Handle case when rowHeight prop value is a callback

Author: fritz-c

src/react-sortable-tree.js

@@ -357,7 +357,7 @@ class ReactSortableTree extends Component {
                             height={height}
                             style={innerStyle}
                             rowCount={rows.length}
-                            estimatedRowSize={rowHeight}
+                            estimatedRowSize={typeof rowHeight !== 'function' ? rowHeight : undefined}
                             rowHeight={rowHeight}
                             rowRenderer={({ index, key, style: rowStyle }) => this.renderRow(
                                 rows[index],
@@ -381,7 +381,7 @@ class ReactSortableTree extends Component {
                     node:      row.node,
                     treeIndex: row.treeIndex,
                 }),
-                { height: rowHeight },
+                { height: typeof rowHeight !== 'function' ? rowHeight : rowHeight({ index }) },
                 () => (rows[index - 1] || null),
                 matchKeys
             ));

src/react-sortable-tree.test.js

@@ -158,13 +158,19 @@ describe('<SortableTree />', () => {
     it('should change height according to rowHeight prop', () => {
         const wrapper = mount(
             <SortableTree
-                treeData={[{ title: 'a' }]}
+                treeData={[{ title: 'a' }, { title: 'b' }]}
                 onChange={() => {}}
                 rowHeight={12}
             />
         );
 
-        expect(wrapper.find(TreeNode)).toHaveStyle('height', 12);
+        // Works with static value
+        expect(wrapper.find(TreeNode).first()).toHaveStyle('height', 12);
+
+        // Works with function callback
+        wrapper.setProps({ rowHeight: ({ index }) => 42 + index });
+        expect(wrapper.find(TreeNode).first()).toHaveStyle('height', 42);
+        expect(wrapper.find(TreeNode).last()).toHaveStyle('height', 43);
     });
 
     it('should change scaffold width according to scaffoldBlockPxWidth prop', () => {