feat(ssr): render portals (#714)

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

@@ -5,11 +5,16 @@ import {
   withScopeId,
   resolveComponent,
   ComponentOptions,
+  Portal,
   ref,
   defineComponent
 } from 'vue'
 import { escapeHtml, mockWarn } from '@vue/shared'
-import { renderToString, renderComponent } from '../src/renderToString'
+import {
+  renderToString,
+  renderComponent,
+  SSRContext
+} from '../src/renderToString'
 import { ssrRenderSlot } from '../src/helpers/ssrRenderSlot'
 
 mockWarn()
@@ -508,6 +513,21 @@ describe('ssr: renderToString', () => {
     })
   })
 
+  test('portal', async () => {
+    const ctx: SSRContext = {}
+    await renderToString(
+      h(
+        Portal,
+        {
+          target: `#target`
+        },
+        h('span', 'hello')
+      ),
+      ctx
+    )
+    expect(ctx.portals!['#target']).toBe('<span>hello</span>')
+  })
+
   describe('scopeId', () => {
     // note: here we are only testing scopeId handling for vdom serialization.
     // compiled srr render functions will include scopeId directly in strings.