wip: root Vue compat

packages/core/src/componentUtils.ts

@@ -1,5 +1,6 @@
 import { VNodeFlags } from './flags'
 import { EMPTY_OBJ } from './utils'
+import { h } from './h'
 import { VNode, createFragment } from './vdom'
 import { Component, MountedComponent, ComponentClass } from './component'
 import { createTextVNode, cloneVNode } from './vdom'
@@ -153,6 +154,7 @@ export function shouldUpdateFunctionalComponent(
   return shouldUpdate
 }
 
+// compat only
 export function createComponentClassFromOptions(
   options: ComponentOptions
 ): ComponentClass {
@@ -165,7 +167,13 @@ export function createComponentClassFromOptions(
   for (const key in options) {
     const value = options[key]
     if (typeof value === 'function') {
-      ;(ObjectComponent.prototype as any)[key] = value
+      ;(ObjectComponent.prototype as any)[key] =
+        key === 'render'
+          ? // normalize render for legacy signature
+            function render() {
+              return value.call(this, h)
+            }
+          : value
     }
     if (key === 'computed') {
       const isGet = typeof value === 'function'

packages/core/src/createRenderer.ts

@@ -1174,11 +1174,11 @@ export function createRenderer(options: RendererOptions) {
     isSVG: boolean,
     endNode: RenderNode | RenderFragment | null
   ): RenderNode {
-    const instance = createComponentInstance(
-      parentVNode,
-      Component,
-      parentComponent
-    )
+    // a vnode may already have an instance if this is a compat call
+    // with new Vue()
+    const instance =
+      (__COMPAT__ && (parentVNode.children as MountedComponent)) ||
+      createComponentInstance(parentVNode, Component, parentComponent)
 
     const queueUpdate = (instance.$forceUpdate = () => {
       queueJob(instance._updateHandle, flushHooks)

packages/core/src/index.ts

@@ -10,8 +10,11 @@ export const Component = InternalComponent as ComponentClass
 // observer api
 export * from '@vue/observer'
 
+// internal api
+export { createComponentInstance } from './componentUtils'
+
 // flags & types
-export { FunctionalComponent } from './component'
+export { ComponentClass, FunctionalComponent } from './component'
 export { ComponentOptions, PropType } from './componentOptions'
 export { VNodeFlags, ChildrenFlags } from './flags'
 export { VNode, VNodeData, VNodeChildren, Key, Ref, Slots, Slot } from './vdom'