fix: insertion order when dropping at folder (#315)

Author: lukasbach

packages/core/src/uncontrolledEnvironment/UncontrolledTreeEnvironment.tsx

@@ -131,7 +131,12 @@ export const UncontrolledTreeEnvironment = React.forwardRef<
       }}
       onDrop={async (items, target) => {
         const promises: Promise<void>[] = [];
-        for (const item of items) {
+
+        // when dropped between items, items are injected at top of insertion point each
+        const orderedItems =
+          target.targetType === 'between-items' ? [...items].reverse() : items;
+
+        for (const item of orderedItems) {
           const parent = Object.values(currentItems).find(potentialParent =>
             potentialParent.children?.includes(item.index)
           );

packages/core/test/dnd-basics.spec.tsx

@@ -202,6 +202,23 @@ describe('dnd basics', () => {
       ]);
     });
 
+    it('drag items with scrambled order into another folder', async () => {
+      const test = await new TestUtil().renderOpenTree();
+      await test.selectItems('aac', 'aad', 'aab');
+      await test.startDrag('aab');
+      await test.dragOver('target-parent');
+      await test.drop();
+      await test.expectVisibleItemContents('aa', ['aaa']);
+      await test.expectVisibleItemContents('target-parent', [
+        'before',
+        'target',
+        'after',
+        'aab',
+        'aac',
+        'aad',
+      ]);
+    });
+
     it('drag folders into another opened folder', async () => {
       const test = await new TestUtil().renderOpenTree();
       await test.selectItems('ab', 'ac', 'ad');