Fix Added behaviour for QueryOne get. (bevyengine#543)

Query unchanged as impacts performances.
Added tests in bevy_ecs/hecs

crates/bevy_ecs/hecs/src/query_one.rs

@@ -37,7 +37,11 @@ impl<'a, Q: Query> QueryOne<'a, Q> {
     pub fn get(&mut self) -> Option<<Q::Fetch as Fetch<'_>>::Item> {
         unsafe {
             let mut fetch = Q::Fetch::get(self.archetype, self.index)?;
-            Some(fetch.next())
+            if fetch.should_skip() {
+                None
+            } else {
+                Some(fetch.next())
+            }
         }
     }
 
@@ -104,7 +108,11 @@ where
     {
         unsafe {
             let mut fetch = Q::Fetch::get(self.archetype, self.index)?;
-            Some(fetch.next())
+            if fetch.should_skip() {
+                None
+            } else {
+                Some(fetch.next())
+            }
         }
     }
 

crates/bevy_ecs/hecs/tests/tests.rs

@@ -365,3 +365,35 @@ fn remove_tracking() {
         "world clears result in 'removed component' states"
     );
 }
+
+#[test]
+fn added_tracking() {
+    let mut world = World::new();
+    let a = world.spawn((123,));
+
+    assert_eq!(world.query::<&i32>().iter().count(), 1);
+    assert_eq!(world.query::<Added<i32>>().iter().count(), 1);
+    assert_eq!(world.query_mut::<&i32>().iter().count(), 1);
+    assert_eq!(world.query_mut::<Added<i32>>().iter().count(), 1);
+    assert!(world.query_one::<&i32>(a).unwrap().get().is_some());
+    assert!(world.query_one::<Added<i32>>(a).unwrap().get().is_some());
+    assert!(world.query_one_mut::<&i32>(a).unwrap().get().is_some());
+    assert!(world
+        .query_one_mut::<Added<i32>>(a)
+        .unwrap()
+        .get()
+        .is_some());
+
+    world.clear_trackers();
+
+    assert_eq!(world.query::<&i32>().iter().count(), 1);
+    assert_eq!(world.query::<Added<i32>>().iter().count(), 0);
+    assert_eq!(world.query_mut::<&i32>().iter().count(), 1);
+    assert_eq!(world.query_mut::<Added<i32>>().iter().count(), 0);
+    assert!(world.query_one_mut::<&i32>(a).unwrap().get().is_some());
+    assert!(world
+        .query_one_mut::<Added<i32>>(a)
+        .unwrap()
+        .get()
+        .is_none());
+}