try_insert_with)
 - #151726 (Remove duplicated code in `slice/index.rs`)
 - #151812 (Add `shift_{left,right}` on slices)
 - #151829 (Implement `BinaryHeap::pop_if()`)
 - #151838 (Fix typo for Maybe dangling docs)

Author: bors

library/alloc/src/collections/binary_heap/mod.rs

@@ -649,6 +649,33 @@ impl<T: Ord, A: Allocator> BinaryHeap<T, A> {
         })
     }
 
+    /// Removes and returns the greatest item from the binary heap if the predicate
+    /// returns `true`, or [`None`] if the predicate returns false or the heap
+    /// is empty (the predicate will not be called in that case).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(binary_heap_pop_if)]
+    /// use std::collections::BinaryHeap;
+    /// let mut heap = BinaryHeap::from([1, 2]);
+    /// let pred = |x: &i32| *x % 2 == 0;
+    ///
+    /// assert_eq!(heap.pop_if(pred), Some(2));
+    /// assert_eq!(heap.as_slice(), [1]);
+    /// assert_eq!(heap.pop_if(pred), None);
+    /// assert_eq!(heap.as_slice(), [1]);
+    /// ```
+    ///
+    /// # Time complexity
+    ///
+    /// The worst case cost of `pop_if` on a heap containing *n* elements is *O*(log(*n*)).
+    #[unstable(feature = "binary_heap_pop_if", issue = "151828")]
+    pub fn pop_if(&mut self, predicate: impl FnOnce(&T) -> bool) -> Option<T> {
+        let first = self.peek()?;
+        if predicate(first) { self.pop() } else { None }
+    }
+
     /// Pushes an item onto the binary heap.
     ///
     /// # Examples

library/alloctests/tests/collections/binary_heap.rs

@@ -136,6 +136,18 @@ fn test_peek_and_pop() {
     }
 }
 
+#[test]
+fn test_pop_if() {
+    let data = vec![9, 8, 7, 6, 5, 4, 3, 2, 1, 0];
+    let mut sorted = data.clone();
+    sorted.sort();
+    let mut heap = BinaryHeap::from(data);
+    while let Some(popped) = heap.pop_if(|x| *x > 2) {
+        assert_eq!(popped, sorted.pop().unwrap());
+    }
+    assert_eq!(heap.into_sorted_vec(), vec![0, 1, 2]);
+}
+
 #[test]
 fn test_peek_mut() {
     let data = vec![2, 4, 6, 2, 1, 8, 10, 3, 5, 7, 0, 9, 1];

library/alloctests/tests/lib.rs

@@ -1,4 +1,5 @@
 #![feature(allocator_api)]
+#![feature(binary_heap_pop_if)]
 #![feature(const_heap)]
 #![feature(deque_extend_front)]
 #![feature(iter_array_chunks)]

library/core/src/mem/maybe_dangling.rs

@@ -29,7 +29,7 @@ use crate::{mem, ptr};
 /// mem::forget(boxed); // <-- this is UB!
 /// ```
 ///
-/// Even though the `Box`e's destructor is not run (and thus we don't have a double free bug), this
+/// Even though the `Box`'s destructor is not run (and thus we don't have a double free bug), this
 /// code is still UB. This is because when moving `boxed` into `forget`, its validity invariants
 /// are asserted, causing UB since the `Box` is dangling. The safety comment is as such wrong, as
 /// moving the `boxed` variable as part of the `forget` call *is* a use.

library/core/src/ops/range.rs

@@ -773,7 +773,7 @@ impl<T: Copy> Bound<&T> {
     /// ```
     #[unstable(feature = "bound_copied", issue = "145966")]
     #[must_use]
-    pub fn copied(self) -> Bound<T> {
+    pub const fn copied(self) -> Bound<T> {
         match self {
             Bound::Unbounded => Bound::Unbounded,
             Bound::Included(x) => Bound::Included(*x),

library/core/src/option.rs

@@ -584,7 +584,7 @@
 use crate::clone::TrivialClone;
 use crate::iter::{self, FusedIterator, TrustedLen};
 use crate::marker::Destruct;
-use crate::ops::{self, ControlFlow, Deref, DerefMut};
+use crate::ops::{self, ControlFlow, Deref, DerefMut, Residual, Try};
 use crate::panicking::{panic, panic_display};
 use crate::pin::Pin;
 use crate::{cmp, convert, hint, mem, slice};
@@ -1816,6 +1816,49 @@ impl<T> Option<T> {
         unsafe { self.as_mut().unwrap_unchecked() }
     }
 
+    /// If the option is `None`, calls the closure and inserts its output if successful.
+    ///
+    /// If the closure returns a residual value such as `Err` or `None`,
+    /// that residual value is returned and nothing is inserted.
+    ///
+    /// If the option is `Some`, nothing is inserted.
+    ///
+    /// Unless a residual is returned, a mutable reference to the value
+    /// of the option will be output.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(option_get_or_try_insert_with)]
+    /// let mut o1: Option<u32> = None;
+    /// let mut o2: Option<u8> = None;
+    ///
+    /// let number = "12345";
+    ///
+    /// assert_eq!(o1.get_or_try_insert_with(|| number.parse()).copied(), Ok(12345));
+    /// assert!(o2.get_or_try_insert_with(|| number.parse()).is_err());
+    /// assert_eq!(o1, Some(12345));
+    /// assert_eq!(o2, None);
+    /// ```
+    #[inline]
+    #[unstable(feature = "option_get_or_try_insert_with", issue = "143648")]
+    pub fn get_or_try_insert_with<'a, R, F>(
+        &'a mut self,
+        f: F,
+    ) -> <R::Residual as Residual<&'a mut T>>::TryType
+    where
+        F: FnOnce() -> R,
+        R: Try<Output = T, Residual: Residual<&'a mut T>>,
+    {
+        if let None = self {
+            *self = Some(f()?);
+        }
+        // SAFETY: a `None` variant for `self` would have been replaced by a `Some`
+        // variant in the code above.
+
+        Try::from_output(unsafe { self.as_mut().unwrap_unchecked() })
+    }
+
     /////////////////////////////////////////////////////////////////////////
     // Misc
     /////////////////////////////////////////////////////////////////////////

library/core/src/slice/index.rs

@@ -910,29 +910,7 @@ where
     R: [const] ops::RangeBounds<usize> + [const] Destruct,
 {
     let len = bounds.end;
-
-    let end = match range.end_bound() {
-        ops::Bound::Included(&end) if end >= len => slice_index_fail(0, end, len),
-        // Cannot overflow because `end < len` implies `end < usize::MAX`.
-        ops::Bound::Included(&end) => end + 1,
-
-        ops::Bound::Excluded(&end) if end > len => slice_index_fail(0, end, len),
-        ops::Bound::Excluded(&end) => end,
-        ops::Bound::Unbounded => len,
-    };
-
-    let start = match range.start_bound() {
-        ops::Bound::Excluded(&start) if start >= end => slice_index_fail(start, end, len),
-        // Cannot overflow because `start < end` implies `start < usize::MAX`.
-        ops::Bound::Excluded(&start) => start + 1,
-
-        ops::Bound::Included(&start) if start > end => slice_index_fail(start, end, len),
-        ops::Bound::Included(&start) => start,
-
-        ops::Bound::Unbounded => 0,
-    };
-
-    ops::Range { start, end }
+    into_slice_range(len, (range.start_bound().copied(), range.end_bound().copied()))
 }
 
 /// Performs bounds checking of a range without panicking.
@@ -972,20 +950,8 @@ where
     R: ops::RangeBounds<usize>,
 {
     let len = bounds.end;
-
-    let start = match range.start_bound() {
-        ops::Bound::Included(&start) => start,
-        ops::Bound::Excluded(start) => start.checked_add(1)?,
-        ops::Bound::Unbounded => 0,
-    };
-
-    let end = match range.end_bound() {
-        ops::Bound::Included(end) => end.checked_add(1)?,
-        ops::Bound::Excluded(&end) => end,
-        ops::Bound::Unbounded => len,
-    };
-
-    if start > end || end > len { None } else { Some(ops::Range { start, end }) }
+    let r = into_range(len, (range.start_bound().copied(), range.end_bound().copied()))?;
+    if r.start > r.end || r.end > len { None } else { Some(r) }
 }
 
 /// Converts a pair of `ops::Bound`s into `ops::Range` without performing any
@@ -1011,6 +977,7 @@ pub(crate) const fn into_range_unchecked(
 /// Converts pair of `ops::Bound`s into `ops::Range`.
 /// Returns `None` on overflowing indices.
 #[rustc_const_unstable(feature = "const_range", issue = "none")]
+#[inline]
 pub(crate) const fn into_range(
     len: usize,
     (start, end): (ops::Bound<usize>, ops::Bound<usize>),
@@ -1036,7 +1003,8 @@ pub(crate) const fn into_range(
 
 /// Converts pair of `ops::Bound`s into `ops::Range`.
 /// Panics on overflowing indices.
-pub(crate) fn into_slice_range(
+#[inline]
+pub(crate) const fn into_slice_range(
     len: usize,
     (start, end): (ops::Bound<usize>, ops::Bound<usize>),
 ) -> ops::Range<usize> {