wip: initial compat build setup

packages/runtime-dom/src/index.ts

@@ -13,7 +13,15 @@ import {
 import { nodeOps } from './nodeOps'
 import { patchProp, forcePatchProp } from './patchProp'
 // Importing from the compiler, will be tree-shaken in prod
-import { isFunction, isString, isHTMLTag, isSVGTag, extend } from '@vue/shared'
+import {
+  isFunction,
+  isString,
+  isHTMLTag,
+  isSVGTag,
+  extend,
+  warnDeprecation,
+  DeprecationTypes
+} from '@vue/shared'
 
 declare module '@vue/reactivity' {
   export interface RefUnwrapBailTypes {
@@ -63,8 +71,24 @@ export const createApp = ((...args) => {
   app.mount = (containerOrSelector: Element | ShadowRoot | string): any => {
     const container = normalizeContainer(containerOrSelector)
     if (!container) return
+
+    // 2.x compat check
+    if (__COMPAT__ && __DEV__) {
+      for (let i = 0; i < container.attributes.length; i++) {
+        const attr = container.attributes[i]
+        if (attr.name !== 'v-cloak' && /^(v-|:|@)/.test(attr.name)) {
+          warnDeprecation(DeprecationTypes.DOM_TEMPLATE_MOUNT)
+          break
+        }
+      }
+    }
+
     const component = app._component
     if (!isFunction(component) && !component.render && !component.template) {
+      // __UNSAFE__
+      // Reason: potential execution of JS expressions in in-DOM template.
+      // The user must make sure the in-DOM template is trusted. If it's
+      // rendered by the server, the template should not contain any user data.
       component.template = container.innerHTML
     }
     // clear content before mounting