Rollup merge of #92953 - azdavis:azdavis-copy-example, r=dtolnay

Copy an example to PartialOrd as well

In https://github.com/rust-lang/rust/pull/88202 I added an example for deriving PartialOrd on enums, but only later did I realize that I actually put the example on Ord.

This copies the example to PartialOrd as well, which is where I intended for it to be.

We could also delete the example on Ord, but I see there's already some highly similar examples shared between Ord and PartialOrd, so I figured we could leave it.

I also changed some type annotations in an example from `x : T` to the more common style (in Rust) of `x: T`.

library/core/src/cmp.rs

@@ -661,20 +661,37 @@ impl<T: Clone> Clone for Reverse<T> {
 ///
 /// ## Derivable
 ///
-/// This trait can be used with `#[derive]`. When `derive`d on structs, it will produce a
-/// [lexicographic](https://en.wikipedia.org/wiki/Lexicographic_order) ordering based on the top-to-bottom declaration order of the struct's members.
-/// When `derive`d on enums, variants are ordered by their top-to-bottom discriminant order.
-/// This means variants at the top are less than variants at the bottom.
-/// Here's an example:
+/// This trait can be used with `#[derive]`.
+///
+/// When `derive`d on structs, it will produce a
+/// [lexicographic](https://en.wikipedia.org/wiki/Lexicographic_order) ordering
+/// based on the top-to-bottom declaration order of the struct's members.
+///
+/// When `derive`d on enums, variants are ordered by their discriminants.
+/// By default, the discriminant is smallest for variants at the top, and
+/// largest for variants at the bottom. Here's an example:
 ///
 /// ```
-/// #[derive(PartialEq, PartialOrd)]
-/// enum Size {
-///     Small,
-///     Large,
+/// #[derive(PartialEq, Eq, PartialOrd, Ord)]
+/// enum E {
+///     Top,
+///     Bottom,
 /// }
 ///
-/// assert!(Size::Small < Size::Large);
+/// assert!(E::Top < E::Bottom);
+/// ```
+///
+/// However, manually setting the discriminants can override this default
+/// behavior:
+///
+/// ```
+/// #[derive(PartialEq, Eq, PartialOrd, Ord)]
+/// enum E {
+///     Top = 2,
+///     Bottom = 1,
+/// }
+///
+/// assert!(E::Bottom < E::Top);
 /// ```
 ///
 /// ## Lexicographical comparison
@@ -895,9 +912,38 @@ impl PartialOrd for Ordering {
 ///
 /// ## Derivable
 ///
-/// This trait can be used with `#[derive]`. When `derive`d on structs, it will produce a
-/// lexicographic ordering based on the top-to-bottom declaration order of the struct's members.
-/// When `derive`d on enums, variants are ordered by their top-to-bottom discriminant order.
+/// This trait can be used with `#[derive]`.
+///
+/// When `derive`d on structs, it will produce a
+/// [lexicographic](https://en.wikipedia.org/wiki/Lexicographic_order) ordering
+/// based on the top-to-bottom declaration order of the struct's members.
+///
+/// When `derive`d on enums, variants are ordered by their discriminants.
+/// By default, the discriminant is smallest for variants at the top, and
+/// largest for variants at the bottom. Here's an example:
+///
+/// ```
+/// #[derive(PartialEq, PartialOrd)]
+/// enum E {
+///     Top,
+///     Bottom,
+/// }
+///
+/// assert!(E::Top < E::Bottom);
+/// ```
+///
+/// However, manually setting the discriminants can override this default
+/// behavior:
+///
+/// ```
+/// #[derive(PartialEq, PartialOrd)]
+/// enum E {
+///     Top = 2,
+///     Bottom = 1,
+/// }
+///
+/// assert!(E::Bottom < E::Top);
+/// ```
 ///
 /// ## How can I implement `PartialOrd`?
 ///
@@ -970,8 +1016,8 @@ impl PartialOrd for Ordering {
 /// # Examples
 ///
 /// ```
-/// let x : u32 = 0;
-/// let y : u32 = 1;
+/// let x: u32 = 0;
+/// let y: u32 = 1;
 ///
 /// assert_eq!(x < y, true);
 /// assert_eq!(x.lt(&y), true);