fix(ssr): handle fallthrough attrs in ssr compile output

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

@@ -0,0 +1,78 @@
+import { createApp } from 'vue'
+import { renderToString } from '../src/renderToString'
+
+describe('ssr: attr fallthrough', () => {
+  test('basic', async () => {
+    const Child = {
+      template: `<div class="foo" />`
+    }
+    const Parent = {
+      components: { Child },
+      template: `<child class="bar"/>`
+    }
+    const app = createApp(Parent)
+    expect(await renderToString(app)).toBe(`<div class="foo bar"></div>`)
+  })
+
+  test('with v-if', async () => {
+    const Child = {
+      props: ['ok'],
+      template: `<div v-if="ok" class="foo" /><span v-else />`
+    }
+    const Parent = {
+      props: ['ok'],
+      components: { Child },
+      template: `<child :ok="ok" class="bar"/>`
+    }
+    expect(await renderToString(createApp(Parent, { ok: true }))).toBe(
+      `<div class="foo bar"></div>`
+    )
+    expect(await renderToString(createApp(Parent, { ok: false }))).toBe(
+      `<span class="bar"></span>`
+    )
+  })
+
+  test('with v-model', async () => {
+    const Child = {
+      props: ['text'],
+      template: `<input v-model="text">`
+    }
+    const Parent = {
+      components: { Child },
+      template: `<child text="hello" class="bar"/>`
+    }
+    expect(await renderToString(createApp(Parent))).toBe(
+      `<input class="bar" value="hello">`
+    )
+  })
+
+  test('with v-bind', async () => {
+    const Child = {
+      props: ['obj'],
+      template: `<div v-bind="obj" />`
+    }
+    const Parent = {
+      components: { Child },
+      template: `<child :obj="{ class: 'foo' }" class="bar"/>`
+    }
+    expect(await renderToString(createApp(Parent))).toBe(
+      `<div class="foo bar"></div>`
+    )
+  })
+
+  test('nested fallthrough', async () => {
+    const Child = {
+      props: ['id'],
+      template: `<div :id="id"></div>`
+    }
+    const Parent = {
+      components: { Child },
+      template: `<child id="foo" class="bar"/>`
+    }
+    // pass to parent, fallthrough to child and merge
+    const app = createApp(Parent, { class: 'baz' })
+    expect(await renderToString(app)).toBe(
+      `<div id="foo" class="bar baz"></div>`
+    )
+  })
+})