Rollup merge of #85666 - fee1-dead:document-shared-from-cow, r=dtolnay

Document shared_from_cow functions

library/alloc/src/rc.rs

@@ -1859,6 +1859,18 @@ where
  B: ToOwned + ?Sized,
  Rc<B>: From<&'a B> + From<B::Owned>,
 {
+ /// Create a reference-counted pointer from
+ /// a clone-on-write pointer by copying its content.
+ ///
+ /// # Example
+ ///
+ /// ```rust
+ /// # use std::rc::Rc;
+ /// # use std::borrow::Cow;
+ /// let cow: Cow<str> = Cow::Borrowed("eggplant");
+ /// let shared: Rc<str> = Rc::from(cow);
+ /// assert_eq!("eggplant", &shared[..]);
+ /// ```
  #[inline]
  fn from(cow: Cow<'a, B>) -> Rc<B> {
  match cow {

library/alloc/src/sync.rs

@@ -2413,6 +2413,18 @@ where
  B: ToOwned + ?Sized,
  Arc<B>: From<&'a B> + From<B::Owned>,
 {
+ /// Create an atomically reference-counted pointer from
+ /// a clone-on-write pointer by copying its content.
+ ///
+ /// # Example
+ ///
+ /// ```rust
+ /// # use std::sync::Arc;
+ /// # use std::borrow::Cow;
+ /// let cow: Cow<str> = Cow::Borrowed("eggplant");
+ /// let shared: Arc<str> = Arc::from(cow);
+ /// assert_eq!("eggplant", &shared[..]);
+ /// ```
  #[inline]
  fn from(cow: Cow<'a, B>) -> Arc<B> {
  match cow {