BinaryHeap: fix missing safety doc

Author: newAM

src/binary_heap.rs

@@ -389,7 +389,25 @@ where
 
     /// Removes the *top* (greatest if max-heap, smallest if min-heap) item from the binary heap and
     /// returns it, without checking if the binary heap is empty.
-    #[allow(clippy::missing_safety_doc)] // TODO
+    ///
+    /// # Safety
+    ///
+    /// The binary heap must not be empty.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use heapless::binary_heap::{BinaryHeap, Max};
+    ///
+    /// let mut heap: BinaryHeap<_, Max, 8> = BinaryHeap::new();
+    /// heap.push(42).unwrap();
+    ///
+    /// if !heap.is_empty() {
+    ///     // SAFETY: the heap is not empty
+    ///     let val = unsafe { heap.pop_unchecked() };
+    ///     assert_eq!(val, 42);
+    /// }
+    /// ```
     pub unsafe fn pop_unchecked(&mut self) -> T {
         let mut item = self.data.pop_unchecked();