feat(runtime-core): add expose() API

WIP - ref: vuejs/rfcs#210

packages/runtime-core/__tests__/apiExposed.spec.ts

@@ -0,0 +1,39 @@
+import { nodeOps, render } from '@vue/runtime-test'
+import { h, expose, ref } from '../src'
+
+describe('api: expose', () => {
+  test('component ref should only expose exposed properties', () => {
+    const Child = {
+      render() {},
+      setup() {
+        expose({
+          foo: ref(1),
+          bar: ref(2)
+        })
+        return {
+          bar: ref(3),
+          baz: ref(4)
+        }
+      }
+    }
+    const childRef = ref()
+    const Parent = {
+      setup() {
+        return () => h(Child, { ref: childRef })
+      }
+    }
+    const root = nodeOps.createElement('div')
+    render(h(Parent), root)
+    expect(childRef.value).toBeTruthy()
+    expect(childRef.value.foo).toBe(1)
+    expect(childRef.value.bar).toBe(2)
+    expect(childRef.value.baz).toBeUndefined()
+  })
+
+  test('expose called outside of setup()', () => {
+    expose({})
+    expect(
+      `expose() is called when there is no active component instance`
+    ).toHaveBeenWarned()
+  })
+})

packages/runtime-core/src/apiExpose.ts

@@ -0,0 +1,21 @@
+import { proxyRefs } from '@vue/reactivity'
+import { getCurrentInstance } from './component'
+import { warn } from './warning'
+
+// TODO: refine and merge RFC (https://github.com/vuejs/rfcs/pull/210)
+// TODO: corresponding option (https://github.com/vuejs/rfcs/pull/135)
+
+export function expose(values: Record<string, any>) {
+  const instance = getCurrentInstance()
+  if (instance) {
+    Object.assign(
+      instance.exposed || (instance.exposed = proxyRefs({})),
+      values
+    )
+  } else if (__DEV__) {
+    warn(
+      `expose() is called when there is no active component instance to be ` +
+        `associated with.`
+    )
+  }
+}

packages/runtime-core/src/component.ts

@@ -270,6 +270,9 @@ export interface ComponentInternalInstance {
   // main proxy that serves as the public instance (`this`)
   proxy: ComponentPublicInstance | null
 
+  // exposed properties via expose()
+  exposed: Record<string, any> | null
+
   /**
    * alternative proxy used only for runtime-compiled render functions using
    * `with` block
@@ -416,6 +419,7 @@ export function createComponentInstance(
     render: null,
     proxy: null,
     withProxy: null,
+    exposed: null,
     effects: null,
     provides: parent ? parent.provides : Object.create(appContext.provides),
     accessCache: null!,

packages/runtime-core/src/index.ts

@@ -40,6 +40,7 @@ export {
   onErrorCaptured
 } from './apiLifecycle'
 export { provide, inject } from './apiInject'
+export { expose } from './apiExpose'
 export { nextTick } from './scheduler'
 export { defineComponent } from './apiDefineComponent'
 export { defineAsyncComponent } from './apiAsyncComponent'

packages/runtime-core/src/renderer.ts

@@ -300,12 +300,12 @@ export const setRef = (
     return
   }
 
-  let value: ComponentPublicInstance | RendererNode | null
+  let value: ComponentPublicInstance | RendererNode | Record<string, any> | null
   if (!vnode) {
     value = null
   } else {
     if (vnode.shapeFlag & ShapeFlags.STATEFUL_COMPONENT) {
-      value = vnode.component!.proxy
+      value = vnode.component!.exposed || vnode.component!.proxy
     } else {
       value = vnode.el
     }