feat: allow plugin to be installed in localVue

src/install.ts

@@ -1,12 +1,8 @@
 import type { VueConstructor } from 'vue'
 import { AnyObject } from './types/basic'
-import { hasSymbol, hasOwn, isPlainObject, assert } from './utils'
+import { hasSymbol, hasOwn, isPlainObject, assert, warn } from './utils'
 import { isRef } from './reactivity'
-import {
-  setVueConstructor,
-  isVueRegistered,
-  isPluginInstalled,
-} from './runtimeContext'
+import { setVueConstructor, isVueRegistered } from './runtimeContext'
 import { mixin } from './mixin'
 
 /**
@@ -44,7 +40,7 @@ function mergeData(from: AnyObject, to: AnyObject): Object {
 }
 
 export function install(Vue: VueConstructor) {
-  if (isPluginInstalled() || isVueRegistered(Vue)) {
+  if (isVueRegistered(Vue)) {
     if (__DEV__) {
       assert(
         false,
@@ -55,8 +51,12 @@ export function install(Vue: VueConstructor) {
   }
 
   if (__DEV__) {
-    if (Vue.version[0] !== '2' || Vue.version[1] !== '.') {
-      assert(false, `only works with Vue 2, v${Vue.version} found.`)
+    if (Vue.version) {
+      if (Vue.version[0] !== '2' || Vue.version[1] !== '.') {
+        assert(false, `only works with Vue 2, v${Vue.version} found.`)
+      }
+    } else {
+      warn('Vue version not found')
     }
   }
 

src/runtimeContext.ts

@@ -1,6 +1,6 @@
 import type { VueConstructor } from 'vue'
 import { ComponentInstance } from './component'
-import { assert, hasOwn } from './utils'
+import { assert, hasOwn, warn } from './utils'
 
 let vueConstructor: VueConstructor | null = null
 let currentInstance: ComponentInstance | null = null
@@ -27,6 +27,9 @@ export function getVueConstructor(): VueConstructor {
 }
 
 export function setVueConstructor(Vue: VueConstructor) {
+  if (__DEV__ && vueConstructor) {
+    warn('Another instance of vue installed')
+  }
   vueConstructor = Vue
   Object.defineProperty(Vue, PluginInstalledFlag, {
     configurable: true,

test/helpers/create-local-vue.ts

@@ -0,0 +1,33 @@
+import Vue, { VueConstructor } from 'vue'
+
+// based on https://github.com/vuejs/vue-test-utils/blob/dev/packages/test-utils/src/create-local-vue.js
+
+export function createLocalVue(_Vue: VueConstructor = Vue) {
+  const instance = _Vue.extend()
+
+  Object.keys(_Vue).forEach((key) => {
+    // @ts-ignore
+    instance[key] = _Vue[key]
+  })
+
+  // @ts-ignore
+  if (instance._installedPlugins && instance._installedPlugins.length) {
+    // @ts-ignore
+    instance._installedPlugins.length = 0
+  }
+
+  instance.config = _Vue.config
+
+  const use = instance.use
+  //@ts-ignore
+  instance.use = (plugin, ...rest) => {
+    if (plugin.installed === true) {
+      plugin.installed = false
+    }
+    if (plugin.install && plugin.install.installed === true) {
+      plugin.install.installed = false
+    }
+    use.call(instance, plugin, ...rest)
+  }
+  return instance
+}

test/use.spec.ts

@@ -0,0 +1,35 @@
+import CompositionApi from '../src'
+import { createLocalVue } from './helpers/create-local-vue'
+import { mockWarn } from './helpers'
+
+describe('use', () => {
+  mockWarn(true)
+
+  it('should allow install in multiple vue', () => {
+    const localVueOne = createLocalVue()
+    localVueOne.use(CompositionApi)
+
+    const localVueTwo = createLocalVue()
+    localVueTwo.use(CompositionApi)
+
+    expect('Another instance of vue installed').toHaveBeenWarned()
+  })
+
+  it('should warn installing multiple times', () => {
+    const localVueOne = createLocalVue()
+    localVueOne.use(CompositionApi)
+
+    expect(() => {
+      // vue prevents the same plugin of being installed, this will create a new plugin instance
+      localVueOne.use({
+        install(...args: any[]) {
+          CompositionApi.install(...args)
+        },
+      })
+    }).toThrowError(
+      'already installed. Vue.use(VueCompositionAPI) should be called only once.'
+    )
+
+    expect('Another instance of vue installed').toHaveBeenWarned()
+  })
+})