Double the capacity of a full BlobVec after push

crates/bevy_ecs/src/storage/blob_vec.rs

@@ -119,6 +119,17 @@ impl BlobVec {
         }
     }
 
+    /// Similar to `reserve_exact`. This method ensures that the capacity will grow at least `self.capacity()` if there is no
+    /// enough space to hold `additional` more elements.
+    pub fn reserve(&mut self, additional: usize) {
+        let available_space = self.capacity - self.len;
+        if available_space < additional && self.item_layout.size() > 0 {
+            let extra_space = self.capacity.max(additional - available_space);
+            let increment = unsafe { NonZeroUsize::new_unchecked(extra_space) };
+            unsafe { self.grow_exact(increment) };
+        }
+    }
+
     // SAFETY: must not be called for a ZST item layout
     #[warn(unsafe_op_in_unsafe_fn)] // to allow unsafe blocks in unsafe fn
     unsafe fn grow_exact(&mut self, increment: NonZeroUsize) {
@@ -230,7 +241,7 @@ impl BlobVec {
     /// The `value` must match the [`layout`](`BlobVec::layout`) of the elements in the [`BlobVec`].
     #[inline]
     pub unsafe fn push(&mut self, value: OwningPtr<'_>) {
-        self.reserve_exact(1);
+        self.reserve(1);
         let index = self.len;
         self.len += 1;
         self.initialize_unchecked(index, value);
@@ -519,7 +530,7 @@ mod tests {
         }
 
         assert_eq!(blob_vec.len(), 1_000);
-        assert_eq!(blob_vec.capacity(), 1_000);
+        assert_eq!(blob_vec.capacity(), 1_024);
     }
 
     #[derive(Debug, Eq, PartialEq, Clone)]
@@ -579,19 +590,19 @@ mod tests {
 
                 push(&mut blob_vec, foo3.clone());
                 assert_eq!(blob_vec.len(), 3);
-                assert_eq!(blob_vec.capacity(), 3);
+                assert_eq!(blob_vec.capacity(), 4);
 
                 let last_index = blob_vec.len() - 1;
                 let value = swap_remove::<Foo>(&mut blob_vec, last_index);
                 assert_eq!(foo3, value);
 
                 assert_eq!(blob_vec.len(), 2);
-                assert_eq!(blob_vec.capacity(), 3);
+                assert_eq!(blob_vec.capacity(), 4);
 
                 let value = swap_remove::<Foo>(&mut blob_vec, 0);
                 assert_eq!(foo1, value);
                 assert_eq!(blob_vec.len(), 1);
-                assert_eq!(blob_vec.capacity(), 3);
+                assert_eq!(blob_vec.capacity(), 4);
 
                 foo2.a = 8;
                 assert_eq!(get_mut::<Foo>(&mut blob_vec, 0), &foo2);