feat: provide ability to overwrite feature flags in esm-bundler builds

e.g. by replacing `__VUE_OPTIONS_API__` to `false` using webpack's
`DefinePlugin`, the final bundle will drop all code supporting the
options API.

This does not break existing usage, but requires the user to explicitly
configure the feature flags via bundlers to properly tree-shake the
disabled branches. As a result, users will see a console warning if
the flags have not been properly configured.

packages/runtime-core/src/apiCreateApp.ts

@@ -13,7 +13,7 @@ import { isFunction, NO, isObject } from '@vue/shared'
 import { warn } from './warning'
 import { createVNode, cloneVNode, VNode } from './vnode'
 import { RootHydrateFunction } from './hydration'
-import { initApp, appUnmounted } from './devtools'
+import { devtoolsInitApp, devtoolsUnmountApp } from './devtools'
 import { version } from '.'
 
 export interface App<HostElement = any> {
@@ -32,7 +32,7 @@ export interface App<HostElement = any> {
   unmount(rootContainer: HostElement | string): void
   provide<T>(key: InjectionKey<T> | string, value: T): this
 
-  // internal. We need to expose these for the server-renderer and devtools
+  // internal, but we need to expose these for the server-renderer and devtools
   _component: Component
   _props: Data | null
   _container: HostElement | null
@@ -50,7 +50,6 @@ export interface AppConfig {
   // @private
   readonly isNativeTag?: (tag: string) => boolean
 
-  devtools: boolean
   performance: boolean
   optionMergeStrategies: Record<string, OptionMergeFunction>
   globalProperties: Record<string, any>
@@ -68,15 +67,13 @@ export interface AppConfig {
 }
 
 export interface AppContext {
+  app: App // for devtools
   config: AppConfig
   mixins: ComponentOptions[]
   components: Record<string, PublicAPIComponent>
   directives: Record<string, Directive>
   provides: Record<string | symbol, any>
   reload?: () => void // HMR only
-
-  // internal for devtools
-  __app?: App
 }
 
 type PluginInstallFunction = (app: App, ...options: any[]) => any
@@ -89,9 +86,9 @@ export type Plugin =
 
 export function createAppContext(): AppContext {
   return {
+    app: null as any,
     config: {
       isNativeTag: NO,
-      devtools: true,
       performance: false,
       globalProperties: {},
       optionMergeStrategies: {},
@@ -126,7 +123,7 @@ export function createAppAPI<HostElement>(
 
     let isMounted = false
 
-    const app: App = {
+    const app: App = (context.app = {
       _component: rootComponent as Component,
       _props: rootProps,
       _container: null,
@@ -165,7 +162,7 @@ export function createAppAPI<HostElement>(
       },
 
       mixin(mixin: ComponentOptions) {
-        if (__FEATURE_OPTIONS__) {
+        if (__FEATURE_OPTIONS_API__) {
           if (!context.mixins.includes(mixin)) {
             context.mixins.push(mixin)
           } else if (__DEV__) {
@@ -230,8 +227,12 @@ export function createAppAPI<HostElement>(
           }
           isMounted = true
           app._container = rootContainer
+          // for devtools and telemetry
+          ;(rootContainer as any).__vue_app__ = app
 
-          __DEV__ && initApp(app, version)
+          if (__DEV__ || __FEATURE_PROD_DEVTOOLS__) {
+            devtoolsInitApp(app, version)
+          }
 
           return vnode.component!.proxy
         } else if (__DEV__) {
@@ -247,8 +248,7 @@ export function createAppAPI<HostElement>(
       unmount() {
         if (isMounted) {
           render(null, app._container)
-
-          __DEV__ && appUnmounted(app)
+          devtoolsUnmountApp(app)
         } else if (__DEV__) {
           warn(`Cannot unmount an app that is not mounted.`)
         }
@@ -267,9 +267,7 @@ export function createAppAPI<HostElement>(
 
         return app
       }
-    }
-
-    context.__app = app
+    })
 
     return app
   }