types: avoid plain objects with value being mistaken as refs

packages/reactivity/src/collectionHandlers.ts

@@ -16,7 +16,7 @@ function get(target: any, key: any, wrap: (t: any) => any): any {
   return wrap(res)
 }
 
-function has(key: any): boolean {
+function has(this: any, key: any): boolean {
   const target = toRaw(this)
   key = toRaw(key)
   const proto: any = Reflect.getPrototypeOf(target)
@@ -31,7 +31,7 @@ function size(target: any) {
   return Reflect.get(proto, 'size', target)
 }
 
-function add(value: any) {
+function add(this: any, value: any) {
   value = toRaw(value)
   const target = toRaw(this)
   const proto: any = Reflect.getPrototypeOf(this)
@@ -48,7 +48,7 @@ function add(value: any) {
   return result
 }
 
-function set(key: any, value: any) {
+function set(this: any, key: any, value: any) {
   value = toRaw(value)
   const target = toRaw(this)
   const proto: any = Reflect.getPrototypeOf(this)
@@ -75,7 +75,7 @@ function set(key: any, value: any) {
   return result
 }
 
-function deleteEntry(key: any) {
+function deleteEntry(this: any, key: any) {
   const target = toRaw(this)
   const proto: any = Reflect.getPrototypeOf(this)
   const hadKey = proto.has.call(target, key)
@@ -93,7 +93,7 @@ function deleteEntry(key: any) {
   return result
 }
 
-function clear() {
+function clear(this: any) {
   const target = toRaw(this)
   const proto: any = Reflect.getPrototypeOf(this)
   const hadItems = target.size !== 0
@@ -112,7 +112,7 @@ function clear() {
 }
 
 function createForEach(isReadonly: boolean) {
-  return function forEach(callback: Function, thisArg?: any) {
+  return function forEach(this: any, callback: Function, thisArg?: any) {
     const observed = this
     const target = toRaw(observed)
     const proto: any = Reflect.getPrototypeOf(target)
@@ -129,7 +129,7 @@ function createForEach(isReadonly: boolean) {
 }
 
 function createIterableMethod(method: string | symbol, isReadonly: boolean) {
-  return function(...args: any[]) {
+  return function(this: any, ...args: any[]) {
     const target = toRaw(this)
     const proto: any = Reflect.getPrototypeOf(target)
     const isPair =
@@ -163,7 +163,7 @@ function createReadonlyMethod(
   method: Function,
   type: OperationTypes
 ): Function {
-  return function(...args: any[]) {
+  return function(this: any, ...args: any[]) {
     if (LOCKED) {
       if (__DEV__) {
         const key = args[0] ? `on key "${args[0]}" ` : ``

packages/reactivity/src/computed.ts

@@ -1,27 +1,38 @@
 import { effect, ReactiveEffect, activeReactiveEffectStack } from './effect'
-import { UnwrapNestedRefs, knownRefs, Ref } from './ref'
+import { UnwrapNestedRefs, isRefSymbol, knownRefs } from './ref'
 import { isFunction } from '@vue/shared'
 
 export interface ComputedRef<T> {
+  [isRefSymbol]: true
   readonly value: UnwrapNestedRefs<T>
   readonly effect: ReactiveEffect
 }
 
-export interface ComputedOptions<T> {
+export interface WritableComputedRef<T> {
+  [isRefSymbol]: true
+  value: UnwrapNestedRefs<T>
+  readonly effect: ReactiveEffect
+}
+
+export interface WritableComputedOptions<T> {
   get: () => T
   set: (v: T) => void
 }
 
 export function computed<T>(getter: () => T): ComputedRef<T>
-export function computed<T>(options: ComputedOptions<T>): Ref<T>
 export function computed<T>(
-  getterOrOptions: (() => T) | ComputedOptions<T>
-): Ref<T> {
+  options: WritableComputedOptions<T>
+): WritableComputedRef<T>
+export function computed<T>(
+  getterOrOptions: (() => T) | WritableComputedOptions<T>
+): any {
   const isReadonly = isFunction(getterOrOptions)
   const getter = isReadonly
     ? (getterOrOptions as (() => T))
-    : (getterOrOptions as ComputedOptions<T>).get
-  const setter = isReadonly ? null : (getterOrOptions as ComputedOptions<T>).set
+    : (getterOrOptions as WritableComputedOptions<T>).get
+  const setter = isReadonly
+    ? null
+    : (getterOrOptions as WritableComputedOptions<T>).set
 
   let dirty: boolean = true
   let value: any = undefined
@@ -34,7 +45,7 @@ export function computed<T>(
       dirty = true
     }
   })
-  const computedValue = {
+  const computedRef = {
     // expose effect so computed can be stopped
     effect: runner,
     get value() {
@@ -56,8 +67,8 @@ export function computed<T>(
       }
     }
   }
-  knownRefs.add(computedValue)
-  return computedValue
+  knownRefs.add(computedRef)
+  return computedRef
 }
 
 function trackChildRun(childRunner: ReactiveEffect) {

packages/reactivity/src/index.ts

@@ -8,7 +8,7 @@ export {
   markReadonly,
   markNonReactive
 } from './reactive'
-export { computed, ComputedRef, ComputedOptions } from './computed'
+export { computed, ComputedRef, WritableComputedOptions } from './computed'
 export {
   effect,
   stop,

packages/reactivity/src/ref.ts

@@ -5,7 +5,12 @@ import { reactive } from './reactive'
 
 export const knownRefs = new WeakSet()
 
+export const isRefSymbol = Symbol()
+
 export interface Ref<T> {
+  // this is a type-only field to avoid objects with 'value' property being
+  // treated as a ref by TypeScript
+  [isRefSymbol]: true
   value: UnwrapNestedRefs<T>
 }