types(defineProps): remove optional properties from type

packages/runtime-core/src/apiSetupHelpers.ts

@@ -58,7 +58,14 @@ export function defineProps<
   PP extends ComponentObjectPropsOptions = ComponentObjectPropsOptions
 >(props: PP): Readonly<ExtractPropTypes<PP>>
 // overload 3: typed-based declaration
-export function defineProps<TypeProps>(): Readonly<TypeProps>
+export function defineProps<T>(): T extends object
+  ? {
+      // use needed to remove the optional property
+      [K in keyof Required<T>]: K extends OptionalPropertyOf<T>
+        ? T[K] | undefined
+        : T[K]
+    }
+  : Readonly<T>
 // implementation
 export function defineProps() {
   if (__DEV__) {

packages/shared/src/typeUtils.ts

@@ -10,3 +10,12 @@ export type LooseRequired<T> = { [P in string & keyof T]: T[P] }
 // If the the type T accepts type "any", output type Y, otherwise output type N.
 // https://stackoverflow.com/questions/49927523/disallow-call-with-any/49928360#49928360
 export type IfAny<T, Y, N> = 0 extends 1 & T ? Y : N
+
+// Extract optional properties from a type
+// https://stackoverflow.com/a/53899815
+export type OptionalPropertyOf<T extends object> = Exclude<
+  {
+    [K in keyof T]: T extends Record<K, T[K]> ? never : K
+  }[keyof T],
+  undefined
+>

test-dts/setupHelpers.test-d.ts

@@ -13,9 +13,15 @@ describe('defineProps w/ type declaration', () => {
   // type declaration
   const props = defineProps<{
     foo: string
+    x?: string
   }>()
   // explicitly declared type should be refined
   expectType<string>(props.foo)
+
+  // force check the actual type doing expectType<string|undefined>(props.x) does not
+  // error when is not undefined, this way it does
+  // #6420
+  expectType<typeof props['x']>({} as unknown as string | undefined)
   // @ts-expect-error
   props.bar
 })