close #6097: Allow defining optional inject dependency with default values

src/core/instance/inject.js

@@ -49,7 +49,7 @@ export function resolveInject (inject: any, vm: Component): ?Object {
 
     for (let i = 0; i < keys.length; i++) {
       const key = keys[i]
-      const provideKey = inject[key]
+      const provideKey = inject[key].name
       let source = vm
       while (source) {
         if (source._provided && provideKey in source._provided) {
@@ -58,8 +58,15 @@ export function resolveInject (inject: any, vm: Component): ?Object {
         }
         source = source.$parent
       }
-      if (process.env.NODE_ENV !== 'production' && !source) {
-        warn(`Injection "${key}" not found`, vm)
+      if (!source) {
+        if ('default' in inject[key]) {
+          const provideDefault = inject[key].default
+          result[key] = typeof provideDefault === 'function'
+            ? provideDefault.call(vm)
+            : provideDefault
+        } else if (process.env.NODE_ENV !== 'production') {
+          warn(`Injection "${key}" not found`, vm)
+        }
       }
     }
     return result

src/core/util/options.js

@@ -270,10 +270,17 @@ function normalizeProps (options: Object) {
  */
 function normalizeInject (options: Object) {
   const inject = options.inject
+  const normalized = options.inject = {}
   if (Array.isArray(inject)) {
-    const normalized = options.inject = {}
     for (let i = 0; i < inject.length; i++) {
-      normalized[inject[i]] = inject[i]
+      normalized[inject[i]] = { name: inject[i] }
+    }
+  } else if (isPlainObject(inject)) {
+    for (const key in inject) {
+      const val = inject[key]
+      normalized[key] = isPlainObject(val)
+        ? extend({ name: key }, val)
+        : { name: val }
     }
   }
 }

test/unit/features/options/inject.spec.js

@@ -370,6 +370,45 @@ describe('Options provide/inject', () => {
     expect(`Injection "__ob__" not found`).not.toHaveBeenWarned()
   })
 
+  // Github issue #6097
+  it('should not warn when injections cannot be found but have default value', () => {
+    const vm = new Vue({})
+    new Vue({
+      parent: vm,
+      inject: {
+        foo: { default: 1 },
+        bar: { default: false },
+        baz: { default: undefined }
+      },
+      created () {}
+    })
+    expect(`Injection "foo" not found`).not.toHaveBeenWarned()
+    expect(`Injection "bar" not found`).not.toHaveBeenWarned()
+    expect(`Injection "baz" not found`).not.toHaveBeenWarned()
+  })
+
+  it('should use provided value even if inject has default', () => {
+    const vm = new Vue({
+      provide: {
+        foo: 1,
+        bar: false,
+        baz: undefined
+      }
+    })
+    new Vue({
+      parent: vm,
+      inject: {
+        foo: { default: 2 },
+        bar: { default: 2 },
+        baz: { default: 2 }
+      },
+      created () {
+        injected = [this.foo, this.bar, this.baz]
+      }
+    })
+    expect(injected).toEqual([1, false, undefined])
+  })
+
   // Github issue #6008
   it('should merge provide from mixins (objects)', () => {
     const mixinA = { provide: { foo: 'foo' }}