fix: replaceDeepEqual special case for non-plain arrays (TanStack#3669)

* Fix case where replaceDeepEqual was returning incorrect value for non-plain arrays

* fix pr comments

Author: jxom

src/core/tests/utils.test.tsx

@@ -6,6 +6,7 @@ import {
   matchMutation,
   scheduleMicrotask,
   sleep,
+  isPlainArray,
 } from '../utils'
 import { Mutation } from '../mutation'
 import { createQueryClient } from '../../tests/utils'
@@ -56,6 +57,16 @@ describe('core/utils', () => {
     })
   })
 
+  describe('isPlainArray', () => {
+    it('should return `true` for plain arrays', () => {
+      expect(isPlainArray([1, 2])).toEqual(true)
+    })
+
+    it('should return `false` for non plain arrays', () => {
+      expect(isPlainArray(Object.assign([1, 2], { a: 'b' }))).toEqual(false)
+    })
+  })
+
   describe('partialDeepEqual', () => {
     it('should return `true` if a includes b', () => {
       const a = { a: { b: 'b' }, c: 'c', d: [{ d: 'd ' }] }
@@ -258,6 +269,13 @@ describe('core/utils', () => {
       expect(result[1]).toBe(prev[1])
     })
 
+    it('should support objects which are not plain arrays', () => {
+      const prev = Object.assign([1, 2], { a: { b: 'b' }, c: 'c' })
+      const next = Object.assign([1, 2], { a: { b: 'b' }, c: 'c' })
+      const result = replaceEqualDeep(prev, next)
+      expect(result).toBe(next)
+    })
+
     it('should replace all parent objects if some nested value changes', () => {
       const prev = {
         todo: { id: '1', meta: { createdAt: 0 }, state: { done: false } },

src/core/utils.ts

@@ -314,7 +314,7 @@ export function replaceEqualDeep(a: any, b: any): any {
     return a
   }
 
-  const array = Array.isArray(a) && Array.isArray(b)
+  const array = isPlainArray(a) && isPlainArray(b)
 
   if (array || (isPlainObject(a) && isPlainObject(b))) {
     const aSize = array ? a.length : Object.keys(a).length
@@ -355,6 +355,10 @@ export function shallowEqualObjects<T>(a: T, b: T): boolean {
   return true
 }
 
+export function isPlainArray(value: unknown) {
+  return Array.isArray(value) && value.length === Object.keys(value).length
+}
+
 // Copied from: https://github.com/jonschlinkert/is-plain-object
 export function isPlainObject(o: any): o is Object {
   if (!hasObjectPrototype(o)) {