Tree respects size prop regardless of virtualization (#2327)

.changeset/few-apples-jog.md

@@ -0,0 +1,5 @@
+---
+'@itwin/itwinui-react': patch
+---
+
+Fixed a `Tree` bug where the `size` prop was not respected when virtualization was enabled.

packages/itwinui-react/src/core/Tree/Tree.test.tsx

@@ -348,8 +348,13 @@ it('should set correct computed aria attributes to nodes', () => {
   expect(node3_1.getAttribute('aria-posinset')).toBe('1');
 });
 
-it('should respect size prop', () => {
-  const { container } = renderComponent({ props: { size: 'small' } });
-  const tree = container.querySelector('.iui-tree') as HTMLElement;
-  expect(tree).toHaveAttribute('data-iui-size', 'small');
-});
+it.each([true, false])(
+  'should respect size prop (enableVirtualization=%s)',
+  (enableVirtualization) => {
+    const { container } = renderComponent({
+      props: { size: 'small', enableVirtualization },
+    });
+    const tree = container.querySelector('.iui-tree') as HTMLElement;
+    expect(tree).toHaveAttribute('data-iui-size', 'small');
+  },
+);

packages/itwinui-react/src/core/Tree/Tree.tsx

@@ -353,6 +353,7 @@ export const Tree = <T,>(props: TreeProps<T>) => {
           onKeyDown={handleKeyDown}
           ref={treeRef}
           className={className}
+          data-iui-size={size === 'small' ? 'small' : undefined}
           style={style}
           {...rest}
         />