Add <Datagrid empty> prop to display column headers even on empty lists

docs/List.md

@@ -1981,6 +1981,7 @@ Here are all the props accepted by the component:
 * [`isRowExpandable`](#isrowexpandable)
 * [`isRowSelectable`](#isrowselectable)
 * [`optimized`](#performance)
+* [`empty`](#empty)
 
 Additional props are passed down to [the material-ui `<Table>` element](https://material-ui.com/api/table/).
 
@@ -2261,6 +2262,10 @@ const PostList = props => (
 export default withStyles(styles)(PostList);
 ```
 
+### Empty
+
+It's possible that a Datagrid will have no records to display. If the Datagrid's parent component handles the loading state, the Datagrid will return `null` and render nothing.
+Passing through a component to the `empty` prop will cause the Datagrid to render the `empty` component instead of `null`.
 ### CSS API
 
 The `Datagrid` component accepts the usual `className` prop but you can override many class names injected to the inner components by React-admin thanks to the `classes` property (as most Material UI components, see their [documentation about it](https://material-ui.com/customization/components/#overriding-styles-with-classes)). This property accepts the following keys:

packages/ra-ui-materialui/src/list/datagrid/Datagrid.spec.tsx

@@ -47,6 +47,26 @@ describe('<Datagrid />', () => {
         expect(contextValue.onSelect).toHaveBeenCalledTimes(0);
     });
 
+    it('should display the correct empty component', () => {
+        const Empty = () => <div>No records to show</div>;
+
+        const emptyData = {
+            ...contextValue,
+            data: [],
+            ids: [],
+        };
+
+        const { queryByText } = renderWithRedux(
+            <ListContextProvider value={emptyData}>
+                <Datagrid empty={<Empty />} hasBulkActions>
+                    <TitleField />
+                </Datagrid>
+            </ListContextProvider>
+        );
+
+        expect(queryByText('No records to show')).toBeTruthy();
+    });
+
     describe('selecting items with the shift key', () => {
         it('should call onSelect with the correct ids when the last selection is after the first', () => {
             const Test = ({ selectedIds = [] }) => (

packages/ra-ui-materialui/src/list/datagrid/Datagrid.tsx

@@ -117,6 +117,7 @@ const Datagrid: FC<DatagridProps> = React.forwardRef((props, ref) => {
         children,
         classes: classesOverride,
         className,
+        empty,
         expand,
         hasBulkActions = false,
         hover,
@@ -242,9 +243,13 @@ const Datagrid: FC<DatagridProps> = React.forwardRef((props, ref) => {
     /**
      * Once loaded, the data for the list may be empty. Instead of
      * displaying the table header with zero data rows,
-     * the datagrid displays nothing in this case.
+     * the datagrid displays nothing or a custom empty component.
      */
     if (loaded && (ids.length === 0 || total === 0)) {
+        if (empty) {
+            return empty;
+        }
+
         return null;
     }
 
@@ -353,6 +358,7 @@ Datagrid.propTypes = {
         order: PropTypes.string.isRequired,
     }),
     data: PropTypes.any,
+    empty: PropTypes.element,
     // @ts-ignore
     expand: PropTypes.oneOfType([PropTypes.element, PropTypes.elementType]),
     hasBulkActions: PropTypes.bool,
@@ -387,6 +393,7 @@ export interface DatagridProps<RecordType extends Record = Record>
           }>;
     hasBulkActions?: boolean;
     hover?: boolean;
+    empty?: ReactElement;
     isRowSelectable?: (record: Record) => boolean;
     isRowExpandable?: (record: Record) => boolean;
     optimized?: boolean;