fix(compiler-sfc): lang="" on a html tag produces error

Author: edison1105

packages/compiler-sfc/__tests__/parse.spec.ts

@@ -144,14 +144,10 @@ h1 { color: red }
     expect(descriptor.template!.content).toBe(content)
   })
 
-  test('error tolerance', () => {
-    const { errors } = parse(`<template>`)
-    expect(errors.length).toBe(1)
-  })
-
-  test('should parse as DOM by default', () => {
+  //#2566
+  test('only template lang be treated as plain text', () => {
     const { errors } = parse(`
-    <template>
+    <template lang="pug">
       <div lang="">
         <div></div>
       </div>
@@ -160,6 +156,16 @@ h1 { color: red }
     expect(errors.length).toBe(0)
   })
 
+  test('error tolerance', () => {
+    const { errors } = parse(`<template>`)
+    expect(errors.length).toBe(1)
+  })
+
+  test('should parse as DOM by default', () => {
+    const { errors } = parse(`<template><input></template>`)
+    expect(errors.length).toBe(0)
+  })
+
   test('custom compiler', () => {
     const { errors } = parse(`<template><input></template>`, {
       compiler: {