Replace ad hoc implementations with `slice::check_range`

6 files changed, 24 insertions, 90 deletions

diff --git a/library/alloc/src/collections/vec_deque.rs b/library/alloc/src/collections/vec_deque.rs
index d3c6d493d6d..54cf548fac5 100644
--- a/library/alloc/src/collections/vec_deque.rs
+++ b/library/alloc/src/collections/vec_deque.rs
@@ -14,8 +14,7 @@ use core::fmt;
 use core::hash::{Hash, Hasher};
 use core::iter::{once, repeat_with, FromIterator, FusedIterator};
 use core::mem::{self, replace, ManuallyDrop};
-use core::ops::Bound::{Excluded, Included, Unbounded};
-use core::ops::{Index, IndexMut, RangeBounds, Try};
+use core::ops::{Index, IndexMut, Range, RangeBounds, Try};
 use core::ptr::{self, NonNull};
 use core::slice;
 
@@ -1083,24 +1082,16 @@ impl<T> VecDeque<T> {
         self.tail == self.head
     }
 
-    fn range_start_end<R>(&self, range: R) -> (usize, usize)
+    fn range_tail_head<R>(&self, range: R) -> (usize, usize)
     where
         R: RangeBounds<usize>,
     {
-        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,
-        };
-        assert!(start <= end, "lower bound was too large");
-        assert!(end <= len, "upper bound was too large");
-        (start, end)
+        // SAFETY: This buffer is only used to check the range.
+        let buffer = unsafe { slice::from_raw_parts(self.ptr(), self.len()) };
+        let Range { start, end } = buffer.check_range(range);
+        let tail = self.wrap_add(self.tail, start);
+        let head = self.wrap_add(self.tail, end);
+        (tail, head)
     }
 
     /// Creates an iterator that covers the specified range in the `VecDeque`.
@@ -1131,9 +1122,7 @@ impl<T> VecDeque<T> {
     where
         R: RangeBounds<usize>,
     {
-        let (start, end) = self.range_start_end(range);
-        let tail = self.wrap_add(self.tail, start);
-        let head = self.wrap_add(self.tail, end);
+        let (tail, head) = self.range_tail_head(range);
         Iter {
             tail,
             head,
@@ -1174,9 +1163,7 @@ impl<T> VecDeque<T> {
     where
         R: RangeBounds<usize>,
     {
-        let (start, end) = self.range_start_end(range);
-        let tail = self.wrap_add(self.tail, start);
-        let head = self.wrap_add(self.tail, end);
+        let (tail, head) = self.range_tail_head(range);
         IterMut {
             tail,
             head,
@@ -1230,7 +1217,7 @@ impl<T> VecDeque<T> {
         // When finished, the remaining data will be copied back to cover the hole,
         // and the head/tail values will be restored correctly.
         //
-        let (start, end) = self.range_start_end(range);
+        let (drain_tail, drain_head) = self.range_tail_head(range);
 
         // The deque's elements are parted into three segments:
         // * self.tail  -> drain_tail
@@ -1248,8 +1235,6 @@ impl<T> VecDeque<T> {
         //        T   t   h   H
         // [. . . o o x x o o . . .]
         //
-        let drain_tail = self.wrap_add(self.tail, start);
-        let drain_head = self.wrap_add(self.tail, end);
         let head = self.head;
 
         // "forget" about the values after the start of the drain until after
diff --git a/library/alloc/src/lib.rs b/library/alloc/src/lib.rs
index 9ac23886d4e..514b0bf918a 100644
--- a/library/alloc/src/lib.rs
+++ b/library/alloc/src/lib.rs
@@ -114,6 +114,7 @@
 #![feature(rustc_attrs)]
 #![feature(receiver_trait)]
 #![feature(min_specialization)]
+#![feature(slice_check_range)]
 #![feature(slice_ptr_get)]
 #![feature(slice_ptr_len)]
 #![feature(staged_api)]
diff --git a/library/alloc/src/string.rs b/library/alloc/src/string.rs
index d7d7b6bd157..b3ac4397f17 100644
--- a/library/alloc/src/string.rs
+++ b/library/alloc/src/string.rs
@@ -47,7 +47,7 @@ use core::fmt;
 use core::hash;
 use core::iter::{FromIterator, FusedIterator};
 use core::ops::Bound::{Excluded, Included, Unbounded};
-use core::ops::{self, Add, AddAssign, Index, IndexMut, RangeBounds};
+use core::ops::{self, Add, AddAssign, Index, IndexMut, Range, RangeBounds};
 use core::ptr;
 use core::str::{lossy, pattern::Pattern};
 
@@ -1506,23 +1506,15 @@ impl String {
         // of the vector version. The data is just plain bytes.
         // Because the range removal happens in Drop, if the Drain iterator is leaked,
         // the removal will not happen.
-        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,
-        };
+        let Range { start, end } = self.as_bytes().check_range(range);
+        assert!(self.is_char_boundary(start));
+        assert!(self.is_char_boundary(end));
 
         // Take out two simultaneous borrows. The &mut String won't be accessed
         // until iteration is over, in Drop.
         let self_ptr = self as *mut _;
-        // slicing does the appropriate bounds checks
-        let chars_iter = self[start..end].chars();
+        // SAFETY: `check_range` and `is_char_boundary` do the appropriate bounds checks.
+        let chars_iter = unsafe { self.get_unchecked(start..end) }.chars();
 
         Drain { start, end, iter: chars_iter, string: self_ptr }
     }
diff --git a/library/alloc/src/vec.rs b/library/alloc/src/vec.rs
index 786d1b6ba82..a29985256aa 100644
--- a/library/alloc/src/vec.rs
+++ b/library/alloc/src/vec.rs
@@ -66,8 +66,7 @@ use core::intrinsics::{arith_offset, assume};
 use core::iter::{FromIterator, FusedIterator, TrustedLen};
 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};
 
@@ -1311,35 +1310,7 @@ 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
diff --git a/library/core/src/slice/mod.rs b/library/core/src/slice/mod.rs
index dafb3e44d75..066368d5de5 100644
--- a/library/core/src/slice/mod.rs
+++ b/library/core/src/slice/mod.rs
@@ -2511,26 +2511,11 @@ impl<T> [T] {
     /// ```
     #[stable(feature = "copy_within", since = "1.37.0")]
     #[track_caller]
-    pub fn copy_within<R: ops::RangeBounds<usize>>(&mut self, src: R, dest: usize)
+    pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
     where
         T: Copy,
     {
-        let src_start = match src.start_bound() {
-            ops::Bound::Included(&n) => n,
-            ops::Bound::Excluded(&n) => {
-                n.checked_add(1).unwrap_or_else(|| slice_start_index_overflow_fail())
-            }
-            ops::Bound::Unbounded => 0,
-        };
-        let src_end = match src.end_bound() {
-            ops::Bound::Included(&n) => {
-                n.checked_add(1).unwrap_or_else(|| slice_end_index_overflow_fail())
-            }
-            ops::Bound::Excluded(&n) => n,
-            ops::Bound::Unbounded => self.len(),
-        };
-        assert!(src_start <= src_end, "src end is before src start");
-        assert!(src_end <= self.len(), "src is out of bounds");
+        let Range { start: src_start, end: src_end } = self.check_range(src);
         let count = src_end - src_start;
         assert!(dest <= self.len() - count, "dest is out of bounds");
         unsafe {
diff --git a/library/core/tests/slice.rs b/library/core/tests/slice.rs
index 42b483f33ba..abe321c9daa 100644
--- a/library/core/tests/slice.rs
+++ b/library/core/tests/slice.rs
@@ -1797,7 +1797,7 @@ fn test_copy_within() {
 }
 
 #[test]
-#[should_panic(expected = "src is out of bounds")]
+#[should_panic(expected = "range end index 14 out of range for slice of length 13")]
 fn test_copy_within_panics_src_too_long() {
     let mut bytes = *b"Hello, World!";
     // The length is only 13, so 14 is out of bounds.
@@ -1812,7 +1812,7 @@ fn test_copy_within_panics_dest_too_long() {
     bytes.copy_within(0..4, 10);
 }
 #[test]
-#[should_panic(expected = "src end is before src start")]
+#[should_panic(expected = "slice index starts at 2 but ends at 1")]
 fn test_copy_within_panics_src_inverted() {
     let mut bytes = *b"Hello, World!";
     // 2 is greater than 1, so this range is invalid.