fix(vdom): svg inside foreignObject should be rendered with correct namespace (fix #7330) (#7350)

* add failed test case

* fix failed test case

* fix(vdom): svg inside foreignObject should be rendered with correct namespace

* adjust comments

Author: javoski

src/core/vdom/create-element.js

@@ -139,7 +139,8 @@ function applyNS (vnode, ns, force) {
   if (isDef(vnode.children)) {
     for (let i = 0, l = vnode.children.length; i < l; i++) {
       const child = vnode.children[i]
-      if (isDef(child.tag) && (isUndef(child.ns) || isTrue(force))) {
+      if (isDef(child.tag) && (
+        isUndef(child.ns) || (isTrue(force) && child.tag !== 'svg'))) {
         applyNS(child, ns, force)
       }
     }

test/unit/modules/vdom/create-element.spec.js

@@ -135,10 +135,12 @@ describe('create-element', () => {
   it('render svg foreignObject with correct namespace', () => {
     const vm = new Vue({})
     const h = vm.$createElement
-    const vnode = h('svg', [h('foreignObject', [h('p')])])
+    const vnode = h('svg', [h('foreignObject', [h('p'), h('svg')])])
     expect(vnode.ns).toBe('svg')
     expect(vnode.children[0].ns).toBe('svg')
     expect(vnode.children[0].children[0].ns).toBeUndefined()
+    // #7330
+    expect(vnode.children[0].children[1].ns).toBe('svg')
   })
 
   // #6642