mustache in class compiles to undefined

[xuanyan0x7c7]

var child = {
  template: '<div class="one"></div>'
}
var parent = {
  template: '<child class="pre-{{name}}"></child>',
  data() {
    return {name: "two"}
  },
  components: {child}
}

It compiles to <div class="one pre-undefined"></div>.
The bug won't appear if there is no class attribute on the root of child component.

[yyx990803]

Note after the fix, the parent class will overwrite the child class. This is because class="{{ abc }}" always sets the entire class. If you want to preserve child class you should still use v-bind:class instead.