feat(sfc): withDefaults helper

packages/runtime-core/src/apiSetupHelpers.ts

@@ -4,63 +4,104 @@ import {
   createSetupContext
 } from './component'
 import { EmitFn, EmitsOptions } from './componentEmits'
-import { ComponentObjectPropsOptions, ExtractPropTypes } from './componentProps'
+import {
+  ComponentObjectPropsOptions,
+  PropOptions,
+  ExtractPropTypes
+} from './componentProps'
 import { warn } from './warning'
 
-type InferDefaults<T> = {
-  [K in keyof T]?: NonNullable<T[K]> extends object
-    ? () => NonNullable<T[K]>
-    : NonNullable<T[K]>
-}
+// dev only
+const warnRuntimeUsage = (method: string) =>
+  warn(
+    `${method}() is a compiler-hint helper that is only usable inside ` +
+      `<script setup> of a single file component. Its arguments should be ` +
+      `compiled away and passing it at runtime has no effect.`
+  )
 
 /**
- * Compile-time-only helper used for declaring props inside `<script setup>`.
- * This is stripped away in the compiled code and should never be actually
- * called at runtime.
+ * Vue `<script setup>` compiler macro for declaring component props. The
+ * expected argument is the same as the component `props` option.
+ *
+ * Example runtime declaration:
+ * ```js
+ * // using Array syntax
+ * const props = defineProps(['foo', 'bar'])
+ * // using Object syntax
+ * const props = defineProps({
+ *   foo: String,
+ *   bar: {
+ *     type: Number,
+ *     required: true
+ *   }
+ * })
+ * ```
+ *
+ * Equivalent type-based decalration:
+ * ```ts
+ * // will be compiled into equivalent runtime declarations
+ * const props = defineProps<{
+ *   foo?: string
+ *   bar: number
+ * }>()
+ * ```
+ *
+ * This is only usable inside `<script setup>`, is compiled away in the
+ * output and should **not** be actually called at runtime.
  */
-// overload 1: string props
+// overload 1: runtime props w/ array
+export function defineProps<PropNames extends string = string>(
+  props: PropNames[]
+): Readonly<{ [key in PropNames]?: any }>
+// overload 2: runtime props w/ object
 export function defineProps<
-  TypeProps = undefined,
-  PropNames extends string = string,
-  InferredProps = { [key in PropNames]?: any }
->(
-  props?: PropNames[]
-): Readonly<TypeProps extends undefined ? InferredProps : TypeProps>
-// overload 2: object props
-export function defineProps<
-  TypeProps = undefined,
-  PP extends ComponentObjectPropsOptions = ComponentObjectPropsOptions,
-  InferredProps = ExtractPropTypes<PP>
->(
-  props?: PP,
-  defaults?: InferDefaults<TypeProps>
-): Readonly<TypeProps extends undefined ? InferredProps : TypeProps>
+  PP extends ComponentObjectPropsOptions = ComponentObjectPropsOptions
+>(props: PP): Readonly<ExtractPropTypes<PP>>
+// overload 3: typed-based declaration
+export function defineProps<TypeProps>(): Readonly<TypeProps>
 // implementation
 export function defineProps() {
   if (__DEV__) {
-    warn(
-      `defineProps() is a compiler-hint helper that is only usable inside ` +
-        `<script setup> of a single file component. Its arguments should be ` +
-        `compiled away and passing it at runtime has no effect.`
-    )
+    warnRuntimeUsage(`defineProps`)
   }
   return null as any
 }
 
-export function defineEmits<
-  TypeEmit = undefined,
-  E extends EmitsOptions = EmitsOptions,
-  EE extends string = string,
-  InferredEmit = EmitFn<E>
->(emitOptions?: E | EE[]): TypeEmit extends undefined ? InferredEmit : TypeEmit
+/**
+ * Vue `<script setup>` compiler macro for declaring a component's emitted
+ * events. The expected argument is the same as the component `emits` option.
+ *
+ * Example runtime declaration:
+ * ```js
+ * const emit = defineEmits(['change', 'update'])
+ * ```
+ *
+ * Example type-based decalration:
+ * ```ts
+ * const emit = defineEmits<{
+ *   (event: 'change'): void
+ *   (event: 'update', id: number): void
+ * }>()
+ *
+ * emit('change')
+ * emit('update', 1)
+ * ```
+ *
+ * This is only usable inside `<script setup>`, is compiled away in the
+ * output and should **not** be actually called at runtime.
+ */
+// overload 1: runtime emits w/ array
+export function defineEmits<EE extends string = string>(
+  emitOptions: EE[]
+): EmitFn<EE[]>
+export function defineEmits<E extends EmitsOptions = EmitsOptions>(
+  emitOptions: E
+): EmitFn<E>
+export function defineEmits<TypeEmit>(): TypeEmit
 // implementation
 export function defineEmits() {
   if (__DEV__) {
-    warn(
-      `defineEmits() is a compiler-hint helper that is only usable inside ` +
-        `<script setup> of a single file component. Its arguments should be ` +
-        `compiled away and passing it at runtime has no effect.`
-    )
+    warnRuntimeUsage(`defineEmits`)
   }
   return null as any
 }
@@ -70,16 +111,70 @@ export function defineEmits() {
  */
 export const defineEmit = defineEmits
 
+/**
+ * Vue `<script setup>` compiler macro for declaring a component's exposed
+ * instance properties when it is accessed by a parent component via template
+ * refs.
+ *
+ * `<script setup>` components are closed by default - i.e. varaibles inside
+ * the `<script setup>` scope is not exposed to parent unless explicitly exposed
+ * via `defineExpose`.
+ *
+ * This is only usable inside `<script setup>`, is compiled away in the
+ * output and should **not** be actually called at runtime.
+ */
 export function defineExpose(exposed?: Record<string, any>) {
   if (__DEV__) {
-    warn(
-      `defineExpose() is a compiler-hint helper that is only usable inside ` +
-        `<script setup> of a single file component. Its usage should be ` +
-        `compiled away and calling it at runtime has no effect.`
-    )
+    warnRuntimeUsage(`defineExpose`)
   }
 }
 
+type NotUndefined<T> = T extends undefined ? never : T
+
+type InferDefaults<T> = {
+  [K in keyof T]?: NotUndefined<T[K]> extends (
+    | number
+    | string
+    | boolean
+    | symbol
+    | Function)
+    ? NotUndefined<T[K]>
+    : (props: T) => NotUndefined<T[K]>
+}
+
+type PropsWithDefaults<Base, Defaults> = Base &
+  {
+    [K in keyof Defaults]: K extends keyof Base ? NotUndefined<Base[K]> : never
+  }
+
+/**
+ * Vue `<script setup>` compiler macro for providing props default values when
+ * using type-based `defineProps` decalration.
+ *
+ * Example usage:
+ * ```ts
+ * withDefaults(defineProps<{
+ *   size?: number
+ *   labels?: string[]
+ * }>(), {
+ *   size: 3,
+ *   labels: () => ['default label']
+ * })
+ * ```
+ *
+ * This is only usable inside `<script setup>`, is compiled away in the output
+ * and should **not** be actually called at runtime.
+ */
+export function withDefaults<Props, Defaults extends InferDefaults<Props>>(
+  props: Props,
+  defaults: Defaults
+): PropsWithDefaults<Props, Defaults> {
+  if (__DEV__) {
+    warnRuntimeUsage(`withDefaults`)
+  }
+  return null as any
+}
+
 /**
  * @deprecated use `useSlots` and `useAttrs` instead.
  */
@@ -93,6 +188,14 @@ export function useContext(): SetupContext {
   return getContext()
 }
 
+export function useSlots(): SetupContext['slots'] {
+  return getContext().slots
+}
+
+export function useAttrs(): SetupContext['attrs'] {
+  return getContext().attrs
+}
+
 function getContext(): SetupContext {
   const i = getCurrentInstance()!
   if (__DEV__ && !i) {
@@ -101,10 +204,25 @@ function getContext(): SetupContext {
   return i.setupContext || (i.setupContext = createSetupContext(i))
 }
 
-export function useSlots(): SetupContext['slots'] {
-  return getContext().slots
-}
-
-export function useAttrs(): SetupContext['attrs'] {
-  return getContext().attrs
+/**
+ * Runtime helper for merging default declarations. Imported by compiled code
+ * only.
+ * @internal
+ */
+export function mergeDefaults(
+  // the base props is compiler-generated and guaranteed to be in this shape.
+  props: Record<string, PropOptions | null>,
+  defaults: Record<string, any>
+) {
+  for (const key in defaults) {
+    const val = props[key]
+    if (val) {
+      val.default = defaults[key]
+    } else if (val === null) {
+      props[key] = { default: defaults[key] }
+    } else if (__DEV__) {
+      warn(`props default key "${key}" has no corresponding declaration.`)
+    }
+  }
+  return props
 }

packages/runtime-core/src/componentProps.ts

@@ -51,7 +51,7 @@ export type Prop<T, D = T> = PropOptions<T, D> | PropType<T>
 
 type DefaultFactory<T> = (props: Data) => T | null | undefined
 
-interface PropOptions<T = any, D = T> {
+export interface PropOptions<T = any, D = T> {
   type?: PropType<T> | true | null
   required?: boolean
   default?: D | DefaultFactory<D> | null | undefined | object

packages/runtime-core/src/index.ts

@@ -44,9 +44,17 @@ export { provide, inject } from './apiInject'
 export { nextTick } from './scheduler'
 export { defineComponent } from './apiDefineComponent'
 export { defineAsyncComponent } from './apiAsyncComponent'
+
+// <script setup> API ----------------------------------------------------------
+
 export {
   defineProps,
   defineEmits,
+  defineExpose,
+  withDefaults,
+  // internal
+  mergeDefaults,
+  // deprecated
   defineEmit,
   useContext
 } from './apiSetupHelpers'
@@ -140,7 +148,6 @@ export {
   DeepReadonly
 } from '@vue/reactivity'
 export {
-  // types
   WatchEffect,
   WatchOptions,
   WatchOptionsBase,