fix #1655: extend Vue parent with options to support accessing root.$store in Composition API plugin

packages/create-instance/create-instance.js

@@ -123,7 +123,13 @@ export default function createInstance(
       createChildren(this, h, options)
     )
   }
-  const Parent = _Vue.extend(parentComponentOptions)
+
+  // options  "propsData" can only be used during instance creation with the `new` keyword
+  const { propsData, ...rest } = options // eslint-disable-line
+  const Parent = _Vue.extend({
+    ...rest,
+    ...parentComponentOptions
+  })
 
   return new Parent()
 }

test/specs/mount.spec.js

@@ -419,6 +419,24 @@ describeRunIf(process.env.TEST_ENV !== 'node', 'mount', () => {
     expect(wrapper.html()).toEqual('<div>composition api</div>')
   })
 
+  it('allows accessing $root with composition api plugin', () => {
+    const localVue = createLocalVue()
+    localVue.use(Vuex)
+    localVue.use(CompositionAPI)
+    const store = new Vuex.Store({
+      state: {
+        msg: 'msg'
+      }
+    })
+    const Comp = {
+      setup(props, ctx) {
+        return () => createElement('div', ctx.root.$store.state.msg)
+      }
+    }
+    const wrapper = mount(Comp, { localVue, store })
+    expect(wrapper.html()).toEqual('<div>msg</div>')
+  })
+
   itDoNotRunIf.skip(
     vueVersion >= 2.5,
     'throws if component throws during update',