fix(ssr): render components returning render function from setup (#720)

packages/server-renderer/__tests__/renderToString.spec.ts

@@ -4,7 +4,9 @@ import {
   createCommentVNode,
   withScopeId,
   resolveComponent,
-  ComponentOptions
+  ComponentOptions,
+  ref,
+  defineComponent
 } from 'vue'
 import { escapeHtml, mockWarn } from '@vue/shared'
 import { renderToString, renderComponent } from '../src/renderToString'
@@ -43,6 +45,32 @@ describe('ssr: renderToString', () => {
       ).toBe(`<div>hello</div>`)
     })
 
+    test('option components returning render from setup', async () => {
+      expect(
+        await renderToString(
+          createApp({
+            setup() {
+              const msg = ref('hello')
+              return () => h('div', msg.value)
+            }
+          })
+        )
+      ).toBe(`<div>hello</div>`)
+    })
+
+    test('setup components returning render from setup', async () => {
+      expect(
+        await renderToString(
+          createApp(
+            defineComponent((props: {}) => {
+              const msg = ref('hello')
+              return () => h('div', msg.value)
+            })
+          )
+        )
+      ).toBe(`<div>hello</div>`)
+    })
+
     test('optimized components', async () => {
       expect(
         await renderToString(

packages/server-renderer/src/renderToString.ts

@@ -177,7 +177,7 @@ function renderComponentSubTree(
   if (isFunction(comp)) {
     renderVNode(push, renderComponentRoot(instance), instance)
   } else {
-    if (!comp.ssrRender && !comp.render && isString(comp.template)) {
+    if (!instance.render && !comp.ssrRender && isString(comp.template)) {
       comp.ssrRender = ssrCompile(comp.template, instance)
     }
 
@@ -187,7 +187,7 @@ function renderComponentSubTree(
       setCurrentRenderingInstance(instance)
       comp.ssrRender(instance.proxy, push, instance)
       setCurrentRenderingInstance(null)
-    } else if (comp.render) {
+    } else if (instance.render) {
       renderVNode(push, renderComponentRoot(instance), instance)
     } else {
       throw new Error(