Improve panic sections for sort*, sort_unstable* and select_nth_unsta…

…ble*

- Move panic information into # Panics section
- Fix mentions of T: Ord that should be compare
- Add missing information

library/alloc/src/slice.rs

@@ -199,7 +199,9 @@ impl<T> [T] {
     /// handled without allocation, medium sized slices allocate `self.len()` and beyond that it
     /// clamps at `self.len() / 2`.
     ///
-    /// If `T: Ord` does not implement a total order, the implementation may panic.
+    /// # Panics
+    ///
+    /// May panic if `T: Ord` does not implement a total order.
     ///
     /// # Examples
     ///
@@ -258,7 +260,9 @@ impl<T> [T] {
     /// handled without allocation, medium sized slices allocate `self.len()` and beyond that it
     /// clamps at `self.len() / 2`.
     ///
-    /// If `T: Ord` does not implement a total order, the implementation may panic.
+    /// # Panics
+    ///
+    /// May panic if `compare` does not implement a total order.
     ///
     /// # Examples
     ///
@@ -304,7 +308,9 @@ impl<T> [T] {
     /// handled without allocation, medium sized slices allocate `self.len()` and beyond that it
     /// clamps at `self.len() / 2`.
     ///
-    /// If `K: Ord` does not implement a total order, the implementation may panic.
+    /// # Panics
+    ///
+    /// May panic if `K: Ord` does not implement a total order.
     ///
     /// # Examples
     ///
@@ -356,6 +362,10 @@ impl<T> [T] {
     /// In the worst case, the algorithm allocates temporary storage in a `Vec<(K, usize)>` the
     /// length of the slice.
     ///
+    /// # Panics
+    ///
+    /// May panic if `K: Ord` does not implement a total order.
+    ///
     /// # Examples
     ///
     /// ```

library/core/src/slice/mod.rs

@@ -2898,7 +2898,9 @@ impl<T> [T] {
     /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
     /// slice is partially sorted.
     ///
-    /// If `T: Ord` does not implement a total order, the implementation may panic.
+    /// # Panics
+    ///
+    /// May panic if `T: Ord` does not implement a total order.
     ///
     /// # Examples
     ///
@@ -2955,7 +2957,9 @@ impl<T> [T] {
     /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
     /// slice is partially sorted.
     ///
-    /// If `T: Ord` does not implement a total order, the implementation may panic.
+    /// # Panics
+    ///
+    /// May panic if `compare` does not implement a total order.
     ///
     /// # Examples
     ///
@@ -2999,7 +3003,9 @@ impl<T> [T] {
     /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
     /// slice is partially sorted.
     ///
-    /// If `K: Ord` does not implement a total order, the implementation may panic.
+    /// # Panics
+    ///
+    /// May panic if `K: Ord` does not implement a total order.
     ///
     /// # Examples
     ///
@@ -3042,15 +3048,14 @@ impl<T> [T] {
     /// Median of Medians using Tukey's Ninther for pivot selection, which guarantees linear runtime
     /// for all inputs.
     ///
-    /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
-    /// slice is nearly fully sorted, where `slice::sort` may be faster.
-    ///
     /// [`sort_unstable`]: slice::sort_unstable
     ///
     /// # Panics
     ///
     /// Panics when `index >= len()`, meaning it always panics on empty slices.
     ///
+    /// May panic if `T: Ord` does not implement a total order.
+    ///
     /// # Examples
     ///
     /// ```
@@ -3103,15 +3108,14 @@ impl<T> [T] {
     /// Median of Medians using Tukey's Ninther for pivot selection, which guarantees linear runtime
     /// for all inputs.
     ///
-    /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
-    /// slice is nearly fully sorted, where `slice::sort` may be faster.
-    ///
     /// [`sort_unstable`]: slice::sort_unstable
     ///
     /// # Panics
     ///
     /// Panics when `index >= len()`, meaning it always panics on empty slices.
     ///
+    /// May panic if `compare` does not implement a total order.
+    ///
     /// # Examples
     ///
     /// ```
@@ -3168,15 +3172,14 @@ impl<T> [T] {
     /// Median of Medians using Tukey's Ninther for pivot selection, which guarantees linear runtime
     /// for all inputs.
     ///
-    /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
-    /// slice is nearly fully sorted, where `slice::sort` may be faster.
-    ///
     /// [`sort_unstable`]: slice::sort_unstable
     ///
     /// # Panics
     ///
     /// Panics when `index >= len()`, meaning it always panics on empty slices.
     ///
+    /// May panic if `K: Ord` does not implement a total order.
+    ///
     /// # Examples
     ///
     /// ```