feat(inject): add treatDefaultAsFactory argument (#503)

src/apis/inject.ts

@@ -1,5 +1,5 @@
 import { ComponentInstance } from '../component'
-import { hasOwn, warn, currentVMInFn } from '../utils'
+import { hasOwn, warn, currentVMInFn, isFunction } from '../utils'
 import { getCurrentInstance } from '../runtimeContext'
 
 const NOT_FOUND = {}
@@ -38,10 +38,15 @@ export function provide<T>(key: InjectionKey<T> | string, value: T): void {
 }
 
 export function inject<T>(key: InjectionKey<T> | string): T | undefined
-export function inject<T>(key: InjectionKey<T> | string, defaultValue: T): T
+export function inject<T>(
+  key: InjectionKey<T> | string,
+  defaultValue: T,
+  treatDefaultAsFactory?: boolean
+): T
 export function inject(
   key: InjectionKey<any> | string,
-  defaultValue?: unknown
+  defaultValue?: unknown,
+  treatDefaultAsFactory = false
 ) {
   if (!key) {
     return defaultValue
@@ -55,12 +60,14 @@ export function inject(
 
   const val = resolveInject(key, vm)
   if (val !== NOT_FOUND) {
-    return val;
+    return val
   }
-  
+
   if (defaultValue === undefined && __DEV__) {
     warn(`Injection "${String(key)}" not found`, vm)
   }
 
-  return defaultValue
+  return treatDefaultAsFactory && isFunction(defaultValue)
+    ? defaultValue()
+    : defaultValue
 }

test/apis/inject.spec.js

@@ -145,4 +145,25 @@ describe('Hooks provide/inject', () => {
     expect(obj1.msg).toBe('foo')
     expect(obj2.msg).toBe('bar')
   })
+
+  it('should call default value as factory', () => {
+    const State = Symbol()
+    let fn = jest.fn()
+    new Vue({
+      template: `<child/>`,
+      setup() {},
+      provide: {
+        X: { msg: 'bar' },
+      },
+      components: {
+        child: {
+          setup() {
+            inject(State, fn, true)
+          },
+          template: `<div/>`,
+        },
+      },
+    }).$mount()
+    expect(fn).toHaveBeenCalled()
+  })
 })