fix(types/sfc): fix withDefaults type inference when using union types (#4925)

packages/runtime-core/src/apiSetupHelpers.ts

@@ -127,18 +127,19 @@ export function defineExpose(exposed?: Record<string, any>) {
 type NotUndefined<T> = T extends undefined ? never : T
 
 type InferDefaults<T> = {
-  [K in keyof T]?: NotUndefined<T[K]> extends
+  [K in keyof T]?: InferDefault<T, NotUndefined<T[K]>>
+}
+
+type InferDefault<P, T> = T extends
   | number
   | string
   | boolean
   | symbol
   | Function
-    ? NotUndefined<T[K]>
-    : (props: T) => NotUndefined<T[K]>
-}
+  ? T
+  : (props: P) => T
 
-type PropsWithDefaults<Base, Defaults> = Base &
-  {
+type PropsWithDefaults<Base, Defaults> = Base & {
   [K in keyof Defaults]: K extends keyof Base ? NotUndefined<Base[K]> : never
 }
 

test-dts/setupHelpers.test-d.ts

@@ -45,6 +45,21 @@ describe('defineProps w/ type declaration + withDefaults', () => {
   res.x.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 }
+    }>(),
+    {
+      union1: 123,
+      union2: () => [123],
+      union3: () => ({ x: 123 })
+    }
+  )
+})
+
 describe('defineProps w/ runtime declaration', () => {
   // runtime declaration
   const props = defineProps({