fix: avoid array length truncation in mergeWith and add sparse merge test

src/test/mergeWith.test.ts

@@ -0,0 +1,16 @@
+import { mergeWith } from '../utils/set';
+
+describe('mergeWith array merge', () => {
+  it('should keep existing array length when merging sparse updates', () => {
+    const allValues = { list: ['A', 'B', 'C', 'D'] };
+    const changedValues = { list: new Array(2) };
+    changedValues.list[1] = 'BB'; // 仅更新第 2 项，长度为 2
+
+    const merged = mergeWith([allValues, changedValues], {
+      prepareArray: current => [...(current || [])],
+    });
+
+    expect(merged.list).toEqual(['A', 'BB', 'C', 'D']);
+    expect(merged.list).toHaveLength(4);
+  });
+});

src/utils/set.ts

@@ -111,7 +111,9 @@ export function mergeWith<T extends object>(
           }
 
           keys(value).forEach(key => {
-            internalMerge([...path, key], loopSet);
+            if (Object.getOwnPropertyDescriptor(value, key).enumerable) {
+              internalMerge([...path, key], loopSet);
+            }
           });
         }
       } else {