fix(validators): support components returning render function from setup

fix vuejs#1596

Author: LeBenLeBen

packages/shared/validators.js

@@ -45,6 +45,10 @@ export function isVueComponent(c: any): boolean {
     return true
   }
 
+  if (typeof c.setup === 'function' && !c.render) {
+    return true
+  }
+
   return typeof c.render === 'function'
 }
 

test/specs/mount.spec.js

@@ -452,6 +452,27 @@ describeRunIf(process.env.TEST_ENV !== 'node', 'mount', () => {
     expect(wrapper.html()).to.equal('<div>composition api</div>')
   })
 
+  it('supports components returning render function from setup as stubs', () => {
+    const localVue = createLocalVue()
+    localVue.use(CompositionAPI)
+    const Parent = {
+      setup(props, { slots }) {
+        return () => createElement('div', slots.default())
+      }
+    }
+    const Child = {
+      setup() {
+        return () => createElement('div', 'child')
+      }
+    }
+    const wrapper = mount(Parent, {
+      localVue,
+      stubs: { child: Child },
+      slots: { default: [`<child />`] }
+    })
+    expect(wrapper.html()).to.equal('<div>\n  <div>child</div>\n</div>')
+  })
+
   itDoNotRunIf.skip(
     vueVersion >= 2.5,
     'throws if component throws during update',