fix(vue-template-compiler): allow comments on the root node in templates (fix #9407)

src/compiler/parser/index.js

@@ -377,16 +377,20 @@ export function parse (
       }
     },
     comment (text: string, start, end) {
-      const child: ASTText = {
-        type: 3,
-        text,
-        isComment: true
-      }
-      if (process.env.NODE_ENV !== 'production' && options.outputSourceRange) {
-        child.start = start
-        child.end = end
+      // adding anyting as a sibling to the root node is forbidden
+      // comments should still be allowed, but ignored
+      if (currentParent) {
+        const child: ASTText = {
+          type: 3,
+          text,
+          isComment: true
+        }
+        if (process.env.NODE_ENV !== 'production' && options.outputSourceRange) {
+          child.start = start
+          child.end = end
+        }
+        currentParent.children.push(child)
       }
-      currentParent.children.push(child)
     }
   })
   return root

test/unit/modules/compiler/parser.spec.js

@@ -786,6 +786,16 @@ describe('parser', () => {
     expect(ast.children[1].text).toBe('comment here')
   })
 
+  // #9407
+  it('should parse templates with comments anywhere', () => {
+    const options = extend({
+      comments: true
+    }, baseOptions)
+    const ast = parse(`<!--comment here--><div>123</div>`, options)
+    expect(ast.tag).toBe('div')
+    expect(ast.children.length).toBe(1)
+  })
+
   // #8103
   it('should allow CRLFs in string interpolations', () => {
     const ast = parse(`<p>{{\r\nmsg\r\n}}</p>`, baseOptions)
@@ -797,7 +807,7 @@ describe('parser', () => {
       preserveWhitespace: false
     }, baseOptions)
 
-     const ast = parse('<p>\n  Welcome to <b>Vue.js</b>    <i>world</i>  \n  <span>.\n  Have fun!\n</span></p>', options)
+    const ast = parse('<p>\n  Welcome to <b>Vue.js</b>    <i>world</i>  \n  <span>.\n  Have fun!\n</span></p>', options)
     expect(ast.tag).toBe('p')
     expect(ast.children.length).toBe(4)
     expect(ast.children[0].type).toBe(3)