diff --git a/src/core/util/options.ts b/src/core/util/options.ts
index e9b7c489e1..baddeb09b6 100644
--- a/src/core/util/options.ts
+++ b/src/core/util/options.ts
@@ -467,7 +467,7 @@ export function resolveAsset(
   // fallback to prototype chain
   const res = assets[id] || assets[camelizedId] || assets[PascalCaseId]
   if (__DEV__ && warnMissing && !res) {
-    warn('Failed to resolve ' + type.slice(0, -1) + ': ' + id, options)
+    warn('Failed to resolve ' + type.slice(0, -1) + ': ' + id)
   }
   return res
 }
diff --git a/src/types/options.ts b/src/types/options.ts
index b5626acb25..27b3d7afc3 100644
--- a/src/types/options.ts
+++ b/src/types/options.ts
@@ -26,7 +26,9 @@ export type ComponentOptions = {
 
   // data
   data: object | Function | void
-  props?: { [key: string]: PropOptions }
+  props?:
+    | string[]
+    | Record<string, Function | Array<Function> | null | PropOptions>
   propsData?: object
   computed?: {
     [key: string]:
@@ -105,8 +107,8 @@ export type ComponentOptions = {
 }
 
 export type PropOptions = {
-  type: Function | Array<Function> | null
-  default: any
-  required: boolean | null
-  validator: Function | null
+  type?: Function | Array<Function> | null
+  default?: any
+  required?: boolean | null
+  validator?: Function | null
 }
diff --git a/src/v3/apiSetup.ts b/src/v3/apiSetup.ts
index e4cadb1067..811453b996 100644
--- a/src/v3/apiSetup.ts
+++ b/src/v3/apiSetup.ts
@@ -1,7 +1,14 @@
 import { Component } from 'types/component'
+import { PropOptions } from 'types/options'
 import { def, invokeWithErrorHandling, isReserved, warn } from '../core/util'
 import VNode from '../core/vdom/vnode'
-import { bind, emptyObject, isFunction, isObject } from '../shared/util'
+import {
+  bind,
+  emptyObject,
+  isArray,
+  isFunction,
+  isObject
+} from '../shared/util'
 import { currentInstance, setCurrentInstance } from './currentInstance'
 import { isRef } from './reactivity/ref'
 
@@ -193,3 +200,35 @@ function getContext(): SetupContext {
   const vm = currentInstance!
   return vm._setupContext || (vm._setupContext = createSetupContext(vm))
 }
+
+/**
+ * Runtime helper for merging default declarations. Imported by compiled code
+ * only.
+ * @internal
+ */
+export function mergeDefaults(
+  raw: string[] | Record<string, PropOptions>,
+  defaults: Record<string, any>
+): Record<string, PropOptions> {
+  const props = isArray(raw)
+    ? raw.reduce(
+        (normalized, p) => ((normalized[p] = {}), normalized),
+        {} as Record<string, PropOptions>
+      )
+    : raw
+  for (const key in defaults) {
+    const opt = props[key]
+    if (opt) {
+      if (isArray(opt) || isFunction(opt)) {
+        props[key] = { type: opt, default: defaults[key] }
+      } else {
+        opt.default = defaults[key]
+      }
+    } else if (opt === null) {
+      props[key] = { default: defaults[key] }
+    } else if (__DEV__) {
+      warn(`props default key "${key}" has no corresponding declaration.`)
+    }
+  }
+  return props
+}
diff --git a/src/v3/apiWatch.ts b/src/v3/apiWatch.ts
index 67aafc5fd1..909bd0258e 100644
--- a/src/v3/apiWatch.ts
+++ b/src/v3/apiWatch.ts
@@ -179,10 +179,8 @@ function doWatch(
 
   const warnInvalidSource = (s: unknown) => {
     warn(
-      `Invalid watch source: `,
-      s,
-      `A watch source can only be a getter/effect function, a ref, ` +
-        `a reactive object, or an array of these types.`
+      `Invalid watch source: ${s}. A watch source can only be a getter/effect ` +
+        `function, a ref, a reactive object, or an array of these types.`
     )
   }
 
diff --git a/src/v3/index.ts b/src/v3/index.ts
index 2e6a71c5bf..7a9779eedb 100644
--- a/src/v3/index.ts
+++ b/src/v3/index.ts
@@ -70,7 +70,7 @@ export { provide, inject, InjectionKey } from './apiInject'
 
 export { h } from './h'
 export { getCurrentInstance } from './currentInstance'
-export { useSlots, useAttrs } from './apiSetup'
+export { useSlots, useAttrs, mergeDefaults } from './apiSetup'
 export { nextTick } from 'core/util/next-tick'
 export { set, del } from 'core/observer'
 
diff --git a/types/index.d.ts b/types/index.d.ts
index d8722c3b8d..dd5aab503d 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -35,6 +35,8 @@ export {
 
 export * from './v3-manual-apis'
 export * from './v3-generated'
+// <script setup> helpers
+export * from './v3-setup-helpers'
 
 export { Data } from './common'
 export { SetupContext } from './v3-setup-context'
diff --git a/types/test/setup-helpers-test.ts b/types/test/setup-helpers-test.ts
new file mode 100644
index 0000000000..744c2a5336
--- /dev/null
+++ b/types/test/setup-helpers-test.ts
@@ -0,0 +1,134 @@
+import { useAttrs, useSlots, SetupContext } from '../index'
+import { describe, expectType } from './utils'
+
+describe('defineProps w/ type declaration', () => {
+  // type declaration
+  const props = defineProps<{
+    foo: string
+  }>()
+  // explicitly declared type should be refined
+  expectType<string>(props.foo)
+  // @ts-expect-error
+  props.bar
+})
+
+describe('defineProps w/ type declaration + withDefaults', () => {
+  const res = withDefaults(
+    defineProps<{
+      number?: number
+      arr?: string[]
+      obj?: { x: number }
+      fn?: (e: string) => void
+      x?: string
+      genStr?: string
+    }>(),
+    {
+      number: 123,
+      arr: () => [],
+      obj: () => ({ x: 123 }),
+      fn: () => {},
+      genStr: () => ''
+    }
+  )
+
+  res.number + 1
+  res.arr.push('hi')
+  res.obj.x
+  res.fn('hi')
+  // @ts-expect-error
+  res.x.slice()
+  res.genStr.slice()
+})
+
+describe('defineProps w/ union type declaration + withDefaults', () => {
+  withDefaults(
+    defineProps<{
+      union1?: number | number[] | { x: number }
+      union2?: number | number[] | { x: number }
+      union3?: number | number[] | { x: number }
+      union4?: number | number[] | { x: number }
+    }>(),
+    {
+      union1: 123,
+      union2: () => [123],
+      union3: () => ({ x: 123 }),
+      union4: () => 123
+    }
+  )
+})
+
+describe('defineProps w/ runtime declaration', () => {
+  // runtime declaration
+  const props = defineProps({
+    foo: String,
+    bar: {
+      type: Number,
+      default: 1
+    },
+    baz: {
+      type: Array,
+      required: true
+    }
+  })
+  expectType<{
+    foo?: string
+    bar: number
+    baz: unknown[]
+  }>(props)
+
+  props.foo && props.foo + 'bar'
+  props.bar + 1
+  // @ts-expect-error should be readonly
+  props.bar++
+  props.baz.push(1)
+
+  const props2 = defineProps(['foo', 'bar'])
+  props2.foo + props2.bar
+  // @ts-expect-error
+  props2.baz
+})
+
+describe('defineEmits w/ type declaration', () => {
+  const emit = defineEmits<(e: 'change') => void>()
+  emit('change')
+  // @ts-expect-error
+  emit()
+  // @ts-expect-error
+  emit('bar')
+
+  type Emits = { (e: 'foo' | 'bar'): void; (e: 'baz', id: number): void }
+  const emit2 = defineEmits<Emits>()
+
+  emit2('foo')
+  emit2('bar')
+  emit2('baz', 123)
+  // @ts-expect-error
+  emit2('baz')
+})
+
+describe('defineEmits w/ runtime declaration', () => {
+  const emit = defineEmits({
+    foo: () => {},
+    bar: null
+  })
+  emit('foo')
+  emit('bar', 123)
+  // @ts-expect-error
+  emit('baz')
+
+  const emit2 = defineEmits(['foo', 'bar'])
+  emit2('foo')
+  emit2('bar', 123)
+  // @ts-expect-error
+  emit2('baz')
+})
+
+describe('useAttrs', () => {
+  const attrs = useAttrs()
+  expectType<Record<string, unknown>>(attrs)
+})
+
+describe('useSlots', () => {
+  const slots = useSlots()
+  expectType<SetupContext['slots']>(slots)
+})
diff --git a/types/v3-setup-helpers.d.ts b/types/v3-setup-helpers.d.ts
new file mode 100644
index 0000000000..6a62fd16fe
--- /dev/null
+++ b/types/v3-setup-helpers.d.ts
@@ -0,0 +1,150 @@
+import { EmitFn, EmitsOptions } from './v3-setup-context'
+import {
+  ComponentObjectPropsOptions,
+  ExtractPropTypes
+} from './v3-component-props'
+
+/**
+ * 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 declaration:
+ * ```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: 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<
+  PP extends ComponentObjectPropsOptions = ComponentObjectPropsOptions
+>(props: PP): Readonly<ExtractPropTypes<PP>>
+// overload 3: typed-based declaration
+export function defineProps<TypeProps>(): Readonly<TypeProps>
+
+/**
+ * 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 declaration:
+ * ```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
+
+/**
+ * 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. variables 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 extends Record<string, any> = Record<string, any>
+>(exposed?: Exposed): void
+
+type NotUndefined<T> = T extends undefined ? never : T
+
+type InferDefaults<T> = {
+  [K in keyof T]?: InferDefault<T, NotUndefined<T[K]>>
+}
+
+type InferDefault<P, T> = T extends
+  | null
+  | number
+  | string
+  | boolean
+  | symbol
+  | Function
+  ? T | ((props: P) => T)
+  : (props: P) => T
+
+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` declaration.
+ *
+ * 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>
+
+// make them global
+type _defineProps = typeof defineProps
+type _defineEmits = typeof defineEmits
+type _defineExpose = typeof defineExpose
+type _withDefaults = typeof withDefaults
+
+declare global {
+  const defineProps: _defineProps
+  const defineEmits: _defineEmits
+  const defineExpose: _defineExpose
+  const withDefaults: _withDefaults
+}