Auto merge of #75207 - dylni:add-slice-check-range, r=KodrAus

Add `slice::check_range`

This method is useful for [`RangeBounds`] parameters. It's even been [rewritten](https://github.com/rust-lang/rust/blob/22ee68dc586440f96b76b32fbd6087507c6afdb9/src/librustc_data_structures/sorted_map.rs#L214) [many](https://github.com/rust-lang/rust/blob/22ee68dc586440f96b76b32fbd6087507c6afdb9/library/alloc/src/vec.rs#L1299) [times](https://github.com/rust-lang/rust/blob/22ee68dc586440f96b76b32fbd6087507c6afdb9/library/core/src/slice/mod.rs#L2441) in the standard library, sometimes assuming that the bounds won't be [`usize::MAX`].

For example, [`Vec::drain`] creates an empty iterator when [`usize::MAX`] is used as an inclusive end bound:

```rust
assert!(vec![1].drain(..=usize::max_value()).eq(iter::empty()));
```

If this PR is merged, I'll create another to use it for those methods.

[`RangeBounds`]: https://doc.rust-lang.org/std/ops/trait.RangeBounds.html
[`usize::MAX`]: https://doc.rust-lang.org/std/primitive.usize.html#associatedconstant.MAX
[`Vec::drain`]: https://doc.rust-lang.org/std/vec/struct.Vec.html#method.drain

1 files changed, 2 insertions, 31 deletions

diff --git a/library/alloc/src/vec.rs b/library/alloc/src/vec.rs
index 9013e3fc16a..6a4fc8e3962 100644
--- a/library/alloc/src/vec.rs
+++ b/library/alloc/src/vec.rs
@@ -63,8 +63,7 @@ use core::iter::{
 };
 use core::marker::PhantomData;
 use core::mem::{self, ManuallyDrop, MaybeUninit};
-use core::ops::Bound::{Excluded, Included, Unbounded};
-use core::ops::{self, Index, IndexMut, RangeBounds};
+use core::ops::{self, Index, IndexMut, Range, RangeBounds};
 use core::ptr::{self, NonNull};
 use core::slice::{self, SliceIndex};
 
@@ -1306,35 +1305,7 @@ impl<T> Vec<T> {
         // the hole, and the vector length is restored to the new length.
         //
         let len = self.len();
-        let start = match range.start_bound() {
-            Included(&n) => n,
-            Excluded(&n) => n + 1,
-            Unbounded => 0,
-        };
-        let end = match range.end_bound() {
-            Included(&n) => n + 1,
-            Excluded(&n) => n,
-            Unbounded => len,
-        };
-
-        #[cold]
-        #[inline(never)]
-        fn start_assert_failed(start: usize, end: usize) -> ! {
-            panic!("start drain index (is {}) should be <= end drain index (is {})", start, end);
-        }
-
-        #[cold]
-        #[inline(never)]
-        fn end_assert_failed(end: usize, len: usize) -> ! {
-            panic!("end drain index (is {}) should be <= len (is {})", end, len);
-        }
-
-        if start > end {
-            start_assert_failed(start, end);
-        }
-        if end > len {
-            end_assert_failed(end, len);
-        }
+        let Range { start, end } = self.check_range(range);
 
         unsafe {
             // set self.vec length's to start, to be safe in case Drain is leaked