Add pop_if() to Vec (#301)

* Added pop_if() to Vec, which has been stable in the stdlib since 1.86

* Fixed formatting

Author: timtom-rs

src/collections/vec.rs

@@ -1511,6 +1511,33 @@ impl<'bump, T: 'bump> Vec<'bump, T> {
         }
     }
 
+    /// Removes and returns the last element from a vector if the predicate
+    /// returns `true`, or [`None`] if the predicate returns false or the vector
+    /// is empty (the predicate will not be called in that case).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    /// let mut vec = bumpalo::vec![in &b; 1, 2, 3, 4];
+    /// let pred = |x: &mut i32| *x % 2 == 0;
+    ///
+    /// assert_eq!(vec.pop_if(pred), Some(4));
+    /// assert_eq!(vec, [1, 2, 3]);
+    /// assert_eq!(vec.pop_if(pred), None);
+    /// ```
+    #[inline]
+    pub fn pop_if(&mut self, predicate: impl FnOnce(&mut T) -> bool) -> Option<T> {
+        let last = self.last_mut()?;
+        if predicate(last) {
+            self.pop()
+        } else {
+            None
+        }
+    }
+
     /// Moves all the elements of `other` into `Self`, leaving `other` empty.
     ///
     /// # Panics