[DataGrid] Ensure referential integrity of focused cell

src/components/datagrid/utils/focus.test.tsx

@@ -60,16 +60,22 @@ describe('useFocus', () => {
   });
 
   describe('focusedCell / setFocusedCell', () => {
+    const {
+      return: { focusedCell, setFocusedCell },
+      getUpdatedState,
+    } = testCustomHook(() => useFocus(mockArgs));
+
     it('gets and sets the focusedCell state', () => {
-      const {
-        return: { focusedCell, setFocusedCell },
-        getUpdatedState,
-      } = testCustomHook(() => useFocus(mockArgs));
       expect(focusedCell).toEqual(undefined);
-
       act(() => setFocusedCell([2, 2]));
       expect(getUpdatedState().focusedCell).toEqual([2, 2]);
     });
+
+    it('does not update if setFocusedCell is called with the same cell X/Y coordinates', () => {
+      const focusedCellInMemory = getUpdatedState().focusedCell;
+      act(() => getUpdatedState().setFocusedCell([2, 2]));
+      expect(getUpdatedState().focusedCell).toBe(focusedCellInMemory); // Would fail if the exact same array wasn't returned
+    });
   });
 
   describe('focusFirstVisibleInteractiveCell', () => {

src/components/datagrid/utils/focus.ts

@@ -67,10 +67,22 @@ export const useFocus = ({
     EuiDataGridFocusedCell | undefined
   >(undefined);
 
-  const setFocusedCell = useCallback((focusedCell: EuiDataGridFocusedCell) => {
-    _setFocusedCell(focusedCell);
-    setIsFocusedCellInView(true); // scrolling.ts ensures focused cells are fully in view
-  }, []);
+  const setFocusedCell = useCallback(
+    (nextFocusedCell: EuiDataGridFocusedCell) => {
+      // If the x/y coordinates remained the same, don't update. This keeps the focusedCell
+      // reference stable, and allows it to be used in places that need reference equality.
+      if (
+        nextFocusedCell[0] === focusedCell?.[0] &&
+        nextFocusedCell[1] === focusedCell?.[1]
+      ) {
+        return;
+      }
+
+      _setFocusedCell(nextFocusedCell);
+      setIsFocusedCellInView(true); // scrolling.ts ensures focused cells are fully in view
+    },
+    [focusedCell]
+  );
 
   const previousCell = useRef<EuiDataGridFocusedCell | undefined>(undefined);
   useEffect(() => {

upcoming_changelogs/6007.md

@@ -0,0 +1,4 @@
+**Bug fixes**
+
+- Fixed the focus context of `EuiDataGrid` to ensure that focusedCell maintains it's referential integrity. This ensures that React hooks can use this safely as a dependency. 
+