fix(compat): handle and warn config.optionMergeStrategies

packages/vue-compat/README.md

@@ -321,6 +321,7 @@ Features that start with `COMPILER_` are compiler-specific: if you are using the
 | GLOBAL_OBSERVABLE            | ●    | `Vue.observable` removed (use `reactive`)                             | [link](https://v3.vuejs.org/api/basic-reactivity.html)                                                         |
 | CONFIG_KEY_CODES             | ●    | config.keyCodes rmeoved                                               | [link](https://v3.vuejs.org/guide/migration/keycode-modifiers.html)                                            |
 | CONFIG_WHITESPACE            | ●    | In Vue 3 whitespace defaults to `"condense"`                          |                                                                                                                |
+| CONFIG_OPTION_MERGE_STRATS   | ●    | Vue 3 no longer exposes internal option merge strats                  |                                                                                                                |
 | INSTANCE_SET                 | ●    | `vm.$set` removed (no longer needed)                                  |                                                                                                                |
 | INSTANCE_DELETE              | ●    | `vm.$delete` removed (no longer needed)                               |                                                                                                                |
 | INSTANCE_EVENT_EMITTER       | ●    | `vm.$on`, `vm.$off`, `vm.$once` removed                               | [link](https://v3.vuejs.org/guide/migration/events-api.html)                                                   |

packages/vue-compat/__tests__/globalConfig.spec.ts

@@ -1,5 +1,8 @@
 import Vue from '@vue/compat'
-import { toggleDeprecationWarning } from '../../runtime-core/src/compat/compatConfig'
+import {
+  DeprecationTypes,
+  toggleDeprecationWarning
+} from '../../runtime-core/src/compat/compatConfig'
 import { createApp } from '../src/esm-index'
 import { triggerEvent } from './utils'
 
@@ -74,3 +77,9 @@ test('singleton config should affect apps created with createApp()', () => {
   }).mount(el)
   expect(el.innerHTML).toBe(`<v-foo></v-foo><foo></foo>`)
 })
+
+test('config.optionMergeStrategies', () => {
+  toggleDeprecationWarning(true)
+  expect(typeof Vue.config.optionMergeStrategies.created).toBe('function')
+  expect(DeprecationTypes.CONFIG_OPTION_MERGE_STRATS).toHaveBeenWarned()
+})