Rollup merge of #140526 - Natr1x:sort-direction-documentation, r=dtolnay

docs: Specify that common sort functions sort in an ascending direction

From [forum discussion](https://users.rust-lang.org/t/is-there-a-way-to-sort-a-slice-in-specifically-ascending-or-descending-order/128998?u=natr1x) it seems like the sorting direction can be expected to always be ascending (in terms of `cmp::Ordering`).

If this is the case then it would be nice to have this stated in the documentation.

Author: matthiaskrgr

library/alloc/src/slice.rs

@@ -69,7 +69,7 @@ use crate::boxed::Box;
 use crate::vec::Vec;
 
 impl<T> [T] {
-    /// Sorts the slice, preserving initial order of equal elements.
+    /// Sorts the slice in ascending order, preserving initial order of equal elements.
     ///
     /// This sort is stable (i.e., does not reorder equal elements) and *O*(*n* \* log(*n*))
     /// worst-case.
@@ -137,7 +137,8 @@ impl<T> [T] {
         stable_sort(self, T::lt);
     }
 
-    /// Sorts the slice with a comparison function, preserving initial order of equal elements.
+    /// Sorts the slice in ascending order with a comparison function, preserving initial order of
+    /// equal elements.
     ///
     /// This sort is stable (i.e., does not reorder equal elements) and *O*(*n* \* log(*n*))
     /// worst-case.
@@ -197,7 +198,8 @@ impl<T> [T] {
         stable_sort(self, |a, b| compare(a, b) == Less);
     }
 
-    /// Sorts the slice with a key extraction function, preserving initial order of equal elements.
+    /// Sorts the slice in ascending order with a key extraction function, preserving initial order
+    /// of equal elements.
     ///
     /// This sort is stable (i.e., does not reorder equal elements) and *O*(*m* \* *n* \* log(*n*))
     /// worst-case, where the key function is *O*(*m*).
@@ -252,7 +254,8 @@ impl<T> [T] {
         stable_sort(self, |a, b| f(a).lt(&f(b)));
     }
 
-    /// Sorts the slice with a key extraction function, preserving initial order of equal elements.
+    /// Sorts the slice in ascending order with a key extraction function, preserving initial order
+    /// of equal elements.
     ///
     /// This sort is stable (i.e., does not reorder equal elements) and *O*(*m* \* *n* + *n* \*
     /// log(*n*)) worst-case, where the key function is *O*(*m*).

library/core/src/slice/mod.rs

@@ -2986,7 +2986,7 @@ impl<T> [T] {
         self.binary_search_by(|k| f(k).cmp(b))
     }
 
-    /// Sorts the slice **without** preserving the initial order of equal elements.
+    /// Sorts the slice in ascending order **without** preserving the initial order of equal elements.
     ///
     /// This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not
     /// allocate), and *O*(*n* \* log(*n*)) worst-case.
@@ -3047,8 +3047,8 @@ impl<T> [T] {
         sort::unstable::sort(self, &mut T::lt);
     }
 
-    /// Sorts the slice with a comparison function, **without** preserving the initial order of
-    /// equal elements.
+    /// Sorts the slice in ascending order with a comparison function, **without** preserving the
+    /// initial order of equal elements.
     ///
     /// This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not
     /// allocate), and *O*(*n* \* log(*n*)) worst-case.
@@ -3102,8 +3102,8 @@ impl<T> [T] {
         sort::unstable::sort(self, &mut |a, b| compare(a, b) == Ordering::Less);
     }
 
-    /// Sorts the slice with a key extraction function, **without** preserving the initial order of
-    /// equal elements.
+    /// Sorts the slice in ascending order with a key extraction function, **without** preserving
+    /// the initial order of equal elements.
     ///
     /// This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not
     /// allocate), and *O*(*n* \* log(*n*)) worst-case.