Slightly improve panic messages when range indices are out of bounds

Author: LukasKalbertodt

src/libcore/slice/mod.rs

@@ -2974,8 +2974,15 @@ where
 #[inline(never)]
 #[cold]
 #[track_caller]
-fn slice_index_len_fail(index: usize, len: usize) -> ! {
-    panic!("index {} out of range for slice of length {}", index, len);
+fn slice_start_index_len_fail(index: usize, len: usize) -> ! {
+    panic!("range start index {} out of range for slice of length {}", index, len);
+}
+
+#[inline(never)]
+#[cold]
+#[track_caller]
+fn slice_end_index_len_fail(index: usize, len: usize) -> ! {
+    panic!("range end index {} out of range for slice of length {}", index, len);
 }
 
 #[inline(never)]
@@ -3160,7 +3167,7 @@ unsafe impl<T> SliceIndex<[T]> for ops::Range<usize> {
         if self.start > self.end {
             slice_index_order_fail(self.start, self.end);
         } else if self.end > slice.len() {
-            slice_index_len_fail(self.end, slice.len());
+            slice_end_index_len_fail(self.end, slice.len());
         }
         unsafe { &*self.get_unchecked(slice) }
     }
@@ -3170,7 +3177,7 @@ unsafe impl<T> SliceIndex<[T]> for ops::Range<usize> {
         if self.start > self.end {
             slice_index_order_fail(self.start, self.end);
         } else if self.end > slice.len() {
-            slice_index_len_fail(self.end, slice.len());
+            slice_end_index_len_fail(self.end, slice.len());
         }
         unsafe { &mut *self.get_unchecked_mut(slice) }
     }
@@ -3242,15 +3249,15 @@ unsafe impl<T> SliceIndex<[T]> for ops::RangeFrom<usize> {
     #[inline]
     fn index(self, slice: &[T]) -> &[T] {
         if self.start > slice.len() {
-            slice_index_len_fail(self.start, slice.len());
+            slice_start_index_len_fail(self.start, slice.len());
         }
         unsafe { &*self.get_unchecked(slice) }
     }
 
     #[inline]
     fn index_mut(self, slice: &mut [T]) -> &mut [T] {
         if self.start > slice.len() {
-            slice_index_len_fail(self.start, slice.len());
+            slice_start_index_len_fail(self.start, slice.len());
         }
         unsafe { &mut *self.get_unchecked_mut(slice) }
     }

src/test/codegen/issue-69101-bounds-check.rs

@@ -12,7 +12,7 @@
 // CHECK-LABEL: @already_sliced_no_bounds_check
 #[no_mangle]
 pub fn already_sliced_no_bounds_check(a: &[u8], b: &[u8], c: &mut [u8]) {
-    // CHECK: slice_index_len_fail
+    // CHECK: slice_end_index_len_fail
     // CHECK-NOT: panic_bounds_check
     let _ = (&a[..2048], &b[..2048], &mut c[..2048]);
     for i in 0..1024 {
@@ -23,7 +23,7 @@ pub fn already_sliced_no_bounds_check(a: &[u8], b: &[u8], c: &mut [u8]) {
 // CHECK-LABEL: @already_sliced_no_bounds_check_exact
 #[no_mangle]
 pub fn already_sliced_no_bounds_check_exact(a: &[u8], b: &[u8], c: &mut [u8]) {
-    // CHECK: slice_index_len_fail
+    // CHECK: slice_end_index_len_fail
     // CHECK-NOT: panic_bounds_check
     let _ = (&a[..1024], &b[..1024], &mut c[..1024]);
     for i in 0..1024 {
@@ -35,7 +35,7 @@ pub fn already_sliced_no_bounds_check_exact(a: &[u8], b: &[u8], c: &mut [u8]) {
 // CHECK-LABEL: @already_sliced_bounds_check
 #[no_mangle]
 pub fn already_sliced_bounds_check(a: &[u8], b: &[u8], c: &mut [u8]) {
-    // CHECK: slice_index_len_fail
+    // CHECK: slice_end_index_len_fail
     // CHECK: panic_bounds_check
     let _ = (&a[..1023], &b[..2048], &mut c[..2048]);
     for i in 0..1024 {