add v-model dynamic type warning

src/platforms/web/compiler/directives/model.js

@@ -15,6 +15,15 @@ export default function model (
   const modifiers = dir.modifiers
   const tag = el.tag
   const type = el.attrsMap.type
+  if (process.env.NODE_ENV !== 'production') {
+    const dynamicType = el.attrsMap['v-bind:type'] || el.attrsMap[':type']
+    if (tag === 'input' && dynamicType) {
+      warn(
+        `<input :type="${dynamicType}" v-model="${value}">:\n` +
+        `v-model does not support dynamic input types. Use v-if branches instead.`
+      )
+    }
+  }
   if (tag === 'select') {
     return genSelect(el, value)
   } else if (tag === 'input' && type === 'checkbox') {

test/unit/features/directives/model-dynamic.spec.js

@@ -0,0 +1,14 @@
+import Vue from 'vue'
+
+describe('Directive v-model dynamic input type', () => {
+  it('should warn', function () {
+    new Vue({
+      data: {
+        type: 'text',
+        text: 'hi'
+      },
+      template: `<input :type="type" v-model="text">`
+    }).$mount()
+    expect(`v-model does not support dynamic input types`).toHaveBeenWarned()
+  })
+})