fix: messages deepCopy mutates src arguments

packages/shared/src/messages.ts

@@ -12,8 +12,15 @@ export function deepCopy(src: any, des: any): void {
  while (stack.length) {
  const { src, des } = stack.pop()!
 
+ // using `Object.keys` which skips prototype properties
  Object.keys(src).forEach(key => {
- if (isNotObjectOrIsArray(src[key]) || isNotObjectOrIsArray(des[key])) {
+ // if src[key] is an object/array, set des[key]
+ // to empty object/array to prevent setting by reference
+ if (isObject(src[key]) && !isObject(des[key])) {
+ des[key] = Array.isArray(src[key]) ? [] : {}
+ }
+
+ if (isNotObjectOrIsArray(des[key]) || isNotObjectOrIsArray(src[key])) {
  // replace with src[key] when:
  // src[key] or des[key] is not an object, or
  // src[key] or des[key] is an array

packages/shared/test/messages.test.ts

@@ -0,0 +1,50 @@
+import { deepCopy } from '../src/index'
+
+test('deepCopy merges without mutating src argument', () => {
+ const msg1 = {
+ hello: 'Greetings',
+ about: {
+ title: 'About us'
+ },
+ overwritten: 'Original text',
+ fruit: [{ name: 'Apple' }]
+ }
+ const copy1 = structuredClone(msg1)
+
+ const msg2 = {
+ bye: 'Goodbye',
+ about: {
+ content: 'Some text'
+ },
+ overwritten: 'New text',
+ fruit: [{ name: 'Strawberry' }],
+ // @ts-ignore
+ car: ({ plural }) => plural(['car', 'cars'])
+ }
+
+ const merged = {}
+
+ deepCopy(msg1, merged)
+ deepCopy(msg2, merged)
+
+ expect(merged).toMatchInlineSnapshot(`
+ {
+ "about": {
+ "content": "Some text",
+ "title": "About us",
+ },
+ "bye": "Goodbye",
+ "car": [Function],
+ "fruit": [
+ {
+ "name": "Strawberry",
+ },
+ ],
+ "hello": "Greetings",
+ "overwritten": "New text",
+ }
+ `)
+
+ // should not mutate source object
+ expect(msg1).toStrictEqual(copy1)
+})