fix(shallowReadonly): align behavior with vue-next (#741)

Author: ygj6

src/reactivity/readonly.ts

@@ -1,5 +1,5 @@
 import { reactive, Ref, UnwrapRef } from '.'
-import { isArray, isPlainObject, warn } from '../utils'
+import { isArray, isPlainObject, isObject, warn } from '../utils'
 import { readonlySet } from '../utils/sets'
 import { isReactive, observe } from './reactive'
 import { isRef, RefImpl } from './ref'
@@ -49,6 +49,13 @@ export function readonly<T extends object>(
 
 export function shallowReadonly<T extends object>(obj: T): Readonly<T>
 export function shallowReadonly(obj: any): any {
+  if (!isObject(obj)) {
+    if (__DEV__) {
+      warn(`value cannot be made reactive: ${String(obj)}`)
+    }
+    return obj
+  }
+
   if (
     !(isPlainObject(obj) || isArray(obj)) ||
     (!Object.isExtensible(obj) && !isRef(obj))

test/v3/reactivity/readonly.spec.ts

@@ -382,6 +382,12 @@ describe('reactivity/readonly', () => {
       ).not.toHaveBeenWarned()
     })
 
+    test('should not process non-object data', () => {
+      // @ts-ignore
+      shallowReadonly(25)
+      expect(`value cannot be made reactive: 25`).toHaveBeenWarned()
+    })
+
     // #669
     test('shallowReadonly should work for refs', () => {
       const vm = new Vue({